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Aglai P. B. Sousa - One of the best experts on this subject based on the ideXlab platform.
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Third tier ventral extrastriate cortex in the New World monkey, Cebus apella
Experimental Brain Research, 2000Co-Authors: Marcello G .p. Rosa, Maria Carmen Piñon, Ricardo Gattass, Aglai P. B. SousaAbstract:The ventral extrastriate cortex adjacent to the second Visual Area was studied in the New World monkey Cebus apella , using anaesthetised preparations. The visuotopic organisation and myeloarchitecture of this region demonstrate the existence of a distinct strip of cortex, 3–4 mm wide, with an ordered representation of the contralateral upper Visual quadrant, up to 60° eccentricity. This upper-quadrant representation is probably homologous to the ventral subdivision of the third Visual complex (V3v) of Old World monkeys, also known as the ventral posterior Area. The representation of the horizontal meridian in V3v forms its posterior and medial border with V2, while the upper vertical meridian is represented anterior and laterally, forming a congruent border with the fourth Visual Area (V4). Central Visual fields are represented in posterior and lateral portions of V3v, in the inferior occipital sulcus, while the periphery of the Visual field is represented anteriorly, on the tentorial surface. Cortex anterior to V3v, at the ventral occipitotemporal transition, had neurones that had poor Visual responses. No representation of the lower quadrant was found adjacent to V3v in ventral cortex. However, we observed cells with perifoveal receptive fields centred in the lower quadrant immediately dorsal to V3v, around the junction of the inferior occipital and lunate sulci. These observations argue against the idea that V3v is an Area restricted to the ventral cortex in New World monkeys and support the conclusions of previous anatomical studies in Cebus that showed a continuity of myeloarchitecture and connectional patterns between ventral and lateral extrastriate cortices. Together, these data suggest that V3v may be part of a larger Area that extends into dorsolateral extrastriate cortex, overlapping to some extent with the caudal subdivision of the dorsolateral Area described in other New World monkeys.
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Third tier" ventral extrastriate cortex in the New World monkey, Cebus apella.
Experimental Brain Research, 2000Co-Authors: Marcello G .p. Rosa, Maria Carmen Piñon, Ricardo Gattass, Aglai P. B. SousaAbstract:The ventral extrastriate cortex adjacent to the second Visual Area was studied in the New World monkey Cebus apella, using anaesthetised preparations. The visuotopic organisation and myeloarchitecture of this region demonstrate the existence of a distinct strip of cortex, 3-4 mm wide, with an ordered representation of the contralateral upper Visual quadrant, up to 60 degrees eccentricity. This upper-quadrant representation is probably homologous to the ventral subdivision of the third Visual complex (V3v) of Old World monkeys, also known as the ventral posterior Area. The representation of the horizontal meridian in V3v forms its posterior and medial border with V2, while the upper vertical meridian is represented anterior and laterally, forming a congruent border with the fourth Visual Area (V4). Central Visual fields are represented in posterior and lateral portions of V3v, in the inferior occipital sulcus, while the periphery of the Visual field is represented anteriorly, on the tentorial surface. Cortex anterior to V3v, at the ventral occipitotemporal transition, had neurones that had poor Visual responses. No representation of the lower quadrant was found adjacent to V3v in ventral cortex. However, we observed cells with perifoveal receptive fields centred in the lower quadrant immediately dorsal to V3v, around the junction of the inferior occipital and lunate sulci. These observations argue against the idea that V3v is an Area restricted to the ventral cortex in New World monkeys and support the conclusions of previous anatomical studies in Cebus that showed a continuity of myeloarchitecture and connectional patterns between ventral and lateral extrastriate cortices. Together, these data suggest that V3v may be part of a larger Area that extends into dorsolateral extrastriate cortex, overlapping to some extent with the caudal subdivision of the dorsolateral Area described in other New World monkeys.
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Area V4 in Cebus monkey: extent and visuotopic organization.
