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| Publications of Marc A. Sommer :chronological alphabetical combined listing:%% Journal Articles @article{fds351254, Author = {Akbar, N and Yarossi, M and Martinez-Gost, M and Sommer, MA and Dannhauer, M and Rampersad, S and Brooks, D and Tunik, E and Erdoğmuş, D}, Title = {Mapping Motor Cortex Stimulation to Muscle Responses: A Deep Neural Network Modeling Approach.}, Journal = {The ... International Conference on PErvasive Technologies Related to Assistive Environments : PETRA ... International Conference on PErvasive Technologies Related to Assistive Environments}, Volume = {2020}, Pages = {15}, Year = {2020}, Month = {June}, ISBN = {9781450377737}, url = {http://dx.doi.org/10.1145/3389189.3389203}, Abstract = {A deep neural network (DNN) that can reliably model muscle responses from corresponding brain stimulation has the potential to increase knowledge of coordinated motor control for numerous basic science and applied use cases. Such cases include the understanding of abnormal movement patterns due to neurological injury from stroke, and stimulation based interventions for neurological recovery such as paired associative stimulation. In this work, potential DNN models are explored and the one with the minimum squared errors is recommended for the optimal performance of the M2M-Net, a network that maps transcranial magnetic stimulation of the motor cortex to corresponding muscle responses, using: a finite element simulation, an empirical neural response profile, a convolutional autoencoder, a separate deep network mapper, and recordings of multi-muscle activation. We discuss the rationale behind the different modeling approaches and architectures, and contrast their results. Additionally, to obtain a comparative insight of the trade-o between complexity and performance analysis, we explore different techniques, including the extension of two classical information criteria for M2M-Net. Finally, we find that the model analogous to mapping the motor cortex stimulation to a combination of direct and synergistic connection to the muscles performs the best, when the neural response profile is used at the input.}, Doi = {10.1145/3389189.3389203}, Key = {fds351254} } @article{fds349697, Author = {Yeung, AH-F and Subramanian, D and Desai, AD and Soltanian-Zadeh, S and Roy, A and Vajzovic, L and Sommer, M and Farsiu, S}, Title = {Spatio-temporal image modulation for enhancing the quality of vision with potential application in patients with retinal prostheses}, Journal = {INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE}, Volume = {60}, Number = {9}, Pages = {3 pages}, Publisher = {ASSOC RESEARCH VISION OPHTHALMOLOGY INC}, Year = {2019}, Month = {July}, Key = {fds349697} } @article{fds343771, Author = {Yarossi, M and Quivira, F and Dannhauer, M and Sommer, MA and Brooks, DH and Erdoǧmuş, D and Tunik, E}, Title = {An experimental and computational framework for modeling multi-muscle responses to transcranial magnetic stimulation of the human motor cortex}, Journal = {International IEEE/EMBS Conference on Neural Engineering, NER}, Volume = {2019-March}, Pages = {1122-1125}, Year = {2019}, Month = {May}, ISBN = {9781538679210}, url = {http://dx.doi.org/10.1109/NER.2019.8717159}, Abstract = {Current knowledge of coordinated motor control of multiple muscles is derived primarily from invasive stimulation-recording techniques in animal models. Similar studies are not generally feasible in humans, so a modeling framework is needed to facilitate knowledge transfer from animal studies. We describe such a framework that uses a deep neural network model to map finite element simulation of transcranial magnetic stimulation induced electric fields (E-fields) in motor cortex to recordings of multi-muscle activation. Critically, we show that model generalization is improved when we incorporate empirically derived physiological models for E-field to neuron firing rate and low-dimensional control via muscle synergies.}, Doi = {10.1109/NER.2019.8717159}, Key = {fds343771} } @article{fds338442, Author = {Clements, JM and Kopper, R and Zielinski, DJ and Rao, H and Sommer, MA and Kirsch, E and Mainsah, BO and Collins, LM and Appelbaum, LG}, Title = {Neurophysiology of Visual-Motor Learning during a Simulated Marksmanship Task in Immersive Virtual Reality}, Journal = {25th IEEE Conference on Virtual Reality and 3D User Interfaces, VR 2018 - Proceedings}, Pages = {451-458}, Publisher = {IEEE}, Year = {2018}, Month = {August}, ISBN = {9781538633656}, url = {http://dx.doi.org/10.1109/VR.2018.8446068}, Abstract = {Immersive virtual reality (VR) systems offer flexible control of an interactive environment, along with precise position and orientation tracking of realistic movements. Immersive VR can also be used in conjunction with neurophysiological monitoring techniques, such as electroencephalography (EEG), to record neural activity as users perform complex tasks. As such, the fusion of VR, kinematic tracking, and EEG offers a powerful testbed for naturalistic neuroscience research. In this study, we combine these elements to investigate the cognitive and neural mechanisms that underlie motor skill learning during a multi-day simulated marksmanship training regimen conducted with 20 participants. On each of 3 days, participants performed 8 blocks of 60 trials in which a simulated clay pigeon was launched from behind a trap house. Participants attempted to shoot the moving target with a firearm game controller, receiving immediate positional feedback and running scores after each shot. Over the course of the 3 days that individuals practiced this protocol, shot accuracy and precision improved significantly while reaction times got significantly faster. Furthermore, results demonstrate that more negative EEG amplitudes produced over the visual cortices correlate with better shooting performance measured by accuracy, reaction times, and response times, indicating that early visual system plasticity underlies behavioral learning in this task. These findings point towards a naturalistic neuroscience approach that can be used to identify neural markers of marksmanship performance.}, Doi = {10.1109/VR.2018.8446068}, Key = {fds338442} } %% Book Chapters @misc{fds334788, Author = {Abzug, ZM and Sommer, MA}, Title = {Supplementary Eye Fields}, Booktitle = {Reference Module in Neuroscience and Biobehavioral Psychology}, Publisher = {Elevier}, Year = {2017}, ISBN = {9780128093245}, Abstract = {The supplementary eye fields (SEFs) are located in dorsomedial frontal cortex and contribute to high-level control of eye movements. Recordings in the SEF reveal neural activity related to vision, saccades, and fixations, and electrical stimulation in the SEF evokes saccades and fixations. Inactivations and lesions of the SEF, however, cause minimal oculomotor deficits. The SEF thus processes information relevant to eye movements and influences critical oculomotor centers but seems unnecessary for generating action. Instead, the SEF has overarching, subtle functions that include limb-eye coordination, the timing and sequencing of actions, learning, monitoring conflict, prediction, supervising behavior, value-based decision making, and the monitoring of decisions.}, Key = {fds334788} } @misc{fds334803, Author = {Middlebrooks, PG and Abzug, Z and Sommer, MA}, Title = {Studying metacognitive processes at the single-neuron level}, Pages = {225-244}, Booktitle = {The Cognitive Neuroscience of Metacognition}, Publisher = {Springer}, Editor = {Fleming, SM and Frith, CD}, Year = {2014}, Month = {June}, ISBN = {978-3-642-45189-8}, url = {http://dx.doi.org/10.1007/978-3-642-45190-4_10}, Abstract = {Over the past few decades, strides have been made toward understanding how higher level cognitive processes are mediated by neuronal spiking activity. Neuronal correlates of functions such as attention, executive control, working memory, decision-making, and reward processing have all been elucidated, to an impressive level of detail, at the single cell and circuit levels.}, Doi = {10.1007/978-3-642-45190-4_10}, Key = {fds334803} } @misc{fds334802, Author = {Sommer, MA and Wurtz, RH}, Title = {The Dialogue between Cerebral Cortex and Superior Colliculus: Multiple Ascending Pathways for Corollary Discharge}, Volume = {TBD}, Pages = {TBD}, Booktitle = {The New Visual Neurosciences}, Publisher = {MIT Press}, Address = {Cambridge, Massachusetts}, Editor = {Leo M. Chalupa and Jack S. Werner}, Year = {2014}, url = {https://dl.dropbox.com/u/27738651/Publications/SommerWurtz-NewVisNeurosci-InPress.pdf}, Key = {fds334802} } @misc{fds334824, Author = {Sommer, MA}, Title = {Supplementary eye fields}, Pages = {635-643}, Booktitle = {Encyclopedia of Neuroscience}, Publisher = {Academic Press}, Address = {Oxford}, Editor = {Squire, LR}, Year = {2009}, ISBN = {978-0-08-045046-9}, url = {https://dl.dropboxusercontent.com/u/27738651/Publications/Sommer2009-SEFreview-EncyclOfNeurosci.pdf}, Abstract = {The supplementary eye fields (SEFs) are located in dorsomedial frontal cortex and contribute to high-level control of eye movements. Recordings in the SEF reveal visual-, saccade-, and fixation-related activity, and stimulations in the SEF evoke saccades and fixations. Inactivations and lesions of the SEF, however, cause minimal oculomotor deficits. The SEF thus processes information relevant to eye movements and influences critical oculomotor centers but seems unnecessary for generating action. Instead, the SEF has overarching, subtle functions that include representing space in multiple ways, supervising behavior, monitoring conflict, prediction, learning, planning sequences, and coordination of the limbs and eyes. © 2009 Elsevier Ltd All rights reserved.}, Doi = {10.1016/B978-008045046-9.01122-0}, Key = {fds334824} } @misc{fds334820, Author = {Crapse, TB and Sommer, MA}, Title = {Corollary Discharge}, Pages = {325-327}, Booktitle = {Encyclopedia of Perception}, Publisher = {SAGE Publications}, Editor = {Goldstein, RB}, Year = {2009}, ISBN = {9781412940818}, Key = {fds334820} } @misc{fds334821, Author = {Shin, SY and Crapse, TB and Mayo, JP and Sommer, MA}, Title = {Visuomotor Integration}, Pages = {4354-4359}, Booktitle = {Encyclopedia of Neuroscience}, Publisher = {Springer}, Editor = {Binder, MD and Hirokawa, N and Windhorst, U}, Year = {2009}, ISBN = {978-3-540-23735-8}, url = {http://dx.doi.org/10.1007/978-3-540-29678-2_6384}, Doi = {10.1007/978-3-540-29678-2_6384}, Key = {fds334821} } @misc{fds334822, Author = {Sommer, MA and Wurtz, RH}, Title = {Single Neurons and Primate Behavior}, Pages = {123-139}, Booktitle = {Methods in Mind}, Publisher = {MIT Press}, Editor = {Senior, C and Russell, T and Gazzaniga, M}, Year = {2009}, ISBN = {9780262513432}, Key = {fds334822} } @misc{fds207861, Author = {Wurtz, Robert H. and Sommer, Marc A.}, Title = {Single Neurons and Primate Behavior}, Pages = {123-139}, Booktitle = {Methods in Mind}, Publisher = {MIT Press}, Address = {Cambridge, Massachusetts}, Editor = {Carl Senior and Tamara Russell and Michael S. Gazzaniga}, Year = {2006}, ISBN = {978-0262195416}, url = {https://dl.dropbox.com/u/27738651/Publications/WurtzSommer_MethodsInMind2006.pdf}, Abstract = {Understanding the brain mechanisms mediating cognitive behavior requires combining two experimental steps. First, the brain must actually be engaged in the cognitive behavior under study. Second, the brain activity must be measured during this behavior and the recording sufficiently described to permit replication of the experiment. There are a number of ways of meeting the second prerequisite, many discussed elsewhere in this volume; our chapter will address one with unsurpassed spatial and temporal resolution: the recording of the action potentials of single neurons. Recording single neurons in the brain is a mature technique that has been used extensively for over a quarter century. In outlining the technique requirements and comparing them to those of other techniques, we will focus on what has become a cornerstone for the study of brain mechanisms underlying cognitive behavior: single-neuron recording from awake monkeys trained on behavioral tasks. Our description and comments are based on our own experience in studying awake monkeys; we also provide references on specific technical points not addressed in this chapter.}, Key = {fds207861} } @misc{fds207859, Author = {Sommer, Marc A. and Wurtz, Robert H.}, Title = {The Dialogue between Cerebral Cortex and Superior Colliculus: Implications for Saccadic Target Selection and Corollary Discharge.}, Volume = {2}, Pages = {1466-1484}, Booktitle = {The Visual Neurosciences}, Publisher = {MIT Press}, Address = {Cambridge, Massachusetts}, Editor = {Leo M. Chalupa and Jack S. Werner}, Year = {2004}, ISBN = {978-0-262-03308-4}, url = {https://dl.dropbox.com/u/27738651/Publications/SommerWurtz_TheVisualNeurosciences2004.pdf}, Key = {fds207859} } @misc{fds349698, Author = {Wurtz, RH and Sommer, MA}, Title = {Identifying corollary discharges for movement in the primate brain}, Pages = {47-60}, Booktitle = {Progress in Brain Research}, Publisher = {Elsevier}, Year = {2004}, ISBN = {9780444509789}, url = {http://dx.doi.org/10.1016/s0079-6123(03)14403-2}, Doi = {10.1016/s0079-6123(03)14403-2}, Key = {fds349698} } @misc{fds334846, Author = {Wurtz, RH and Basso, MA and Paré, M and Sommer, MA}, Title = {The Superior Colliculus and the Cognitive Control of Movement}, Pages = {573-587}, Booktitle = {The New Cognitive Neurosciences}, Publisher = {MIT Press}, Editor = {Gazzaniga, MS}, Year = {2000}, ISBN = {9780262071956}, Key = {fds334846} } @misc{fds334859, Author = {Smith, MA and Sadler, RH and Sommer, MA}, Title = {The Macrophage as the Demyelinative Agent: A Role for Antimyelin Antibodies}, Pages = {51-66}, Booktitle = {Multiple Sclerosis: Current Status of Research and Treatment}, Publisher = {Demos Publications}, Editor = {Herndon, RM and Seil, FJ}, Year = {1994}, ISBN = {9780939957286}, Key = {fds334859} } %% Papers Published @article{fds371675, Author = {Subramanian, D and Pearson, JM and Sommer, MA}, Title = {Bayesian and Discriminative Models for Active Visual Perception across Saccades.}, Journal = {eNeuro}, Volume = {10}, Number = {7}, Pages = {ENEURO.0403-ENEU22.2023}, Year = {2023}, Month = {July}, url = {http://dx.doi.org/10.1523/ENEURO.0403-22.2023}, Abstract = {The brain interprets sensory inputs to guide behavior, but behavior itself disrupts sensory inputs. Perceiving a coherent world while acting in it constitutes active perception. For example, saccadic eye movements displace visual images on the retina and yet the brain perceives visual stability. Because this percept of visual stability has been shown to be influenced by prior expectations, we tested the hypothesis that it is Bayesian. The key prediction was that priors would be used more as sensory uncertainty increases. Humans and rhesus macaques reported whether an image moved during saccades. We manipulated both prior expectations and levels of sensory uncertainty. All psychophysical data were compared with the predictions of Bayesian ideal observer models. We found that humans were Bayesian for continuous judgments. For categorical judgments, however, they were anti-Bayesian: they used their priors less with greater uncertainty. We studied this categorical result further in macaques. The animals' judgments were similarly anti-Bayesian for sensory uncertainty caused by external, image noise, but Bayesian for uncertainty due to internal, motor-driven noise. A discriminative learning model explained the anti-Bayesian effects. We conclude that active vision uses both Bayesian and discriminative models depending on task requirements (continuous vs categorical) and the source of uncertainty (image noise vs motor-driven noise). In the context of previous knowledge about the saccadic system, our results provide an example of how the comparative analysis of Bayesian versus non-Bayesian models of perception offers novel insights into underlying neural organization.}, Doi = {10.1523/ENEURO.0403-22.2023}, Key = {fds371675} } @article{fds369379, Author = {Daw, TB and El-Nahal, HG and Basso, MA and Jun, EJ and Bautista, AR and Samulski, RJ and Sommer, MA and Bohlen, MO}, Title = {Direct Comparison of Epifluorescence and Immunostaining for Assessing Viral Mediated Gene Expression in the Primate Brain.}, Journal = {Human gene therapy}, Volume = {34}, Number = {5-6}, Pages = {228-246}, Year = {2023}, Month = {March}, url = {http://dx.doi.org/10.1089/hum.2022.194}, Abstract = {Viral vector technologies are commonly used in neuroscience research to understand and manipulate neural circuits, but successful applications of these technologies in non-human primate models have been inconsistent. An essential component to improve these technologies is an impartial and accurate assessment of the effectiveness of different viral constructs in the primate brain. We tested a diverse array of viral vectors delivered to the brain and extraocular muscles of macaques and compared three methods for histological assessment of viral-mediated fluorescent transgene expression: epifluorescence (Epi), immunofluorescence (IF), and immunohistochemistry (IHC). Importantly, IF and IHC identified a greater number of transduced neurons compared to Epi. Furthermore, IF and IHC reliably provided enhanced visualization of transgene in most cellular compartments (<i>i.e.</i>, dendritic, axonal, and terminal fields), whereas the degree of labeling provided by Epi was inconsistent and predominantly restricted to somas and apical dendrites. Because Epi signals are unamplified (in contrast to IF and IHC), Epi may provide a more veridical assessment for the amount of accumulated transgene and, thus, the potential to chemogenetically or optogenetically manipulate neuronal activity. The comparatively weak Epi signals suggest that the current generations of viral constructs, regardless of delivered transgene, are not optimized for primates. This reinforces an emerging viewpoint that viral vectors tailored for the primate brain are necessary for basic research and human gene therapy.}, Doi = {10.1089/hum.2022.194}, Key = {fds369379} } @article{fds363007, Author = {Goetz, SM and Howell, B and Wang, B and Li, Z and Sommer, MA and Peterchev, AV and Grill, WM}, Title = {Isolating two sources of variability of subcortical stimulation to quantify fluctuations of corticospinal tract excitability.}, Journal = {Clin Neurophysiol}, Volume = {138}, Pages = {134-142}, Year = {2022}, Month = {June}, url = {http://dx.doi.org/10.1016/j.clinph.2022.02.009}, Abstract = {OBJECTIVE: Investigate the variability previously found with cortical stimulation and handheld transcranial magnetic stimulation (TMS) coils, criticized for its high potential of coil position fluctuations, bypassing the cortex using deep brain electrical stimulation (DBS) of the corticospinal tract with fixed electrodes where both latent variations of the coil position of TMS are eliminated and cortical excitation fluctuations should be absent. METHODS: Ten input-output curves were recorded from five anesthetized cats with implanted DBS electrodes targeting the corticospinal tract. Goodness of fit of regressions with a conventional single variability source as well as a dual variability source model was quantified using a Schwarz Bayesian Information approach to avoid overfitting. RESULTS: Motor evoked potentials (MEPs) through DBS of the corticospinal tract revealed short-term fluctuations in excitability of the targeted neuron pathway reflecting endogenous input-side variability at similar magnitude as TMS despite bypassing cortical networks. CONCLUSION: Input-side variability, i.e., variability resulting in changing MEP amplitudes as if the stimulation strength was modulated, also emerges in electrical stimulation at a similar degree and is not primarily a result of varying stimulation, such as minor coil movements in TMS. More importantly, this variability component is present, although the cortex is bypassed. Thus, it may be of spinal origin, which can include cortical input from spinal projections. Further, the nonlinearity of the compound variability entails complex heteroscedastic non-Gaussian distributions and typically does not allow simple linear averages in statistical analysis of MEPs. As the average is dominated by outliers, it risks bias. With appropriate regression, the net effects of excitatory and inhibitory inputs to the targeted neuron pathways become noninvasively observable and quantifiable. SIGNIFICANCE: The neural responses evoked by artificial stimulation in the cerebral cortex are variable. For example, MEPs in response to repeated presentations of the same stimulus can vary from no response to saturation across trials. Several sources of such variability have been suggested, and most of them may be technical in nature, but localization is missing.}, Doi = {10.1016/j.clinph.2022.02.009}, Key = {fds363007} } @article{fds357280, Author = {Caruso, VC and Pages, DS and Sommer, MA and Groh, JM}, Title = {Compensating for a shifting world: evolving reference frames of visual and auditory signals across three multimodal brain areas.