Kagan, Igor

[["dc.bibliographiccitation.firstpage","125"],["dc.bibliographiccitation.issue","7"],["dc.bibliographiccitation.journal","Journal of Vision"],["dc.bibliographiccitation.lastpage","125a"],["dc.bibliographiccitation.volume","2"],["dc.contributor.author","Max, D."],["dc.contributor.author","Kagan, Igor"],["dc.contributor.author","Gur, Moshe"],["dc.date.accessioned","2018-02-08T10:53:58Z"],["dc.date.available","2018-02-08T10:53:58Z"],["dc.date.issued","2010"],["dc.description.abstract","Although it has long been routine to classify neurons in V1 of anesthetized animals into simple and complex categories, it has not been easy to apply the original criteria to alert animals because of the omnipresent eye movements. In our experiments, effects of eye movements were minimized by compensating for them and by data processing. Activating regions (ARs) of 228 cells in parafoveal V1 of alert monkeys were mapped with increment and decrement moving and flashing bars. Most cells had two ARs, one responsive to increments (INC) and one responsive to decrements (DEC). The majority of the cells (78%, “duplex”) had completely or partially overlapping INC and DEC ARs. Simple cells with minimal spatial overlap of INC and DEC ARs comprised 14% of our sample. 114 neurons were also studied with drifting gratings of varied spatial frequencies and window widths. Responses to the stimulus condition generating the maximal harmonic (F0 or F1) and the one generating the maximal relative modulation, RM (F1/F0), were analyzed. Most duplex cells responded with considerable modulation at the stimulus temporal frequency in both the maximal harmonic condition (mean RM 0.60±0.41 to 0.92±0.45) and the maximal RM condition (RM = 0.79±0.43 to 1.12±0.46), with the range dependent on the method of correcting for eye movements. A subset of duplex cells had RM>1, the traditional criterion for identifying simple cells, even though variations in stimulus conditions evoked clearly nonlinear behavior. There was little or no correlation between the degree of overlap of INC and DEC ARs and the value of RM, indicating that neither linearity nor the spatial organization of receptive fields can be predicted reliably from RM values. Our results suggest that nonlinear duplex cells represent the largest neuronal class in primate V1, whereas the linear simple cells are less numerous, more homogeneous, and probably preferentially associated with the magnocellular pathway. Support: NIH R01 EY12243, Technion VPR Funds 130347; 130358."],["dc.identifier.doi","10.1167/2.7.125"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/12059"],["dc.language.iso","en"],["dc.notes.status","zu prüfen"],["dc.relation.eissn","1534-7362"],["dc.title","Receptive fields and quasi-linear response modulation in V1 of alert macaques"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","21"],["dc.bibliographiccitation.issue","9"],["dc.bibliographiccitation.journal","Journal of Vision"],["dc.bibliographiccitation.lastpage","21a"],["dc.bibliographiccitation.volume","3"],["dc.contributor.author","Gur, Moshe"],["dc.contributor.author","Kagan, Igor"],["dc.contributor.author","Eye, Schepens"],["dc.contributor.author","Snodderly, Max D."],["dc.date.accessioned","2018-02-08T11:07:35Z"],["dc.date.available","2018-02-08T11:07:35Z"],["dc.date.issued","2010"],["dc.description.abstract","Area V1 is known for its neural cell density and intricate histology. Physiological recordings, however, often are not integrated into this complex anatomy. We have previously shown, in alert monkeys, that physiological properties of single cells reflect an alternating arrangement of anatomical layers. Here we report how orientation selectivity is related to the cortical layers and to the cell properties of spontaneous activity, classical receptive field (CRF) size, and spatial organization. Recordings were made from single cells in area V1 of alert monkeys performing a fixation task. The cells' spatial organization was studied with drifting increment and decrement bars while compensating for fixational drift. Orientation selectivity was measured by the orientation tuning curve bandwidth and by circular variance. Orientation selectivity by either measure was clearly correlated with CRF size and spontaneous activity but not with overlap of increment and decrement zones (Simple/Complex) or with relative modulation in response to sinusoidal gratings. The former 3 measures were strongly predicted by the layer of origin such that small CRFs, low spontaneous activity, and a high degree of orientation selectivity were found in the output layers 2/3, 4B and 5 while the reverse was true for the input layers 4A, 4C and 6. We conclude that the conjunction of these physiological measures with their anatomical locations reflect interactions between excitatory and inhibitory mechanisms