Cerebral Cortex, 1998Co-Authors: Maria Carmen Piñon, Ricardo Gattass, Aglai P. B. SousaAbstract:We used electrophysiological mapping and myeloarchitectural criteria in order to define the location, extent and Visual topography of the fourth Visual Area (V4) in anesthetized and paralyzed Cebus monkey. Based on these criteria, the borders of V4 with surrounding Areas were defined both on the dorsal and ventral cortical surfaces. In addition, to better Visualize the visuotopic organization and to evaluate its regularity, we constructed bidimensional maps and projected the recording sites onto them. Area V4 has an almost complete representation of the binocular Visual field with the lower Visual field represented dorsally (V4d) and the upper field ventrally (V4v). We found this representation to be more extensive than those previously described. The representation of the central portion of the Visual field is largely expanded in comparison with that of the periphery. This emphasis in central vision could be related with the involvement of V4 in the ventral stream of Visual information processing. Receptive field size increases with increasing eccentricity, while cortical magnification factor decreases. The cortical magnification factor measured along isopolar lines is, on average, 1.5‐2.0 times greater than that measured along the isoeccentric lines, suggesting the existence of a small anisotropy in central and peripheral V4.
Marcello G .p. Rosa - One of the best experts on this subject based on the ideXlab platform.
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Third tier ventral extrastriate cortex in the New World monkey, Cebus apella
Experimental Brain Research, 2000Co-Authors: Marcello G .p. Rosa, Maria Carmen Piñon, Ricardo Gattass, Aglai P. B. SousaAbstract:The ventral extrastriate cortex adjacent to the second Visual Area was studied in the New World monkey Cebus apella , using anaesthetised preparations. The visuotopic organisation and myeloarchitecture of this region demonstrate the existence of a distinct strip of cortex, 3–4 mm wide, with an ordered representation of the contralateral upper Visual quadrant, up to 60° eccentricity. This upper-quadrant representation is probably homologous to the ventral subdivision of the third Visual complex (V3v) of Old World monkeys, also known as the ventral posterior Area. The representation of the horizontal meridian in V3v forms its posterior and medial border with V2, while the upper vertical meridian is represented anterior and laterally, forming a congruent border with the fourth Visual Area (V4). Central Visual fields are represented in posterior and lateral portions of V3v, in the inferior occipital sulcus, while the periphery of the Visual field is represented anteriorly, on the tentorial surface. Cortex anterior to V3v, at the ventral occipitotemporal transition, had neurones that had poor Visual responses. No representation of the lower quadrant was found adjacent to V3v in ventral cortex. However, we observed cells with perifoveal receptive fields centred in the lower quadrant immediately dorsal to V3v, around the junction of the inferior occipital and lunate sulci. These observations argue against the idea that V3v is an Area restricted to the ventral cortex in New World monkeys and support the conclusions of previous anatomical studies in Cebus that showed a continuity of myeloarchitecture and connectional patterns between ventral and lateral extrastriate cortices. Together, these data suggest that V3v may be part of a larger Area that extends into dorsolateral extrastriate cortex, overlapping to some extent with the caudal subdivision of the dorsolateral Area described in other New World monkeys.
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Third tier" ventral extrastriate cortex in the New World monkey, Cebus apella.
Experimental Brain Research, 2000Co-Authors: Marcello G .p. Rosa, Maria Carmen Piñon, Ricardo Gattass, Aglai P. B. SousaAbstract:The ventral extrastriate cortex adjacent to the second Visual Area was studied in the New World monkey Cebus apella, using anaesthetised preparations. The visuotopic organisation and myeloarchitecture of this region demonstrate the existence of a distinct strip of cortex, 3-4 mm wide, with an ordered representation of the contralateral upper Visual quadrant, up to 60 degrees eccentricity. This upper-quadrant representation is probably homologous to the ventral subdivision of the third Visual complex (V3v) of Old World monkeys, also known as the ventral posterior Area. The representation of the horizontal meridian in V3v forms its posterior and medial border with V2, while the upper vertical meridian is represented anterior and laterally, forming a congruent border with the fourth Visual Area (V4). Central Visual fields are represented in posterior and lateral portions of V3v, in the inferior occipital sulcus, while the periphery of the Visual field is represented anteriorly, on the tentorial surface. Cortex anterior to V3v, at the ventral occipitotemporal transition, had neurones that had poor Visual responses. No representation of the lower quadrant was found adjacent to V3v in ventral cortex. However, we observed cells with perifoveal receptive fields centred in the lower quadrant immediately dorsal to V3v, around the junction of the inferior occipital and lunate sulci. These observations argue against the idea that V3v is an Area restricted to the ventral cortex in New World monkeys and support the conclusions of previous anatomical studies in Cebus that showed a continuity of myeloarchitecture and connectional patterns between ventral and lateral extrastriate cortices. Together, these data suggest that V3v may be part of a larger Area that extends into dorsolateral extrastriate cortex, overlapping to some extent with the caudal subdivision of the dorsolateral Area described in other New World monkeys.