}, Journal = {Journal of neurophysiology}, Volume = {126}, Number = {1}, Pages = {82-94}, Year = {2021}, Month = {July}, url = {http://dx.doi.org/10.1152/jn.00385.2020}, Abstract = {Stimulus locations are detected differently by different sensory systems, but ultimately they yield similar percepts and behavioral responses. How the brain transcends initial differences to compute similar codes is unclear. We quantitatively compared the reference frames of two sensory modalities, vision and audition, across three interconnected brain areas involved in generating saccades, namely the frontal eye fields (FEF), lateral and medial parietal cortex (M/LIP), and superior colliculus (SC). We recorded from single neurons in head-restrained monkeys performing auditory- and visually guided saccades from variable initial fixation locations and evaluated whether their receptive fields were better described as eye-centered, head-centered, or hybrid (i.e. not anchored uniquely to head- or eye-orientation). We found a progression of reference frames across areas and across time, with considerable hybrid-ness and persistent differences between modalities during most epochs/brain regions. For both modalities, the SC was more eye-centered than the FEF, which in turn was more eye-centered than the predominantly hybrid M/LIP. In all three areas and temporal epochs from stimulus onset to movement, visual signals were more eye-centered than auditory signals. In the SC and FEF, auditory signals became more eye-centered at the time of the saccade than they were initially after stimulus onset, but only in the SC at the time of the saccade did the auditory signals become "predominantly" eye-centered. The results indicate that visual and auditory signals both undergo transformations, ultimately reaching the same final reference frame but via different dynamics across brain regions and time.<b>NEW & NOTEWORTHY</b> Models for visual-auditory integration posit that visual signals are eye-centered throughout the brain, whereas auditory signals are converted from head-centered to eye-centered coordinates. We show instead that both modalities largely employ hybrid reference frames: neither fully head- nor eye-centered. Across three hubs of the oculomotor network (intraparietal cortex, frontal eye field, and superior colliculus) visual and auditory signals evolve from hybrid to a common eye-centered format via different dynamics across brain areas and time.}, Doi = {10.1152/jn.00385.2020}, Key = {fds357280} } @article{fds358004, Author = {Liu, S and Clements, JM and Kirsch, EP and Rao, HM and Zielinski, DJ and Lu, Y and Mainsah, BO and Potter, ND and Sommer, MA and Kopper, R and Appelbaum, LG}, Title = {Psychophysiological Markers of Performance and Learning during Simulated Marksmanship in Immersive Virtual Reality.}, Journal = {J Cogn Neurosci}, Volume = {33}, Number = {7}, Pages = {1253-1270}, Year = {2021}, Month = {June}, url = {http://dx.doi.org/10.1162/jocn_a_01713}, Abstract = {The fusion of immersive virtual reality, kinematic movement tracking, and EEG offers a powerful test bed for naturalistic neuroscience research. Here, we combined these elements to investigate the neuro-behavioral mechanisms underlying precision visual-motor control as 20 participants completed a three-visit, visual-motor, coincidence-anticipation task, modeled after Olympic Trap Shooting and performed in immersive and interactive virtual reality. Analyses of the kinematic metrics demonstrated learning of more efficient movements with significantly faster hand RTs, earlier trigger response times, and higher spatial precision, leading to an average of 13% improvement in shot scores across the visits. As revealed through spectral and time-locked analyses of the EEG beta band (13-30 Hz), power measured prior to target launch and visual-evoked potential amplitudes measured immediately after the target launch correlated with subsequent reactive kinematic performance in the shooting task. Moreover, both launch-locked and shot/feedback-locked visual-evoked potentials became earlier and more negative with practice, pointing to neural mechanisms that may contribute to the development of visual-motor proficiency. Collectively, these findings illustrate EEG and kinematic biomarkers of precision motor control and changes in the neurophysiological substrates that may underlie motor learning.}, Doi = {10.1162/jocn_a_01713}, Key = {fds358004} } @article{fds353025, Author = {Tremblay, S and Acker, L and Afraz, A and Albaugh, DL and Amita, H and Andrei, AR and Angelucci, A and Aschner, A and Balan, PF and Basso, MA and Benvenuti, G and Bohlen, MO and Caiola, MJ and Calcedo, R and Cavanaugh, J and Chen, Y and Chen, S and Chernov, MM and Clark, AM and Dai, J and Debes, SR and Deisseroth, K and Desimone, R and Dragoi, V and Egger, SW and Eldridge, MAG and El-Nahal, HG and Fabbrini, F and Federer, F and Fetsch, CR and Fortuna, MG and Friedman, RM and Fujii, N and Gail, A and Galvan, A and Ghosh, S and Gieselmann, MA and Gulli, RA and Hikosaka, O and Hosseini, EA and Hu, X and Hüer, J and Inoue, K-I and Janz, R and Jazayeri, M and Jiang, R and Ju, N and Kar, K and Klein, C and Kohn, A and Komatsu, M and Maeda, K and Martinez-Trujillo, JC and Matsumoto, M and Maunsell, JHR and Mendoza-Halliday, D and Monosov, IE and Muers, RS and Nurminen, L and Ortiz-Rios, M and O'Shea, DJ and Palfi, S and Petkov, CI and Pojoga, S and Rajalingham, R and Ramakrishnan, C and Remington, ED and Revsine, C and Roe, AW and Sabes, PN and Saunders, RC and Scherberger, H and Schmid, MC and Schultz, W and Seidemann, E and Senova, Y-S and Shadlen, MN and Sheinberg, DL and Siu, C and Smith, Y and Solomon, SS and Sommer, MA and Spudich, JL and Stauffer, WR and Takada, M and Tang, S and Thiele, A and Treue, S and Vanduffel, W and Vogels, R and Whitmire, MP and Wichmann, T and Wurtz, RH and Xu, H and Yazdan-Shahmorad, A and Shenoy, KV and DiCarlo, JJ and Platt, ML}, Title = {An Open Resource for Non-human Primate Optogenetics.}, Journal = {Neuron}, Volume = {108}, Number = {6}, Pages = {1075-1090.e6}, Year = {2020}, Month = {December}, url = {http://dx.doi.org/10.1016/j.neuron.2020.09.027}, Abstract = {Optogenetics has revolutionized neuroscience in small laboratory animals, but its effect on animal models more closely related to humans, such as non-human primates (NHPs), has been mixed. To make evidence-based decisions in primate optogenetics, the scientific community would benefit from a centralized database listing all attempts, successful and unsuccessful, of using optogenetics in the primate brain. We contacted members of the community to ask for their contributions to an open science initiative. As of this writing, 45 laboratories around the world contributed more than 1,000 injection experiments, including precise details regarding their methods and outcomes. Of those entries, more than half had not been published. The resource is free for everyone to consult and contribute to on the Open Science Framework website. Here we review some of the insights from this initial release of the database and discuss methodological considerations to improve the success of optogenetic experiments in NHPs.}, Doi = {10.1016/j.neuron.2020.09.027}, Key = {fds353025} } @article{fds350573, Author = {Cushnie, AK and El-Nahal, HG and Bohlen, MO and May, PJ and Basso, MA and Grimaldi, P and Wang, MZ and de Velasco Ezequiel and MF and Sommer, MA and Heilbronner, SR}, Title = {Using rAAV2-retro in rhesus macaques: Promise and caveats for circuit manipulation.}, Journal = {Journal of neuroscience methods}, Volume = {345}, Pages = {108859}, Publisher = {Elsevier BV}, Year = {2020}, Month = {November}, url = {http://dx.doi.org/10.1016/j.jneumeth.2020.108859}, Abstract = {<h4>Background</h4>Recent genetic technologies such as opto- and chemogenetics allow for the manipulation of brain circuits with unprecedented precision. Most studies employing these techniques have been undertaken in rodents, but a more human-homologous model for studying the brain is the nonhuman primate (NHP). Optimizing viral delivery of transgenes encoding actuator proteins could revolutionize the way we study neuronal circuits in NHPs. NEW METHOD: rAAV2-retro, a popular new capsid variant, produces robust retrograde labeling in rodents. Whether rAAV2-retro's highly efficient retrograde transport would translate to NHPs was unknown. Here, we characterized the anatomical distribution of labeling following injections of rAAV2-retro encoding opsins or DREADDs in the cortico-basal ganglia and oculomotor circuits of rhesus macaques.<h4>Results</h4>rAAV2-retro injections in striatum, frontal eye field, and superior colliculus produced local labeling at injection sites and robust retrograde labeling in many afferent regions. In every case, however, a few brain regions with well-established projections to the injected structure lacked retrogradely labeled cells. We also observed robust terminal field labeling in downstream structures.<h4>Comparison with existing method(s)</h4>Patterns of labeling were similar to those obtained with traditional tract-tracers, except for some afferent labeling that was noticeably absent.<h4>Conclusions</h4>rAAV2-retro promises to be useful for circuit manipulation via retrograde transduction in NHPs, but caveats were revealed by our findings. Some afferently connected regions lacked retrogradely labeled cells, showed robust axon terminal labeling, or both. This highlights the importance of anatomically characterizing rAAV2-retro's expression in target circuits in NHPs before moving to manipulation studies.}, Doi = {10.1016/j.jneumeth.2020.108859}, Key = {fds350573} } @article{fds352422, Author = {Bohlen, MO and McCown, TJ and Powell, SK and El-Nahal, HG and Daw, T and Basso, MA and Sommer, MA and Samulski, RJ}, Title = {Adeno-Associated Virus Capsid-Promoter Interactions in the Brain Translate from Rat to the Nonhuman Primate.}, Journal = {Human gene therapy}, Volume = {31}, Number = {21-22}, Pages = {1155-1168}, Year = {2020}, Month = {November}, url = {http://dx.doi.org/10.1089/hum.2020.196}, Abstract = {Recently, we established an adeno-associated virus (AAV9) capsid-promoter interaction that directly determined cell-specific gene expression across two synthetic promoters, Cbh and CBA, in the rat striatum. These studies not only expand this capsid-promoter interaction to include another promoter in the rat striatum but also establish AAV capsid-promoter interactions in the nonhuman primate brain. When AAV serotype 9 (AAV9) vectors were injected into the rat striatum, the minimal synthetic promoter JetI drove green fluorescent protein (GFP) gene expression predominantly in oligodendrocytes. However, similar to our previous findings, the insertion of six alanines into VP1/VP2 of the AAV9 capsid (AAV9AU) significantly shifted JetI-driven GFP gene expression to neurons. In addition, previous retrograde tracing studies in the nonhuman primate brain also revealed the existence of a capsid-promoter interaction. When rAAV2-Retro vectors were infused into the frontal eye field (FEF) of rhesus macaques, local gene expression was prominent using either the hybrid chicken beta actin (CAG) or human synapsin (hSyn) promoters. However, only the CAG promoter, not the hSyn promoter, led to gene expression in the ipsilateral claustrum and contralateral FEF. Conversely, infusion of rAAV2-retro-hSyn vectors, but not rAAV2-retro-CAG, into the macaque superior colliculus led to differential and selective retrograde gene expression in cerebellotectal afferent cells. Clearly, this differential promoter/capsid expression profile could not be attributed to promoter inactivation from retrograde transport of the rAAV2-Retro vector. In summary, we document the potential for AAV capsid/promoter interactions to impact cell-specific gene expression across species, experimental manipulations, and engineered capsids, independent of capsid permissivity.}, Doi = {10.1089/hum.2020.196}, Key = {fds352422} } @article{fds351415, Author = {Gamboa Arana and OL and Palmer, H and Dannhauer, M and Hile, C and Liu, S and Hamdan, R and Brito, A and Cabeza, R and Davis, SW and Peterchev, AV and Sommer, MA and Appelbaum, LG}, Title = {Intensity- and timing-dependent modulation of motion perception with transcranial magnetic stimulation of visual cortex.}, Journal = {Neuropsychologia}, Volume = {147}, Pages = {107581}, Year = {2020}, Month = {October}, url = {http://dx.doi.org/10.1016/j.neuropsychologia.2020.107581}, Abstract = {Despite the widespread use of transcranial magnetic stimulation (TMS) in research and clinical care, the dose-response relations and neurophysiological correlates of modulatory effects remain relatively unexplored. To fill this gap, we studied modulation of visual processing as a function of TMS parameters. Our approach combined electroencephalography (EEG) with application of single pulse TMS to visual cortex as participants performed a motion perception task. During each participants' first visit, motion coherence thresholds, 64-channel visual evoked potentials (VEPs), and TMS resting motor thresholds (RMT) were measured. In second and third visits, single pulse TMS was delivered at one of two latencies, either 30 ms before the onset of motion or at the onset latency of the N2 VEP component derived from the first session. TMS was delivered at 0%, 80%, 100%, or 120% of RMT over the site of N2 peak activity, or at 120% over vertex. Behavioral results demonstrated a significant main effect of TMS timing on accuracy, with better performance when TMS was applied at the N2-Onset timing versus Pre-Onset, as well as a significant interaction, indicating that 80% intensity produced higher accuracy than other conditions at the N2-Onset. TMS effects on the P3 VEP showed reduced amplitudes in the 80% Pre-Onset condition, an increase for the 120% N2-Onset condition, and monotonic amplitude scaling with stimulation intensity. The N2 component was not affected by TMS. These findings reveal the influence of TMS intensity and timing on visual perception and electrophysiological responses, with optimal facilitation at stimulation intensities below RMT.}, Doi = {10.1016/j.neuropsychologia.2020.107581}, Key = {fds351415} } @article{fds349696, Author = {Gamboa, OL and Brito, A and Abzug, Z and D'Arbeloff, T and Beynel, L and Wing, EA and Dannhauer, M and Palmer, H and Hilbig, SA and Crowell, CA and Liu, S and Donaldson, R and Cabeza, R and Davis, SW and Peterchev, AV and Sommer, MA and Appelbaum, LG}, Title = {Application of long-interval paired-pulse transcranial magnetic stimulation to motion-sensitive visual cortex does not lead to changes in motion discrimination.}, Journal = {Neurosci Lett}, Volume = {730}, Pages = {135022}, Year = {2020}, Month = {June}, url = {http://dx.doi.org/10.1016/j.neulet.2020.135022}, Abstract = {The perception of visual motion is dependent on a set of occipitotemporal regions that are readily accessible to neuromodulation. The current study tested if paired-pulse Transcranial Magnetic Stimulation (ppTMS) could modulate motion perception by stimulating the occipital cortex as participants viewed near-threshold motion dot stimuli. In this sham-controlled study, fifteen subjects completed two sessions. On the first visit, resting motor threshold (RMT) was assessed, and participants performed an adaptive direction discrimination task to determine individual motion sensitivity. During the second visit, subjects performed the task with three difficulty levels as TMS pulses were delivered 150 and 50 ms prior to motion stimulus onset at 120% RMT, under the logic that the cumulative inhibitory effect of these pulses would alter motion sensitivity. ppTMS was delivered at one of two locations: 3 cm dorsal and 5 cm lateral to inion (scalp-based coordinate), or at the site of peak activation for "motion" according to the NeuroSynth fMRI database (meta-analytic coordinate). Sham stimulation was delivered on one-third of trials by tilting the coil 90°. Analyses showed no significant active-versus-sham effects of ppTMS when stimulation was delivered to the meta-analytic (p = 0.15) or scalp-based coordinates (p = 0.17), which were separated by 29 mm on average. Active-versus-sham stimulation differences did not interact with either stimulation location (p = 0.12) or difficulty (p = 0.33). These findings fail to support the hypothesis that long-interval ppTMS recruits inhibitory processes in motion-sensitive cortex but must be considered within the limited parameters used in this design.}, Doi = {10.1016/j.neulet.2020.135022}, Key = {fds349696} } @article{fds350632, Author = {Gamboa Arana and OL and Palmer, H and Dannhauer, M and Hile, C and Liu, S and Hamdan, R and Brito, A and Cabeza, R and Davis, S and Peterchev, A and Sommer, M and Appelbaum, L}, Title = {Dose-dependent enhancement of motion direction discrimination with transcranial magnetic stimulation of visual cortex}, Year = {2020}, url = {http://dx.doi.org/10.1101/2020.06.14.151118}, Abstract = {Despite the widespread use of transcranial magnetic stimulation (TMS) in research and clinical care, the underlying mechanisms-of-actions that mediate modulatory effects remain poorly understood. To fill this gap, we studied dose–response functions of TMS for modulation of visual processing. Our approach combined electroencephalography (EEG) with application of single pulse TMS to visual cortex as participants performed a motion perception task. During participants’ first visit, motion coherence thresholds, 64-channel visual evoked potentials (VEPs), and TMS resting motor thresholds (RMT) were measured. In second and third visits, single pulse TMS was delivered 30 ms before the onset of motion or at the onset latency of the N2 VEP component derived from the first session. TMS was delivered at 0%, 80%, 100%, or 120% of RMT over the site of N2 peak activity, or at 120% over vertex. Behavioral results demonstrated a significant main effect of TMS timing on accuracy, with better performance when TMS was applied at N2-Onset timing versus Pre-Onset, as well as a significant interaction, indicating that 80% intensity produced higher accuracy than other conditions. TMS effects on VEPs showed reduced amplitudes in the 80% Pre-Onset condition, an increase for the 120% N2-Onset condition, and monotonic amplitude scaling with stimulation intensity. The N2 component was not affected by TMS. These findings reveal dose–response relationships between intensity and timing of TMS on visual perception and electrophysiological brain activity, generally indicating greater facilitation at stimulation intensities below RMT.}, Doi = {10.1101/2020.06.14.151118}, Key = {fds350632} } @article{fds366058, Author = {Abzug, ZM and Sommer, MA and Beck, JM}, Title = {Properties of decision-making tasks govern the tradeoff between model-based and model-free learning}, Year = {2019}, Month = {August}, url = {http://dx.doi.org/10.1101/730663}, Abstract = {<jats:title>Abstract</jats:title><jats:p>When decisions must be made between uncertain options, optimal behavior depends on accurate estimations of the likelihoods of different outcomes. The contextual factors that govern whether these estimations depend on model-free learning (tracking outcomes) vs. model-based learning (learning generative stimulus distributions) are poorly understood. We studied model-free and model-based learning using serial decision-making tasks in which subjects selected a rule and then used it to flexibly act on visual stimuli. A factorial approach defined a family of behavioral models that could integrate model-free and model-based strategies to predict rule selection trial-by-trial. Bayesian model selection demonstrated that the subjects strategies varied depending on lower-level task characteristics such as the identities of the rule options. In certain conditions, subjects integrated learned stimulus distributions and tracked reward rates to guide their behavior. The results thus identify tradeoffs between model-based and model-free decision strategies, and in some cases parallel utilization, depending on task context.</jats:p>}, Doi = {10.1101/730663}, Key = {fds366058} } @article{fds341566, Author = {Toader, AC and Rao, HM and Ryoo, M and Bohlen, MO and Cruger, JS and Oh-Descher, H and Ferrari, S and Egner, T and Beck, J and Sommer, MA}, Title = {Probabilistic inferential decision-making under time pressure in rhesus macaques (Macaca mulatta).}, Journal = {Journal of comparative psychology (Washington, D.C. : 1983)}, Volume = {133}, Number = {3}, Pages = {380-396}, Year = {2019}, Month = {August}, url = {http://dx.doi.org/10.1037/com0000168}, Abstract = {Decisions often involve the consideration of multiple cues, each of which may inform selection on the basis of learned probabilities. Our ability to use probabilistic inference for decisions is bounded by uncertainty and constraints such as time pressure. Previous work showed that when humans choose between visual objects in a multiple-cue, probabilistic task, they cope with time pressure by discounting the least informative cues, an example of satisficing or "good enough" decision-making. We tested two rhesus macaques (Macaca mulatta) on a similar task to assess their capacity for probabilistic inference and satisficing in comparison with humans. In each trial, a monkey viewed two compound stimuli consisting of four cue dimensions. Each dimension (e.g., color) had two possible states (e.g., red or blue) with different probabilistic weights. Selecting the stimulus with highest total weight yielded higher odds of receiving reward. Both monkeys learned the assigned weights at high accuracy. Under time pressure, both monkeys were less accurate as a result of decreased use of cue information. One monkey adopted the same satisficing strategy used by humans, ignoring the least informative cue dimension. Both monkeys, however, exhibited a strategy not reported for humans, a "group-the-best" strategy in which the top two cues were used similarly despite their different assigned weights. The results validate macaques as an animal model of probabilistic decision-making, establishing their capacity to discriminate between objects using at least four visual dimensions simultaneously. The time pressure data suggest caution, however, in using macaques as models of human satisficing. (PsycINFO Database Record (c) 2019 APA, all rights reserved).