Honors & Awards
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Elected Member, National Academy of Medicine (2017)
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Investigator, Howard Hughes Medical Institute (2014-)
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Early Career Scientist, Howard Hughes Medical Institute (2009-2014)
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Troland Award, National Academy of Sciences (2009)
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CAREER Award, National Science Foundation (2006-2011)
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McKnight Scholar Award, McKnight Endowment Fund (2006-2009)
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Pew Scholar, Pew Charitable Trust (2004-2008)
Professional Education
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Ph.D., Princeton, Neuroscience (1995)
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Postdoc, M.I.T., Neuroscience
Current Research and Scholarly Interests
We study neural mechanisms of visual-motor integration and the neural basis of cognition (e.g. attention). We study the activity of single neurons in visual and motor structures within the brain, examine how perturbing that activity affects neurons in other brain structures, and also how it affects the perceptual and motor performance of behaving animals. Questions currently addressed by our group include:
(1) How are the signals conveyed by visual cortical neurons used to guide eye movements?
(2) How does oculomotor feedback affect processing in visual cortex?
(3) What is the impact of planned movements on visual perception?
(4) What are the neural circuits and neural computations that control selective attention?
Our laboratory is also driven to develop more powerful approaches to systems-level neurobiological questions.
2018-19 Courses
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Independent Studies (10)
- Bioengineering Problems and Experimental Investigation
BIOE 191 (Win, Spr, Sum) - Directed Investigation
BIOE 392 (Aut, Win, Spr, Sum) - Directed Reading in Neurobiology
NBIO 198 (Aut, Win, Spr, Sum) - Directed Reading in Neurobiology
NBIO 299 (Aut, Win, Spr, Sum) - Directed Reading in Neurosciences
NEPR 299 (Aut, Win, Spr, Sum) - Directed Study
BIOE 391 (Aut, Win, Spr, Sum) - Graduate Research
NBIO 399 (Aut, Win, Spr, Sum) - Graduate Research
NEPR 399 (Aut, Win, Spr, Sum) - Medical Scholars Research
NBIO 370 (Aut, Win, Spr, Sum) - Undergraduate Research
NBIO 199 (Aut, Win, Spr, Sum)
- Bioengineering Problems and Experimental Investigation
All Publications
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Exploration Disrupts Choice-Predictive Signals and Alters Dynamics in Prefrontal Cortex
NEURON
2018; 97 (2): 450-+
Abstract
In uncertain environments, decision-makers must balance two goals: they must "exploit" rewarding options but also "explore" in order to discover rewarding alternatives. Exploring and exploiting necessarily change how the brain responds to identical stimuli, but little is known about how these states, and transitions between them, change how the brain transforms sensory information into action. To address this question, we recorded neural activity in a prefrontal sensorimotor area while monkeys naturally switched between exploring and exploiting rewarding options. We found that exploration profoundly reduced spatially selective, choice-predictive activity in single neurons and delayed choice-predictive population dynamics. At the same time, reward learning was increased in brain and behavior. These results indicate that exploration is related to sudden disruptions in prefrontal sensorimotor control and rapid, reward-dependent reorganization of control dynamics. This may facilitate discovery through trial and error.
View details for DOI 10.1016/j.neuron.2017.12.007
View details for Web of Science ID 000422692000020
View details for PubMedID 29290550
View details for PubMedCentralID PMC5774994
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Spatial working memory alters the efficacy of input to visual cortex
NATURE COMMUNICATIONS
2017; 8
Abstract
Prefrontal cortex modulates sensory signals in extrastriate visual cortex, in part via its direct projections from the frontal eye field (FEF), an area involved in selective attention. We find that working memory-related activity is a dominant signal within FEF input to visual cortex. Although this signal alone does not evoke spiking responses in areas V4 and MT during memory, the gain of visual responses in these areas increases, and neuronal receptive fields expand and shift towards the remembered location, improving the stimulus representation by neuronal populations. These results provide a basis for enhancing the representation of working memory targets and implicate persistent FEF activity as a basis for the interdependence of working memory and selective attention.
View details for DOI 10.1038/ncomms15041
View details for Web of Science ID 000400155500001
View details for PubMedID 28447609
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Neural Mechanisms of Selective Visual Attention.
Annual review of psychology
2017; 68: 47-72
Abstract
Selective visual attention describes the tendency of visual processing to be confined largely to stimuli that are relevant to behavior. It is among the most fundamental of cognitive functions, particularly in humans and other primates for whom vision is the dominant sense. We review recent progress in identifying the neural mechanisms of selective visual attention. We discuss evidence from studies of different varieties of selective attention and examine how these varieties alter the processing of stimuli by neurons within the visual system, current knowledge of their causal basis, and methods for assessing attentional dysfunctions. In addition, we identify some key questions that remain in identifying the neural mechanisms that give rise to the selective processing of visual information.
View details for DOI 10.1146/annurev-psych-122414-033400
View details for PubMedID 28051934
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Selective modulation of cortical state during spatial attention
SCIENCE
2016; 354 (6316): 1140-1144
Abstract
Neocortical activity is permeated with endogenously generated fluctuations, but how these dynamics affect goal-directed behavior remains a mystery. We found that ensemble neural activity in primate visual cortex spontaneously fluctuated between phases of vigorous (On) and faint (Off) spiking synchronously across cortical layers. These On-Off dynamics, reflecting global changes in cortical state, were also modulated at a local scale during selective attention. Moreover, the momentary phase of local ensemble activity predicted behavioral performance. Our results show that cortical state is controlled locally within a cortical map according to cognitive demands and reveal the impact of these local changes in cortical state on goal-directed behavior.
View details for DOI 10.1126/science.aag1420
View details for Web of Science ID 000388916400040
View details for PubMedID 27934763
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Eye movement preparation modulates neuronal responses in area v4 when dissociated from attentional demands.
Neuron
2014; 83 (2): 496-506
Abstract
We examined whether the preparation of saccadic eye movements, when behaviorally dissociated from covert attention, modulates activity within visual cortex. We measured single-neuron and local field potential (LFP) responses to visual stimuli in area V4 while monkeys covertly attended a stimulus at one location and prepared saccades to a potential target at another. In spite of the irrelevance of visual information at the saccade target, visual activity at that location was modulated at least as much as, and often more than, activity at the covertly attended location. Modulations of activity at the attended and saccade target locations were qualitatively similar and included increased response magnitude, stimulus selectivity, and spiking reliability, as well as increased gamma and decreased low-frequency power of LFPs. These results demonstrate that saccade preparation is sufficient to modulate visual cortical representations and suggest that the interrelationship of oculomotor and attention-related mechanisms extends to posterior visual cortex.
View details for DOI 10.1016/j.neuron.2014.06.014
View details for PubMedID 25033188
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Visual space is compressed in prefrontal cortex before eye movements.
Nature
2014; 507 (7493): 504-507
Abstract
We experience the visual world through a series of saccadic eye movements, each one shifting our gaze to bring objects of interest to the fovea for further processing. Although such movements lead to frequent and substantial displacements of the retinal image, these displacements go unnoticed. It is widely assumed that a primary mechanism underlying this apparent stability is an anticipatory shifting of visual receptive fields (RFs) from their presaccadic to their postsaccadic locations before movement onset. Evidence of this predictive 'remapping' of RFs has been particularly apparent within brain structures involved in gaze control. However, critically absent among that evidence are detailed measurements of visual RFs before movement onset. Here we show that during saccade preparation, rather than remap, RFs of neurons in a prefrontal gaze control area massively converge towards the saccadic target. We mapped the visual RFs of prefrontal neurons during stable fixation and immediately before the onset of eye movements, using multi-electrode recordings in monkeys. Following movements from an initial fixation point to a target, RFs remained stationary in retinocentric space. However, in the period immediately before movement onset, RFs shifted by as much as 18 degrees of visual angle, and converged towards the target location. This convergence resulted in a threefold increase in the proportion of RFs responding to stimuli near the target region. In addition, like in human observers, the population of prefrontal neurons grossly mislocalized presaccadic stimuli as being closer to the target. Our results show that RF shifts do not predict the retinal displacements due to saccades, but instead reflect the overriding perception of target space during eye movements.
View details for DOI 10.1038/nature13149
View details for PubMedID 24670771
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Visions for the Future of Neuroscience
NEURON
2018; 98 (3): 464–65
Abstract
Neuroscience is a broad discipline that embraces technology at multiple scales to understand the brain and to develop potential therapies. Scientists share their perspectives on the evolution of neuroscience research and what excites them about the future prospects for the field.