specific to each lamina. When excitation is stronger than inhibition, large CRFs, high spontaneous activity and a low degree of orientation tuning are found. When inhibition becomes dominant, CRFs shrink, spontaneous activity almost disappears and orientation selectivity is high."],["dc.identifier.doi","10.1167/3.9.21"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/12060"],["dc.language.iso","en"],["dc.notes.status","zu prüfen"],["dc.relation.eissn","1534-7362"],["dc.title","Orientation selectivity in V1 of alert monkeys"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.journal","Neuroscience Letters"],["dc.contributor.author","Kagan, Igor"],["dc.contributor.author","Gur, Moshe"],["dc.contributor.author","Snodderly, D.M."],["dc.date.accessioned","2018-02-08T13:22:27Z"],["dc.date.available","2018-02-08T13:22:27Z"],["dc.date.issued","1999"],["dc.description.abstract","In alert monkeys, as in humans, small eye movements- tremor, drift and small saccades- occur during fixation periods. These movements constantly shift retinal image, thusmodifying the stimulus-generated responses. We analyzed the effects of eye movementson responses of simple and duplex (“complex-like”) cells to drifting sinusoidal gratings.Eye positions were recorded from monkeys trained to perform a fixation task. Duringfixation extracellular responses of V1 neurons in parafoveal region and eye positionswere recorded. From the eye position records we identified epochs of fast movements,slow drifts and stable fixation and compared patterns of neuronal firing during thevarious eye movement phases. Neuronal responses were sensitive to both fast and sloweye movements that occurred during grating presentations. In the case when no periodsof eye movements were excluded from the records, averaging across many repetitionsof the grating temporal cycle resulted in smearing of the response time course, althougheach individual sweep produced a modulated response. Eye movements affect neuronalresponses in a way that depends on eye movement trajectory, stimulus parameters andreceptive field properties. In particular, eye movements caused shifts in response phaseand/or duration, produced spurious firing bursts or caused cells to miss a response. Ourresults suggest that fixational eye movements account for variations in neuronalresponses over successive grating presentations and that these movements should beconsidered in analysis of grating-evoked activity"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/12067"],["dc.language.iso","en"],["dc.notes.status","zu prüfen"],["dc.title","The influence of fixational eye movements on grating-elicited responses of V1 neurons"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","259"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Visual Neuroscience"],["dc.bibliographiccitation.lastpage","277"],["dc.bibliographiccitation.volume","18"],["dc.contributor.author","Snodderly, D. M."],["dc.contributor.author","Kagan, Igor"],["dc.contributor.author","Gur, Moshe"],["dc.date.accessioned","2017-09-07T11:47:57Z"],["dc.date.available","2017-09-07T11:47:57Z"],["dc.date.issued","2002"],["dc.description.abstract","During normal vision, when subjects attempt to fix their gaze on a small stimulus feature, small fixational eye movements persist. We have recorded the impulse activity of single neurons in primary visual cortex (V1) of macaque monkeys while their fixational eye movements moved the receptive-field activating region (AR) over and around a stationary stimulus. Three types of eye movement activation were found. (1) Saccade cells discharged when a fixational saccade moved the AR onto the stimulus, off the stimulus, or across the stimulus. (2) Position/drift cells discharged during the intersaccadic (drift) intervals and were not activated by saccades that swept the AR across the stimulus without remaining on it. To activate these neurons, it was essential that the AR be placed on the stimulus and many of these cells were selective for the sign of contrast. They had smaller ARs than the other cell types. (3) Mixed cells fired bursts of activity immediately following saccades and continued to fire at a lower rate during intersaccadic intervals. The tendency of each neuron to fire transient bursts or sustained trains of impulses following saccades was strongly correlated with the transiency of its response to stationary flashed stimuli. For one monkey, an extraretinal influence accompanying fixational saccades was identified. During natural viewing, the different eye movement classes probably make different contributions to visual processing. Position/drift neurons are well suited for coding spatial details of the visual scene because of their small AR size and their selectivity for sign of contrast and retinal position. However, saccade neurons transmit information that is