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morphological variation of layer iii pyramidal neurones in the occipitotemporal pathway of the macaque monkey Visual cortex
Cerebral Cortex, 1998Co-Authors: Guy N Elston, Marcello G .p. RosaAbstract:We compared the morphological characteristics of layer III pyramidal neurones in different Visual Areas of the occipitotemporal cortical ‘stream’, which processes information related to object recognition in the Visual field (including shape, colour and texture). Pyramidal cells were intracellularly injected with Lucifer Yellow in cortical slices cut tangential to the cortical layers, allowing quantitative comparisons of dendritic field morphology, spine density and cell body size between the blobs and interblobs of the primary Visual Area (V1), the interstripe compartments of the second Visual Area (V2), the fourth Visual Area (V4) and cytoarchitectonic Area TEO. We found that the tangential dimension of basal dendritic fields of layer III pyramidal neurones increases from caudal to rostral Visual Areas in the occipitotemporal pathway, such that TEO cells have, on average, dendritic fields spanning an Area 5‐6 times larger than V1 cells. In addition, the data indicate that V1 cells located within blobs have significantly larger dendritic fields than those of interblob cells. Sholl analysis of dendritic fields demonstrated that pyramidal cells in V4 and TEO are more complex (i.e. exhibit a larger number of branches at comparable distances from the cell body) than cells in V1 or V2. Moreover, this analysis demonstrated that the dendrites of many cells in V1 cluster along specific axes, while this tendency is less marked in extrastriate Areas. Most notably, there is a relatively large proportion of neurones with ‘morphologically orientationbiased’ dendritic fields (i.e. branches tend to cluster along two diametrically opposed directions from the cell body) in the interblobs in V1, as compared with the blobs in V1 and extrastriate Areas. Finally, counts of dendritic spines along the length of basal dendrites revealed similar peak spine densities in the blobs and the interblobs of V1 and in the V2 interstripes, but markedly higher spine densities in V4 and TEO. Estimates of the number of dendritic spines on the basal dendritic fields of layer III pyramidal cells indicate that cells in V2 have on average twice as many spines as V1 cells, that V4 cells have 3.8 times as many spines as V1 cells, and that TEO cells have 7.5 times as many spines as V1 cells. These findings suggest the possibility that the complex response properties of neurones in rostral stations in the occipitotemporal pathway may, in part, be attributed to their larger and more complex basal dendritic fields, and to the increase in both number and density of spines on their basal dendrites.
Ricardo Gattass - One of the best experts on this subject based on the ideXlab platform.
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GABA inactivation of Area V4 changes receptive-field properties of V2 neurons in Cebus monkeys.
Experimental Neurology, 2012Co-Authors: Ana Karla Jansen-amorim, Mario Fiorani, Ricardo GattassAbstract:To investigate the contribution of feedback circuits from Area V4 to the receptive-field properties of V2 neurons, we used tungsten microelectrodes to record extracellular single units in these Visual Areas, before and after pressure injections of a solution of 0.25 mol/L of GABA in two anesthetized and paralyzed Cebus apella monkeys. The Visual stimulus consisted of a single bar moving in one of eight directions. Using a device made of four stainless steel pipettes and one central tungsten electrode, we inactivated, with different amounts of GABA, topographically corresponding Areas of V4, while studying V2 neurons. We studied a total of 36 V2 neurons during six sessions of GABA injections into Area V4. GABA inactivation of Visual Area V4 produced a general decrease in the excitability of the neurons, which included a decrease in spontaneous and driven activities, followed by changes in direction selectivity. The changes in selectivity were toward an increase in directional selectivity and decrease in orientation selectivity. Thus, feedback connections arising from V4, an Area of the ventral steams of Visual information processing, are capable of not only modulating the spontaneous and driven activity of V2 neurons, but also of modifying V2 receptive field properties, such as its direction and/or orientation selectivity.