View details for DOI 10.1016/j.neuron.2018.03.037
View details for Web of Science ID 000432473700005
View details for PubMedID 29723499
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Dissonant Representations of Visual Space in Prefrontal Cortex during Eye Movements
CELL REPORTS
2018; 22 (8): 2039–52
Abstract
We used local field potentials (LFPs) and spikes to investigate representations of visual space in prefrontal cortex and the dynamics of those representations during eye movements. Spatial information contained in LFPs of the frontal eye field (FEF) was differentially distributed across frequencies, with a majority of that information being carried in alpha and high-gamma bands and minimal signal in the low-gamma band. During fixation, spatial information from alpha and high-gamma bands and spiking activity was robust across cortical layers. Receptive fields (RFs) derived from alpha and high-gamma bands were retinocentrically organized, and they were spatially correlated both with each other and with spiking RFs. However, alpha and high-gamma RFs probed before eye movements were dissociated. Whereas high-gamma and spiking RFs immediately converged toward the movement goal, alpha RFs remained largely unchanged during the initial probe response, but they converged later. These observations reveal possible mechanisms of dynamic spatial representations that underlie visual perception during eye movements.
View details for DOI 10.1016/j.celrep.2018.01.078
View details for Web of Science ID 000425489700010
View details for PubMedID 29466732
View details for PubMedCentralID PMC5850980
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Differential Expression of Dopamine D5 Receptors across Neuronal Subtypes in Macaque Frontal Eye Field
FRONTIERS IN NEURAL CIRCUITS
2018; 12: 12
Abstract
Dopamine signaling in the prefrontal cortex (PFC) is important for cognitive functions, yet very little is known about the expression of the D5 class of dopamine receptors (D5Rs) in this region. To address this, we co-stained for D5Rs, pyramidal neurons (neurogranin+), putative long-range projection pyramidal neurons (SMI-32+), and several classes of inhibitory interneuron (parvalbumin+, calbindin+, calretinin+, somatostatin+) within the frontal eye field (FEF): an area within the PFC involved in the control of visual spatial attention. We then quantified the co-expression of D5Rs with markers of different cell types across different layers of the FEF. We show that: (1) D5Rs are more prevalent on pyramidal neurons than on inhibitory interneurons. (2) D5Rs are disproportionately expressed on putative long-range projecting pyramidal neurons. The disproportionately high expression of D5Rs on long-range projecting pyramidals, compared to interneurons, was particularly pronounced in layers II-III. Together these results indicate that the engagement of D5R-dependent mechanisms in the FEF varies depending on cell type and cortical layer, and suggests that non-locally projecting neurons contribute disproportionately to functions involving the D5R subtype.
View details for DOI 10.3389/fncir.2018.00012
View details for Web of Science ID 000424771200001
View details for PubMedID 29483863
View details for PubMedCentralID PMC5816032
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Linking ADHD to the Neural Circuitry of Attention
TRENDS IN COGNITIVE SCIENCES
2017; 21 (6): 474-488
Abstract
Attention deficit hyperactivity disorder (ADHD) is a complex condition with a heterogeneous presentation. Current diagnosis is primarily based on subjective experience and observer reports of behavioral symptoms - an approach that has significant limitations. Many studies show that individuals with ADHD exhibit poorer performance on cognitive tasks than neurotypical controls, and at least seven main functional domains appear to be implicated in ADHD. We discuss the underlying neural mechanisms of cognitive functions associated with ADHD, with emphasis on the neural basis of selective attention, demonstrating the feasibility of basic research approaches for further understanding cognitive behavioral processes as they relate to human psychopathology. The study of circuit-level mechanisms underlying executive functions in nonhuman primates holds promise for advancing our understanding, and ultimately the treatment, of ADHD.
View details for DOI 10.1016/j.tics.2017.03.009
View details for Web of Science ID 000401315700010
View details for PubMedID 28483638
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Social and attention-to-detail subclusters of autistic traits differentially predict looking at eyes and face identity recognition ability
BRITISH JOURNAL OF PSYCHOLOGY
2017; 108 (1): 191-219
Abstract
This study distinguished between different subclusters of autistic traits in the general population and examined the relationships between these subclusters, looking at the eyes of faces, and the ability to recognize facial identity. Using the Autism Spectrum Quotient (AQ) measure in a university-recruited sample, we separate the social aspects of autistic traits (i.e., those related to communication and social interaction; AQ-Social) from the non-social aspects, particularly attention-to-detail (AQ-Attention). We provide the first evidence that these social and non-social aspects are associated differentially with looking at eyes: While AQ-Social showed the commonly assumed tendency towards reduced looking at eyes, AQ-Attention was associated with increased looking at eyes. We also report that higher attention-to-detail (AQ-Attention) was then indirectly related to improved face recognition, mediated by increased number of fixations to the eyes during face learning. Higher levels of socially relevant autistic traits (AQ-Social) trended in the opposite direction towards being related to poorer face recognition (significantly so in females on the Cambridge Face Memory Test). There was no evidence of any mediated relationship between AQ-Social and face recognition via reduced looking at the eyes. These different effects of AQ-Attention and AQ-Social suggest face-processing studies in Autism Spectrum Disorder might similarly benefit from considering symptom subclusters. Additionally, concerning mechanisms of face recognition, our results support the view that more looking at eyes predicts better face memory.
View details for DOI 10.1111/bjop.12188
View details for Web of Science ID 000397119800014
View details for PubMedID 26988108
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Does the Superior Colliculus Control Perceptual Sensitivity or Choice Bias during Attention? Evidence from a Multialternative Decision Framework.
journal of neuroscience
2017; 37 (3): 480-511
Abstract
Distinct networks in the forebrain and the midbrain coordinate to control spatial attention. The critical involvement of the superior colliculus (SC)-the central structure in the midbrain network-in visuospatial attention has been shown by four seminal, published studies in monkeys (Macaca mulatta) performing multialternative tasks. However, due to the lack of a mechanistic framework for interpreting behavioral data in such tasks, the nature of the SC's contribution to attention remains unclear. Here we present and validate a novel decision framework for analyzing behavioral data in multialternative attention tasks. We apply this framework to re-examine the behavioral evidence from these published studies. Our model is a multidimensional extension to signal detection theory that distinguishes between two major classes of attentional mechanisms: those that alter the quality of sensory information or "sensitivity," and those that alter the selective gating of sensory information or "choice bias." Model-based simulations and model-based analyses of data from these published studies revealed a converging pattern of results that indicated that choice-bias changes, rather than sensitivity changes, were the primary outcome of SC manipulation. Our results suggest that the SC contributes to attentional performance predominantly by generating a spatial choice bias for stimuli at a selected location, and that this bias operates downstream of forebrain mechanisms that enhance sensitivity. The findings lead to a testable mechanistic framework of how the midbrain and forebrain networks interact to control spatial attention.Attention involves the selection of the most relevant information for differential sensory processing and decision making. While the mechanisms by which attention alters sensory encoding (sensitivity control) are well studied, the mechanisms by which attention alters decisional weighting of sensory evidence (choice-bias control) are poorly understood. Here, we introduce a model of multialternative decision making that distinguishes bias from sensitivity effects in attention tasks. With our model, we simulate experimental data from four seminal studies that microstimulated or inactivated a key attention-related midbrain structure, the superior colliculus (SC). We demonstrate that the experimental effects of SC manipulation are entirely consistent with the SC controlling attention by changing choice bias, thereby shedding new light on how the brain mediates attention.
View details for DOI 10.1523/JNEUROSCI.4505-14.2017
View details for PubMedID 28100734
View details for PubMedCentralID PMC5242403
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Two Types of Receptive Field Dynamics in Area V4 at the Time of Eye Movements?
Frontiers in systems neuroscience
2017; 11: 13-?
Abstract
How we perceive the world as stable despite the frequent disruptions of the retinal image caused by eye movements is one of the fundamental questions in sensory neuroscience. Seemingly convergent evidence points towards a mechanism which dynamically updates representations of visual space in anticipation of a movement (Wurtz, 2008). In particular, receptive fields (RFs) of neurons, predominantly within oculomotor and attention related brain structures (Duhamel et al., 1992; Walker et al., 1995; Umeno and Goldberg, 1997), are thought to "remap" to their future, post-movement location prior to an impending eye movement. New studies (Neupane et al., 2016a,b) report observations on RF dynamics at the time of eye movements of neurons in area V4. These dynamics are interpreted as being largely dominated by a remapping of RFs. Critically, these observations appear at odds with a previous study reporting a different type of RF dynamics within the same brain structure (Tolias et al., 2001), consisting of a shrinkage and shift of RFs towards the movement target. Importantly, RFs have been measured with different techniques in those studies. Here, we measured V4 RFs comparable to Neupane et al. (2016a,b) and observe a shrinkage and shift of RFs towards the movement target when analyzing the immediate stimulus response (Zirnsak et al., 2014). When analyzing the late stimulus response (Neupane et al., 2016a,b), we observe RF shifts resembling remapping. We discuss possible causes for these shifts and point out important issues which future studies on RF dynamics need to address.