}, Doi = {10.1037/com0000168}, Key = {fds341566} } @article{fds366059, Author = {Caruso, VC and Pages, DS and Sommer, MA and Groh, JM}, Title = {Compensating for a shifting world: evolving reference frames of visual and auditory signals across three multimodal brain areas}, Year = {2019}, Month = {June}, url = {http://dx.doi.org/10.1101/669333}, Abstract = {<jats:title>ABSTRACT</jats:title><jats:p>Stimulus locations are detected differently by different sensory systems, but ultimately they yield similar percepts and behavioral responses. How the brain transcends initial differences to compute similar codes is unclear. We quantitatively compared the reference frames of two sensory modalities, vision and audition, across three interconnected brain areas involved in generating saccades, namely the frontal eye fields (FEF), lateral and medial parietal cortex (M/LIP), and superior colliculus (SC). We recorded from single neurons in head-restrained monkeys performing auditory- and visually-guided saccades from variable initial fixation locations, and evaluated whether their receptive fields were better described as eye-centered, head-centered, or hybrid (i.e. not anchored uniquely to head- or eye-orientation). We found a progression of reference frames across areas and across time, with considerable hybrid-ness and persistent differences between modalities during most epochs/brain regions. For both modalities, the SC was more eye-centered than the FEF, which in turn was more eye-centered than the predominantly hybrid M/LIP. In all three areas and temporal epochs from stimulus onset to movement, visual signals were more eye-centered than auditory signals. In the SC and FEF, auditory signals became more eye-centered at the time of the saccade than they were initially after stimulus onset, but only in the SC at the time of the saccade did the auditory signals become <jats:italic>predominantly</jats:italic> eye-centered. The results indicate that visual and auditory signals both undergo transformations, ultimately reaching the same final reference frame but via different dynamics across brain regions and time.</jats:p><jats:sec><jats:title>New and Noteworthy</jats:title><jats:p>Models for visual-auditory integration posit that visual signals are eye-centered throughout the brain, while auditory signals are converted from head-centered to eye-centered coordinates. We show instead that both modalities largely employ hybrid reference frames: neither fully head-nor eye-centered. Across three hubs of the oculomotor network (intraparietal cortex, frontal eye field and superior colliculus) visual and auditory signals evolve from hybrid to a common eye-centered format via different dynamics across brain areas and time.</jats:p></jats:sec>}, Doi = {10.1101/669333}, Key = {fds366059} } @article{fds343467, Author = {Subramanian, D and Alers, A and Sommer, M}, Title = {Corollary discharge for action and cognition}, Journal = {Biological Psychiatry: Cognitive Neuroscience and Neuroimaging}, Volume = {4}, Number = {9}, Pages = {782-790}, Publisher = {Elsevier}, Year = {2019}, Month = {May}, url = {http://dx.doi.org/10.1016/j.bpsc.2019.05.010}, Abstract = {In motor systems, a copy of the movement command known as corollary discharge is broadcast to other regions of the brain to warn them of the impending movement. The premise of this review is that the concept of corollary discharge may generalize in revealing ways to the brain’s cognitive systems. An oculomotor pathway from the brainstem to frontal cortex provides a well-established example of how corollary discharge is instantiated for sensorimotor processing. Building on causal evidence from inactivation of the pathway, we motivate forward models as a tool for understanding the contributions of corollary discharge to perception and movement. Finally, we extend the definition of corollary discharge to account for signals that may be used for cognitive forward models of decision-making. This framework may provide new insights into signals and circuits that contribute to sequential decision processes, the breakdown of which may account for some symptoms of psychiatric disorders.}, Doi = {10.1016/j.bpsc.2019.05.010}, Key = {fds343467} } @article{fds346630, Author = {Bohlen, M and El-Nahal, H and Sommer, M}, Title = {Transduction of Craniofacial Motoneurons Following Intramuscular Injections of Canine Adenovirus Type-2 (CAV-2) in Rhesus Macaques}, Journal = {Frontiers in Neuroanatomy}, Volume = {In Press}, Pages = {84}, Publisher = {Frontiers Media}, Year = {2019}, Month = {January}, url = {http://dx.doi.org/10.3389/fnana.2019.00084}, Abstract = {Reliable viral vector-mediated transgene expression in primate motoneurons would improve our ability to anatomically and physiologically interrogate motor systems. We therefore investigated the efficacy of replication defective, early region 1-deleted canine adenovirus type-2 (CAV-2) vectors for mediating transgene expression of fluorescent proteins into brainstem motoneurons following craniofacial intramuscular injections in four rhesus monkeys (Macaca mulatta). Vector injections were placed into surgically identified and isolated craniofacial muscles. After a one- to two-month survival time, animals were sacrificed and transgene expression was assessed with immunohistochemistry in the corresponding motoneuronal populations. We found that injections of CAV-2 into individual craniofacial muscles at doses in the range of ~10^10 to 10^11 physical particles/muscle resulted in robust motoneuronal transduction and expression of immunohistochemically identified fluorescent proteins across multiple animals. By using different titers in separate muscles, with the resulting transduction patterns tracked via fluorophore expression and labeled motoneuron location, we established qualitative dose-response relationships in two animals. In one animal that received an atypically high titer (5.7 x 10^11 total CAV-2 physical particles) distributed across numerous injection sites, no transduction was detected, likely due to a retaliatory immune response. We conclude that CAV-2 vectors show promise for genetic modification of primate motoneurons following craniofacial intramuscular injections. Our findings warrant focused attention toward the use of CAV-2 vectors to deliver opsins, DREADDs, and other molecular probes to improve genetics-based methods for primate research. Further work is required to optimize CAV-2 transduction parameters. CAV-2 vectors encoding proteins could provide a new, reliable route for modifying activity in targeted neuronal populations of the primate central nervous system.}, Doi = {10.3389/fnana.2019.00084}, Key = {fds346630} } @article{fds337180, Author = {Abzug, ZM and Sommer, MA}, Title = {Neuronal correlates of serial decision-making in the supplementary eye field}, Journal = {Journal of Neuroscience}, Volume = {38}, Number = {33}, Pages = {7280-7292}, Publisher = {Society for Neuroscience}, Year = {2018}, Month = {August}, url = {http://dx.doi.org/10.1523/jneurosci.3643-17.2018}, Abstract = {Human behavior is influenced by serial decision-making: past decisions affect choices that set the context for selecting future options. A primate brain region that may be involved in linking decisions across time is the supplementary eye field (SEF), which, in addition to its well-known visual responses and saccade-related activity, also signals the rules that govern flexible decisions and the outcomes of those decisions. Our hypotheses were that SEF neurons encode events during serial decision-making and link the sequential decisions with sustained activity. We recorded from neurons in the SEF of two rhesus monkeys (Macaca mulatta, one male, one female) that performed a serial decision-making task. The monkeys used saccades to select a rule that had to be applied later in the same trial to discriminate between visual stimuli. We found, first, that SEF neurons encoded the spatial parameters of saccades during rule selection but not during visual discrimination, suggesting a malleability to their movement-related tuning. Second, SEF activity linked the sequential decisions of rule selection and visual discrimination, but not continuously. Instead, rule-encoding activity appeared in a “just-in-time” manner before the visual discrimination. Third, SEF neurons encoded trial outcomes both prospectively, before decisions within a trial, and retrospectively, across multiple trials. The results thus identify neuronal correlates of rule selection and application in the SEF, including transient signals that link these sequential decisions. Its activity patterns suggest that the SEF participates in serial decision-making in a contextually-dependent manner as part of a broader network.}, Doi = {10.1523/jneurosci.3643-17.2018}, Key = {fds337180} } @article{fds334786, Author = {Abzug, ZM and Sommer, MA}, Title = {Serial decision-making in monkeys during an oculomotor task}, Journal = {Journal of Experimental Psychology: Animal Learning and Cognition}, Volume = {44}, Number = {1}, Pages = {95-102}, Publisher = {American Psychological Association}, Year = {2018}, Month = {January}, url = {http://dx.doi.org/10.1037/xan0000154}, Abstract = {Much of everyday behavior involves serial decision-making, in which the outcome of one choice affects another. An example is setting rules for oneself: choosing a behavioral rule guides appropriate choices in the future. How the brain links decisions across time is poorly understood. Neural mechanisms could be studied in monkeys, as it is known that they can select and use behavioral rules, but existing psychophysical paradigms are poorly suited for the constraints of neurophysiology. Therefore we designed a streamlined task that requires sequential, linked decisions, and trained two rhesus monkeys (Macaca mulatta) to perform it. The task features trial-by-trial consistency, visual stimuli, and eye movement responses to optimize it for simultaneous electrophysiological inquiry. In the first stage of each trial, the monkeys selected a rule or a rule was provided to them. In the second stage, they used the rule to discriminate between two test stimuli. Our hypotheses were that they could use self-selected rules and could deliberately select rules based on reinforcement history. We found that the monkeys were as proficient at using self-selected rules as instructed rules. Their preferences for selecting rules correlated with their performance in using them, consistent with systematic, rather than random, strategies for accomplishing the task. The results confirm and extend prior findings on rule selection in monkeys and establish a viable, experimentally flexible paradigm for studying the neural basis of serial decision-making.}, Doi = {10.1037/xan0000154}, Key = {fds334786} } @article{fds334785, Author = {Rao, HM and Khanna, R and Zielinski, DJ and Lu, Y and Clements, JM and Potter, ND and Sommer, MA and Kopper, R and Appelbaum, LG}, Title = {Sensorimotor Learning during a Marksmanship Task in Immersive Virtual Reality.}, Journal = {Front Psychol}, Volume = {9}, Pages = {58}, Year = {2018}, url = {http://dx.doi.org/10.3389/fpsyg.2018.00058}, Abstract = {Sensorimotor learning refers to improvements that occur through practice in the performance of sensory-guided motor behaviors. Leveraging novel technical capabilities of an immersive virtual environment, we probed the component kinematic processes that mediate sensorimotor learning. Twenty naïve subjects performed a simulated marksmanship task modeled after Olympic Trap Shooting standards. We measured movement kinematics and shooting performance as participants practiced 350 trials while receiving trial-by-trial feedback about shooting success. Spatiotemporal analysis of motion tracking elucidated the ballistic and refinement phases of hand movements. We found systematic changes in movement kinematics that accompanied improvements in shot accuracy during training, though reaction and response times did not change over blocks. In particular, we observed longer, slower, and more precise ballistic movements that replaced effort spent on corrections and refinement. Collectively, these results leverage developments in immersive virtual reality technology to quantify and compare the kinematics of movement during early learning of full-body sensorimotor orienting.}, Doi = {10.3389/fpsyg.2018.00058}, Key = {fds334785} } @article{fds334784, Author = {Caruso, V and Pages, D and Sommer, MA and Groh, J}, Title = {Beyond the labeled line: variation in visual reference frames from intraparietal cortex to frontal eye fields and the superior colliculus}, Journal = {Journal of Neurophysiology}, Volume = {In Press}, Number = {4}, Pages = {1411-1421}, Publisher = {American Physiological Society}, Year = {2017}, Month = {December}, url = {http://dx.doi.org/10.1152/jn.00584.2017}, Abstract = {We accurately perceive the visual scene despite moving our eyes ~3 times per second, an ability that requires incorporation of eye position and retinal information. In this study, we assessed how this neural computation unfolds across three interconnected structures: frontal eye fields (FEF), intraparietal cortex (LIP/MIP), and the superior colliculus (SC). Single unit activity was assessed in head-restrained monkeys performing visually-guided saccades from different initial fixations. As previously shown, the receptive fields of most LIP/MIP neurons shifted to novel positions on the retina for each eye position, and these locations were not clearly related to each other in either eye- or head-centered coordinates (defined as hybrid coordinates). In contrast, the receptive fields of most SC neurons were stable in eye-centered coordinates. In FEF, visual signals were intermediate between those patterns: around 60% were eye-centered, whereas the remainder showed changes in receptive field location, boundaries, or responsiveness that rendered the response patterns hybrid or occasionally head-centered. These results suggest that FEF may act as a transitional step in an evolution of coordinates between LIP/MIP and SC. The persistence across cortical areas of mixed representations that do not provide unequivocal location labels in a consistent reference frame has implications for how these representations must be read-out.}, Doi = {10.1152/jn.00584.2017}, Key = {fds334784} } @article{fds334787, Author = {Oh-Descher, H and Beck, JM and Ferrari, S and Sommer, MA and Egner, T}, Title = {Probabilistic inference under time pressure leads to a cortical-to-subcortical shift in decision evidence integration}, Journal = {NeuroImage}, Volume = {162}, Pages = {138-150}, Publisher = {Elsevier}, Year = {2017}, Month = {November}, url = {http://dx.doi.org/10.1016/j.neuroimage.2017.08.069}, Abstract = {Real-life decision-making often involves combining multiple probabilistic sources of information under finite time and cognitive resources. To mitigate these pressures, people “satisfice”, foregoing a full evaluation of all available evidence to focus on a subset of cues that allow for fast and “good-enough” decisions. Although this form of decision-making likely mediates many of our everyday choices, very little is known about the way in which the neural encoding of cue information changes when we satisfice under time pressure. Here, we combined human functional magnetic resonance imaging (fMRI) with a probabilistic classification task to characterize neural substrates of multi-cue decision-making under low (1500 ms) and high (500 ms) time pressure. Using variational Bayesian inference, we analyzed participants’ choices to track and quantify cue usage under each experimental condition, which was then applied to model the fMRI data. Under low time pressure, participants performed near-optimally, appropriately integrating all available cues to guide choices. Both cortical (prefrontal and parietal cortex) and subcortical (hippocampal and striatal) regions encoded individual cue weights, and activity linearly tracked trial-by-trial variations in amount of evidence and decision uncertainty. Under increased time pressure, participants adaptively shifted to using a satisficing strategy by discounting the least informative cue in their decision process. This strategic change in decision-making was associated with an increased involvement of the dopaminergic midbrain, striatum, thalamus, and cerebellum in representing and integrating cue values. We conclude that satisficing the probabilistic inference process under time pressure leads to a cortical-to-subcortical shift in the neural drivers of decisions.}, Doi = {10.1016/j.neuroimage.2017.08.069}, Key = {fds334787} } @article{fds334789, Author = {Rao, HM and Mayo, JP and Sommer, MA}, Title = {Circuits for presaccadic visual remapping.}, Journal = {J Neurophysiol}, Volume = {116}, Number = {6}, Pages = {2624-2636}, Year = {2016}, Month = {December}, url = {http://dx.doi.org/10.1152/jn.00182.2016}, Abstract = {Saccadic eye movements rapidly displace the image of the world that is projected onto the retinas. In anticipation of each saccade, many neurons in the visual system shift their receptive fields. This presaccadic change in visual sensitivity, known as remapping, was first documented in the parietal cortex and has been studied in many other brain regions. Remapping requires information about upcoming saccades via corollary discharge. Analyses of neurons in a corollary discharge pathway that targets the frontal eye field (FEF) suggest that remapping may be assembled in the FEF's local microcircuitry. Complementary data from reversible inactivation, neural recording, and modeling studies provide evidence that remapping contributes to transsaccadic continuity of action and perception. Multiple forms of remapping have been reported in the FEF and other brain areas, however, and questions remain about the reasons for these differences. In this review of recent progress, we identify three hypotheses that may help to guide further investigations into the structure and function of circuits for remapping.}, Doi = {10.1152/jn.00182.2016}, Key = {fds334789} } @article{fds334790, Author = {Oh, H and Beck, JM and Zhu, P and Sommer, MA and Ferrari, S and Egner, T}, Title = {Satisficing in split-second decision making is characterized by strategic cue discounting}, Journal = {Journal of Experimental Psychology: Learning, Memory, and Cognition}, Volume = {42}, Number = {12}, Pages = {1937-1956}, Publisher = {American Psychological Association}, Year = {2016}, Month = {December}, url = {http://dx.doi.org/10.1037/xlm0000284}, Abstract = {Much of our real-life decision making is bounded by uncertain information, limitations in cognitive resources, and a lack of time to allocate to the decision process. It is thought that humans overcome these limitations through satisficing, fast but “good-enough” heuristic decision making that prioritizes some sources of information (cues) while ignoring others. However, the decision-making strategies we adopt under uncertainty and time pressure, for example during emergencies that demand split-second choices, are presently unknown. To characterize these decision strategies quantitatively, the present study examined how people solve a novel multi-cue probabilistic classification task under varying time pressure, by tracking shifts in decision strategies using variational Bayesian inference. We found that under low time pressure, participants correctly weighted and integrated all available cues to arrive at near-optimal decisions. With increasingly demanding, sub-second time pressures, however, participants systematically discounted a subset of the cue information by dropping the least informative cue(s) from their decision making process. Thus, the human cognitive apparatus copes with uncertainty and severe time pressure by adopting a “Drop-the-Worst” cue decision making strategy that minimizes cognitive time and effort investment while preserving the consideration of the most diagnostic cue information, thus maintaining “good-enough” accuracy. This advance in our understanding of satisficing strategies could form the basis of predicting human choices in high time pressure scenarios.