ambiguous with respect to the spatial details of the retinal image because they are activated whether the AR lands on a stimulus contour, or the AR leaves or crosses the contour and lands in another location. Saccade neurons may be involved in constructing a stable world in spite of incessant retinal image motion, as well as in suppressing potentially confusing input associated with saccades."],["dc.identifier.doi","10.1017/s0952523801182118"],["dc.identifier.gro","3150760"],["dc.identifier.pmid","11417801"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/7550"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.relation.issn","0952-5238"],["dc.subject","Fixational eye movements; Neural coding; Macaca; V1; Receptive fields"],["dc.title","Selective activation of visual cortex neurons by fixational eye movements: Implications for neural coding"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dc.type.peerReviewed","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.journal","Journal of Vision"],["dc.contributor.author","Snodderly, D. M."],["dc.contributor.author","Kagan, Igor"],["dc.contributor.author","Gur, Moshe"],["dc.date.accessioned","2017-11-13T15:00:18Z"],["dc.date.available","2017-11-13T15:00:18Z"],["dc.date.issued","2010"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/9946"],["dc.language.iso","en"],["dc.notes.status","new -primates"],["dc.title","Linearity and selectivity of neuronal responses in awake visual cortex. Importance of the cell sample"],["dc.title.subtitle","Reply to: The linearity and selectivity of neuronal responses in awake visual cortex, Chen et al. (2009)"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","S20"],["dc.bibliographiccitation.issue","Sup. 1"],["dc.bibliographiccitation.journal","Neuroscience Letters"],["dc.bibliographiccitation.lastpage","S21"],["dc.bibliographiccitation.volume","258"],["dc.contributor.author","Kagan, Igor"],["dc.contributor.author","Gur, Moshe"],["dc.contributor.author","Snodderly, Donald Max"],["dc.date.accessioned","2018-02-08T13:02:21Z"],["dc.date.available","2018-02-08T13:02:21Z"],["dc.date.issued","1998"],["dc.description.abstract","Much theorizing on functional processing in primary visual cortex is based on simple cells, the major cell type found in anesthetized and paralyzed cats. The role usually ascribed to complex cells is to generalize over position and contrast polarity and perform accessory functions such as gain control, normalization, and cross-orientation inhibition. We report that in primate cortex the major cell type is not simple cell but rather a type we call “duplex”. Extracellular responses of V1 neurons in parafoveal region of monkeys performing a fixation task were recorded. Activation regions (AR) were mapped with increment and decrement drifting bars and flashes. The AR widths of duplex cells were quite restricted in space and most cells had completely or partially overlapping increment and decrement ARs. However, Fourier analysis of responses to drifting gratings often revealed a significant modulation at the stimulus temporal frequency. These cells are similar to complex cells in having overlapping increments and decrements fields while, like simple cells, able to encode information about the stimulus temporal modulation, rather than just signaling its presence by the unmodulated elevation of their firing rate. The dependency of the relative strength of the response DC component and other harmonics on various stimulation parameters implies a combination of linear and non-linear properties which may derive from interplay of inputs from “increment” and “decrement” subunits, suppressive interactions between them, and an inhibitory surround. The cells\\’ relatively small ARs allow precise localization of a stimulus in space. We suggest that these cells represent the basic functional unit in the primate visual cortex"],["dc.identifier.doi","10.1016/S0304-3940(98)00843-X"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/12066"],["dc.language.iso","en"],["dc.notes.status","zu prüfen"],["dc.relation.issn","0304-3940"],["dc.title","\"Duplex\", not simple, cells are the major cell type in striate cortex of alert monkeys"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.issue","14"],["dc.bibliographiccitation.journal","Journal of Vision"],["dc.bibliographiccitation.volume","8"],["dc.contributor.author","Kagan, Igor"],["dc.contributor.author","Gur, Moshe"],["dc.contributor.author","Snodderly, D. M."],["dc.date.accessioned","2017-09-07T11:47:54Z"],["dc.date.available","2017-09-07T11:47:54Z"],["dc.date.issued","2009"],["dc.description.abstract","In natural vision, continuously changing input is generated by fast saccadic eye movements and slow drifts. We analyzed effects of fixational saccades, voluntary saccades, and drifts on the activity of macaque V1 neurons. Effects of