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Third tier ventral extrastriate cortex in the New World monkey, Cebus apella
Experimental Brain Research, 2000Co-Authors: Marcello G .p. Rosa, Maria Carmen Piñon, Ricardo Gattass, Aglai P. B. SousaAbstract:The ventral extrastriate cortex adjacent to the second Visual Area was studied in the New World monkey Cebus apella , using anaesthetised preparations. The visuotopic organisation and myeloarchitecture of this region demonstrate the existence of a distinct strip of cortex, 3–4 mm wide, with an ordered representation of the contralateral upper Visual quadrant, up to 60° eccentricity. This upper-quadrant representation is probably homologous to the ventral subdivision of the third Visual complex (V3v) of Old World monkeys, also known as the ventral posterior Area. The representation of the horizontal meridian in V3v forms its posterior and medial border with V2, while the upper vertical meridian is represented anterior and laterally, forming a congruent border with the fourth Visual Area (V4). Central Visual fields are represented in posterior and lateral portions of V3v, in the inferior occipital sulcus, while the periphery of the Visual field is represented anteriorly, on the tentorial surface. Cortex anterior to V3v, at the ventral occipitotemporal transition, had neurones that had poor Visual responses. No representation of the lower quadrant was found adjacent to V3v in ventral cortex. However, we observed cells with perifoveal receptive fields centred in the lower quadrant immediately dorsal to V3v, around the junction of the inferior occipital and lunate sulci. These observations argue against the idea that V3v is an Area restricted to the ventral cortex in New World monkeys and support the conclusions of previous anatomical studies in Cebus that showed a continuity of myeloarchitecture and connectional patterns between ventral and lateral extrastriate cortices. Together, these data suggest that V3v may be part of a larger Area that extends into dorsolateral extrastriate cortex, overlapping to some extent with the caudal subdivision of the dorsolateral Area described in other New World monkeys.
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Third tier" ventral extrastriate cortex in the New World monkey, Cebus apella.
Experimental Brain Research, 2000Co-Authors: Marcello G .p. Rosa, Maria Carmen Piñon, Ricardo Gattass, Aglai P. B. SousaAbstract:The ventral extrastriate cortex adjacent to the second Visual Area was studied in the New World monkey Cebus apella, using anaesthetised preparations. The visuotopic organisation and myeloarchitecture of this region demonstrate the existence of a distinct strip of cortex, 3-4 mm wide, with an ordered representation of the contralateral upper Visual quadrant, up to 60 degrees eccentricity. This upper-quadrant representation is probably homologous to the ventral subdivision of the third Visual complex (V3v) of Old World monkeys, also known as the ventral posterior Area. The representation of the horizontal meridian in V3v forms its posterior and medial border with V2, while the upper vertical meridian is represented anterior and laterally, forming a congruent border with the fourth Visual Area (V4). Central Visual fields are represented in posterior and lateral portions of V3v, in the inferior occipital sulcus, while the periphery of the Visual field is represented anteriorly, on the tentorial surface. Cortex anterior to V3v, at the ventral occipitotemporal transition, had neurones that had poor Visual responses. No representation of the lower quadrant was found adjacent to V3v in ventral cortex. However, we observed cells with perifoveal receptive fields centred in the lower quadrant immediately dorsal to V3v, around the junction of the inferior occipital and lunate sulci. These observations argue against the idea that V3v is an Area restricted to the ventral cortex in New World monkeys and support the conclusions of previous anatomical studies in Cebus that showed a continuity of myeloarchitecture and connectional patterns between ventral and lateral extrastriate cortices. Together, these data suggest that V3v may be part of a larger Area that extends into dorsolateral extrastriate cortex, overlapping to some extent with the caudal subdivision of the dorsolateral Area described in other New World monkeys.
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Area V4 in Cebus monkey: extent and visuotopic organization.
Cerebral Cortex, 1998Co-Authors: Maria Carmen Piñon, Ricardo Gattass, Aglai P. B. SousaAbstract:We used electrophysiological mapping and myeloarchitectural criteria in order to define the location, extent and Visual topography of the fourth Visual Area (V4) in anesthetized and paralyzed Cebus monkey. Based on these criteria, the borders of V4 with surrounding Areas were defined both on the dorsal and ventral cortical surfaces. In addition, to better Visualize the visuotopic organization and to evaluate its regularity, we constructed bidimensional maps and projected the recording sites onto them. Area V4 has an almost complete representation of the binocular Visual field with the lower Visual field represented dorsally (V4d) and the upper field ventrally (V4v). We found this representation to be more extensive than those previously described. The representation of the central portion of the Visual field is largely expanded in comparison with that of the periphery. This emphasis in central vision could be related with the involvement of V4 in the ventral stream of Visual information processing. Receptive field size increases with increasing eccentricity, while cortical magnification factor decreases. The cortical magnification factor measured along isopolar lines is, on average, 1.5‐2.0 times greater than that measured along the isoeccentric lines, suggesting the existence of a small anisotropy in central and peripheral V4.