}, Doi = {10.1037/xlm0000284}, Key = {fds334790} } @article{fds334794, Author = {Rao, HM and San Juan and J and Shen, FY and Villa, JE and Rafie, KS and Sommer, MA}, Title = {Neural network evidence for the coupling of presaccadic visual remapping to predictive eye position updating}, Journal = {Frontiers in Computational Neuroscience}, Volume = {10}, Pages = {52}, Publisher = {Frontiers Media}, Year = {2016}, Month = {June}, url = {http://dx.doi.org/10.3389/fncom.2016.00052}, Abstract = {As we look around a scene, we perceive it as continuous and stable even though each saccadic eye movement changes the visual input to the retinas. How the brain achieves this perceptual stabilization is unknown, but a major hypothesis is that it relies on presaccadic remapping, a process in which neurons shift their visual sensitivity to a new location in the scene just before each saccade. This hypothesis is difficult to test in vivo because complete, selective inactivation of remapping is currently intractable. We tested it in silico with a hierarchical, sheet-based neural network model of the visual and oculomotor system. The model generated saccadic commands to move a video camera abruptly. Visual input from the camera and internal copies of the saccadic movement commands, or corollary discharge, converged at a map-level simulation of the frontal eye field (FEF), a primate brain area known to receive such inputs. FEF output was combined with eye position signals to yield a suitable coordinate frame for guiding arm movements of a robot. Our operational definition of perceptual stability was "useful stability,” quantified as continuously accurate pointing to a visual object despite camera saccades. During training, the emergence of useful stability was correlated tightly with the emergence of presaccadic remapping in the FEF. Remapping depended on corollary discharge but its timing was synchronized to the updating of eye position. When coupled to predictive eye position signals, remapping served to stabilize the target representation for continuously accurate pointing. Graded inactivations of pathways in the model replicated, and helped to interpret, previous in vivo experiments. The results support the hypothesis that visual stability requires presaccadic remapping, provide explanations for the function and timing of remapping, and offer testable hypotheses for in vivo studies. We conclude that remapping allows for seamless coordinate frame transformations and quick actions despite visual afferent lags. With visual remapping in place for behavior, it may be exploited for perceptual continuity.}, Doi = {10.3389/fncom.2016.00052}, Key = {fds334794} } @article{fds334793, Author = {Raghavan, RT and Prevosto, V and Sommer, MA}, Title = {Contribution of cerebellar loops to action timing}, Journal = {Current Opinion in Behavioral Sciences}, Volume = {8}, Pages = {28-34}, Publisher = {Elsevier}, Year = {2016}, Month = {March}, url = {http://dx.doi.org/10.1016/j.cobeha.2016.01.008}, Abstract = {Recent studies of sensorimotor processing have benefited from decision-making paradigms that emphasize the selection of appropriate movements. Selecting when to make those responses, or action timing, is important as well. Although the cerebellum is commonly viewed as a controller of movement dynamics, its role in action timing is also firmly supported. Several lines of research have now extended this idea. Anatomical findings have revealed connections between the cerebellum and broader timing circuits, neurophysiological results have suggested mechanisms for timing within its microcircuitry, and theoretical work has indicated how temporal signals are processed through it and decoded by its targets. These developments are inspiring renewed studies of the role of the cerebellar loops in action timing.}, Doi = {10.1016/j.cobeha.2016.01.008}, Key = {fds334793} } @article{fds334791, Author = {Caruso, VC and Pages, DS and Sommer, MA and Groh, JM}, Title = {Similar prevalence and magnitude of auditory-evoked and visually-evoked activity in the frontal eye fields: Implications for multisensory motor control}, Journal = {Journal of Neurophysiology}, Volume = {in press}, Number = {6}, Pages = {3162-3173}, Year = {2016}, Month = {March}, url = {http://dx.doi.org/10.1152/jn.00935.2015}, Abstract = {Saccadic eye movements can be elicited by more than one type of sensory stimulus. This implies substantial transformations of signals originating in different sense organs as they reach a common motor output pathway. In this study, we compared the prevalence and magnitude of auditory- and visually-evoked activity in a structure implicated in oculomotor processing, the primate frontal eye fields (FEF). We recorded from 324 single neurons while 2 monkeys performed delayed saccades to visual or auditory targets. We found that 64% of FEF neurons were active upon presentation of auditory targets and 87% were active during auditory-guided saccades, compared to 75% and 84% for visual targets and saccades. As saccade onset approached, the average level of population activity in the FEF became indistinguishable on visual and auditory trials. FEF activity was better correlated with the movement vector than with the target location for both modalities In summary, the large proportion of auditory responsive neurons in the FEF, the similarity between visual and auditory activity levels at the time of the saccade and the strong correlation between the activity and the saccade vector suggest that auditory signals undergo tailoring to roughly match the strength of visual signals present in the FEF, facilitating accessing of a common motor output pathway.}, Doi = {10.1152/jn.00935.2015}, Key = {fds334791} } @article{fds334795, Author = {Rao, HM and Abzug, ZM and Sommer, MA}, Title = {Visual continuity across saccades is influenced by expectations.}, Journal = {Journal of vision}, Volume = {16}, Number = {5}, Pages = {7}, Year = {2016}, Month = {January}, url = {http://dx.doi.org/10.1167/16.5.7}, Abstract = {As we make saccades, the image on each retina is displaced, yet our visual perception is uninterrupted. This is commonly referred to as transsaccadic perceptual stability, but such a description is inadequate. Some visual objects are stable (e.g., rocks) and should be perceived as such across saccades, but other objects may move at any time (e.g., birds). Stability is probabilistic in natural scenes. Here we extend the common notion of transsaccadic visual stability to a more general, ecologically based hypothesis of transsaccadic visual continuity in which postsaccadic percepts of objects depend on expectations about their probability of movement. Subjects made a saccade to a target and reported whether it seemed displaced after the saccade. Targets had varying probabilities of movement (ranging from 0.1-0.9) that corresponded to their color (spectrum from blue to red). Performance was compared before and after subjects were told about the color-probability pairings ("uninformed" vs. "informed" conditions). Analyses focused on signal detection and psychometric threshold measures. We found that in the uninformed condition, performance was similar across color-probability pairings, but in the informed condition, response biases varied with probability of movement, and movement-detection sensitivities were higher for rarely moving targets. We conclude that subjects incorporate priors about object movement into their judgments of visual continuity across saccades.}, Doi = {10.1167/16.5.7}, Key = {fds334795} } @article{fds334792, Author = {Zielinski, DJ and Rao, HM and Potter, ND and Sommer, MA and Appelbaum, LG and Kopper, R}, Title = {Evaluating the Effects of Image Persistence on Dynamic Target Acquisition in Low Frame Rate Virtual Environments}, Journal = {3D User Interfaces (3DUI), 2016 IEEE Symposium on}, Pages = {133-140}, Publisher = {IEEE}, Year = {2016}, url = {http://dx.doi.org/10.1109/3DUI.2016.7460043}, Abstract = {User performance in virtual environments with degraded visual conditions due to low frame rates is an interesting area of inquiry. Visual content shown in a low frame rate simulation has the quality of the original image, but persists for an extended period until the next frame is displayed (so-called high persistence-HP). An alternative, called low persistence (LP), involves displaying the rendered frame for a single display frame and blanking the screen while waiting for the next frame to be generated. Previous research has evaluated the usefulness of the LP technique in low frame rate simulations during a static target acquisition task. To gain greater knowledge about the LP technique, we have conducted a user study to evaluate user performance and learning during a dynamic target acquisition task. The acquisition task was evaluated under a high frame rate, (60 fps) condition, a traditional low frame rate HP condition (10 fps), and the experimental low frame rate LP technique. The task involved the acquisition of targets moving along several different trajectories, modeled after a shotgun trap shooting task. The results of our study indicate the LP condition approaches high frame rate performance within certain classes of target trajectories. Interestingly we also see that learning is consistent across conditions, indicating that it may not always be necessary to train under a visually high frame rate system to learn a particular task. We discuss implications of using the LP technique to mitigate low frame rate issues as well as its potential usefulness for training in low frame rate virtual environments.}, Doi = {10.1109/3DUI.2016.7460043}, Key = {fds334792} } @article{fds334796, Author = {Mayo, JP and DiTomasso, AR and Sommer, MA and Smith, MA}, Title = {Dynamics of visual receptive fields in the macaque frontal eye field.}, Journal = {J Neurophysiol}, Volume = {114}, Number = {6}, Pages = {3201-3210}, Year = {2015}, Month = {December}, url = {http://dx.doi.org/10.1152/jn.00746.2015}, Abstract = {Neuronal receptive fields (RFs) provide the foundation for understanding systems-level sensory processing. In early visual areas, investigators have mapped RFs in detail using stochastic stimuli and sophisticated analytical approaches. Much less is known about RFs in prefrontal cortex. Visual stimuli used for mapping RFs in prefrontal cortex tend to cover a small range of spatial and temporal parameters, making it difficult to understand their role in visual processing. To address these shortcomings, we implemented a generalized linear model to measure the RFs of neurons in the macaque frontal eye field (FEF) in response to sparse, full-field stimuli. Our high-resolution, probabilistic approach tracked the evolution of RFs during passive fixation, and we validated our results against conventional measures. We found that FEF neurons exhibited a surprising level of sensitivity to stimuli presented as briefly as 10 ms or to multiple dots presented simultaneously, suggesting that FEF visual responses are more precise than previously appreciated. FEF RF spatial structures were largely maintained over time and between stimulus conditions. Our results demonstrate that the application of probabilistic RF mapping to FEF and similar association areas is an important tool for clarifying the neuronal mechanisms of cognition.}, Doi = {10.1152/jn.00746.2015}, Key = {fds334796} } @article{fds334797, Author = {Grigsby, EM and Koval, MJ and Smith, MV and Mueller, JK and Deng, ZD and Peterchev, A and Grill, WM and Sommer, MA}, Title = {Neural Effects of rTMS: Single Neuron Recordings From a Rhesus Macaque}, Journal = {JOURNAL OF ECT}, Volume = {31}, Number = {3}, Pages = {E33-E33}, Publisher = {LIPPINCOTT WILLIAMS & WILKINS}, Year = {2015}, Month = {September}, Key = {fds334797} } @article{fds334798, Author = {Zielinski, DJ and Rao, HM and Sommer, MA and Kopper, R}, Title = {Exploring the Effects of Image Persistence in Low Frame Rate Virtual Environments}, Journal = {Proceedings of the IEEE Virtual Reality Conference}, Pages = {19-26}, Publisher = {IEEE Computer Society}, Year = {2015}, url = {http://dx.doi.org/10.1109/vr.2015.7223319}, Abstract = {© 2015 IEEE. In virtual reality applications, there is an aim to provide real time graphics which run at high refresh rates. However, there are many situations in which this is not possible due to simulation or rendering issues. When running at low frame rates, several aspects of the user experience are affected. For example, each frame is displayed for an extended period of time, causing a high persistence image artifact. The effect of this artifact is that movement may lose continuity, and the image jumps from one frame to another. In this paper, we discuss our initial exploration of the effects of high persistence frames caused by low refresh rates and compare it to high frame rates and to a technique we developed to mitigate the effects of low frame rates. In this technique, the low frame rate simulation images are displayed with low persistence by blanking out the display during the extra time such image would be displayed. In order to isolate the visual effects, we constructed a simulator for low and high persistence displays that does not affect input latency. A controlled user study comparing the three conditions for the tasks of 3D selection and navigation was conducted. Results indicate that the low persistence display technique may not negatively impact user experience or performance as compared to the high persistence case. Directions for future work on the use of low persistence displays for low frame rate situations are discussed.}, Doi = {10.1109/vr.2015.7223319}, Key = {fds334798} } @article{fds334799, Author = {Matthews, WJ and Terhune, DB and van Rijn, H and Eagleman, DM and Sommer, MA and Meck, WA}, Title = {Subjective duration as a signature of coding efficiency: Emerging links among stimulus repetition, predictive coding, and cortical GABA levels}, Journal = {Timing & Time Perception Reviews}, Volume = {1}, Pages = {11 pages}, Publisher = {Brill Publishers}, Year = {2014}, Month = {December}, Abstract = {Immediate repetition of a stimulus reduces its apparent duration relative to a novel item. Recent work indicates that this may reflect suppressed cortical responses to repeated stimuli, arising from neural adaptation and/or the predictive coding of expected stimuli. This article summarizes recent behavioral and neurobiological studies linking perceived time to the magnitude of cortical responses, including work suggesting that variations in GABA-mediated cortical inhibition may underlie some of the individual differences in time perception. We suggest that the firing of cortical neurons can be modified using simple recurrent networks with time-dependent processes that are modulated by GABA levels. These local networks feed into a core-timing network used to integrate across stimulus inputs/modalities, thereby allowing for the coordination of multiple duration ranges and effector systems.}, Key = {fds334799} } @article{fds334800, Author = {Mitchell, AS and Sherman, SM and Sommer, MA and Mair, RG and Vertes, RP and Chudasama, Y}, Title = {Advances in understanding mechanisms of thalamic relays in cognition and behavior.}, Journal = {The Journal of neuroscience : the official journal of the Society for Neuroscience}, Volume = {34}, Number = {46}, Pages = {15340-15346}, Year = {2014}, Month = {November}, url = {http://dx.doi.org/10.1523/jneurosci.3289-14.2014}, Abstract = {The main impetus for a mini-symposium on corticothalamic interrelationships was the recent number of studies highlighting the role of the thalamus in aspects of cognition beyond sensory processing. The thalamus contributes to a range of basic cognitive behaviors that include learning and memory, inhibitory control, decision-making, and the control of visual orienting responses. Its functions are deeply intertwined with those of the better studied cortex, although the principles governing its coordination with the cortex remain opaque, particularly in higher-level aspects of cognition. How should the thalamus be viewed in the context of the rest of the brain? Although its role extends well beyond relaying of sensory information from the periphery, the main function of many of its subdivisions does appear to be that of a relay station, transmitting neural signals primarily to the cerebral cortex from a number of brain areas. In cognition, its main contribution may thus be to coordinate signals between diverse regions of the telencephalon, including the neocortex, hippocampus, amygdala, and striatum. This central coordination is further subject to considerable extrinsic control, for example, inhibition from the basal ganglia, zona incerta, and pretectal regions, and chemical modulation from ascending neurotransmitter systems. What follows is a brief review on the role of the thalamus in aspects of cognition and behavior, focusing on a summary of the topics covered in a mini-symposium held at the Society for Neuroscience meeting, 2014.}, Doi = {10.1523/jneurosci.3289-14.2014}, Key = {fds334800} } @article{fds334801, Author = {Mueller, JK and Grigsby, EM and Prevosto, V and Petraglia, FW and Rao, H and Deng, Z-D and Peterchev, AV and Sommer, MA and Egner, T and Platt, ML and Grill, WM}, Title = {Simultaneous transcranial magnetic stimulation and single-neuron recording in alert non-human primates.}, Journal = {Nat Neurosci}, Volume = {17}, Number = {8}, Pages = {1130-1136}, Year = {2014}, Month = {August}, url = {http://dx.doi.org/10.1038/nn.3751}, Abstract = {Transcranial magnetic stimulation (TMS) is a widely used, noninvasive method for stimulating nervous tissue, yet its mechanisms of effect are poorly understood. Here we report new methods for studying the influence of TMS on single neurons in the brain of alert non-human primates. We designed a TMS coil that focuses its effect near the tip of a recording electrode and recording electronics that enable direct acquisition of neuronal signals at the site of peak stimulus strength minimally perturbed by stimulation artifact in awake monkeys (Macaca mulatta). We recorded action potentials within ∼1 ms after 0.4-ms TMS pulses and observed changes in activity that differed significantly for active stimulation as compared with sham stimulation. This methodology is compatible with standard equipment in primate laboratories, allowing easy implementation. Application of these tools will facilitate the refinement of next generation TMS devices, experiments and treatment protocols.}, Doi = {10.1038/nn.3751}, Key = {fds334801} } @article{fds334804, Author = {Prevosto, V and Sommer, MA}, Title = {Cognitive control of movement via the cerebellar-recipient thalamus.}, Journal = {Frontiers in systems neuroscience}, Volume = {7}, Pages = {56}, Year = {2013}, Month = {October}, url = {http://dx.doi.org/10.3389/fnsys.2013.00056}, Abstract = {The cognitive control of behavior was long considered to be centralized in cerebral cortex. More recently, subcortical structures such as cerebellum and basal ganglia have been implicated in cognitive functions as well. The fact that subcortico-cortical circuits for the control of movement involve the thalamus prompts the notion that activity in movement-related thalamus may also reflect elements of cognitive behavior. Yet this hypothesis has rarely been investigated. Using the pathways linking cerebellum to cerebral cortex via the thalamus as a template, we review evidence that the motor thalamus, together with movement-related central thalamus have the requisite connectivity and activity to mediate cognitive aspects of movement control.}, Doi = {10.3389/fnsys.2013.00056}, Key = {fds334804} } @article{fds334805, Author = {Ashmore, RC and Sommer, MA}, Title = {Delay activity of saccade-related neurons in the caudal dentate nucleus of the macaque cerebellum.}, Journal = {Journal of neurophysiology}, Volume = {109}, Number = {8}, Pages = {2129-2144}, Year = {2013}, Month = {April}, ISSN = {0022-3077}, url = {https://dl.dropboxusercontent.com/u/27738651/Publications/AshmoreSommer2013-CaudalDentateNucleus.pdf}, Abstract = {The caudal dentate nucleus (DN) in lateral cerebellum is connected with two visual/oculomotor areas of the cerebrum: the frontal eye field and lateral intraparietal cortex. Many neurons in frontal eye field and lateral intraparietal cortex produce "delay activity" between stimulus and response that correlates with processes such as motor planning. Our hypothesis was that caudal DN neurons would have prominent delay activity as well. From lesion studies, we predicted that this activity would be related to self-timing, i.e., the triggering of saccades based on the internal monitoring of time. We recorded from neurons in the caudal DN of monkeys (Macaca mulatta) that made delayed saccades with or without a self-timing requirement. Most (84%) of the caudal DN neurons had delay activity. These neurons conveyed at least three types of information. First, their activity was often correlated, trial by trial, with saccade initiation. Correlations were found more frequently in a task that required self-timing of saccades (53% of neurons) than in a task that did not (27% of neurons). Second, the delay activity was often tuned for saccade direction (in 65% of neurons). This tuning emerged continuously during a trial. Third, the time course of delay activity associated with self-timed saccades differed significantly from that associated with visually guided saccades (in 71% of neurons). A minority of neurons had sensory-related activity. None had presaccadic bursts, in contrast to DN neurons recorded more rostrally. We conclude that caudal DN neurons convey saccade-related delay activity that may contribute to the motor preparation of when and where to move.}, Doi = {10.1152/jn.00906.2011}, Key = {fds334805} } @article{fds334806, Author = {Smith, MA and Sommer, MA}, Title = {Spatial and temporal scales of neuronal correlation in visual area V4.