View details for DOI 10.3389/fnsys.2017.00013
View details for PubMedID 28377700
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Visual sensitivity of frontal eye field neurons during the preparation of saccadic eye movements
JOURNAL OF NEUROPHYSIOLOGY
2016; 116 (6): 2882-2891
Abstract
Primate vision is continuously disrupted by saccadic eye movements, and yet this disruption goes unperceived. One mechanism thought to reduce perception of this self-generated movement is saccadic suppression, a global loss of visual sensitivity just before, during, and after saccadic eye movements. The frontal eye field (FEF) is a candidate source of neural correlates of saccadic suppression previously observed in visual cortex, because it contributes to the generation of visually guided saccades and modulates visual cortical responses. However, whether the FEF exhibits a perisaccadic reduction in visual sensitivity that could be transmitted to visual cortex is unknown. To determine whether the FEF exhibits a signature of saccadic suppression, we recorded the visual responses of FEF neurons to brief, full-field visual probe stimuli presented during fixation and before onset of saccades directed away from the receptive field in rhesus macaques (Macaca mulatta) We measured visual sensitivity during both epochs and found that it declines before saccade onset. Visual sensitivity was significantly reduced in visual but not visuomotor neurons. This reduced sensitivity was also present in visual neurons with no movement-related modulation during visually guided saccades and thus occurred independently from movement-related activity. Across the population of visual neurons, sensitivity began declining ∼80 ms before saccade onset. We also observed a similar presaccadic reduction in sensitivity to isoluminant, chromatic stimuli. Our results demonstrate that the signaling of visual information by FEF neurons is reduced during saccade preparation, and thus these neurons exhibit a signature of saccadic suppression.
View details for DOI 10.1152/jn.01140.2015
View details for Web of Science ID 000394019600005
View details for PubMedID 27683894
View details for PubMedCentralID PMC5174155
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Copula Regression Analysis of Simultaneously Recorded Frontal Eye Field and Inferotemporal Spiking Activity during Object-Based Working Memory
JOURNAL OF NEUROSCIENCE
2015; 35 (23): 8745-8757
View details for DOI 10.1523/JNEUROSCI.5041-14.2015
View details for Web of Science ID 000358249000008
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Combined contributions of feedforward and feedback inputs to bottom-up attention
FRONTIERS IN PSYCHOLOGY
2015; 6
Abstract
In order to deal with a large amount of information carried by visual inputs entering the brain at any given point in time, the brain swiftly uses the same inputs to enhance processing in one part of visual field at the expense of the others. These processes, collectively called bottom-up attentional selection, are assumed to solely rely on feedforward processing of the external inputs, as it is implied by the nomenclature. Nevertheless, evidence from recent experimental and modeling studies points to the role of feedback in bottom-up attention. Here, we review behavioral and neural evidence that feedback inputs are important for the formation of signals that could guide attentional selection based on exogenous inputs. Moreover, we review results from a modeling study elucidating mechanisms underlying the emergence of these signals in successive layers of neural populations and how they depend on feedback from higher visual areas. We use these results to interpret and discuss more recent findings that can further unravel feedforward and feedback neural mechanisms underlying bottom-up attention. We argue that while it is descriptively useful to separate feedforward and feedback processes underlying bottom-up attention, these processes cannot be mechanistically separated into two successive stages as they occur at almost the same time and affect neural activity within the same brain areas using similar neural mechanisms. Therefore, understanding the interaction and integration of feedforward and feedback inputs is crucial for better understanding of bottom-up attention.
View details for DOI 10.3389/fpsyg.2015.00155
View details for Web of Science ID 000350277200001
View details for PubMedID 25784883
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Saccades and shifting receptive fields: anticipating consequences or selecting targets?
TRENDS IN COGNITIVE SCIENCES
2014; 18 (12): 621-628
Abstract
Saccadic eye movements cause frequent and substantial displacements of the retinal image, but those displacements go unnoticed. It has been widely assumed that this perceived stability emerges from the shifting of visual receptive fields from their current, presaccadic locations to their future, postsaccadic locations in anticipation of the retinal consequences of saccades. Although evidence consistent with this anticipatory remapping has accumulated over the years, more recent work suggests an alternative view. In this opinion article, we examine the evidence of presaccadic receptive field shifts and their relationship to the perceptual changes that accompany saccades. We argue that both reflect the selection of targets for saccades rather than the anticipation of a displaced retinal image.
View details for DOI 10.1016/j.tics.2014.10.002
View details for Web of Science ID 000347131000004
View details for PubMedID 25455690
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Persistent Spatial Information in the FEF during Object-based Short-term Memory Does Not Contribute to Task Performance
JOURNAL OF COGNITIVE NEUROSCIENCE
2014; 26 (6): 1292-1299
Abstract
We previously reported the existence of a persistent spatial signal in the FEF during object-based STM. This persistent activity reflected the location at which the sample appeared, irrespective of the location of upcoming targets. We hypothesized that such a spatial signal could be used to maintain or enhance object-selective memory activity elsewhere in cortex, analogous to the role of a spatial signal during attention. Here, we inactivated a portion of the FEF with GABAa agonist muscimol to test whether the observed activity contributes to object memory performance. We found that, although RTs were slowed for saccades into the inactivated portion of retinotopic space, performance for samples appearing in that region was unimpaired. This contrasts with the devastating effects of the same FEF inactivation on purely spatial working memory, as assessed with the memory-guided saccade task. Thus, in a task in which a significant fraction of FEF neurons displayed persistent, sample location-based activity, disrupting this activity had no impact on task performance.
View details for DOI 10.1162/jocn_a_00599
View details for Web of Science ID 000335506100009
View details for PubMedID 24673408
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Global selection of saccadic target features by neurons in area v4.
journal of neuroscience
2014; 34 (19): 6700-6706
Abstract
Psychophysical and neurophysiological studies indicate that during the preparation of saccades, visual processing at the target location is facilitated automatically by the deployment of attention. It has been assumed that the neural mechanisms involved in presaccadic shifts of attention are purely spatial in nature. Saccade preparation modulates the visual responses of neurons within extrastriate area V4, where the responses to targets are enhanced and responses to nontargets are suppressed. We tested whether this effect also engages a nonspatial form of modulation. We measured the responses of area V4 neurons to oriented gratings in two monkeys (Macaca mulatta) making delayed saccades to targets distant from the neuronal receptive field (RF). We varied the orientation of both the RF stimulus and the saccadic target. We found that, in addition to the spatial modulation, saccade preparation involves a feature-dependent modulation of V4 neuronal responses. Specifically, we found that the suppression of area V4 responses to nontarget stimuli during the preparation of saccades depends on the features of the saccadic target. Presaccadic suppression was absent when the features of the saccadic target matched the features preferred by individual V4 neurons. This feature-dependent modulation occurred in the absence of any feature-attention task. We show that our observations are consistent with a computational framework in which feature-based effects automatically emerge from saccade-related feedback signals that are spatial in nature.
View details for DOI 10.1523/JNEUROSCI.0867-13.2014
View details for PubMedID 24806696
View details for PubMedCentralID PMC4012320
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Latency of chromatic information in area V4.
Journal of physiology, Paris
2014; 108 (1): 11-17
Abstract
In the primate visual system, information about color is known to be carried in separate divisions of the retino-geniculo-cortical pathway. From the retina, responses of photoreceptors to short (S), medium (M), and long (L) wavelengths of light are processed in two different opponent pathways. Signals in the S-opponent pathway, or blue/yellow channel, have been found to lag behind signals in the L/M-opponent pathway, or red/green channel in primary visual area V1, and psychophysical studies have suggested similar perceptual delays. However, more recent psychophysical studies have found that perceptual differences are negligible with the proper controls, suggesting that information between the two channels is integrated at some stage of processing beyond V1. To study the timing of color signals further downstream in visual cortex, we examined the responses of neurons in area V4 to colored stimuli varying along the two cardinal axes of the equiluminant opponent color space. We used information theory to measure the mutual information between the stimuli presented and the neural responses in short time windows in order to estimate the latency of color information in area V4. We found that on average, despite the latency difference in V1, information about S-opponent signals arrives in V4 at the same time as information about L/M-opponent signals. This work indicates a convergence of signal timing among chromatic channels within extrastriate cortex.
View details for DOI 10.1016/j.jphysparis.2013.05.006
View details for PubMedID 23811158
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Distinguishing bias from sensitivity effects in multialternative detection tasks.
