[Comparison of its and orientation tuning dynamics in neurons located in different functional domains of cat's primary visual cortex].

Orientation tuning and its dynamics of cat's primary visual cortex neurons located in pinwheel centers and orientation columns were studied during development of response in time. Functional domains in the Cortex were revealed by intrinsic signal optical imaging on functional and vascular maps of cortex. Both maps were used for precise placement of electrodes during recordings. Orientation tuning dynamic of each neuron was analyzed by temporary slices technique. Several types of neurons were observed in different functional domains: neurons with stable preferred orientation (14.5%); cells with preferred orientation dynamically shifted by 102 +/- 5 degrees (40.8%) and neurons with mixed dynamics type (44.7%). In pinwheel centers neurons with stable preferred orientation are differed from neurons with unstable preferred orientation in their features. In particular, they are showing greater response strength for preferred orientation. In orientation columns neurons with stable tuning are demonstrating larger latent periods for all orientations including preferred and non-preferred in comparison to cells with unstable response dynamics. We observed better detection quality of stable orientation neurons than in unstable preferred orientation neurons. Further coding features of neurons belonging to one functional type but located in different domains were compared. In general, located in pinwheel centers stable neurons have shorter latencies and stronger responses than for the stable cells located in orientation columns. Detection features were similar for this functional type of neurons. Unstable neurons located in different functional domains don't differ from each other in orientation tuning characteristics. Functional significance of neurons with stable and unstable preferred orientation located in pinwheel center and orientation columns in visual information processing are discussed.

[Alpha- and beta-oscillations of dynamics of the area and weight of receptive fields of cat striate neurons under conditions of classical and combined mapping].

In 22 acute experiments in anesthetized and immobilized adult cats the dynamics of 83 receptive fields (RF) of 47 striate neurons was studied by temporal slices method. Classical mapping revealed wave-like changes in the area and weight of neuronal RFs. Special mathematical analysis showed that such changes represented a sum of a slow non-oscillatory and comparatively fast components. The slow component was a biphasic up and down RF dynamics. In most cases, the oscillation frequencies were within the alpha- and beta- EEG frequency ranges. When the RF center was activated additionally during combined mapping, the oscillations frequencies remained unchanged, but the duration and amplitude of non-oscillatory component substantially decreased. Mechanisms underlying the RF dynamics and its functional significance are discussed.

[Receptive fields of cat striate neurons: dynamics of weight and topographical characteristics of the excitatory zone of the neuron receptive fields in the visual cortex].

In 22 acute experiments on anesthetized and immobilized adult cats, the dynamics of 83 on- and/or off-receptive fields (RF) was studied in 47 striate neurons with the method of temporal slices by mapping with single-flash stimuli. The latency of the RF appearance was 88 +/- 5 ms, and its duration was 192 +/- 12 ms. Dynamical wavy changes in the RF sizes and weights repeating up to three times were revealed. The mean duration of one wave was 95 +/- 4 ms. In 99% of cases, the RF discharge center defined for one temporal slice also displaced in an undulatory way relatively the RF's center defined for whole analysis period. The mean duration of this undulatory cycle was 67.3 +/- 3 ms. In 72.5% of cases, the displacement of the discharge center followed different trajectories inscribed in an ellipse. The functional significance of such changes in the RFs of striate neurons is discussed with regard to the dynamics of their detector features and underlying mechanisms.

[Receptive fields of detectors of bar and cross-like figures in classical and combined mapping].

Excitatory and inhibitory zones of receptive fields (RF) of detectors of cross-like figures and bars were studied in a primary visual cortex of cats under conditions of classical and combined mapping. Factor and correlation analysis demonstrated that detectors of bars and crosses differ in those interrelations, which are formed between the basic characteristics of neurons and their RF in each of group. The factor analysis of these connections showed that variables with the greatest weights, combined into the same factor, are different for different detectors. In detectors of bars, positive correlation was found between the background activity and weight characteristics of the RF excitatory and inhibitory zones. In detectors of crosses, inhibition indices showed a positive correlation with sensitivity to this figure, characteristics of excitatory RF zone and the background activity. Enlargement of the additional excitatory zones of cross detectors in combined mapping was significantly greater than in bar detectors. Formation of the RF and orientation sensitivity of bar and cross detectors is discussed, with account made of the finding that the sensitivity to bars is mostly formed by direct excitatory connections, whereas sensitivity to cross-like stimuli is formed by direct and recurrent intracortical inhibitory connections between the nearby neurons.