}, Journal = {The Journal of neuroscience : the official journal of the Society for Neuroscience}, Volume = {33}, Number = {12}, Pages = {5422-5432}, Year = {2013}, Month = {March}, ISSN = {0270-6474}, url = {https://dl.dropbox.com/u/27738651/Publications/SmithSommer2013-SpatialTemporalCorrelationsV4.pdf}, Abstract = {The spiking activity of nearby cortical neurons is correlated on both short and long time scales. Understanding this shared variability in firing patterns is critical for appreciating the representation of sensory stimuli in ensembles of neurons, the coincident influences of neurons on common targets, and the functional implications of microcircuitry. Our knowledge about neuronal correlations, however, derives largely from experiments that used different recording methods, analysis techniques, and cortical regions. Here we studied the structure of neuronal correlation in area V4 of alert macaques using recording and analysis procedures designed to match those used previously in primary visual cortex (V1), the major input to V4. We found that the spatial and temporal properties of correlations in V4 were remarkably similar to those of V1, with two notable differences: correlated variability in V4 was approximately one-third the magnitude of that in V1 and synchrony in V4 was less temporally precise than in V1. In both areas, spontaneous activity (measured during fixation while viewing a blank screen) was approximately twice as correlated as visual-evoked activity. The results provide a foundation for understanding how the structure of neuronal correlation differs among brain regions and stages in cortical processing and suggest that it is likely governed by features of neuronal circuits that are shared across the visual cortex.}, Doi = {10.1523/jneurosci.4782-12.2013}, Key = {fds334806} } @article{fds334807, Author = {Mayo, JP and Sommer, MA}, Title = {Neuronal correlates of visual time perception at brief timescales.}, Journal = {Proc Natl Acad Sci U S A}, Volume = {110}, Number = {4}, Pages = {1506-1511}, Year = {2013}, Month = {January}, url = {https://dl.dropbox.com/u/27738651/Publications/MayoSommer2013-ReprintIncludingSupplInfo.pdf}, Abstract = {Successful interaction with the world depends on accurate perception of the timing of external events. Neurons at early stages of the primate visual system represent time-varying stimuli with high precision. However, it is unknown whether this temporal fidelity is maintained in the prefrontal cortex, where changes in neuronal activity generally correlate with changes in perception. One reason to suspect that it is not maintained is that humans experience surprisingly large fluctuations in the perception of time. To investigate the neuronal correlates of time perception, we recorded from neurons in the prefrontal cortex and midbrain of monkeys performing a temporal-discrimination task. Visual time intervals were presented at a timescale relevant to natural behavior (<500 ms). At this brief timescale, neuronal adaptation--time-dependent changes in the size of successive responses--occurs. We found that visual activity fluctuated with timing judgments in the prefrontal cortex but not in comparable midbrain areas. Surprisingly, only response strength, not timing, predicted task performance. Intervals perceived as longer were associated with larger visual responses and shorter intervals with smaller responses, matching the dynamics of adaptation. These results suggest that the magnitude of prefrontal activity may be read out to provide temporal information that contributes to judging the passage of time.}, Doi = {10.1073/pnas.1217177110}, Key = {fds334807} } @article{fds334811, Author = {Shin, S and Sommer, MA}, Title = {Division of labor in frontal eye field neurons during presaccadic remapping of visual receptive fields.}, Journal = {Journal of neurophysiology}, Volume = {108}, Number = {8}, Pages = {2144-2159}, Year = {2012}, Month = {October}, url = {https://dl.dropbox.com/u/27738651/Publications/ShinSommer2012.pdf}, Abstract = {Our percept of visual stability across saccadic eye movements may be mediated by presaccadic remapping. Just before a saccade, neurons that remap become visually responsive at a future field (FF), which anticipates the saccade vector. Hence, the neurons use corollary discharge of saccades. Many of the neurons also decrease their response at the receptive field (RF). Presaccadic remapping occurs in several brain areas including the frontal eye field (FEF), which receives corollary discharge of saccades in its layer IV from a collicular-thalamic pathway. We studied, at two levels, the microcircuitry of remapping in the FEF. At the laminar level, we compared remapping between layers IV and V. At the cellular level, we compared remapping between different neuron types of layer IV. In the FEF in four monkeys (Macaca mulatta), we identified 27 layer IV neurons with orthodromic stimulation and 57 layer V neurons with antidromic stimulation from the superior colliculus. With the use of established criteria, we classified the layer IV neurons as putative excitatory (n = 11), putative inhibitory (n = 12), or ambiguous (n = 4). We found that just before a saccade, putative excitatory neurons increased their visual response at the RF, putative inhibitory neurons showed no change, and ambiguous neurons increased their visual response at the FF. None of the neurons showed presaccadic visual changes at both RF and FF. In contrast, neurons in layer V showed full remapping (at both the RF and FF). Our data suggest that elemental signals for remapping are distributed across neuron types in early cortical processing and combined in later stages of cortical microcircuitry.}, Doi = {10.1152/jn.00204.2012}, Key = {fds334811} } @article{fds334808, Author = {Mayo, JP and DiTomasso, A and Sommer, M and Smith, MA}, Title = {An improved method for mapping neuronal receptive fields in prefrontal cortex}, Journal = {Journal of Vision}, Volume = {12}, Number = {9}, Pages = {81-81}, Publisher = {Association for Research in Vision and Ophthalmology (ARVO)}, Year = {2012}, Month = {August}, url = {http://dx.doi.org/10.1167/12.9.81}, Doi = {10.1167/12.9.81}, Key = {fds334808} } @article{fds334810, Author = {Middlebrooks, PG and Sommer, MA}, Title = {Neuronal correlates of metacognition in primate frontal cortex.}, Journal = {Neuron}, Volume = {75}, Number = {3}, Pages = {517-530}, Year = {2012}, Month = {August}, ISSN = {08966273}, url = {https://dl.dropbox.com/u/27738651/Publications/MiddlebrooksSommer2012-MetacogNeurons-TextSupplPreview.pdf}, Abstract = {Humans are metacognitive: they monitor and control their cognition. Our hypothesis was that neuronal correlates of metacognition reside in the same brain areas responsible for cognition, including frontal cortex. Recent work demonstrated that nonhuman primates are capable of metacognition, so we recorded from single neurons in the frontal eye field, dorsolateral prefrontal cortex, and supplementary eye field of monkeys (Macaca mulatta) that performed a metacognitive visual-oculomotor task. The animals made a decision and reported it with a saccade, but received no immediate reward or feedback. Instead, they had to monitor their decision and bet whether it was correct. Activity was correlated with decisions and bets in all three brain areas, but putative metacognitive activity that linked decisions to appropriate bets occurred exclusively in the SEF. Our results offer a survey of neuronal correlates of metacognition and implicate the SEF in linking cognitive functions over short periods of time.}, Doi = {10.1016/j.neuron.2012.05.028}, Key = {fds334810} } @article{fds334809, Author = {Crapse, TB and Sommer, MA}, Title = {Frontal eye field neurons assess visual stability across saccades.}, Journal = {The Journal of neuroscience : the official journal of the Society for Neuroscience}, Volume = {32}, Number = {8}, Pages = {2835-2845}, Year = {2012}, Month = {February}, ISSN = {0270-6474}, url = {https://dl.dropbox.com/u/27738651/Publications/CrapseSommer2012.pdf}, Abstract = {The image on the retina may move because the eyes move, or because something in the visual scene moves. The brain is not fooled by this ambiguity. Even as we make saccades, we are able to detect whether visual objects remain stable or move. Here we test whether this ability to assess visual stability across saccades is present at the single-neuron level in the frontal eye field (FEF), an area that receives both visual input and information about imminent saccades. Our hypothesis was that neurons in the FEF report whether a visual stimulus remains stable or moves as a saccade is made. Monkeys made saccades in the presence of a visual stimulus outside of the receptive field. In some trials, the stimulus remained stable, but in other trials, it moved during the saccade. In every trial, the stimulus occupied the center of the receptive field after the saccade, thus evoking a reafferent visual response. We found that many FEF neurons signaled, in the strength and timing of their reafferent response, whether the stimulus had remained stable or moved. Reafferent responses were tuned for the amount of stimulus translation, and, in accordance with human psychophysics, tuning was better (more prevalent, stronger, and quicker) for stimuli that moved perpendicular, rather than parallel, to the saccade. Tuning was sometimes present as well for nonspatial transaccadic changes (in color, size, or both). Our results indicate that FEF neurons evaluate visual stability during saccades and may be general purpose detectors of transaccadic visual change.}, Doi = {10.1523/jneurosci.1320-11.2012}, Key = {fds334809} } @article{fds334813, Author = {Basso, MA and Sommer, MA}, Title = {Exploring the role of the substantia nigra pars reticulata in eye movements.}, Journal = {Neuroscience}, Volume = {198}, Pages = {205-212}, Year = {2011}, Month = {December}, url = {http://dx.doi.org/10.1016/j.neuroscience.2011.08.026}, Abstract = {Experiments that demonstrated a role for the substantia nigra in eye movements have played an important role in our understanding of the function of the basal ganglia in behavior more broadly. In this review we explore more recent experiments that extend the role of the substantia nigra pars reticulata from a simple gate for eye movements to include a role in cognitive processes for eye movements. We review recent evidence suggesting that basal ganglia nuclei beyond the substantia nigra may also play a role in eye movements and the cognitive events leading up to the production of eye movements. We close by pointing out some unresolved questions in our understanding of the relationship of basal ganglia nuclei and eye movements.}, Doi = {10.1016/j.neuroscience.2011.08.026}, Key = {fds334813} } @article{Sommer2009, Author = {Middlebrooks, PG and Sommer, MA}, Title = {Metacognition in monkeys during an oculomotor task.}, Journal = {Journal of experimental psychology. Learning, memory, and cognition}, Volume = {37}, Number = {2}, Pages = {325-337}, Year = {2011}, Month = {March}, ISSN = {0278-7393}, url = {https://dl.dropbox.com/u/27738651/Publications/MiddlebrooksSommer2011-MetacognitionInMonkeys.pdf}, Abstract = {This study investigated whether rhesus monkeys show evidence of metacognition in a reduced, visual oculomotor task that is particularly suitable for use in fMRI and electrophysiology. The 2-stage task involved punctate visual stimulation and saccadic eye movement responses. In each trial, monkeys made a decision and then made a bet. To earn maximum reward, they had to monitor their decision and use that information to bet advantageously. Two monkeys learned to base their bets on their decisions within a few weeks. We implemented an operational definition of metacognitive behavior that relied on trial-by-trial analyses and signal detection theory. Both monkeys exhibited metacognition according to these quantitative criteria. Neither external visual cues nor potential reaction time cues explained the betting behavior; the animals seemed to rely exclusively on internal traces of their decisions. We documented the learning process of one monkey. During a 10-session transition phase, betting switched from random to a decision-based strategy. The results reinforce previous findings of metacognitive ability in monkeys and may facilitate the neurophysiological investigation of metacognitive functions.}, Doi = {10.1037/a0021611}, Key = {Sommer2009} } @article{fds334816, Author = {Mayo, JP and Sommer, MA}, Title = {Shifting attention to neurons.}, Journal = {Trends Cogn Sci}, Volume = {14}, Number = {9}, Pages = {389}, Year = {2010}, Month = {September}, url = {http://dx.doi.org/10.1016/j.tics.2010.06.003}, Doi = {10.1016/j.tics.2010.06.003}, Key = {fds334816} } @article{fds334814, Author = {Crapse, T and Sommer, M}, Title = {Translation of a visual stimulus during a saccade is more detectable if it moves perpendicular, rather than parallel, to the saccade}, Journal = {Journal of Vision}, Volume = {10}, Number = {7}, Pages = {521-521}, Publisher = {Association for Research in Vision and Ophthalmology (ARVO)}, Year = {2010}, Month = {August}, url = {http://dx.doi.org/10.1167/10.7.521}, Doi = {10.1167/10.7.521}, Key = {fds334814} } @article{fds334815, Author = {Shin, S and Sommer, MA}, Title = {Activity of neurons in monkey globus pallidus during oculomotor behavior compared with that in substantia nigra pars reticulata.}, Journal = {Journal of neurophysiology}, Volume = {103}, Number = {4}, Pages = {1874-1887}, Year = {2010}, Month = {April}, ISSN = {0022-3077}, url = {https://dl.dropbox.com/u/27738651/Publications/ShinSommer2010.pdf}, Abstract = {The basal ganglia are a subcortical assembly of nuclei involved in many aspects of behavior. Three of the nuclei have high firing rates and inhibitory influences: the substantia nigra pars reticulata (SNr), globus pallidus interna (GPi), and globus pallidus externa (GPe). The SNr contains a wide range of visual, cognitive, and motor signals that have been shown to contribute to saccadic eye movements. Our hypothesis was that GPe and GPi neurons carry similarly diverse signals during saccadic behavior. We recorded from GPe, GPi, and SNr neurons in monkeys that made memory-guided saccades and found that neurons in all three structures had increases or decreases in activity synchronized with saccade generation, visual stimulation, or reward. Comparing GPe neurons with GPi neurons, we found relatively more visual-related activity in GPe and more reward-related activity in GPi. Comparing both pallidal samples with the SNr, we found a greater resemblance between GPe and SNr neurons than that between GPi and SNr neurons. As expected from a known inhibitory projection from GPe to SNr, there was a general reversal of sign in activity modulations between the structures: bursts of activity were relatively more common in GPe and pauses more common in SNr. We analyzed the response fields of neurons in all three structures and found relatively narrow and lateralized fields early in trials (during visual and saccadic events) followed by a broadening later in trials (during reward). Our data reinforce an emerging, new consensus that the GPe and GPi, in addition to the SNr, contribute to oculomotor behavior.}, Doi = {10.1152/jn.00101.2009}, Key = {fds334815} } @article{fds334817, Author = {Sommer, MA}, Title = {How the visual system monitors where the eyes will move}, Journal = {Journal of Vision}, Volume = {9}, Number = {14}, Pages = {13-13}, Publisher = {Association for Research in Vision and Ophthalmology (ARVO)}, Year = {2009}, Month = {December}, url = {http://dx.doi.org/10.1167/9.14.13}, Doi = {10.1167/9.14.13}, Key = {fds334817} } @article{fds334818, Author = {Sommer, MA}, Title = {Corollary discharge circuits for stabilizing visual perception}, Journal = {PSYCHOPHYSIOLOGY}, Volume = {46}, Pages = {S9-S9}, Publisher = {WILEY-BLACKWELL PUBLISHING, INC}, Year = {2009}, Month = {September}, Key = {fds334818} } @article{fds334819, Author = {Mayo, JP and Sommer, MA}, Title = {Monkey and human performance in a chronostasis task suitable for neurophysiology}, Journal = {Journal of Vision}, Volume = {9}, Number = {8}, Pages = {406-406}, Publisher = {Association for Research in Vision and Ophthalmology (ARVO)}, Year = {2009}, Month = {August}, url = {http://dx.doi.org/10.1167/9.8.406}, Doi = {10.1167/9.8.406}, Key = {fds334819} } @article{Crapse2009, Author = {Crapse, TB and Sommer, MA}, Title = {Frontal eye field neurons with spatial representations predicted by their subcortical input.}, Journal = {The Journal of neuroscience : the official journal of the Society for Neuroscience}, Volume = {29}, Number = {16}, Pages = {5308-5318}, Year = {2009}, Month = {April}, ISSN = {0270-6474}, url = {https://dl.dropbox.com/u/27738651/Publications/CrapseSommer2009_JNeurosci.pdf}, Abstract = {The frontal eye field (FEF) is a cortical structure involved in cognitive aspects of eye movement control. Neurons in the FEF, as in most of cerebral cortex, primarily represent contralateral space. They fire for visual stimuli in the contralateral field and for saccadic eye movements made to those stimuli. Yet many FEF neurons engage in sophisticated functions that require flexible spatial representations such as shifting receptive fields and vector subtraction. Such functions require knowledge about all of space, including the ipsilateral hemifield. How does the FEF gain access to ipsilateral information? Here, we provide evidence that one source of ipsilateral information may be the opposite superior colliculus (SC) in the midbrain. We physiologically identified neurons in the FEF that receive input from the opposite SC, same-side SC, or both. We found a striking structure-function relationship: the laterality of the response field of an FEF neuron was predicted by the laterality of its SC inputs. FEF neurons with input from the opposite SC had ipsilateral fields, whereas neurons with input from the same-side SC had contralateral fields. FEF neurons with input from both SCs had lateralized fields that could point in any direction. The results suggest that signals from the two SCs provide each FEF with information about all of visual space, a prerequisite for higher level sensorimotor computations.}, Doi = {10.1523/jneurosci.4906-08.2009}, Key = {Crapse2009} } @article{Crapse2008a, Author = {Crapse, TB and Sommer, MA}, Title = {Corollary discharge circuits in the primate brain.}, Journal = {Current opinion in neurobiology}, Volume = {18}, Number = {6}, Pages = {552-557}, Year = {2008}, Month = {December}, ISSN = {0959-4388}, url = {https://dl.dropbox.com/u/27738651/Publications/CrapseSommer_CurrOpinionNeurobiology2008.pdf}, Abstract = {Movements are necessary to engage the world, but every movement results in sensorimotor ambiguity. Self-movements cause changes to sensory inflow as well as changes in the positions of objects relative to motor effectors (eyes and limbs). Hence the brain needs to monitor self-movements, and one way this is accomplished is by routing copies of movement commands to appropriate structures. These signals, known as corollary discharge (CD), enable compensation for sensory consequences of movement and preemptive updating of spatial representations. Such operations occur with a speed and accuracy that implies a reliance on prediction. Here we review recent CD studies and find that they arrive at a shared conclusion: CD contributes to prediction for the sake of sensorimotor harmony.}, Doi = {10.1016/j.conb.2008.09.017}, Key = {Crapse2008a} } @article{Mayo2008a, Author = {Mayo, JP and Sommer, MA}, Title = {Neuronal adaptation caused by sequential visual stimulation in the frontal eye field.}, Journal = {J Neurophysiol}, Volume = {100}, Number = {4}, Pages = {1923-1935}, Year = {2008}, Month = {October}, ISSN = {0022-3077}, url = {https://dl.dropbox.com/u/27738651/Publications/MayoSommer2008-FEFadaptation.pdf}, Abstract = {Images on the retina can change drastically in only a few milliseconds. A robust description of visual temporal processing is therefore necessary to understand visual analysis in the real world. To this end, we studied subsecond visual changes and asked how prefrontal neurons in monkeys respond to stimuli presented in quick succession. We recorded the visual responses of single neurons in the frontal eye field (FEF), a prefrontal area polysynaptically removed from the retina that is involved with higher level cognition. For comparison, we also recorded from small groups of neurons in the superficial superior colliculus (supSC), an area that receives direct retinal input. Two sequential flashes of light at varying interstimulus intervals were presented in a neuron's receptive field. We found pervasive neuronal adaptation in FEF and supSC. Visual responses to the second stimulus were diminished for up to half a second after the first stimulus presentation. Adaptation required a similar amount of time to return to full responsiveness in both structures, but there was significantly more neuronal adaptation overall in FEF. Adaptation was not affected by saccades, although visual responses to single stimuli were transiently suppressed postsaccadically. Our FEF and supSC results systematically document subsecond visual adaptation in prefrontal cortex and show that this adaptation is comparable to, but stronger than, adaptation found earlier in the visual system.}, Doi = {10.1152/jn.90549.2008}, Key = {Mayo2008a} } @article{Crapse2008b, Author = {Crapse, TB and Sommer, MA}, Title = {Corollary discharge across the animal kingdom.