Journal of vision
2014; 14 (9)
Abstract
Studies investigating the neural bases of cognitive phenomena increasingly employ multialternative detection tasks that seek to measure the ability to detect a target stimulus or changes in some target feature (e.g., orientation or direction of motion) that could occur at one of many locations. In such tasks, it is essential to distinguish the behavioral and neural correlates of enhanced perceptual sensitivity from those of increased bias for a particular location or choice (choice bias). However, making such a distinction is not possible with established approaches. We present a new signal detection model that decouples the behavioral effects of choice bias from those of perceptual sensitivity in multialternative (change) detection tasks. By formulating the perceptual decision in a multidimensional decision space, our model quantifies the respective contributions of bias and sensitivity to multialternative behavioral choices. With a combination of analytical and numerical approaches, we demonstrate an optimal, one-to-one mapping between model parameters and choice probabilities even for tasks involving arbitrarily large numbers of alternatives. We validated the model with published data from two ternary choice experiments: a target-detection experiment and a length-discrimination experiment. The results of this validation provided novel insights into perceptual processes (sensory noise and competitive interactions) that can accurately and parsimoniously account for observers' behavior in each task. The model will find important application in identifying and interpreting the effects of behavioral manipulations (e.g., cueing attention) or neural perturbations (e.g., stimulation or inactivation) in a variety of multialternative tasks of perception, attention, and decision-making.
View details for DOI 10.1167/14.9.16
View details for PubMedID 25146574
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The Influence of Gaze Control on Visual Perception: Eye Movements and Visual Stability.
Cold Spring Harbor symposia on quantitative biology
2014; 79: 123-130
Abstract
Primates make several saccadic eye movements each second, and yet the retinal motion these movements generate goes unnoticed. Saccadic suppression is a profound loss of visual sensitivity occurring around the time of eye movements, and it is thought to contribute to visual stability by blunting the perception of self-generated motion. Neurophysiological studies have produced evidence that neurons throughout the visual system, including both the dorsal and ventral streams of extrastriate visual cortex, show a reduction in visual responses or sensitivity around the time of saccades. However, the source of this suppression remains unknown. We review evidence that oculomotor regions such as the superior colliculus and frontal eye field may play a role, as well as anatomical data that place constraints on possible mechanisms of suppression.
View details for DOI 10.1101/sqb.2014.79.024836
View details for PubMedID 25752313
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Distinguishing bias from sensitivity effects in multialternative detection tasks.
Journal of vision
2014; 14 (9)
View details for DOI 10.1167/14.9.16
View details for PubMedID 25146574
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Prefrontal contributions to visual selective attention.
Annual review of neuroscience
2013; 36: 451-466
Abstract
The faculty of attention endows us with the capacity to process important sensory information selectively while disregarding information that is potentially distracting. Much of our understanding of the neural circuitry underlying this fundamental cognitive function comes from neurophysiological studies within the visual modality. Past evidence suggests that a principal function of the prefrontal cortex (PFC) is selective attention and that this function involves the modulation of sensory signals within posterior cortices. In this review, we discuss recent progress in identifying the specific prefrontal circuits controlling visual attention and its neural correlates within the primate visual system. In addition, we examine the persisting challenge of precisely defining how behavior should be affected when attentional function is lost.
View details for DOI 10.1146/annurev-neuro-062111-150439
View details for PubMedID 23841841
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Parietal and prefrontal neurons driven to distraction.
Nature neuroscience
2013; 16 (1): 8-9
View details for DOI 10.1038/nn.3291
View details for PubMedID 23257928
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Persistent Spatial Information in the Frontal Eye Field during Object-Based Short-Term Memory
JOURNAL OF NEUROSCIENCE
2012; 32 (32): 10907-10914
Abstract
Spatial attention is known to gate entry into visual short-term memory, and some evidence suggests that spatial signals may also play a role in binding features or protecting object representations during memory maintenance. To examine the persistence of spatial signals during object short-term memory, the activity of neurons in the frontal eye field (FEF) of macaque monkeys was recorded during an object-based delayed match-to-sample task. In this task, monkeys were trained to remember an object image over a brief delay, regardless of the locations of the sample or target presentation. FEF neurons exhibited visual, delay, and target period activity, including selectivity for sample location and target location. Delay period activity represented the sample location throughout the delay, despite the irrelevance of spatial information for successful task completion. Furthermore, neurons continued to encode sample position in a variant of the task in which the matching stimulus never appeared in their response field, confirming that FEF maintains sample location independent of subsequent behavioral relevance. FEF neurons also exhibited target-position-dependent anticipatory activity immediately before target onset, suggesting that monkeys predicted target position within blocks. These results show that FEF neurons maintain spatial information during short-term memory, even when that information is irrelevant for task performance.
View details for DOI 10.1523/JNEUROSCI.1450-12.2012
View details for Web of Science ID 000307640000012
View details for PubMedID 22875925
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Lumping and Splitting the Neural Circuitry of Visual Attention
NEURON
2012; 73 (3): 410-412
Abstract
Shifts of gaze and of covert attention rely on tightly linked yet divergent neural mechanisms. In this issue of Neuron, Gregoriou et al. (2012) provide interesting evidence that different functional classes of neurons within the frontal eye field contribute uniquely to these two functions.
View details for DOI 10.1016/j.neuron.2012.01.011
View details for Web of Science ID 000300140600003
View details for PubMedID 22325195
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Dissociation of Response Variability from Firing Rate Effects in Frontal Eye Field Neurons during Visual Stimulation, Working Memory, and Attention
JOURNAL OF NEUROSCIENCE
2012; 32 (6): 2204-2216
Abstract
Recent studies suggest that trial-to-trial variability of neuronal spiking responses may provide important information about behavioral state. Observed changes in variability during sensory stimulation, attention, motor preparation, and visual discrimination suggest that variability may reflect the engagement of neurons in a behavioral task. We examined changes in spiking variability of frontal eye field (FEF) neurons in a change detection task requiring monkeys to remember a visually cued location and direct attention to that location while ignoring distracters elsewhere. In this task, the firing rates (FRs) of FEF neurons not only continuously reflect the location of the remembered cue and select targets, but also predict detection performance on a trial-by-trial basis. Changes in FEF response variability, as measured by the Fano factor (FF), showed clear dissociations from changes in FR. The FF declined in response to visual stimulation at all tested locations, even in the opposite hemifield, indicating much broader spatial tuning of the FF compared with the FR. Furthermore, despite robust spatial modulation of the FR throughout all epochs of the task, spatial tuning of the FF did not persist throughout the delay period, nor did it show attentional modulation. These results indicate that changes in variability, at least in the FEF, are most effectively driven by visual stimulation, while behavioral engagement is not sufficient. Instead, changes in variability may reflect shifts in the balance between feedforward and recurrent sources of excitatory drive.
View details for DOI 10.1523/JNEUROSCI.2967-11.2012
View details for Web of Science ID 000300207900030
View details for PubMedID 22323732
View details for PubMedCentralID PMC3439504
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The role of neuromodulators in selective attention
TRENDS IN COGNITIVE SCIENCES
2011; 15 (12): 585-591
Abstract
Several classes of neurotransmitters exert modulatory effects on a broad and diverse population of neurons throughout the brain. Some of these neuromodulators, especially acetylcholine and dopamine, have long been implicated in the neural control of selective attention. We review recent evidence and evolving ideas about the importance of these neuromodulatory systems in attention, particularly visual selective attention. We conclude that, although our understanding of their role in the neural circuitry of selective attention remains rudimentary, recent research has begun to suggest unique contributions of neuromodulators to different forms of attention, such as bottom-up and top-down attention.
View details for DOI 10.1016/j.tics.2011.10.006
View details for Web of Science ID 000298127900005
View details for PubMedID 22074811
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Selective Attention from Voluntary Control of Neurons in Prefrontal Cortex
SCIENCE
2011; 332 (6037): 1568-1571
Abstract
Animals can learn to voluntarily control neuronal activity within various brain areas through operant conditioning, but the relevance of that control to cognitive functions is unknown. We found that rhesus monkeys can control the activity of neurons within the frontal eye field (FEF), an oculomotor area of the prefrontal cortex. However, operantly driven FEF activity was primarily associated with selective visual attention, and not oculomotor preparation. Attentional effects were untrained and were observed both behaviorally and neurophysiologically. Furthermore, selective attention correlated with voluntary, but not spontaneous, fluctuations in FEF activity. Our results reveal a specific association of voluntarily driven neuronal activity with "top-down" attention and suggest a basis for the use of neurofeedback training to treat disorders of attention.