fixational saccades and small voluntary saccades were equivalent. In the presence of a near-optimal stimulus, separate populations of neurons fired transient bursts after saccades, sustained discharges during drifts, or both. Strength, time course, and selectivity of activation by fast and slow eye movements were strongly correlated with responses to flashed or to externally moved stimuli. These neuronal properties support complementary functions for post-saccadic bursts and drift responses. Local post-saccadic bursts signal rapid motion or abrupt change of potentially salient stimuli within the receptive field; widespread synchronized bursts signal occurrence of a saccade. Sustained firing during drifts conveys more specific information about location and contrast of small spatial features that contribute to perception of fine detail. In addition to stimulus-driven responses, biphasic extraretinal modulation accompanying saccades was identified in one third of the cells. Brief perisaccadic suppression was followed by stronger and longer-lasting enhancement that could bias perception in favor of saccade targets. These diverse patterns of neuronal activation underlie the dynamic encoding of our visual world."],["dc.identifier.doi","10.1167/8.14.19"],["dc.identifier.gro","3150748"],["dc.identifier.pmid","19146320"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/7538"],["dc.language.iso","en"],["dc.notes.status","public"],["dc.relation.issn","1534-7362"],["dc.title","Saccades and drifts differentially modulate neuronal activity in V1: Effects of retinal image motion, position, and extraretinal influences"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dc.type.peerReviewed","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1207"],["dc.bibliographiccitation.issue","8"],["dc.bibliographiccitation.journal","Cerebral Cortex"],["dc.bibliographiccitation.lastpage","1221"],["dc.bibliographiccitation.volume","15"],["dc.contributor.author","Gur, Moshe"],["dc.contributor.author","Kagan, Igor"],["dc.contributor.author","Snodderly, D. Max"],["dc.date.accessioned","2017-09-07T11:47:53Z"],["dc.date.available","2017-09-07T11:47:53Z"],["dc.date.issued","2005"],["dc.description.abstract","We studied orientation selectivity in V1 of alert monkeys and its relationship to other physiological parameters and to anatomical organization. Single neurons were stimulated with drifting bars or with sinusoidal gratings while compensating for eye position. Orientation selectivity based on spike counts was quantified by circular variance and by the bandwidth of the orientation tuning curve. The circular variance distribution was bimodal, suggesting groups with low and with high selectivity. Orientation selectivity was clearly correlated with spontaneous activity, classical receptive field (CRF) size and the strength of surround suppression. Laminar distributions of neuronal properties were distinct. Neurons in the output layers 2/3, 4B and 5 had low spontaneous activity, small CRFs and high orientation selectivity, while the input layers had greater diversity. Direction-selective cells were among the neurons most selective for orientation and most had small CRFs. A narrow band of direction- and orientation-selective cells with small CRFs was located in the middle of layer 4C, indicating appearance of very selective cells at an early stage of cortical processing. We suggest that these results reflect interactions between excitatory and inhibitory mechanisms specific to each sublamina. Regions with less inhibition have higher spontaneous activity, larger CRFs and broader orientation tuning. Where inhibition is stronger, spontaneous activity almost disappears, CRFs shrink, and orientation selectivity is high."],["dc.identifier.doi","10.1093/cercor/bhi003"],["dc.identifier.gro","3150756"],["dc.identifier.pmid","15616136"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/7547"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.relation.issn","1047-3211"],["dc.title","Orientation and Direction Selectivity of Neurons in V1 of Alert Monkeys: Functional Relationships and Laminar Distributions"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dc.type.peerReviewed","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","2557"],["dc.bibliographiccitation.issue","5"],["dc.bibliographiccitation.journal","Journal of Neurophysiology"],["dc.bibliographiccitation.lastpage","2574"],["dc.bibliographiccitation.volume","88"],["dc.contributor.author","Kagan, Igor"],["dc.contributor.author","Gur, Moshe"],["dc.contributor.author","Snodderly, D. M."],["dc.date.accessioned","2017-09-07T11:47:54Z"],["dc.date.available","2017-09-07T11:47:54Z"],["dc.date.issued","2006"],["dc.description.abstract","We studied the spatial organization of receptive fields and the responses to gratings of neurons in parafoveal V1 of