[Striate receptive fields mapped with single and bipartite stimuli].

In 22 acute experiments with anesthetized and immobilized adult cats, 364 maps of receptive fields (RF) of 47 striate neurons were obtained by means of single local stimuli flashed at different parts of the visual field, or with additional asynchronous activation of the RF excitatory center with oscillating bar of the optimal orientation. Under bipartite stimulation, considerable and significant decrease in the square and weight of the central excitatory RF zone was revealed in more then 75% of the studied cells. Additional excitatory zones appeared in 54% of cases, or the square and weight of the excitatory zones substantially increased, and inhibitory zones developed in 90% of cases. These effects were correlated with the degree of increase in the background firing during transition from the mode of mapping with single stimulation to that with bipartite stimulation. The mechanism and possible functional role of cooperative excitatory and inhibitory intracortical interactions in organization of receptive fields and detection of features of a visual image are discussed.

Neurophysiological and simulation studies of striate cortex receptive field maps: the role of intracortical interneuronal interactions.

Acute experiments on 27 adult anesthetized and immobilized cats investigated 101 on and off receptive fields in 67 neurons in visual cortex field 17 by mapping using single local stimuli presented sequentially at different parts of the visual field, as well as in combination with additional stimulation of the center of the receptive field. Both classical and combined mapping identified receptive fields with single receptive zones (63.4% and 29.3% respectively), along with fields consisting of several (2-5) excitatory and/or inhibitory zones (36.6% and 70.7%). We provide the first report of receptive fields with horseshoe, cross, and T shapes. Simulations of horizontal interneuronal interactions in the visual cortex responsible for the multiplicity of excitatory and inhibitory zones of receptive fields were performed. A role for cooperative interactions of neurons in this effect was demonstrated. The possible functional role of receptive fields of different types in extracting the features of visual images is discussed.

[Neurophysiological and simulation study of the striate receptive fields maps: the role of intracortical interaction].

In 27 acute experiments with anesthetized and immobilized adult cats 101 maps of receptive field (RF) in 67 striate neurons were studied by means of mapping with single flashed stimuli presented in different parts of the visual field and under conditions of additional activation of the RF excitatory center by the local oscillating or flashing grid. Under conditions of both classical and combined modes of mapping, the RFs of the classical shape with a single excitatory zone (63.4 and 29.3% of cases, respectively) and RFs with multiple (2-5) excitatory and/or inhibitory zones (36.6 and 70.7%, respectively) were found. We were the first to describe, also, some RFs of horseshoe-like, cross-like and T-like shapes. Simulation of non-classical RFs revealed possible contributions of cooperative excitatory and inhibitory intracortical interactions to the effects under study. The functional role of RFs of different types in the feature detection is discussed.

The time course of disinhibition of visual cortex neurons and sensitivity to cross-shaped figures.

The relationship between the responses of 74 neurons in field 17 of the cat cortex to presentation of cross-shaped figures flashing in their receptive fields and the asynchronicity with which the lines of the figures were presented were investigated. The cross sensitivity of neurons was studied with simultaneous, leading, and delayed activation of the disinhibitory zone of the receptive field in relation to the time at which its major excitatory and end-stopping inhibitory zones were stimulated. Two types of temporal interaction were identified between the receptive field zones determining cross sensitivity. In cells of the first type (14 of 23 cells), the response was maximal in conditions of simultaneous stimulation of the major and disinhibitory zones of the receptive field; neurons of the second type (nine of 23 cells) showed the opposite temporal relationship. Digital simulation showed that cross sensitivity in neurons of the first type was supported by disinhibition of end-stopping inhibition, while in neurons of the second type it depended on a combination of disinhibitory and convergence mechanisms.