Robert Desimone - One of the best experts on this subject based on the ideXlab platform.
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The role of prefrontal cortex in the control of feature attention in Area V4.
Nature Communications, 2019Co-Authors: Narcisse P. Bichot, Azriel Ghadooshahy, Michael L. Williams, Robert DesimoneAbstract:When searching for an object in a cluttered scene, we can use our memory of the target object features to guide our search, and the responses of neurons in multiple cortical Visual Areas are enhanced when their receptive field contains a stimulus sharing target object features. Here we tested the role of the ventral prearcuate region (VPA) of prefrontal cortex in the control of feature attention in cortical Visual Area V4. VPA was unilaterally inactivated in monkeys performing a free-viewing Visual search for a target stimulus in an array of stimuli, impairing monkeys’ ability to find the target in the array in the affected hemifield, but leaving intact their ability to make saccades to targets presented alone. Simultaneous recordings in V4 revealed that the effects of feature attention on V4 responses were eliminated or greatly reduced while leaving the effects of spatial attention on responses intact. Altogether, the results suggest that feedback from VPA modulates processing in Visual cortex during attention to object features. The neural mechanisms underlying feature based attention to targets in a cluttered scene are not well understood. Here, the authors show that inactivation of the ventral prearcuate region leads to deficits in picking out a target among many stimuli as well as eliminates the feature based modulation of responses of V4 neurons.
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Laminar differences in gamma and alpha coherence in the ventral stream.
Proceedings of the National Academy of Sciences, 2011Co-Authors: Elizabeth A. Buffalo, Pascal Fries, Rogier Landman, Timothy J. Buschman, Robert DesimoneAbstract:Attention to a stimulus enhances both neuronal responses and gamma frequency synchrony in Visual Area V4, both of which should increase the impact of attended information on downstream neurons. To determine whether gamma synchrony is common throughout the ventral stream, we recorded from neurons in the superficial and deep layers of V1, V2, and V4 in two rhesus monkeys. We found an unexpected striking difference in gamma synchrony in the superficial vs. deep layers. In all three Areas, spike-field coherence in the gamma (40–60 Hz) frequency range was largely confined to the superficial layers, whereas the deep layers showed maximal coherence at low frequencies (6–16 Hz), which included the alpha range. In the superficial layers of V2 and V4, gamma synchrony was enhanced by attention, whereas in the deep layers, alpha synchrony was reduced by attention. Unlike these major differences in synchrony, attentional effects on firing rates and noise correlation did not differ substantially between the superficial and deep layers. The results suggest that synchrony plays very different roles in feedback and feedforward projections.
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gamma band synchronization in Visual cortex predicts speed of change detection
Nature, 2006Co-Authors: Thilo Womelsdorf, Robert Desimone, Pascal Fries, Partha P MitraAbstract:Our capacity to process and respond behaviourally to multiple incoming stimuli is very limited. To optimize the use of this limited capacity, attentional mechanisms give priority to behaviourally relevant stimuli at the expense of irrelevant distractors. In Visual Areas, attended stimuli induce enhanced responses and an improved synchronization of rhythmic neuronal activity in the gamma frequency band (40–70 Hz)1,2,3,4,5,6,7,8,9,10,11. Both effects probably improve the neuronal signalling of attended stimuli within and among brain Areas1,12,13,14,15,16. Attention also results in improved behavioural performance and shortened reaction times. However, it is not known how reaction times are related to either response strength or gamma-band synchronization in Visual Areas. Here we show that behavioural response times to a stimulus change can be predicted specifically by the degree of gamma-band synchronization among those neurons in monkey Visual Area V4 that are activated by the behaviourally relevant stimulus. When there are two Visual stimuli and monkeys have to detect a change in one stimulus while ignoring the other, their reactions are fastest when the relevant stimulus induces strong gamma-band synchronization before and after the change in stimulus. This enhanced gamma-band synchronization is also followed by shorter neuronal response latencies on the fast trials. Conversely, the monkeys' reactions are slowest when gamma-band synchronization is high in response to the irrelevant distractor. Thus, enhanced neuronal gamma-band synchronization and shortened neuronal response latencies to an attended stimulus seem to have direct effects on Visually triggered behaviour, reflecting an early neuronal correlate of efficient visuo-motor integration.