View details for DOI 10.1126/science.1199892
View details for Web of Science ID 000291990000048
View details for PubMedID 21617042
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Probing neural circuitry and function with electrical microstimulation
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
2011; 278 (1709): 1121-1130
Abstract
Since the discovery of the nervous system's electrical excitability more than 200 years ago, neuroscientists have used electrical stimulation to manipulate brain activity in order to study its function. Microstimulation has been a valuable technique for probing neural circuitry and identifying networks of neurons that underlie perception, movement and cognition. In this review, we focus on the use of stimulation in behaving primates, an experimental system that permits causal inferences to be made about the effect of stimulation-induced activity on the resulting behaviour or neural signals elsewhere in the brain.
View details for DOI 10.1098/rspb.2010.2211
View details for Web of Science ID 000288241300001
View details for PubMedID 21247952
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A reliable microinjectrode system for use in behaving monkeys
JOURNAL OF NEUROSCIENCE METHODS
2011; 194 (2): 218-223
Abstract
We describe a modified system for the precise delivery of small volumes of drugs to brain sites of behaving monkeys during simultaneous single-neuron electrophysiology. The system combines a conventional microelectrode for recording single neurons and a small gauge microsyringe in a durable design. It incorporates newly available microfluidic components to achieve high-precision fluidic control. The system is inexpensive, reusable and easy to fabricate; it minimizes neural tissue damage and achieves reliable single-neuron recordings at the injection site.
View details for DOI 10.1016/j.jneumeth.2010.10.009
View details for Web of Science ID 000289923100003
View details for PubMedID 20951736
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Top-down control of visual attention
CURRENT OPINION IN NEUROBIOLOGY
2010; 20 (2): 183-190
Abstract
Top-down visual attention improves perception of selected stimuli and that improvement is reflected in the neural activity at many stages throughout the visual system. Recent studies of top-down attention have elaborated on the signatures of its effects within visual cortex and have begun identifying its causal basis. Evidence from these studies suggests that the correlates of spatial attention exhibited by neurons within the visual system originate from a distributed network of structures involved in the programming of saccadic eye movements. We summarize this evidence and discuss its relationship to the neural mechanisms of spatial working memory.
View details for DOI 10.1016/j.conb.2010.02.003
View details for Web of Science ID 000278258900008
View details for PubMedID 20303256
View details for PubMedCentralID PMC2901796
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Stimulus onset quenches neural variability: a widespread cortical phenomenon
NATURE NEUROSCIENCE
2010; 13 (3): 369-U25
Abstract
Neural responses are typically characterized by computing the mean firing rate, but response variability can exist across trials. Many studies have examined the effect of a stimulus on the mean response, but few have examined the effect on response variability. We measured neural variability in 13 extracellularly recorded datasets and one intracellularly recorded dataset from seven areas spanning the four cortical lobes in monkeys and cats. In every case, stimulus onset caused a decline in neural variability. This occurred even when the stimulus produced little change in mean firing rate. The variability decline was observed in membrane potential recordings, in the spiking of individual neurons and in correlated spiking variability measured with implanted 96-electrode arrays. The variability decline was observed for all stimuli tested, regardless of whether the animal was awake, behaving or anaesthetized. This widespread variability decline suggests a rather general property of cortex, that its state is stabilized by an input.
View details for DOI 10.1038/nn.2501
View details for Web of Science ID 000274860100020
View details for PubMedID 20173745
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Changes in the Response Rate and Response Variability of Area V4 Neurons During the Preparation of Saccadic Eye Movements
JOURNAL OF NEUROPHYSIOLOGY
2010; 103 (3): 1171-1178
Abstract
The visually driven responses of macaque area V4 neurons are modulated during the preparation of saccadic eye movements, but the relationship between presaccadic modulation in area V4 and saccade preparation is poorly understood. Recent neurophysiological studies suggest that the variability across trials of spiking responses provides a more reliable signature of motor preparation than mean firing rate across trials. We compared the dynamics of the response rate and the variability in the rate across trials for area V4 neurons during the preparation of visually guided saccades. As in previous reports, we found that the mean firing rate of V4 neurons was enhanced when saccades were prepared to stimuli within a neuron's receptive field (RF) in comparison with saccades to a non-RF location. Further, we found robust decreases in response variability prior to saccades and found that these decreases predicted saccadic reaction times for saccades both to RF and non-RF stimuli. Importantly, response variability predicted reaction time whether or not there were any accompanying changes in mean firing rate. In addition to predicting saccade direction, the mean firing rate could also predict reaction time, but only for saccades directed to the RF stimuli. These results demonstrate that response variability of area V4 neurons, like mean response rate, provides a signature of saccade preparation. However, the two signatures reflect complementary aspects of that preparation.
View details for DOI 10.1152/jn.00689.2009
View details for Web of Science ID 000275656200003
View details for PubMedID 20018834
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Selection and Maintenance of Spatial Information by Frontal Eye Field Neurons
JOURNAL OF NEUROSCIENCE
2009; 29 (50): 15621-15629
Abstract
Voluntary attention is often allocated according to internally maintained goals. Recent evidence indicates that the frontal eye field (FEF) participates in the deployment of spatial attention, even in the absence of saccadic eye movements. In addition, many FEF neurons maintain persistent representations of impending saccades. However, the role of persistent activity in the general maintenance of spatial information, and its relationship to spatial attention, has not been explored. We recorded the responses of single FEF neurons in monkeys trained to remember cued locations in order to detect changes in targets embedded among distracters in a task that did not involve saccades. We found that FEF neurons persistently encoded the cued location throughout the trial during the delay period, when no visual stimuli were present, and during visual discrimination. Furthermore, FEF activity reliably predicted whether monkeys would detect the target change. Population analyses revealed that FEF neurons with persistent activity were more effective at selecting the target from among distracters than neurons lacking persistent activity. These results demonstrate that FEF neurons maintain spatial information in the absence of saccade preparation and suggest that this maintenance contributes to the selection of relevant visual stimuli.
View details for DOI 10.1523/JNEUROSCI.4465-09.2009
View details for Web of Science ID 000272837000002
View details for PubMedID 20016076
View details for PubMedCentralID PMC3351279
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Influence and Limitations of Popout in the Selection of Salient Visual Stimuli by Area V4 Neurons
JOURNAL OF NEUROSCIENCE
2009; 29 (48): 15169-15177
Abstract
The neural mechanism of bottom-up attention and its relationship to top-down attention are poorly understood. Visual stimuli that differ from others in their component features are salient and tend to draw attention in a bottom-up manner. "Popout" stimuli differ uniformly from surrounding items and are more easily detected than stimuli composed of a conjunction of surrounding features. We compared the responses of single area V4 neurons to popout and conjunction stimuli appearing within the classical receptive field (CRF) and found that their responses are modulated by popout. This selectivity was more robust when larger numbers of surrounding items and multiple features were included in the display, and it was absent when only a few items were presented immediately outside the CRF. In addition, the popout modulation of V4 activity was eliminated when top-down attention was directed to locations outside of the CRFs during saccade preparation, indicating that the salience of popout stimuli is not sufficient to drive selection by V4 neurons. These results demonstrate that neurons in feature-selective cortex are influenced by bottom-up attention, but that this influence is limited by top-down attention.
View details for DOI 10.1523/JNEUROSCI.3710-09.2009
View details for Web of Science ID 000272361700017
View details for PubMedID 19955369
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Dynamic sensitivity of area V4 neurons during saccade preparation
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2009; 106 (31): 13046-13051
Abstract
During the preparation of saccadic eye movements, visual attention is confined to the target of intended fixation and there is a corresponding diminution of visual sensitivity at nontarget locations. Neurons within the macaque visual cortex exhibit correlates of these perceptual changes, such as in area V4, where neuronal responses are enhanced during the preparation of saccades to stimuli within the receptive field (RF), and responses are suppressed during the preparation of saccades to other locations. Both the perceptual and neurophysiological effects suggest that the sensitivity of visual cortical neurons to input is dynamic during saccade preparation. We probed the contrast sensitivity of area V4 neurons to nontarget stimuli at varying times during the preparation of saccades to locations outside of the neuron's receptive field. We found that the contrast sensitivity of many neurons is profoundly altered within 50 ms of saccade onset. The luminance or color contrast sensitivity of individual V4 neurons could increase, decrease, or remain unchanged before saccade onset. For luminance contrast sensitivity, decreases in sensitivity were more frequent and larger in magnitude, resulting in an overall decrement in sensitivity across the population. For color contrast, the effects were smaller and more heterogeneous, resulting in little or no overall change in sensitivity across the population. Our results demonstrate the dynamic influence that saccade preparation has on the sensitivity of visual cortical neurons and suggest a basis for the changes in perception known to occur during saccade preparation.