Dynamic changes in the tuning of striate neurons to the shapes of cross-shaped figures.

Time slice analysis was used to study the dynamics of tuning to the shapes of cross-shaped figures flashing in the receptive fields of 83 neurons in the primary visual cortex (field 17) of the cat brain. Tuning was assessed in terms of the numbers of spikes in the overall response and its sequential 20-msec fragments. Only 11.7% of neurons produced reproducibly developing spike responses to a given shape (defined as the angle between the lines), i.e., had a preferred cross-shaped figure. In the remaining cases (88.3%), tuning of neurons to the shape of the cross showed dynamic changes. In 7.2% of cases, changes in the preferred shape of the cross occurred monophasically; changes were biphasic in 27.0% of cases, while in the remaining 54.1% of cases, the dynamics in changes in the preferred cross shape were undulatory. The tuning of receptive field zones is assessed as the cause of these effects and their difference from the previously observed dynamics of preferred orientations of single bars and cross-shaped figures; the functional significance of these effects is also discussed.

[Temporal course of disinhibition of the visual cortex neurons and their sensitivity to cross-like figures]. / Vremennoi khod rastormazhivaniia neirona zritel'noi kory i ego chuvstvitel'nost' k krestoobraznoi figure.

In acute experiments with narcotized and paralyzed cats, we studied responses of 74 striate neurons to cross-like figure under synchronous and asynchronous presentation of its lines. The aim of the study was to characterize the temporal course of interaction between three RF zones: main excitatory, end-inhibitory, and side disinhibitory ones. Previously we have found that this interaction is responsible for sensitivity to a cross in near 3/4 of cat striate cells with such sensitivity. In neurons with sensitivity to a cross, we found two types of temporal interaction between zones of RF. In the 1st type cells (14/23), the response significantly increased if the disinhibitory and the main excitatory zones of RF were stimulated simultaneously. Neurons of the 2nd type (9/23) revealed opposite temporal function: synchronous activation of RF zones evoked a minimal response. Simulation shows that the 1st type of behavior is connected with disinhibitory mechanism, while that of the 2nd type--with combination of this mechanism with convergence of orientation detectors of the previous functional level.

[Dynamics of tuning to the shape of a cross-like figure in striate neurons]. / Dinamicheskoe izmenenie nastroiki striarnykh neironov na formu krestoobraznoi figury.

Dynamics of tuning to the shape of cross-like figure flashed in receptive field was studied in 83 striate neurons by the method of temporal slices. Tuning was estimated by the total number of spikes in the response and by this number in successive fragments of the response with 20 ms steps. It was found that only in 11.7% cases neurons showed stable tuning to the same shape of the preferred figure (an angle between its lines), in other cases (88.3%) during response generation this tuning changes being one-phase (7.2%) or two-phase (27.0%), or undulatory (54.1%). Different dynamical reorganization of receptive field zones is discussed as a possible mechanism of the revealed effects as well as their correlation with previously described dynamics of tuning to orientation of a single bar and a cross in striate cells.

[Dynamics of tuning to orientation of cross-like figures in neurons from the cat visual cortex]. / Dinamika nastroiki neironov pervichnoi zritel'noi kory koshki na orientatsiiu krestoobraznykh figur.

Dynamics of tuning to orientation of flashing light bar and to orientation of cross-like figure was studied by a temporal slices method in 87 neurons of the cat primary visual cortex. Tuning was plotted by spikes number in the entire response and in its successive fragments with a step of 20 ms. It was found that successive dynamic shift of preferred orientation of a bar was typical for 87% units, white such shift of preferred orientation of a cross was met in 75% of cases. Comparison of tuning dynamics for bar and cross allowed to separate units into three groups: the first one (58.6% of cases) with larger dynamic shift of a bar preferred orientation then of a cross (74.9 +/- 5.8 degrees [symbol: see text] 29.8 +/- 4.1 degrees, correspondingly, p < 0.00001), the second group (21.5%) with opposite effect (24.2 +/- 5.2 degrees and 69.2 +/- 10.0 degrees, p < 0.0002) and the third group (19.8%) without significant shift of preferred orientation of bar and cross and without difference in their dynamics. Possible mechanisms of the preferred orientation dynamics and its difference for bar and cross are discussed.