}, Journal = {Nature reviews. Neuroscience}, Volume = {9}, Number = {8}, Pages = {587-600}, Year = {2008}, Month = {August}, ISSN = {1471-0048}, url = {https://dl.dropbox.com/u/27738651/Publications/CrapseSommer_CDReview2008.pdf}, Abstract = {Our movements can hinder our ability to sense the world. Movements can induce sensory input (for example, when you hit something) that is indistinguishable from the input that is caused by external agents (for example, when something hits you). It is critical for nervous systems to be able to differentiate between these two scenarios. A ubiquitous strategy is to route copies of movement commands to sensory structures. These signals, which are referred to as corollary discharge (CD), influence sensory processing in myriad ways. Here we review the CD circuits that have been uncovered by neurophysiological studies and suggest a functional taxonomic classification of CD across the animal kingdom. This broad understanding of CD circuits lays the groundwork for more challenging studies that combine neurophysiology and psychophysics to probe the role of CD in perception.}, Doi = {10.1038/nrn2457}, Key = {Crapse2008b} } @article{Mayo2008b, Author = {Mayo, JP and Sommer, MA}, Title = {Neuronal adaptation: Delay compensation at the level of single neurons?}, Journal = {Behavioral and Brain Sciences}, Volume = {31}, Number = {2}, Pages = {210-212}, Publisher = {Cambridge University Press (CUP)}, Year = {2008}, Month = {April}, ISSN = {0140-525X}, url = {https://dl.dropbox.com/u/27738651/Publications/MayoSommer2008-BBScommentary.pdf}, Abstract = {Saccades divide visual input into rapid, discontinuous periods of stimulation on the retina. The response of single neurons to such sequential stimuli is neuronal adaptation; a robust first response followed by an interval-dependent diminished second response. Adaptation is pervasive in both early and late stages of visual processing. Given its inherent coding of brief time intervals, neuronal adaptation may play a fundamental role in compensating for visual delays. © 2008 Cambridge University Press 2008.}, Doi = {10.1017/S0140525X08003944}, Key = {Mayo2008b} } @article{Sommer2008a, Author = {Sommer, MA and Wurtz, RH}, Title = {Brain circuits for the internal monitoring of movements.}, Journal = {Annual review of neuroscience}, Volume = {31}, Pages = {317-338}, Year = {2008}, Month = {January}, ISSN = {0147-006X}, url = {https://dl.dropbox.com/u/27738651/Publications/SommerWurtz_AnnualRevNeurosci2008.pdf}, Abstract = {Each movement we make activates our own sensory receptors, thus causing a problem for the brain: the spurious, movement-related sensations must be discriminated from the sensory inputs that really matter, those representing our environment. Here we consider circuits for solving this problem in the primate brain. Such circuits convey a copy of each motor command, known as a corollary discharge (CD), to brain regions that use sensory input. In the visual system, CD signals may help to produce a stable visual percept from the jumpy images resulting from our rapid eye movements. A candidate pathway for providing CD for vision ascends from the superior colliculus to the frontal cortex in the primate brain. This circuit conveys warning signals about impending eye movements that are used for planning subsequent movements and analyzing the visual world. Identifying this circuit has provided a model for studying CD in other primate sensory systems and may lead to a better understanding of motor and mental disorders.}, Doi = {10.1146/annurev.neuro.31.060407.125627}, Key = {Sommer2008a} } @article{Sommer2008b, Author = {Sommer, MA and Wurtz, RH}, Title = {Visual perception and corollary discharge.}, Journal = {Perception}, Volume = {37}, Number = {3}, Pages = {408-418}, Year = {2008}, Month = {January}, ISSN = {0301-0066}, url = {https://dl.dropbox.com/u/27738651/Publications/SommerWurtz2008-Perception.pdf}, Abstract = {Perception depends not only on sensory input but also on the state of the brain receiving that input. A classic example is perception of a stable visual world in spite of the saccadic eye movements that shift the images on the retina. A long-standing hypothesis is that the brain compensates for the disruption of visual input by using advance knowledge of the impending saccade, an internally generated corollary discharge. One possible neuronal mechanism for this compensation has been previously identified in parietal and frontal cortex of monkeys, but the origin of the necessary corollary discharge remained unknown. Here, we consider recent experiments that identified a pathway for a corollary discharge for saccades that extends from the superior colliculus in the midbrain to the frontal eye fields in the cerebral cortex with a relay in the medial dorsal nucleus of the thalamus. We first review the nature of the evidence used to identify a corollary discharge signal in the complexity of the primate brain and show its use for guiding a rapid sequence of eye movements. We then consider two experiments that show this same corollary signal may provide the input to the frontal cortex neurons that alters their activity with saccades in ways that could compensate for the displacements in the visual input produced by saccadic eye movements. The first experiment shows that the corollary discharge signal is spatially and temporally appropriate to produce the alterations in the frontal-cortex neurons. The second shows that this signal is necessary for this alteration because inactivation of the corollary reduces the compensation by frontal-cortex neurons. The identification of this relatively simple circuit specifies the organization of a corollary discharge in the primate brain for the first time and provides a specific example upon which consideration of the roles of corollary activity in other systems and for other functions can be evaluated.}, Doi = {10.1068/p5873}, Key = {Sommer2008b} } @article{fds334831, Author = {Crapse, TB and Sommer, MA}, Title = {The frontal eye field as a prediction map.}, Journal = {Progress in brain research}, Volume = {171}, Pages = {383-390}, Editor = {C. Kennard and R. J. Leigh}, Year = {2008}, Month = {January}, ISSN = {0079-6123}, url = {https://dl.dropbox.com/u/27738651/Publications/CrapseSommer_ProgressBrainRes2008.pdf}, Abstract = {Predictive processes are widespread in the motor and sensory areas of the primate brain. They enable rapid computations despite processing delays and assist in resolving noisy, ambiguous input. Here we propose that the frontal eye field, a cortical area devoted to sensorimotor aspects of eye movement control, implements a prediction map of the postsaccadic visual scene for the purpose of constructing a stable percept despite saccadic eye movements.}, Doi = {10.1016/s0079-6123(08)00656-0}, Key = {fds334831} } @article{Sommer2007a, Author = {Sommer, MA}, Title = {Microcircuits for attention.}, Journal = {Neuron}, Volume = {55}, Number = {1}, Pages = {6-8}, Year = {2007}, Month = {July}, ISSN = {0896-6273}, url = {https://dl.dropbox.com/u/27738651/Publications/Sommer2007-NeuronCommentary.pdf}, Abstract = {Researchers who study the neuronal basis of cognition face a paradox. If they extract the brain, its cognitive functions cannot be assessed. On the other hand, the brain's microcircuits are difficult to study in the intact animal. In this issue of Neuron, Mitchell et al. make use of a promising approach based on waveform analysis to reveal new details about neuronal interactions during visual attention.}, Doi = {10.1016/j.neuron.2007.06.022}, Key = {Sommer2007a} } @article{Sommer2007b, Author = {Sommer, MA}, Title = {The feeling of looking.}, Journal = {Nature neuroscience}, Volume = {10}, Number = {5}, Pages = {538-540}, Year = {2007}, Month = {May}, ISSN = {1097-6256}, url = {https://dl.dropbox.com/u/27738651/Publications/Sommer2007-FeelingOfLooking.pdf}, Abstract = {Sensory cortex area 3a contains a map of the body. A new paper reports the location of eye position signals in this map which should allow researchers to test the functions of eye position signals and visual gain fields in more detail. © 2007 Nature Publishing Group.}, Doi = {10.1038/nn0507-538}, Key = {Sommer2007b} } @article{Sommer2006, Author = {Sommer, MA and Wurtz, RH}, Title = {Influence of the thalamus on spatial visual processing in frontal cortex.}, Journal = {Nature}, Volume = {444}, Number = {7117}, Pages = {374-377}, Year = {2006}, Month = {November}, ISSN = {0028-0836}, url = {https://dl.dropbox.com/u/27738651/Publications/SommerWurtz2006_Nature_Reprint.pdf}, Abstract = {Each of our movements activates our own sensory receptors, and therefore keeping track of self-movement is a necessary part of analysing sensory input. One way in which the brain keeps track of self-movement is by monitoring an internal copy, or corollary discharge, of motor commands. This concept could explain why we perceive a stable visual world despite our frequent quick, or saccadic, eye movements: corollary discharge about each saccade would permit the visual system to ignore saccade-induced visual changes. The critical missing link has been the connection between corollary discharge and visual processing. Here we show that such a link is formed by a corollary discharge from the thalamus that targets the frontal cortex. In the thalamus, neurons in the mediodorsal nucleus relay a corollary discharge of saccades from the midbrain superior colliculus to the cortical frontal eye field. In the frontal eye field, neurons use corollary discharge to shift their visual receptive fields spatially before saccades. We tested the hypothesis that these two components-a pathway for corollary discharge and neurons with shifting receptive fields-form a circuit in which the corollary discharge drives the shift. First we showed that the known spatial and temporal properties of the corollary discharge predict the dynamic changes in spatial visual processing of cortical neurons when saccades are made. Then we moved from this correlation to causation by isolating single cortical neurons and showing that their spatial visual processing is impaired when corollary discharge from the thalamus is interrupted. Thus the visual processing of frontal neurons is spatiotemporally matched with, and functionally dependent on, corollary discharge input from the thalamus. These experiments establish the first link between corollary discharge and visual processing, delineate a brain circuit that is well suited for mediating visual stability, and provide a framework for studying corollary discharge in other sensory systems.}, Doi = {10.1038/nature05279}, Key = {Sommer2006} } @article{fds334835, Author = {Wurtz, RH and Sommer, MA}, Title = {A corollary discharge for perceptual stability}, Journal = {PERCEPTION}, Volume = {35}, Pages = {10-11}, Publisher = {SAGE PUBLICATIONS LTD}, Year = {2006}, Month = {January}, Key = {fds334835} } @article{fds334836, Author = {Wurtz, RH and Sommer, MA and Cavanaugh, J}, Title = {Drivers from the deep: the contribution of collicular input to thalamocortical processing.}, Journal = {Progress in brain research}, Volume = {149}, Pages = {207-225}, Year = {2005}, Month = {January}, ISSN = {0079-6123}, url = {https://dl.dropbox.com/u/27738651/Publications/WurtzSommerCavanaugh_ProgrBrainRes2005.pdf}, Abstract = {A traditional view of the thalamus is that it is a relay station which receives sensory input and conveys this information to cortex. This sensory input determines most of the properties of first order thalamic neurons, and so is said to drive, rather than modulate, these neurons. This holds as a rule for first order thalamic nuclei, but in contrast, higher order thalamic nuclei receive much of their driver input back from cerebral cortex. In addition, higher order thalamic neurons receive inputs from subcortical movement-related centers. In the terminology popularized from studies of the sensory system, can we consider these ascending motor inputs to thalamus from subcortical structures to be modulators, subtly influencing the activity of their target neurons, or drivers, dictating the activity of their target neurons? This chapter summarizes relevant evidence from neuronal recording, inactivation, and stimulation of pathways projecting from the superior colliculus through thalamus to cerebral cortex. The study concludes that many inputs to the higher order nuclei of the thalamus from subcortical oculomotor areas - from the superior colliculus and probably other midbrain and pontine regions - should be regarded as motor drivers analogous to the sensory drivers at the first order thalamic nuclei. These motor drivers at the thalamus are viewed as being at the top of a series of feedback loops that provide information on impending actions, just as sensory drivers provide information about the external environment.}, Doi = {10.1016/s0079-6123(05)49015-9}, Key = {fds334836} } @article{fds334838, Author = {Sommer, MA and Wurtz, RH}, Title = {What the brain stem tells the frontal cortex. II. Role of the SC-MD-FEF pathway in corollary discharge.}, Journal = {Journal of neurophysiology}, Volume = {91}, Number = {3}, Pages = {1403-1423}, Year = {2004}, Month = {March}, url = {http://dx.doi.org/10.1152/jn.00740.2003}, Abstract = {One way we keep track of our movements is by monitoring corollary discharges or internal copies of movement commands. This study tested a hypothesis that the pathway from superior colliculus (SC) to mediodorsal thalamus (MD) to frontal eye field (FEF) carries a corollary discharge about saccades made into the contralateral visual field. We inactivated the MD relay node with muscimol in monkeys and measured corollary discharge deficits using a double-step task: two sequential saccades were made to the locations of briefly flashed targets. To make second saccades correctly, monkeys had to internally monitor their first saccades; therefore deficits in the corollary discharge representation of first saccades should disrupt second saccades. We found, first, that monkeys seemed to misjudge the amplitudes of their first saccades; this was revealed by systematic shifts in second saccade end points. Thus corollary discharge accuracy was impaired. Second, monkeys were less able to detect trial-by-trial variations in their first saccades; this was revealed by reduced compensatory changes in second saccade angles. Thus corollary discharge precision also was impaired. Both deficits occurred only when first saccades went into the contralateral visual field. Single-saccade generation was unaffected. Additional deficits occurred in reaction time and overall performance, but these were bilateral. We conclude that the SC-MD-FEF pathway conveys a corollary discharge used for coordinating sequential saccades and possibly for stabilizing vision across saccades. This pathway is the first elucidated in what may be a multilevel chain of corollary discharge circuits extending from the extraocular motoneurons up into cerebral cortex.}, Doi = {10.1152/jn.00740.2003}, Key = {fds334838} } @article{fds334839, Author = {Sommer, MA and Wurtz, RH}, Title = {What the brain stem tells the frontal cortex. I. Oculomotor signals sent from superior colliculus to frontal eye field via mediodorsal thalamus.}, Journal = {Journal of neurophysiology}, Volume = {91}, Number = {3}, Pages = {1381-1402}, Year = {2004}, Month = {March}, url = {http://dx.doi.org/10.1152/jn.00738.2003}, Abstract = {Neuronal processing in cerebral cortex and signal transmission from cortex to brain stem have been studied extensively, but little is known about the numerous feedback pathways that ascend from brain stem to cortex. In this study, we characterized the signals conveyed through an ascending pathway coursing from the superior colliculus (SC) to the frontal eye field (FEF) via mediodorsal thalamus (MD). Using antidromic and orthodromic stimulation, we identified SC source neurons, MD relay neurons, and FEF recipient neurons of the pathway in Macaca mulatta. The monkeys performed oculomotor tasks, including delayed-saccade tasks, that permitted analysis of signals such as visual activity, delay activity, and presaccadic activity. We found that the SC sends all of these signals into the pathway with no output selectivity, i.e., the signals leaving the SC resembled those found generally within the SC. Visual activity arrived in FEF too late to contribute to short-latency visual responses there, and delay activity was largely filtered out in MD. Presaccadic activity, however, seemed critical because it traveled essentially unchanged from SC to FEF. Signal transmission in the pathway was fast ( approximately 2 ms from SC to FEF) and topographically organized (SC neurons drove MD and FEF neurons having similarly eccentric visual and movement fields). Our analysis of identified neurons in one pathway from brain stem to frontal cortex thus demonstrates that multiple signals are sent from SC to FEF with presaccadic activity being prominent. We hypothesize that a major signal conveyed by the pathway is corollary discharge information about the vector of impending saccades.}, Doi = {10.1152/jn.00738.2003}, Key = {fds334839} } @article{fds334837, Author = {Wurtz, RH and Sommer, MA}, Title = {Identifying corollary discharges for movement in the primate brain.}, Journal = {Progress in brain research}, Volume = {144}, Pages = {47-60}, Year = {2004}, Month = {January}, ISSN = {0079-6123}, url = {https://dl.dropbox.com/u/27738651/Publications/WurtzSommer_ProgBrainRes2004.pdf}, Abstract = {The brain keeps track of the movements it makes so as to process sensory input accurately and coordinate complex movements gracefully. In this chapter we review the brain's strategies for keeping track of fast, saccadic eye movements. One way it does this is by monitoring copies of saccadic motor commands, or corollary discharges. It has been difficult to identify corollary discharge signals in the primate brain, although in some studies the influence of corollary discharge, for example on visual processing, has been found. We propose four criteria for identifying corollary discharge signals in primate brain based on our experiences studying a pathway from superior colliculus, in the brainstem, through mediodorsal thalamus to frontal eye field, in the prefrontal cortex. First, the signals must originate from a brain structure involved in generating movements. Second, they must begin just prior to movements and represent spatial attributes of the movements. Third, eliminating the signals should not impair movements in simple tasks not requiring corollary discharge. Fourth, eliminating the signals should, however, disrupt movements in tasks that require corollary discharge, such as a double-step task in which the monkey must keep track of one saccade in order to correctly generate another. Applying these criteria to the pathway from superior colliculus to frontal eye field, we concluded that it does indeed convey corollary discharge signals. The extent to which cerebral cortex actually uses these signals, particularly in the realm of sensory perception, remains unknown pending further studies. Moreover, many other ascending pathways from brainstem to cortex remain to be explored in behaving monkeys, and some of these, too, may carry corollary discharge signals.}, Doi = {10.1016/s0079-6123(03)14403-2}, Key = {fds334837} } @article{fds334841, Author = {Sommer, MA}, Title = {The role of the thalamus in motor control.}, Journal = {Current opinion in neurobiology}, Volume = {13}, Number = {6}, Pages = {663-670}, Year = {2003}, Month = {December}, url = {http://dx.doi.org/10.1016/j.conb.2003.10.014}, Abstract = {Two characteristics of the thalamus--its apparently simple relay function and its daunting multinuclear structure--have been customarily viewed as good reasons to study something else. Yet, now that many other brain regions have been explored and neurophysiologists are turning to questions of how larger circuits operate, these two characteristics are starting to seem more attractive. First, the relay nature of thalamic neurons means that recording from them, like tapping into a wire, can reveal the signals carried by specific circuits. Second, the concentration of like relay neurons into nuclei means that inactivating or stimulating them can efficiently test the functions of the circuits. Recent studies implementing these principles have revealed pathways through the thalamus that contribute to generating movements and to monitoring one's own actions (corollary discharge).