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Cue-dependent deficits in grating orientation discrimination after V4 lesions in macaques
Visual Neuroscience, 1996Co-Authors: Peter De Weerd, Robert Desimone, Leslie G. UngerleiderAbstract:To examine the role of Visual Area V4 in pattern vision, we tested two monkeys with lesions of V4 on tasks that required them to discriminate the orientation of contours defined by several different cues. The cues used to separate the contours from their background included luminance, color, motion, and texture, as well as phase-shifted abutting gratings that created an "illusory" contour. The monkeys were trained to maintain fixation on a fixation target while discriminating extrafoveal stimuli, which were located in either a normal control quadrant of the Visual field or in a quadrant affected by a lesion of Area V4 in one hemisphere. Comparing performance in the two quadrants, we found significant deficits for contours defined by texture and for the illusory contour, but smaller or no deficits for motion-, color-, and luminance-defined contours. The data suggest a specific role of V4 in the perception of illusory contours and contours defined by texture.
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A role for the corpus callosum in Visual Area V4 of the macaque
Visual Neuroscience, 1993Co-Authors: Robert Desimone, Jeffrey Moran, Stanley J. Schein, Mortimer MishkinAbstract:The classically defined receptive fields of V4 cells are confined almost entirely to the contralateral Visual field. However, these receptive fields are often surrounded by large, silent suppressive regions, and stimulating the surrounds can cause a complete suppression of response to a simultaneously presented stimulus within the receptive field. We investigated whether the suppressive surrounds might extend across the midline into the ipsilateral Visual field and, if so, whether the surrounds were dependent on the corpus callosum, which has a widespread distribution in V4. We found that the surrounds of more than half of the cells tested in the central Visual field representation of V4 crossed into the ipsilateral Visual field, with some extending up to at least 16 deg from the vertical meridian. Much of this suppression from the ipsilateral field was mediated by the corpus callosum, as section of the callosum dramatically reduced both the strength and extent of the surrounds. There remained, however, some residual suppression that was not further reduced by addition of an anterior commissure lesion. Because the residual ipsilateral suppression was similar in magnitude and extent to that found following section of the optic tract contralateral to the V4 recording, we concluded that it was retinal in origin. Using the same techniques employed in V4, we also mapped the ipsilateral extent of surrounds in the foveal representation of V1 in an intact monkey. Results were very similar to those in V4 following commissural or contralateral tract sections. The findings suggest that V4 is a central site for long-range interactions both within and across the two Visual hemifields. Taken with previous work, the results are consistent with the notion that the large suppressive surrounds of V4 neurons contribute to the neural mechanisms of color constancy and figure-ground separation.
Matthew A. Smith - One of the best experts on this subject based on the ideXlab platform.
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Slow drift of neural activity as a signature of impulsivity in macaque Visual and prefrontal cortex
2020Co-Authors: Benjamin R. Cowley, Adam C. Snyder, Katerina Acar, Robert Williamson, Matthew A. SmithAbstract:Abstract An animal’s decision depends not only on incoming sensory evidence but also on its fluctuating internal state. This internal state is a product of cognitive factors, such as fatigue, motivation, and arousal, but it is unclear how these factors influence the neural processes that encode the sensory stimulus and form a decision. We discovered that, over the timescale of tens of minutes during a perceptual decision-making task, animals slowly shifted their likelihood of reporting stimulus changes. They did this unprompted by task conditions. We recorded neural population activity from Visual Area V4 as well as prefrontal cortex, and found that the activity of both Areas slowly drifted together with the behavioral fluctuations. We reasoned that such slow fluctuations in behavior could either be due to slow changes in how the sensory stimulus is processed or due to a process that acts independently of sensory processing. By analyzing the recorded activity in conjunction with models of perceptual decision-making, we found evidence for the slow drift in neural activity acting as an impulsivity signal, overriding sensory evidence to dictate the final decision. Overall, this work uncovers an internal state embedded in the population activity across multiple brain Areas, hidden from typical trial-averaged analyses and revealed only when considering the passage of time within each experimental session. Knowledge of this cognitive factor was critical in elucidating how sensory signals and the internal state together contribute to the decision-making process.