View details for DOI 10.1073/pnas.0902412106
View details for Web of Science ID 000268667600086
View details for PubMedID 19622736
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Presaccadic discrimination of receptive field stimuli by area V4 neurons
Buenos Aires Workshop on Visual Attention
PERGAMON-ELSEVIER SCIENCE LTD. 2009: 1227–32
Abstract
Previous studies have shown that the visual responses of neurons in extrastriate area V4 are enhanced prior to saccadic eye movements that target receptive field (RF) stimuli. We used receiver-operator characteristic (ROC) analysis to quantify how well V4 neurons could discriminate stable RF stimuli targeted by visually-guided saccades or ignored during saccades elsewhere. We found that discrimination was transiently enhanced prior to saccades to RF stimuli whereas it was reduced prior to saccades elsewhere. Similar to what is observed during covert attention and after frontal eye field microstimulation, the changes in stimulus discrimination were due in part to changes in response magnitude. In addition, we found evidence of an increased reliability of responses when saccades were made to the RF stimulus. These results highlight the similarity of mechanisms driving covert spatial attention and the preparation of visually-guided saccades.
View details for DOI 10.1016/j.visres.2008.03.018
View details for Web of Science ID 000267168800018
View details for PubMedID 18501949
View details for PubMedCentralID PMC2724369
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Attention governs action in the primate frontal eye field
NEURON
2007; 56 (3): 541-551
Abstract
While the motor and attentional roles of the frontal eye field (FEF) are well documented, the relationship between them is unknown. We exploited the known influence of visual motion on the apparent positions of targets, and measured how this illusion affects saccadic eye movements during FEF microstimulation. Without microstimulation, saccades to a moving grating are biased in the direction of motion, consistent with the apparent position illusion. Here we show that microstimulation of spatially aligned FEF representations increases the influence of this illusion on saccades. Rather than simply impose a fixed-vector signal, subthreshold stimulation directed saccades away from the FEF movement field, and instead more strongly in the direction of visual motion. These results demonstrate that the attentional effects of FEF stimulation govern visually guided saccades, and suggest that the two roles of the FEF work together to select both the features of a target and the appropriate movement to foveate it.
View details for DOI 10.1016/j.neuron.2007.09.029
View details for Web of Science ID 000250774600012
View details for PubMedID 17988636
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Electrical signals propagate unbiased in cortex
NEURON
2007; 55 (5): 684-686
Abstract
The greater spatial coherence of local field potentials (LFPs) compared with that of spiking activity has been attributed to frequency-dependent propagation of signals through the cortical medium. However, in this issue of Neuron, Logothetis and colleagues show that signal propagation within cortex is largely unbiased across different frequencies, thus suggesting a more functional and interpretable basis of LFP coherence.
View details for DOI 10.1016/j.neuron.2007.08.012
View details for Web of Science ID 000249857000004
View details for PubMedID 17785175
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Temporal patterning of saccadic eye movement signals
JOURNAL OF NEUROSCIENCE
2007; 27 (29): 7619-7630
Abstract
Electrical microstimulation is used widely in experimental neurophysiology to examine causal links between specific brain areas and their behavioral functions and is used clinically to treat neurological and psychiatric disorders in patients. Typically, microstimulation is applied to local brain regions as a train of equally spaced current pulses. We were interested in the sensitivity of a neural circuit to a train of variably spaced pulses, as is observed in physiological spike trains. We compared the effect of fixed, decelerating, accelerating, and randomly varying microstimulation patterns on the likelihood and metrics of eye movements evoked from the frontal eye field of monkeys, while holding the mean interpulse interval constant. Our results demonstrate that the pattern of microstimulation pulses strongly influences the probability of evoking a saccade, as well as the metrics of the saccades themselves. Specifically, the pattern most closely resembling physiological spike trains (accelerating pattern) was most effective at evoking a saccade, three times more so than the least effective decelerating pattern. A saccade-triggered average of effective random trains confirmed the positive relationship between accelerating rate and efficacy. These results have important implications for the use of electrical microstimulation in both experimental and clinical settings and suggest a means to study the role of temporal pattern in the encoding of behavioral and cognitive functions.
View details for DOI 10.1523/JNEUROSCI.0386-07.2007
View details for Web of Science ID 000248177900001
View details for PubMedID 17634356
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Rapid enhancement of visual cortical response discriminability by microstimulation of the frontal eye field
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2007; 104 (22): 9499-9504
Abstract
Visual attention provides a means of selecting among the barrage of information reaching the retina and of enhancing the perceptual discriminability of relevant stimuli. Neurophysiological studies in monkeys and functional imaging studies in humans have demonstrated neural correlates of these perceptual improvements in visual cortex during attention. Importantly, voluntary attention improves the discriminability of visual cortical responses to relevant stimuli. Recent work aimed at identifying sources of attentional modulation has implicated the frontal eye field (FEF) in driving spatial attention. Subthreshold microstimulation of the FEF enhances the responses of area V4 neurons to spatially corresponding stimuli. However, it is not known whether these enhancements include improved visual-response discriminability, a hallmark of voluntary attention. We used receiver-operator characteristic analysis to quantify how well V4 responses discriminated visual stimuli and examined how discriminability was affected by FEF microstimulation. Discriminability of responses to stable visual stimuli decayed over time but was transiently restored after microstimulation of the FEF. As observed during voluntary attention, the enhancement resulted only from changes in the magnitude of V4 responses and not in the relationship between response magnitude and variance. Enhanced response discriminability was apparent immediately after microstimulation and was reliable within 40 ms of microstimulation onset, indicating a direct influence of FEF stimulation on visual representations. These results contribute to the mounting evidence that saccade-related signals are a source of spatial attentive selection.
View details for DOI 10.1073/pnas.0701104104
View details for Web of Science ID 000246935700074
View details for PubMedID 17517599
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Changes in visual receptive fields with microstimulation of frontal cortex
NEURON
2006; 50 (5): 791-798
Abstract
The influence of attention on visual cortical neurons has been described in terms of its effect on the structure of receptive fields (RFs), where multiple stimuli compete to drive neural responses and ultimately behavior. We stimulated the frontal eye field (FEF) of passively fixating monkeys and produced changes in V4 responses similar to known effects of voluntary attention. Subthreshold FEF stimulation enhanced visual responses at particular locations within the RF and altered the interaction between pairs of RF stimuli to favor those aligned with the activated FEF site. Thus, we could influence which stimulus drove the responses of individual V4 neurons. These results suggest that spatial signals involved in saccade preparation are used to covertly select among multiple stimuli appearing within the RFs of visual cortical neurons.
View details for DOI 10.1016/j.neuron.2006.05.010
View details for Web of Science ID 000238165000013
View details for PubMedID 16731516
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The neurobiology of visual attention: finding sources
CURRENT OPINION IN NEUROBIOLOGY
2006; 16 (2): 159-165
Abstract
The profusion of progress during the past twenty years in identifying neural correlates of selective attention within the visual system has left open the question of how visual representations are biased to favor target stimuli. Studies aimed at specifying the mechanisms that can be causally implicated in the control of visual selective attention have only recently begun in earnest. Employing both the psychophysical and the neuroanatomical data, recent neurophysiological experiments in monkeys and neuroimaging studies in humans are converging on the neural circuits that provide the source of at least some forms of attentional control signals.
View details for DOI 10.1016/j.conb.2006.03.009
View details for Web of Science ID 000237234700006
View details for PubMedID 16563729
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Visual and oculomotor selection: links, causes and implications for spatial attention
TRENDS IN COGNITIVE SCIENCES
2006; 10 (3): 124-130
Abstract
Natural scenes contain far more information than can be processed simultaneously. Thus, our visually guided behavior depends crucially on the capacity to attend to relevant stimuli. Past studies have provided compelling evidence of functional overlap of the neural mechanisms that control spatial attention and saccadic eye movements. Recent neurophysiological work demonstrates that the neural circuits involved in the preparation of saccades also play a causal role in directing covert spatial attention. At the same time, other studies have identified separable neural populations that contribute uniquely to visual and oculomotor selection. Taken together, all of the recent work suggests how visual and oculomotor signals are integrated to simultaneously select the visual attributes of targets and the saccades needed to fixate them.
View details for DOI 10.1016/j.tics.2006.01.001
View details for Web of Science ID 000236533800010
View details for PubMedID 16469523
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Representations of faces and body parts in macaque temporal cortex: A functional MRI study
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2005; 102 (19): 6996-7001
Abstract
Human neuroimaging studies suggest that areas in temporal cortex respond preferentially to certain biologically relevant stimulus categories such as faces and bodies. Single-cell studies in monkeys have reported cells in inferior temporal cortex that respond selectively to faces, hands, and bodies but provide little evidence of large clusters of category-specific cells that would form "areas." We probed the category selectivity of macaque temporal cortex for representations of monkey faces and monkey body parts relative to man-made objects using functional MRI in animals trained to fixate. Two face-selective areas were activated bilaterally in the posterior and anterior superior temporal sulcus exhibiting different degrees of category selectivity. The posterior face area was more extensively activated in the right hemisphere than in the left hemisphere. Immediately adjacent to the face areas, regions were activated bilaterally responding preferentially to body parts. Our findings suggest a category-selective organization for faces and body parts in macaque temporal cortex.