}, Doi = {10.1016/j.conb.2003.10.014}, Key = {fds334841} } @article{fds334840, Author = {Sommer, MA and Wurtz, RH}, Title = {The frontal eye field sends predictively remapped visual signals to the superior colliculus}, Journal = {Journal of Vision}, Volume = {3}, Number = {9}, Pages = {146-146}, Publisher = {Association for Research in Vision and Ophthalmology (ARVO)}, Year = {2003}, url = {http://dx.doi.org/10.1167/3.9.146}, Abstract = {We perceive a stable visual world even though saccades often move our retinas. One way the brain may achieve a stable visual percept is through predictive remapping of visual receptive fields: just before a saccade, the receptive field of many neurons moves from its current location ("current receptive field") to the location it is expected to occupy after the saccade ("future receptive field"). Goldberg and colleagues found such remapping in cortical areas, e.g. in the frontal eye field (FEF), as well as in the intermediate layers of the superior colliculus (SC). In the present study we investigated the source of the SC's remapped visual signals. Do some of them come from the FEF? We identified FEF neurons that project to the SC using antidromic stimulation. For neurons with a visual response, we tested whether the receptive field shifted just prior to making a saccade. Saccadic amplitudes were chosen to be as small as possible while clearly separating the current and future receptive fields; they ranged from 5-30 deg. in amplitude and were directed contraversively. The saccadic target was a small red spot. We probed visual responsiveness at the current and future receptive field locations using a white spot flashed at various times before or after the saccade. Predictive remapping was indicated by a visual response to a probe flashed in the future receptive field just before the saccade began. We found that many FEF neurons projecting to the SC exhibited predictive remapping. Moreover, the remapping was as fast and strong as any previously reported for FEF or SC. It is clear, therefore, that remapped visual signals are sent from FEF to SC, providing direct evidence that the FEF is one source of the SC's remapped visual signals. Because remapping requires information about an imminent saccade, we hypothesize that remapping in FEF depends on corollary discharge signals such as those ascending from the SC through MD thalamus (Sommer and Wurtz 2002).}, Doi = {10.1167/3.9.146}, Key = {fds334840} } @article{fds334842, Author = {Sommer, MA and Wurtz, RH}, Title = {A pathway in primate brain for internal monitoring of movements.}, Journal = {Science (New York, N.Y.)}, Volume = {296}, Number = {5572}, Pages = {1480-1482}, Year = {2002}, Month = {May}, ISSN = {0036-8075}, url = {https://dl.dropbox.com/u/27738651/Publications/SommerWurtz2002.pdf}, Abstract = {It is essential to keep track of the movements we make, and one way to do that is to monitor correlates, or corollary discharges, of neuronal movement commands. We hypothesized that a previously identified pathway from brainstem to frontal cortex might carry corollary discharge signals. We found that neuronal activity in this pathway encodes upcoming eye movements and that inactivating the pathway impairs sequential eye movements consistent with loss of corollary discharge without affecting single eye movements. These results identify a pathway in the brain of the primate Macaca mulatta that conveys corollary discharge signals.}, Doi = {10.1126/science.1069590}, Key = {fds334842} } @article{fds334845, Author = {Sommer, MA and Wurtz, RH}, Title = {Frontal eye field sends delay activity related to movement, memory, and vision to the superior colliculus.}, Journal = {Journal of neurophysiology}, Volume = {85}, Number = {4}, Pages = {1673-1685}, Year = {2001}, Month = {April}, url = {http://dx.doi.org/10.1152/jn.2001.85.4.1673}, Abstract = {Many neurons within prefrontal cortex exhibit a tonic discharge between visual stimulation and motor response. This delay activity may contribute to movement, memory, and vision. We studied delay activity sent from the frontal eye field (FEF) in prefrontal cortex to the superior colliculus (SC). We evaluated whether this efferent delay activity was related to movement, memory, or vision, to establish its possible functions. Using antidromic stimulation, we identified 66 FEF neurons projecting to the SC and we recorded from them while monkeys performed a Go/Nogo task. Early in every trial, a monkey was instructed as to whether it would have to make a saccade (Go) or not (Nogo) to a target location, which permitted identification of delay activity related to movement. In half of the trials (memory trials), the target disappeared, which permitted identification of delay activity related to memory. In the remaining trials (visual trials), the target remained visible, which permitted identification of delay activity related to vision. We found that 77% (51/66) of the FEF output neurons had delay activity. In 53% (27/51) of these neurons, delay activity was modulated by Go/Nogo instructions. The modulation preceded saccades made into only part of the visual field, indicating that the modulation was movement-related. In some neurons, delay activity was modulated by Go/Nogo instructions in both memory and visual trials and seemed to represent where to move in general. In other neurons, delay activity was modulated by Go/Nogo instructions only in memory trials, which suggested that it was a correlate of working memory, or only in visual trials, which suggested that it was a correlate of visual attention. In 47% (24/51) of FEF output neurons, delay activity was unaffected by Go/Nogo instructions, which indicated that the activity was related to the visual stimulus. In some of these neurons, delay activity occurred in both memory and visual trials and seemed to represent a coordinate in visual space. In others, delay activity occurred only in memory trials and seemed to represent transient visual memory. In the remainder, delay activity occurred only in visual trials and seemed to be a tonic visual response. In conclusion, the FEF sends diverse delay activity signals related to movement, memory, and vision to the SC, where the signals may be used for saccade generation. Downstream transmission of various delay activity signals may be an important, general way in which the prefrontal cortex contributes to the control of movement.}, Doi = {10.1152/jn.2001.85.4.1673}, Key = {fds334845} } @article{fds334843, Author = {Wurtz, RH and Sommer, MA and Paré, M and Ferraina, S}, Title = {Signal transformations from cerebral cortex to superior colliculus for the generation of saccades.}, Journal = {Vision research}, Volume = {41}, Number = {25-26}, Pages = {3399-3412}, Year = {2001}, Month = {January}, ISSN = {0042-6989}, url = {https://dl.dropbox.com/u/27738651/Publications/WurtzSommerPareFerraina2001.pdf}, Abstract = {The ability of primates to make rapid and accurate saccadic eye movements for exploring the natural world is based on a neuronal system in the brain that has been studied extensively and is known to include multiple brain regions extending throughout the neuraxis. We examined the characteristics of signal flow in this system by recording from identified output neurons of two cortical regions, the lateral intraparietal area (LIP) and the frontal eye field (FEF), and from neurons in a brainstem structure targeted by these output neurons, the superior colliculus (SC). We compared the activity of neurons in these three populations while monkeys performed a delayed saccade task that allowed us to quantify visual responses, motor activity, and intervening delay activity. We examined whether delay activity was related to visual stimulation by comparing the activity during interleaved trials when a target was either present or absent during the delay period. We examined whether delay activity was related to movement by using a Go/Nogo task and comparing the activity during interleaved trials in which a saccade was either made (Go) or not (Nogo). We found that LIP output neurons, FEF output neurons, and SC neurons can all have visual responses, delay activity, and presaccadic bursts; hence in this way they are all quite similar. However, the delay activity tended to be more related to visual stimulation in the cortical output neurons than in the SC neurons. Complementing this, the delay activity tended to be more related to movement in the SC neurons than in the cortical output neurons. We conclude, first, that the signal flow leaving the cortex represents activity at nearly every stage of visuomotor transformation, and second, that there is a gradual evolution of signal processing as one proceeds from cortex to colliculus.}, Doi = {10.1016/s0042-6989(01)00066-9}, Key = {fds334843} } @article{fds334844, Author = {Sommer, M and Wurtz, R}, Title = {A subcortical source of visual input to the frontal eye field}, Journal = {Journal of Vision}, Volume = {1}, Number = {3}, Pages = {259-259}, Publisher = {Association for Research in Vision and Ophthalmology (ARVO)}, Year = {2001}, url = {http://dx.doi.org/10.1167/1.3.259}, Abstract = {Many neurons in the frontal eye field (FEF) exhibit visual responses and are thought to play important roles in visuosaccadic behavior. The FEF, however, is far removed from striate cortex. Where do the FEF's visual signals come from? Usually they are reasonably assumed to enter the FEF through afferents from extrastriate cortex. Here we show that, surprisingly, visual signals also enter the FEF through a subcortical route: a disynaptic, ascending pathway originating in the intermediate layers of the superior colliculus (SC). We recorded from identified neurons at all three stages of this pathway (n=30-40 in each sample): FEF recipient neurons, orthodromically activated from the SC; mediodorsal thalamus (MD) relay neurons, antidromically activated from FEF and orthodromically activated from SC; and SC source neurons, antidromically activated from MD. We studied the neurons while monkeys performed delayed saccade tasks designed to temporally resolve visual responses from presaccadic discharges. We found, first, that most neurons at every stage in the pathway had visual responses, presaccadic bursts, or both. Second, we found marked similarities between the SC source neurons and MD relay neurons: in both samples, about 15% of the neurons had only a visual response, 10% had only a presaccadic burst, and 75% had both. In contrast, FEF recipient neurons tended to be more visual in nature: 50% had only a visual response, none had only a presaccadic burst, and 50% had both a visual response and a presaccadic burst. This suggests that in addition to their subcortical inputs, these FEF neurons also receive other visual inputs, e.g. from extrastriate cortex. We conclude that visual activity in the FEF results not only from cortical afferents but also from subcortical inputs. Intriguingly, this implies that some of the visual signals in FEF are pre-processed by the SC.}, Doi = {10.1167/1.3.259}, Key = {fds334844} } @article{fds334849, Author = {Port, NL and Sommer, MA and Wurtz, RH}, Title = {Multielectrode evidence for spreading activity across the superior colliculus movement map.}, Journal = {Journal of neurophysiology}, Volume = {84}, Number = {1}, Pages = {344-357}, Year = {2000}, Month = {July}, url = {http://dx.doi.org/10.1152/jn.2000.84.1.344}, Abstract = {The monkey superior colliculus (SC) has maps for both visual input and movement output in the superficial and intermediate layers, respectively, and activity on these maps is generally related to visual stimuli only in one part of the visual field and/or to a restricted range of saccadic eye movements to those stimuli. For some neurons within these maps, however, activity has been reported to spread from the caudal SC to the rostral SC during the course of a saccade. This spread of activity was inferred from averages of recordings at different sites on the SC movement map during saccades of different amplitudes and even in different monkeys. In the present experiments, SC activity was recorded simultaneously in pairs of neurons to observe the spread of activity during individual saccades. Two electrodes were positioned along the rostral-caudal axis of the SC with one being more caudal than the other, and 60 neuron pairs whose movement fields were large enough to see a spread of activity were studied. During individual saccades, the relative time of discharge of the two neurons was compared using 1) the time difference between peak discharge of the two neurons, 2) the difference between the "median activation time" of the two neurons, and 3) the shift required to align the two discharge patterns using cross-correlation. All three analysis methods gave comparable results. Many pairs of neurons were activated in sequence during saccade generation, and the order of activation was most frequently caudal to rostral. Such a sequence of activation was not observed in every neuron pair, but over the sample of neuron pairs studied, the spread was statistically significant. When we compared the time of neuronal activity to the time of saccade onset, we found that the caudal neuronal activity was more likely to be before the saccade, whereas the rostral neuronal activity was more likely to be during the saccade. These results demonstrate that when individual pairs of neurons are examined during single saccades there is evidence of a caudal to rostral spread of activity within the monkey SC, and they confirm the previous inferences of a spread of activity drawn from observations on averaged neuronal activity during multiple saccades. The functional contribution of this spread of activity remains to be determined.}, Doi = {10.1152/jn.2000.84.1.344}, Key = {fds334849} } @article{Tehovnik2000, Author = {Tehovnik, EJ and Sommer, MA and Chou, IH and Slocum, WM and Schiller, PH}, Title = {Eye fields in the frontal lobes of primates.}, Journal = {Brain research. Brain research reviews}, Volume = {32}, Number = {2-3}, Pages = {413-448}, Year = {2000}, Month = {April}, ISSN = {0165-0173}, url = {https://dl.dropbox.com/u/27738651/Publications/TehovnikEtAl-2000_EyeFieldsInFrontalCortex-Review.pdf}, Abstract = {Two eye fields have been identified in the frontal lobes of primates: one is situated dorsomedially within the frontal cortex and will be referred to as the eye field within the dorsomedial frontal cortex (DMFC); the other resides dorsolaterally within the frontal cortex and is commonly referred to as the frontal eye field (FEF). This review documents the similarities and differences between these eye fields. Although the DMFC and FEF are both active during the execution of saccadic and smooth pursuit eye movements, the FEF is more dedicated to these functions. Lesions of DMFC minimally affect the production of most types of saccadic eye movements and have no effect on the execution of smooth pursuit eye movements. In contrast, lesions of the FEF produce deficits in generating saccades to briefly presented targets, in the production of saccades to two or more sequentially presented targets, in the selection of simultaneously presented targets, and in the execution of smooth pursuit eye movements. For the most part, these deficits are prevalent in both monkeys and humans. Single-unit recording experiments have shown that the DMFC contains neurons that mediate both limb and eye movements, whereas the FEF seems to be involved in the execution of eye movements only. Imaging experiments conducted on humans have corroborated these findings. A feature that distinguishes the DMFC from the FEF is that the DMFC contains a somatotopic map with eyes represented rostrally and hindlimbs represented caudally; the FEF has no such topography. Furthermore, experiments have revealed that the DMFC tends to contain a craniotopic (i.e., head-centered) code for the execution of saccadic eye movements, whereas the FEF contains a retinotopic (i.e., eye-centered) code for the elicitation of saccades. Imaging and unit recording data suggest that the DMFC is more involved in the learning of new tasks than is the FEF. Also with continued training on behavioural tasks the responsivity of the DMFC tends to drop. Accordingly, the DMFC is more involved in learning operations whereas the FEF is more specialized for the execution of saccadic and smooth pursuit eye movements.}, Doi = {10.1016/s0165-0173(99)00092-2}, Key = {Tehovnik2000} } @article{fds334848, Author = {Sommer, MA and Wurtz, RH}, Title = {Composition and topographic organization of signals sent from the frontal eye field to the superior colliculus.}, Journal = {Journal of neurophysiology}, Volume = {83}, Number = {4}, Pages = {1979-2001}, Year = {2000}, Month = {April}, url = {http://dx.doi.org/10.1152/jn.2000.83.4.1979}, Abstract = {The frontal eye field (FEF) and superior colliculus (SC) contribute to saccadic eye movement generation, and much of the FEF's oculomotor influence may be mediated through the SC. The present study examined the composition and topographic organization of signals flowing from FEF to SC by recording from FEF neurons that were antidromically activated from rostral or caudal SC. The first and most general result was that, in a sample of 88 corticotectal neurons, the types of signals relayed from FEF to SC were highly diverse, reflecting the general population of signals within FEF rather than any specific subset of signals. Second, many neurons projecting from FEF to SC carried signals thought to reflect cognitive operations, namely tonic discharges during the delay period of a delayed-saccade task (delay signals), elevated discharges during the gap period of a gap task (gap increase signals), or both. Third, FEF neurons discharging during fixation were found to project to the SC, although they did not project preferentially to rostral SC, where similar fixation neurons are found. Neurons that did project preferentially to the rostral SC were those with foveal visual responses and those pausing during the gap period of the gap task. Many of the latter neurons also had foveal visual responses, presaccadic pauses in activity, and postsaccadic increases in activity. These two types of rostral-projecting neurons therefore may contribute to the activity of rostral SC fixation neurons. Fourth, conduction velocity was used as an indicator of cell size to correct for sampling bias. The outcome of this correction procedure suggested that among the most prevalent neurons in the FEF corticotectal population are those carrying putative cognitive-related signals, i.e., delay and gap increase signals, and among the least prevalent are those carrying presaccadic burst discharges but lacking peripheral visual responses. Fifth, corticotectal neurons carrying various signals were biased topographically across the FEF. Neurons with peripheral visual responses but lacking presaccadic burst discharges were biased laterally, neurons with presaccadic burst discharges but lacking peripheral visual responses were biased medially, and neurons carrying delay or gap increase signals were biased dorsally. Finally, corticotectal neurons were distributed within the FEF as a function of their visual or movement field eccentricity and projected to the SC such that eccentricity maps in both structures were closely aligned. We conclude that the FEF most likely influences the activity of SC neurons continuously from the start of fixation, through visual analysis and cognitive manipulations, until a saccade is generated and fixation begins anew. Furthermore, the projection from FEF to SC is highly topographically organized in terms of function at both its source and its termination.}, Doi = {10.1152/jn.2000.83.4.1979}, Key = {fds334848} } @article{Sommer1999, Author = {Sommer, MA and Tehovnik, EJ}, Title = {Reversible inactivation of macaque dorsomedial frontal cortex: effects on saccades and fixations.}, Journal = {Experimental brain research}, Volume = {124}, Number = {4}, Pages = {429-446}, Year = {1999}, Month = {February}, ISSN = {0014-4819}, url = {https://dl.dropbox.com/u/27738651/Publications/SommerTehovnik1999-DMFCinactivation.pdf}, Abstract = {Neural recording and electrical stimulation results suggest that the dorsomedial frontal cortex (DMFC) of macaque is involved in oculomotor behavior. We reversibly inactivated the DMFC using lidocaine and examined how saccadic eye movements and fixations were affected. The inactivation methods and monkeys were the same as those used in a previous study of the frontal eye field (FEF), another frontal oculomotor region. In the first stage of the present study, monkeys performed tasks that required the generation of single saccades and fixations. During 15 DMFC inactivations, we found only mild, infrequent deficits. This contrasts with our prior finding that FEF inactivation causes severe, reliable deficits in performance of these tasks. In the second stage of the study, we investigated whether DMFC inactivation affected behavior when a monkey was required to make more than one saccade and fixation. We used a double-step task: two targets were flashed in rapid succession and the monkey had to make two saccades to foveate the target locations. In each of five experiments, DMFC inactivation caused a moderate, significant deficit. Both ipsi- and contraversive saccades were disrupted. In two experiments, the first saccades were made to the wrong place and had increased latencies. In one experiment, first saccades were unaffected, but second saccades were made to the wrong place and had increased latencies. In the remaining two experiments, specific reasons for the deficit were not detected. Saline infusions into DMFC had no effect. Inactivation of FEF caused a larger double-step deficit than did inactivation of DMFC. The FEF inactivation impaired contraversive first or second saccades of the sequence. In conclusion, our results suggest that the DMFC makes an important contribution to generating sequential saccades and fixations but not single saccades and fixations. Compared with the FEF, the DMFC has a weaker, less directional, more task-dependent oculomotor influence.}, Doi = {10.1007/s002210050639}, Key = {Sommer1999} } @article{Chou1999, Author = {Chou, IH and Sommer, MA and Schiller, PH}, Title = {Express averaging saccades in monkeys.