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Slow Drift of Neural Activity as a Signature of Impulsivity in Macaque Visual and Prefrontal Cortex
Neuron, 2020Co-Authors: Benjamin R. Cowley, Adam C. Snyder, Katerina Acar, Robert Williamson, Matthew A. SmithAbstract:An animal's decision depends not only on incoming sensory evidence but also on its fluctuating internal state. This state embodies multiple cognitive factors, such as arousal and fatigue, but it is unclear how these factors influence the neural processes that encode sensory stimuli and form a decision. We discovered that, unprompted by task conditions, animals slowly shifted their likelihood of detecting stimulus changes over the timescale of tens of minutes. Neural population activity from Visual Area V4, as well as from prefrontal cortex, slowly drifted together with these behavioral fluctuations. We found that this slow drift, rather than altering the encoding of the sensory stimulus, acted as an impulsivity signal, overriding sensory evidence to dictate the final decision. Overall, this work uncovers an internal state embedded in population activity across multiple brain Areas and sheds further light on how internal states contribute to the decision-making process.
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What does scalp electroencephalogram coherence tell us about long-range cortical networks?
European Journal of Neuroscience, 2018Co-Authors: Adam C. Snyder, Deepa Issar, Matthew A. SmithAbstract:Long-range interactions between cortical Areas are undoubtedly a key to the computational power of the brain. For healthy human subjects, the premier method for measuring brain activity on fast timescales is electroencephalography (EEG), and coherence between EEG signals is often used to assay functional connectivity between different brain regions. However, the nature of the underlying brain activity that is reflected in EEG coherence is currently the realm of speculation, because seldom have EEG signals been recorded simultaneously with intracranial recordings near cell bodies in multiple brain Areas. Here, we take the early steps towards narrowing this gap in our understanding of EEG coherence by measuring local field potentials with microelectrode arrays in two brain Areas (extrastriate Visual Area V4 and dorsolateral prefrontal cortex) simultaneously with EEG at the nearby scalp in rhesus macaque monkeys. Although we found inter-Area coherence at both scales of measurement, we did not find that scalp-level coherence was reliably related to coherence between brain Areas measured intracranially on a trial-to-trial basis, despite that scalp-level EEG was related to other important features of neural oscillations, such as trial-to-trial variability in overall amplitudes. This suggests that caution must be exercised when interpreting EEG coherence effects, and new theories devised about what aspects of neural activity long-range coherence in the EEG reflects.
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Stimulus-dependent spiking relationships with the EEG
Journal of Neurophysiology, 2015Co-Authors: Adam C. Snyder, Matthew A. SmithAbstract:The development and refinement of noninvasive techniques for imaging neural activity is of paramount importance for human neuroscience. Currently, the most accessible and popular technique is electroencephalography (EEG). However, nearly all of what we know about the neural events that underlie EEG signals is based on inference, because of the dearth of studies that have simultaneously paired EEG recordings with direct recordings of single neurons. From the perspective of electrophysiologists there is growing interest in understanding how spiking activity coordinates with large-scale cortical networks. Evidence from recordings at both scales highlights that sensory neurons operate in very distinct states during spontaneous and Visually evoked activity, which appear to form extremes in a continuum of coordination in neural networks. We hypothesized that individual neurons have idiosyncratic relationships to large-scale network activity indexed by EEG signals, owing to the neurons' distinct computational roles within the local circuitry. We tested this by recording neuronal populations in Visual Area V4 of rhesus macaques while we simultaneously recorded EEG. We found substantial heterogeneity in the timing and strength of spike-EEG relationships and that these relationships became more diverse during Visual stimulation compared with the spontaneous state. The Visual stimulus apparently shifts V4 neurons from a state in which they are relatively uniformly embedded in large-scale network activity to a state in which their distinct roles within the local population are more prominent, suggesting that the specific way in which individual neurons relate to EEG signals may hold clues regarding their computational roles.
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Spatial and Temporal Scales of Neuronal Correlation in Visual Area V4
Journal of Neuroscience, 2013Co-Authors: Matthew A. Smith, Marc A. SommerAbstract: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.