View details for DOI 10.1073/pnas.0502605102
View details for Web of Science ID 000229048500064
View details for PubMedID 15860578
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Methods for functional magnetic resonance imaging in normal and lesioned behaving monkeys
JOURNAL OF NEUROSCIENCE METHODS
2005; 143 (2): 179-195
Abstract
Methods for performing functional magnetic resonance imaging (fMRI) studies in behaving and lesioned monkeys using a human MR scanner are reported. Materials for head implant surgery were selected based on tests for magnetic susceptibility. A primate chair with a rigid head fixation system and a mock scanner environment for training were developed. To perform controlled visual studies, monkeys were trained to maintain fixation for several minutes using a novel training technique that utilized continuous juice rewards. A surface coil was used to acquire anatomical and functional images in four monkeys, one with a partial lesion of striate cortex. High-resolution anatomical images were used after non-uniform intensity correction to create cortical surface reconstructions of both lesioned and normal hemispheres. Our methods were confirmed in two visual experiments, in which functional activations were obtained during both free viewing and fixation conditions. In one experiment, face-selective activity was found in the fundus and banks of the superior temporal sulcus and the middle temporal gyrus in monkeys viewing pictures of faces and objects while maintaining fixation. In a second experiment, regions in occipital, parietal, and frontal cortex were activated in lesioned and normal animals viewing a cartoon movie. Importantly, in the animal with the striate lesion, fMRI signals were obtained in the immediate vicinity of the lesion. Our results extend those previously reported by providing a detailed account of the technique and by demonstrating the feasibility of fMRI in monkeys with lesions.
View details for DOI 10.1016/j.jneumeth.2004.10.003
View details for Web of Science ID 000228708900011
View details for PubMedID 15814151
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A map of complex movements in motor cortex of primates
1st Behavioural Brain Sciences Symposium
PSYCHOLOGY PRESS. 2005: 211–232
View details for Web of Science ID 000289230900010
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Homeland defense begins in precentral cortex. Focus on "Sensorimotor integration in the precentral gyrus: Polysensory neurons and defensive movements"
JOURNAL OF NEUROPHYSIOLOGY
2004; 91 (4): 1456-1456
View details for DOI 10.1152/jn.01085.2003
View details for Web of Science ID 000220086100002
View details for PubMedID 15010494
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Distribution of hand location in monkeys during spontaneous behavior
EXPERIMENTAL BRAIN RESEARCH
2004; 155 (1): 30-36
Abstract
Recently it was shown that electrical stimulation of the precentral gyrus of monkeys can evoke complex, coordinated movements. In the forelimb representation, stimulation of each site caused the arm to move to a specific final posture, and thus the hand to move to a location in space. Among these stimulation-evoked hand locations, certain regions of the hand's workspace were more represented than others. We hypothesized that a similar non-uniform distribution of hand location should be present during a monkey's spontaneous behavior. The present study examined the distribution of hand location of monkeys in their home cages. This distribution was similar to that found by stimulation of the precentral gyrus. That is, arm postures that were over-represented in spontaneous behavior were also over-represented in the movements evoked by cortical stimulation.
View details for DOI 10.1007/s00221-003-1701-4
View details for Web of Science ID 000189201900005
View details for PubMedID 15064882
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Visually guided behavior after V1 lesions in young and adult monkeys and its relation to blindsight in humans.
Progress in brain research
2004; 144: 279-294
Abstract
After lesions of striate cortex in primates, there is still the capacity to detect and localize visual stimuli. In this chapter we review three aspects of our study of this phenomenon in macaques. First, we found that macaques that received their striate lesions as infants had considerably greater ability to detect and localize stimuli than those that received similar lesions as adults. Second, we suggest that the visual functions that survive striate lesions in macaques made in adulthood resemble those in human 'blindsight'. Third, we report that monkeys with striate lesions made in infancy are able to discriminate direction of visual motion.
View details for PubMedID 14650855
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Microstimulation of the frontal eye field and its effects on covert spatial attention
JOURNAL OF NEUROPHYSIOLOGY
2004; 91 (1): 152-162
Abstract
Many studies have established that the strength of visual perception and the strength of visual representations within visual cortex vary according to the focus of covert spatial attention. While it is clear that attention can modulate visual signals, the source of this modulation remains unknown. We have examined the possibility that saccade related mechanisms provide a source of spatial attention by studying the effects of electrical microstimulation of the frontal eye fields (FEF) on spatial attention. Monkeys performed a task in which they had to detect luminance changes of a peripheral target while ignoring a flashing distracter. The target luminance change could be preceded by stimulation of the FEF at current levels below that which evoked saccadic eye movements. We found that when the target change was preceded by stimulation of FEF, the monkey could detect smaller changes in target luminance. The increased sensitivity to the target change only occurred when the target was placed in the part of the visual field represented by neurons at the stimulation site. The magnitude of improvement depended on the temporal asynchrony of the stimulation onset and the target event. No significant effect of stimulation was observed when long intervals (>300 ms) between stimulation and the target event were used, and the magnitude of the increased sensitivity decreased systematically with increasing asynchrony. At the shortest asynchrony, FEF stimulation temporally overlapped the target event and the magnitude of the improvement was comparable to that of removing the distracter from the task. These results demonstrate that transient, but potent improvements in the deployment of covert spatial attention can be obtained by microstimulation of FEF sites from which saccadic eye movements are also evoked.
View details for DOI 10.1152/jn.00741.2002
View details for Web of Science ID 000187964500013
View details for PubMedID 13679398
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Visuomotor origins of covert spatial attention
NEURON
2003; 40 (4): 671-683
Abstract
Covert spatial attention produces biases in perceptual performance and neural processing of behaviorally relevant stimuli in the absence of overt orienting movements. The neural mechanism that gives rise to these effects is poorly understood. This paper surveys past evidence of a relationship between oculomotor control and visual spatial attention and more recent evidence of a causal link between the control of saccadic eye movements by frontal cortex and covert visual selection. Both suggest that the mechanism of covert spatial attention emerges as a consequence of the reciprocal interactions between neural circuits primarily involved in specifying the visual properties of potential targets and those involved in specifying the movements needed to fixate them.
View details for Web of Science ID 000186651200004
View details for PubMedID 14622573
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Complex movements evoked by microstimulation of the ventral intraparietal area
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2003; 100 (10): 6163-6168
Abstract
Most neurons in the ventral intraparietal area (VIP) of the macaque brain respond to both visual and tactile stimuli. The tactile receptive field is usually on the face, and the visual receptive field usually corresponds spatially to the tactile receptive field. In this study, electrical microstimulation of VIP, but not of surrounding tissue, caused a constellation of movements including eye closure, facial grimacing, head withdrawal, elevation of the shoulder, and movements of the hand to the space beside the head or shoulder. A similar set of movements was evoked by an air puff to the monkey's cheek. One interpretation is that VIP contributes to defensive movements triggered by stimuli on or near the head.
View details for Web of Science ID 000182939400106
View details for PubMedID 12719522
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Selective gating of visual signals by microstimulation of frontal cortex
NATURE
2003; 421 (6921): 370-373
Abstract
Several decades of psychophysical and neurophysiological studies have established that visual signals are enhanced at the locus of attention. What remains a mystery is the mechanism that initiates biases in the strength of visual representations. Recent evidence argues that, during spatial attention, these biases reflect nascent saccadic eye movement commands. We examined the functional interaction of saccade preparation and visual coding by electrically stimulating sites within the frontal eye fields (FEF) and measuring its effect on the activity of neurons in extrastriate visual cortex. Here we show that visual responses in area V4 could be enhanced after brief stimulation of retinotopically corresponding sites within the FEF using currents below that needed to evoke saccades. The magnitude of the enhancement depended on the effectiveness of receptive field stimuli as well as on the presence of competing stimuli outside the receptive field. Stimulation of non-corresponding FEF representations could suppress V4 responses. The results suggest that the gain of visual signals is modified according to the strength of spatially corresponding eye movement commands.