}, Journal = {Vision research}, Volume = {39}, Number = {25}, Pages = {4200-4216}, Year = {1999}, Month = {January}, ISSN = {0042-6989}, url = {https://dl.dropbox.com/u/27738651/Publications/ChouEtAl1999-ExpressAveragingSaccades.pdf}, Abstract = {When monkeys are presented simultaneously with multiple stimuli, they can make one of two types of response. Either they make averaging saccades, that land at intermediate locations between the targets, or target-directed saccades, that land close to one of the targets. The two types of saccades occur at different latencies and are thought to reflect different processes; fast reflexive averaging and slower target selection. We investigated the latency of averaging saccades in five monkeys, with particular emphasis on 'express' latency saccades, which are thought to be inhibited by target selection. Express averaging saccades were made prolifically by the two monkeys that made both express and regular latency saccades, but only when no specific instruction was given regarding the saccade target. When these monkeys had to choose one of the targets, on the basis of its color, they still made averaging saccades. However, the endpoints formed two distributions close to the targets as opposed to one single distribution centered between the targets, as was the case when targets were identical; also, express saccades were almost entirely absent. We conclude that express averaging saccades are a form of spatial and temporal optimization of gaze shifting.}, Doi = {10.1016/s0042-6989(99)00133-9}, Key = {Chou1999} } @article{fds334853, Author = {Sommer, MA and Wurtz, RH}, Title = {Frontal eye field neurons orthodromically activated from the superior colliculus.}, Journal = {Journal of neurophysiology}, Volume = {80}, Number = {6}, Pages = {3331-3335}, Year = {1998}, Month = {December}, url = {http://dx.doi.org/10.1152/jn.1998.80.6.3331}, Abstract = {Frontal eye field neurons orthodromically activated from the superior colliculus. J. Neurophysiol. 80: 3331-3333, 1998. Anatomical studies have shown that the frontal eye field (FEF) and superior colliculus (SC) of monkeys are reciprocally connected, and a physiological study described the signals sent from the FEF to the SC. Nothing is known, however, about the signals sent from the SC to the FEF. We physiologically identified and characterized FEF neurons that are likely to receive input from the SC. Fifty-two FEF neurons were found that were orthodromically activated by electrical stimulation of the intermediate or deeper layers of the SC. All the neurons that we tested (n = 34) discharged in response to visual stimulation. One-half also discharged when saccadic eye movements were made. This provides the first direct evidence that the ascending pathway from SC to FEF might carry visual- and saccade-related signals. Our findings support a hypothesis that the SC and the FEF interact bidirectionally during the events leading up to saccade generation.}, Doi = {10.1152/jn.1998.80.6.3331}, Key = {fds334853} } @article{fds334852, Author = {Nichols, AM and Ruffner, TW and Sommer, MA and Wurtz, RH}, Title = {A screw microdrive for adjustable chronic unit recording in monkeys.}, Journal = {Journal of neuroscience methods}, Volume = {81}, Number = {1-2}, Pages = {185-188}, Year = {1998}, Month = {June}, ISSN = {0165-0270}, url = {https://dl.dropbox.com/u/27738651/Publications/NicholsRuffnerSommerWurtz_JNeuroscienceMethods1998.pdf}, Abstract = {A screw microdrive is described that attaches to the grid system used for recording single neurons from brains of awake behaving monkeys. Multiple screwdrives can be mounted on a grid over a single cranial opening. This method allows many electrodes to be implanted chronically in the brain and adjusted as needed to maintain isolation. rights reserved.}, Doi = {10.1016/s0165-0270(98)00036-3}, Key = {fds334852} } @article{Tehovnik1997a, Author = {Tehovnik, EJ and Sommer, MA}, Title = {Electrically evoked saccades from the dorsomedial frontal cortex and frontal eye fields: a parametric evaluation reveals differences between areas.}, Journal = {Experimental brain research}, Volume = {117}, Number = {3}, Pages = {369-378}, Year = {1997}, Month = {December}, ISSN = {0014-4819}, url = {https://dl.dropbox.com/u/27738651/Publications/TehovnikSommer1997.pdf}, Abstract = {Using electrical stimulation to evoke saccades from the dorsomedial frontal cortex (DMFC) and frontal eye fields (FEF) of rhesus monkeys, parametric tests were conducted to compare the excitability properties of these regions. Pulse frequency and pulse current, pulse frequency and train duration, and pulse current and pulse duration were varied to determine threshold functions for a 50% probability of evoking a saccade. Also a wide range of frequencies were tested to evoke saccades, while holding all other parameters constant. For frequencies beyond 150 Hz, the probability of evoking saccades decreased for the DMFC, whereas for the FEF this probability remained at 100%. To evoke saccades readily from the DMFC, train durations of greater than 200 ms were needed; for the FEF, durations of less than 100 ms were sufficient. Even though the chronaxies of neurons residing in the DMFC and FEF were similar (ranging from 0.1 to 0.24 ms) significantly higher currents were required to evoke saccades from the DMFC than FEF. Thus the stimulation parameters that are optimal for evoking saccades from the DMFC differ from those that are optimal for evoking saccades from the FEF. Although the excitability of neurons in the DMFC and FEF are similar (due to similar chronaxies), we suggest that the density of saccade-relevant neurons is higher in the FEF than in the DMFC.}, Doi = {10.1007/s002210050231}, Key = {Tehovnik1997a} } @article{Sommer1997b, Author = {Sommer, MA}, Title = {The spatial relationship between scanning saccades and express saccades.}, Journal = {Vision research}, Volume = {37}, Number = {19}, Pages = {2745-2756}, Year = {1997}, Month = {October}, ISSN = {0042-6989}, url = {https://dl.dropbox.com/u/27738651/Publications/Sommer1997-ScanningAndExpressSaccades.pdf}, Abstract = {When monkeys interrupt their saccadic scanning of a visual scene to look at a suddenly appearing target, saccades to the target are made after an "express" latency or after a longer "regular" latency. The purpose of this study was to analyze the spatial patterns of scanning, express, and regular saccades. Scanning patterns were spatially biased. Express saccade patterns were biased, too, and were directly correlated with scanning patterns. Regular saccade patterns were more uniform and were not directly correlated with scanning patterns. Express saccades, but not regular saccades, seemed to be facilitated by preparation to scan. This study contributes to a general understanding of how monkeys examine scenes containing both unchanging and suddenly appearing stimuli.}, Doi = {10.1016/s0042-6989(97)00078-3}, Key = {Sommer1997b} } @article{Sommer1997a, Author = {Sommer, MA and Tehovnik, EJ}, Title = {Reversible inactivation of macaque frontal eye field.}, Journal = {Experimental brain research}, Volume = {116}, Number = {2}, Pages = {229-249}, Year = {1997}, Month = {September}, ISSN = {0014-4819}, url = {https://dl.dropbox.com/u/27738651/Publications/SommerTehovnik1997.pdf}, Abstract = {The macaque frontal eye field (FEF) is involved in the generation of saccadic eye movements and fixations. To better understand the role of the FEF, we reversibly inactivated a portion of it while a monkey made saccades and fixations in response to visual stimuli. Lidocaine was infused into a FEF and neural inactivation was monitored with a nearby microelectrode. We used two saccadic tasks. In the delay task, a target was presented and then extinguished, but the monkey was not allowed to make a saccade to its location until a cue to move was given. In the step task, the monkey was allowed to look at a target as soon as it appeared. During FEF inactivation, monkeys were severely impaired at making saccades to locations of extinguished contralateral targets in the delay task. They were similarly impaired at making saccades to locations of contralateral targets in the step task if the target was flashed for < or =100 ms, such that it was gone before the saccade was initiated. Deficits included increases in saccadic latency, increases in saccadic error, and increases in the frequency of trials in which a saccade was not made. We varied the initial fixation location and found that the impairment specifically affected contraversive saccades rather than affecting all saccades made into head-centered contralateral space. Monkeys were impaired only slightly at making saccades to contralateral targets in the step task if the target duration was 1000 ms, such that the target was present during the saccade: latency increased, but increases in saccadic error were mild and increases in the frequency of trials in which a saccade was not made were insignificant. During FEF inactivation there usually was a direct correlation between the latency and the error of saccades made in response to contralateral targets. In the delay task, FEF inactivation increased the frequency of making premature saccades to ipsilateral targets. FEF inactivation had inconsistent and mild effects on saccadic peak velocity. FEF inactivation caused impairments in the ability to fixate lights steadily in contralateral space. FEF inactivation always caused an ipsiversive deviation of the eyes in darkness. In summary, our results suggest that the FEF plays major roles in (1) generating contraversive saccades to locations of extinguished or flashed targets, (2) maintaining contralateral fixations, and (3) suppressing inappropriate ipsiversive saccades.}, Doi = {10.1007/pl00005752}, Key = {Sommer1997a} } @article{Tehovnik1997b, Author = {Tehovnik, EJ and Sommer, MA}, Title = {Effective spread and timecourse of neural inactivation caused by lidocaine injection in monkey cerebral cortex.}, Journal = {Journal of neuroscience methods}, Volume = {74}, Number = {1}, Pages = {17-26}, Year = {1997}, Month = {June}, ISSN = {0165-0270}, url = {https://dl.dropbox.com/u/27738651/Publications/TehovnikSommer1997-LidocaineInactivation.pdf}, Abstract = {We studied the effective spread of lidocaine to inactivate neural tissue in the frontal cortex of the rhesus monkey. Injections of 2% lidocaine at 4 microl/min were made while units were recorded 1 or 2 mm away. To inactivate units 1 mm away from the injection site 100% of the time, 7 microl of lidocaine had to be injected. To inactivate units 2 mm away from the injection site 100% of the time, 30 microl of lidocaine were required. Units were maximally inactivated around 8 min after the start of a lidocaine injection, and they gradually recovered, regaining most of their initial activity by around 30 min after the start of an injection. The volume of lidocaine required to inactivate neurons > 90% of the time could be estimated by the spherical volume equation, V = 4/3 pi (r)3. To prolong the inactivation, a slower infusion of lidocaine subsequent to an initial bolus was effective. Saline control injections had no effect. These results allow both a prediction of the timecourse of neural inactivation and an estimate of the spread of neural inactivation following injection of lidocaine into the monkey cerebral cortex.}, Doi = {10.1016/s0165-0270(97)02229-2}, Key = {Tehovnik1997b} } @article{Tehovnik1996, Author = {Tehovnik, EJ and Sommer, MA}, Title = {Compensatory saccades made to remembered targets following orbital displacement by electrically stimulating the dorsomedial frontal cortex or frontal eye fields of primates.}, Journal = {Brain research}, Volume = {727}, Number = {1-2}, Pages = {221-224}, Year = {1996}, Month = {July}, ISSN = {0006-8993}, url = {https://dl.dropbox.com/u/27738651/Publications/TehovnikSommer1996.pdf}, Abstract = {If the eye-position signal during visually-evoked saccades is dependent on the dorsomedial frontal cortex (DMFC), one would expect that saccades generated to briefly presented visual targets would be disrupted after displacement of the eyes via electrical stimulation of this cortical area. Compared are compensatory saccades evoked to brief targets following stimulation of the DMFC and frontal eye fields (FEF). Compensatory saccades produced to brief targets following perturbation via the DMFC were not affected. Accordingly, electrical stimulation of the DMFC does not disrupt the eye-position signal during the execution of visually-evoked saccades.}, Doi = {10.1016/0006-8993(96)00475-1}, Key = {Tehovnik1996} } @article{SOMMER1994, Author = {Sommer, MA}, Title = {Express saccades elicited during visual scan in the monkey.}, Journal = {Vision research}, Volume = {34}, Number = {15}, Pages = {2023-2038}, Year = {1994}, Month = {August}, ISSN = {0042-6989}, url = {https://dl.dropbox.com/u/27738651/Publications/Sommer1994.pdf}, Abstract = {Monkeys trained to saccade to visual targets can develop separate "express" and "regular" modes in their distribution of saccadic latencies. The purpose of this study was to determine whether this occurs under more natural viewing conditions, when targets are suddenly presented in a structured visual field during visual scan. It was found that scanning saccades stopped appearing 60 msec after a target's onset, and subsequent saccades, which were directed toward the suddenly appearing target, had a bimodal distribution of latencies. Express saccades were more likely to occur as the target was presented later in a fixation. Regular mode saccades were more likely to occur with longer target durations. Scanning saccades made to stimuli of the structured visual field always had unimodal inter-saccadic interval distributions. All these effects were apparent after only 2-3 days of training. These findings, taken together with recent physiological results, suggest that the visuomotor cells of the superior colliculus mediate latency bimodality.}, Doi = {10.1016/0042-6989(94)90030-2}, Key = {SOMMER1994} } @article{RICHARDS1994, Author = {Richards, W and Wilson, HR and Sommer, MA}, Title = {Chaos in percepts?}, Journal = {Biological cybernetics}, Volume = {70}, Number = {4}, Pages = {345-349}, Year = {1994}, Month = {January}, ISSN = {0340-1200}, url = {https://dl.dropbox.com/u/27738651/Publications/RichardsWilsonSommer1994_BiologicalCybernetics.pdf}, Abstract = {Multistability in perceptual tasks has suggested that the mechanisms underlying our percepts might be modeled as nonlinear, deterministic systems that exhibit chaotic behavior. We present evidence supporting this view, obtaining an estimate of 3.5 for the dimensionality of such a system. A surprising result is that this estimate applies for a rather diverse range of perceptual tasks.}, Doi = {10.1007/bf00200331}, Key = {RICHARDS1994} } @article{fds334862, Author = {Sommer, MA and Schiller, PH and McPeek, RM}, Title = {What neural pathways mediate express saccades?}, Journal = {Behavioral and Brain Sciences}, Volume = {16}, Number = {3}, Pages = {589-590}, Publisher = {Cambridge University Press (CUP): STM Journals}, Year = {1993}, Month = {September}, url = {http://dx.doi.org/10.1017/S0140525X00031824}, Doi = {10.1017/S0140525X00031824}, Key = {fds334862} } @article{fds334863, Author = {Sommer, MA and Forno, LS and Smith, ME}, Title = {EAE cerebrospinal fluid augments in vitro phagocytosis and metabolism of CNS myelin by macrophages.}, Journal = {Journal of neuroscience research}, Volume = {32}, Number = {3}, Pages = {384-394}, Year = {1992}, Month = {July}, ISSN = {1097-4547}, url = {https://dl.dropbox.com/u/27738651/Publications/SommerFornoSmith_JNeurosciRes1992.pdf}, Abstract = {Previous studies from this laboratory have shown that CNS myelin is phagocytized and metabolized by cultured rat macrophages to a much larger extent when myelin is pretreated with serum containing antibodies to myelin constituents than when it is left untreated or pretreated with non-specific serum. In this study the effect of cerebrospinal fluid (CSF) from rabbits with experimental allergic encephalomyelitis (EAE) in promoting myelin phagocytosis was examined. Fourteen rabbits were immunized with purified myelin in Freund's complete adjuvant, seven of which developed clinical EAE symptoms. Serum and CSF were collected from EAE and control rabbits, and the CSF was centrifuged to remove cells. Sera and CSF from these rabbits and from Freund's adjuvant-immunized controls and untreated controls were measured for IgG content by radial diffusion assay, their myelin antibody characteristics were analyzed by immunoblots, and the ability of these serum and CSF samples to promote myelin phagocytosis when used for myelin opsonization was examined. The ability of a CSF sample to enhance radioactive myelin uptake and phagocytosis by cultured macrophages as measured by the appearance of radioactive cholesterol ester was linearly proportional to its total IgG titer, and correlated approximately both with clinical symptoms of the animal and the presence of antibody against the myelin constituents myelin basic protein, proteolipid protein, and galactocerebroside. The cholesterol esterification activities of EAE sera correlated to a lesser extent with IgG levels and clinical symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)}, Doi = {10.1002/jnr.490320310}, Key = {fds334863} } @article{fds334864, Author = {Smith, ME and Sommer, MA}, Title = {Association between cell-mediated demyelination and astrocyte stimulation.}, Journal = {Progress in brain research}, Volume = {94}, Pages = {411-422}, Year = {1992}, Month = {January}, url = {http://dx.doi.org/10.1016/s0079-6123(08)61768-9}, Doi = {10.1016/s0079-6123(08)61768-9}, Key = {fds334864} } @article{fds334866, Author = {Sadler, RH and Sommer, MA and Forno, LS and Smith, ME}, Title = {Induction of anti-myelin antibodies in EAE and their possible role in demyelination.}, Journal = {Journal of neuroscience research}, Volume = {30}, Number = {4}, Pages = {616-624}, Year = {1991}, Month = {December}, ISSN = {1097-4547}, url = {https://dl.dropbox.com/u/27738651/Publications/SadlerSommerFornoSmith_JNeurosciRes1991.pdf}, Abstract = {Experimental allergic encephalomyelitis is characterized by invasion of lymphocytes and macrophages into the central nervous system resulting in inflammation, edema, and demyelination. Sera from Lewis rats from 7-95 days after immunization with purified guinea pig CNS myelin were examined with respect to their ability to opsonize myelin. This was correlated with the appearance of antibody components and the relative amounts of antibody to myelin basic protein (MBP) and proteolipid protein (PLP). Sera from rats 10-95 days after immunization preincubated with purified myelin induced phagocytosis of myelin by cultured macrophages with the resulting production of cholesterol ester. This opsonization activity as measured by the percentage of cholesterol esterified reached a peak at 26-27 days after immunization but remained significantly elevated up to 95 days post-immunization compared to the activity of serum from the Freund's adjuvant-injected controls. Immunoblots of the sera revealed a gradual increase in antibody activity against myelin components. ELISA assays for MBP and PLP antibody showed a similar pattern. Antibody to galactocerebroside (GC) was not detected by immunostains nor by the ELISA assay. Areas of demyelination were observed histologically by luxol-fast blue stained spinal cords up to 60 days post-immunization. These results indicate that antibodies to myelin protein when given access to myelin through or within the blood brain barrier could initiate or enhance the phagocytic response by peripheral or resident macrophages.}, Doi = {10.1002/jnr.490300404}, Key = {fds334866} } @article{fds334865, Author = {Hrushesky, WJ and Fader, DJ and Berestka, JS and Sommer, M and Hayes, J and Cope, FO}, Title = {Diminishment of respiratory sinus arrhythmia foreshadows doxorubicin-induced cardiomyopathy.}, Journal = {Circulation}, Volume = {84}, Number = {2}, Pages = {697-707}, Year = {1991}, Month = {August}, ISSN = {00097322}, url = {https://dl.dropbox.com/u/27738651/Publications/HrusheskyFaderBerestkaSommerHayesCope_Circulation1991.pdf}, Abstract = {<h4>Background</h4>The development of a microcomputer-based device permits quick, simple, and noninvasive quantification of the respiratory sinus arrhythmia (RSA) during quiet breathing.<h4>Methods and results</h4>We prospectively and serially measured the radionuclide left ventricular ejection fraction and the RSA amplitude in 34 cancer patients receiving up to nine monthly bolus treatments with doxorubicin hydrochloride (60 mg/m2). Of the eight patients who ultimately developed symptomatic doxorubicin-induced congestive heart failure, seven (87.5%) demonstrated a significant decline in RSA amplitude; five of 26 subjects without clinical symptoms of cardiotoxicity (19.2%) showed a similar RSA amplitude decline. On average, significant RSA amplitude decline occurred 3 months before the last planned doxorubicin dose in patients destined to develop clinical congestive heart failure.<h4>Conclusion</h4>Overall, RSA amplitude abnormality proved to be a more specific predictor of clinically significant congestive heart failure than did serial resting radionuclide ejection fractions.}, Doi = {10.1161/01.cir.84.2.697}, Key = {fds334865} } @article{fds334867, Author = {Sommer Marc and A and Berestka John and B}, Title = {RSA -- Respiratory Sinus Arrhythmia: A new measure of cardiac health}, Journal = {Medical Electronics}, Pages = {112-114}, Year = {1987}, Month = {April}, ISSN = {0149-9734}, url = {https://dl.dropbox.com/u/27738651/Publications/SommerBerestka_MedElectronics1987.pdf}, Key = {fds334867} } | |
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