alert monkeys. Activating regions (ARs) of 228 cells were mapped with increment and decrement bars while compensating for fixational eye movements. For cells with two or more ARs, the overlap between ARs responsive to increments (INC) and ARs responsive to decrements (DEC) was characterized by a quantitative overlap index (OI). The distribution of overlap indices was bimodal. The larger group (78% of cells) was composed of complex cells with strongly overlapping ARs (OI >/= 0.5). The smaller group (14%) was composed of simple cells with minimal spatial overlap of ARs (OI 1, the traditional criterion for identifying simple cells. However, unlike simple cells, even those complex cells with high RM could exhibit diverse nonlinear responses when the spatial frequency or window size was changed. Furthermore, the responses of complex cells to counterphase gratings were predominantly nonlinear even harmonics. These results show that RM is not a robust test of linearity. Our results indicate that complex cells are the most frequently encountered neurons in primate V1, and their behavior needs to receive more emphasis in models of visual function."],["dc.identifier.doi","10.1152/jn.00858.2001"],["dc.identifier.gro","3150757"],["dc.identifier.pmid","12424294"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/7548"],["dc.language.iso","en"],["dc.notes.status","public"],["dc.relation.issn","0022-3077"],["dc.title","Spatial Organization of Receptive Fields of V1 Neurons of Alert Monkeys: Comparison With Responses to Gratings"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dc.type.peerReviewed","yes"],["dspace.entity.type","Publication"]]

[["dc.contributor.author","Kagan, Igor"],["dc.contributor.author","Gur, Moshe"],["dc.contributor.author","Snodderly, D.M."],["dc.date.accessioned","2018-02-08T13:30:36Z"],["dc.date.available","2018-02-08T13:30:36Z"],["dc.date.issued","2004"],["dc.description.abstract","Cortical complex cells are usually described as nonlinear energy operators that sum squared outputs of quadrature pairs of linear subunits, responding to drifting sinusoidal gratings with unmodulated elevation of flring rate (F0 harmonic). However, several lines of evidence suggest that the view of complex cells as a uniform class is over-simplifled, since energy models do not capture many complex cell behaviors. In alert monkeys complex cells with strongly overlapping increment and decrement regions exhibit a considerable F1 modulation, and a subset of these cells have a relative modulation (RM=F1/F0) >1. We have also found that most complex cells show profound dependence of the response form (harmonic content), and not only the amplitude, on grating parameters such as spatial and temporal frequency and size, displaying a variety of behaviors ranging from nonlinear unmodulated flring (F0) and frequency doubling (F2) to pseudolinear modulation (F1). One of the parsimonious explanations could be that at least some of these behaviors, e.g. F1 modulation, result from the imbalance of increment and decrement mechanisms such as incomplete spatial overlap and/or difierence in amplitudes of the two regions. We tested this hypothesis using a model that approximates an apparent structure of complex receptive flelds in our data by pooling two linear (increment and decrement) inputs with Gaussian spatial proflle and same biphasic temporal response function. Model cells with various overlaps and amplitude ratios were stimulated with drifting gratings of difierent spatial frequencies. To quantify the measure of spatial (im)balance we computed a product of overlap index and amplitude ratio. In the model, maximal modulation increased with spatial imbalance, and the correlation for the two measures was high (r=-0.86, p0.01) was inconsistent with model predictions. Thus, a static spatial imbalance of increment and decrement mechanisms cannot fully predict the presence of strong F1 harmonic in responses of complex cells. These results and efiects of temporal frequency suggest that temporal properties of input channels and possibly the dynamics of interaction between them play an important role in shaping the responses of complex cells. To account for the response diversity exhibited by complex cells, we are developing more realistic models that also include in∞uences of the surround."],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/12068"],["dc.language.iso","en"],["dc.notes.preprint","yes"],["dc.notes.status","zu prüfen"],["dc.relation.conference","Computational and Systems Neuroscience (COSYNE) 2004"],["dc.relation.eventend","28.03.2004"],["dc.relation.eventlocation","Manhattan"],["dc.relation.eventstart","24.03.2004"],["dc.relation.iserratumof","yes"],["dc.title","Modeling V1 complex cells in alert monkeys"],["dc.type","conference_paper"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]