View details for DOI 10.1038/nature01341
View details for Web of Science ID 000180533000042
View details for PubMedID 12540901
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Visually guided behavior after V1 lesions in young and adult monkeys and its relation to blindsight in humans
Conference on the Roots of Visual Awareness
ELSEVIER SCIENCE BV. 2003: 279–294
View details for DOI 10.1016/S0079-6123(03)14401-9
View details for Web of Science ID 000187421400019
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The cortical control of movement revisited
NEURON
2002; 36 (3): 349-362
Abstract
Recently, we found that electrical stimulation of motor cortex caused monkeys to make coordinated, complex movements. These evoked movements were arranged across the cortex in a map of spatial locations to which the hand moved. We suggest that some of the subdivisions previously described within primary motor and premotor cortex may represent different types of actions that monkeys tend to make in different regions of space. According to this view, primary and premotor cortex may fit together into a larger map of manual space.
View details for Web of Science ID 000178877700006
View details for PubMedID 12408840
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Probing cortical function with electrical stimulation
NATURE NEUROSCIENCE
2002; 5 (10): 921-921
View details for DOI 10.1038/nn1002-921
View details for Web of Science ID 000178242200004
View details for PubMedID 12352975
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Complex movements evoked by microstimulation of precentral cortex
NEURON
2002; 34 (5): 841-851
Abstract
Electrical microstimulation was used to study primary motor and premotor cortex in monkeys. Each stimulation train was 500 ms in duration, approximating the time scale of normal reaching and grasping movements and the time scale of the neuronal activity that normally accompanies movement. This stimulation on a behaviorally relevant time scale evoked coordinated, complex postures that involved many joints. For example, stimulation of one site caused the mouth to open and also caused the hand to shape into a grip posture and move to the mouth. Stimulation of this site always drove the joints toward this final posture, regardless of the direction of movement required to reach the posture. Stimulation of other cortical sites evoked different postures. Postures that involved the arm were arranged across cortex to form a map of hand positions around the body. This stimulation-evoked map encompassed both primary motor and the adjacent premotor cortex. We suggest that these regions fit together into a single map of the workspace around the body.
View details for Web of Science ID 000175951800017
View details for PubMedID 12062029
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Eye movements modulate visual receptive fields of V4 neurons
NEURON
2001; 29 (3): 757-767
Abstract
The receptive field, defined as the spatiotemporal selectivity of neurons to sensory stimuli, is central to our understanding of the neuronal mechanisms of perception. However, despite the fact that eye movements are critical during normal vision, the influence of eye movements on the structure of receptive fields has never been characterized. Here, we map the receptive fields of macaque area V4 neurons during saccadic eye movements and find that receptive fields are remarkably dynamic. Specifically, before the initiation of a saccadic eye movement, receptive fields shrink and shift towards the saccade target. These spatiotemporal dynamics may enhance information processing of relevant stimuli during the scanning of a visual scene, thereby assisting the selection of saccade targets and accelerating the analysis of the visual scene during free viewing.
View details for Web of Science ID 000167868900024
View details for PubMedID 11301034
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Control of eye movements and spatial attention
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2001; 98 (3): 1273-1276
Abstract
Several lines of evidence suggest that planning eye movements and directing visuospatial attention share overlapping brain mechanisms. This study tested whether spatial attention can be enhanced by altering oculomotor signals within the brain. Monkeys performed a spatial attention task while neurons within the frontal eye field, an oculomotor area within prefrontal cortex, were electrically stimulated below the level at which eye movements are evoked. We found that we could improve the monkey's performance with microstimulation when, but only when, the object to be attended was positioned in the space represented by the cortical stimulation site.
View details for Web of Science ID 000166807300091
View details for PubMedID 11158629
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Direction of motion discrimination after early lesions of striate cortex (V1) of the macaque monkey
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2001; 98 (1): 325-330
Abstract
Previous studies have established that humans and monkeys with damage to striate cortex are able to detect and localize bright targets within the resultant scotoma. Electrophysiological evidence in monkeys suggests that residual vision also might include sensitivity to direction of visual motion. We tested whether macaque monkeys with longstanding lesions of striate cortex (V1), sustained in infancy, could discriminate visual stimuli on the basis of direction of motion. Three monkeys with unilateral striate cortex lesions sustained in infancy were tested 2-5 years postlesion on a direction of motion discrimination task. Each monkey was trained to make saccadic eye movements to a field of moving dots or to withhold such eye movements, depending on the direction of motion in a coherent random dot display. With smaller motion displays, monkeys were unable to detect or discriminate motion within the scotoma, although they could discriminate moving from static stimuli. Yet, each monkey was able to discriminate direction of motion when the motion stimulus was larger, but still confined to the scotoma. The results demonstrate that the recovery after infant damage to striate cortex includes some sensitivity to direction of visual motion.
View details for Web of Science ID 000166222600061
View details for PubMedID 11134530
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Shape representations and visual guidance sf saccadic eye movements
SCIENCE
1999; 285 (5435): 1914-1917
Abstract
One hallmark of primate vision is that the direction of gaze is constantly shifting to position objects of interest appropriately on the fovea, where visual acuity is greatest. This process must involve the close cooperation of oculomotor and visual recognition mechanisms because visual details must be translated into specific motor commands. This paper describes the correspondence between the presaccadic activity of V4 neurons and the degree of visual guidance of saccadic eye movements to objects of different form. The results suggest that neurons that participate in coding visual stimuli are also involved in guiding the eyes to prominent features of objects.
View details for Web of Science ID 000082638300051
View details for PubMedID 10489371
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Visual representations during saccadic eye movements
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1998; 95 (15): 8981-8984
Abstract
In normal vision, shifts of attention are usually followed by saccadic eye movements. Neurons in extrastriate area V4 are modulated by focal attention when eye movements are withheld, but they also respond in advance of visually guided saccadic eye movements. We have examined the visual selectivity of saccade-related responses of area V4 neurons in monkeys making delayed eye movements to receptive field stimuli of varying orientation. This task did not require the monkey to attend to orientation per se but merely to foveate the receptive field stimulus. We present evidence that the presaccadic enhancement exhibited by V4 neurons, quite separate from the response at stimulus onset, is a resurgent visual representation that seems as selective as the response is when the stimulus first appears. The presaccadic enhancement appears to provide a strengthening of a decaying featural representation immediately before an eye movement is directed to visual targets. We suggest that this reactivation provides a mechanism by which a clear perception of the saccade goal can be maintained during the execution of the saccade, perhaps for the purpose of establishing continuity across eye movements.
View details for Web of Science ID 000075143900101
View details for PubMedID 9671790
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Man, monkey, and blindsight
NEUROSCIENTIST
1998; 4 (4): 227-230
View details for Web of Science ID 000074948100010
- Man, Monkey and Blindsight. The Neuroscientist 1998; 4: 227-230
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Greater residual vision in monkeys after striate cortex damage in infancy
JOURNAL OF NEUROPHYSIOLOGY
1996; 76 (6): 3928-3933
Abstract
1. Monkeys with large unilateral surgical ablations of striate cortex, sustained either in adulthood or at 5-6 wk of age, were trained on an oculomotor detection and localization task and tested with visual stimuli in the hemifields ipsilateral and contralateral to the lesion 2-5 yr after surgery. 2. Monkeys with lesions sustained in adulthood were largely unable to detect stimuli in the hemifield contralateral to the lesion, with only one monkey showing recovery toward the end of testing. Monkeys with lesions of striate cortex made in infancy, however, each showed residual detection capacity at the beginning of testing and improved to near normal by the end of testing. 3. Each of the monkeys showing a residual ability to detect within the contralateral hemifield was also able to localize visual targets with eye movements. 4. These findings demonstrate that the vision surviving striate cortex damage in primates is more robust after early damage as has been shown to be the case for primary somatosensory, motor, and association cortex.
View details for Web of Science ID A1996WA80300032
View details for PubMedID 8985890
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LOCALIZATION OF VISUAL-STIMULI AFTER STRIATE CORTEX DAMAGE IN MONKEYS - PARALLELS WITH HUMAN BLINDSIGHT
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1995; 92 (18): 8215-8218
Abstract
Blindsight is a phenomenon in which human patients with damage to striate cortex deny any visual sensation in the resultant visual field defect but can nonetheless detect and localize stimuli when persuaded to guess. Although monkeys with striate lesions have also been shown to exhibit some residual vision, it is not yet clear to what extent the residual capacities in monkeys parallel the phenomenon of human blindsight. To clarify this issue, we trained two monkeys with unilateral lesions of striate cortex to make saccadic eye movements to visual targets in both hemifields under two conditions. In the condition analogous to clinical perimetry, they failed to initiate saccades to targets presented in the contralateral hemifield and thus appeared "blind." Only in the condition where the fixation point was turned off simultaneously with the onset of the target--signaling the animal to respond at the appropriate time--were monkeys able to localize targets contralateral to the striate lesion. These results indicate that the conditions under which residual vision is demonstrable are similar for monkeys with striate cortex damage and humans with blindsight.
View details for Web of Science ID A1995RR84400027
View details for PubMedID 7667270