The disinhibitory zone of the striate neuron receptive field and its sensitivity to cross-like figures.

Acute experiments on immobilized anesthetized cats were used to confirm the suggestion that the sensitivity of many neurons on the primary visual cortex to cross-shaped, angular, and Y-shaped figures may be determined by the presence within their receptive fields of disinhibitory zones, which block end-stopping inhibition. A total of 55 neurons (84 functions, i.e.. on and off responses) were used for studies of sensitivity to crosses, and responses to single bars of different lengths were compared before and after stimulation of an additional lateral zone of the field (the presumptive disinhibitory zone), which was located in terms of responses to crosses. Seventeen of the 55 cells in which increases in the length of a single bar decreased responses, i.e., which demonstrated end-stopping inhibition, showed significant increases in responses (by an average factor of 2.06 +/- 0.16) during simultaneous stimulation of the lateral zone of the receptive field, which we interpreted as a disinhibitory effect on end-stopping inhibition. These data provide the first direct evidence for the role of end-stopping inhibition and its blockade by the disinhibitory zone of the receptive field in determining the sensitivity of some neurons in the primary visual cortex of the cat to cross-shaped figures.

[Disinhibitory zone of the striate neuron receptive field and its sensitivity to the cross-like shape]. / Rastormazhivaiushchaia zona retseptivnogo polia striarnogo neirona i ego chuvstvitel'nost' k krestoobraznoi figure.

Sensitivity of 84 neurones to presentation of cross-form figures was studied in cats as well as the lever length function prior to and after stimulation of the RF disinhibitory zone. Responses to lever length of the cross-sensitive cells were augmented in simultaneous stimulation of the RF. The data obtained suggest involvement of the end inhibition and its blocking by a side-disinhibitory zone of the RF.

Tuning to Y-like figures in the cat striate neurons.

Sensitivity to symmetric or asymmetric Y-like figures and crosses of different shapes and orientations flashed in the receptive field was studied in 101 neurons of the cat striate cortex (area 17) and compared with their orientation tuning to a single light bar. Selective sensitivity to the Y-like figure (figure/bar response ratio more than 1.25) was found in 78/101 neurons (77.2% of cases) and to the cross-in 54/101 units (53.4%). In 62.5% of neurons with sensitivity to both figures, sensitivity to the Y-like figure was higher than to a cross. Tuning to Y-like figure was typically (60%) selective to both its shape and orientation. The remaining Y-like selective neurons exhibited invariant tuning to orientation and/or shape of the figure. The preferred angles between two lines of Y-like figures were distributed in the range of 22.5-157.5 degrees with slight preference to 90 degrees, while crosses of 45 degrees and 90 degrees angles were preferable. Response magnitudes to a single bar, a Y-like figure and a cross were positively correlated. Possible mechanisms and functional implication of the striate sensitivity to Y-like figures are discussed.

Interrelation of tuning characteristics to bar, cross and corner in striate neurons.

Characteristics of responses and background activity, as well as of tuning to a single bar orientation and to cross or corner shape and orientation have been compared in one third (561174) of neurons in the cat striate cortex. Shortening of the response latency to cross vs bar, to corner vs bar and to corner vs cross was revealed in most of the units studied. Direct correlation between the response and tuning characteristics for bar, cross and corner was revealed: units with better tuning to one type of stimulus were typically better tuned to the other types of stimuli. At the middle cortical depth (700-1200 microm from the surface) we found a reliable improvement of response magnitude and latency, cross/bar response ratio and selectivity of tuning in comparison with more superficial and deeper layers. Although we could not find a direct correlation between characteristics of tuning to figures and the type of the receptive field (simple, complex or hypercomplex), our data pointed to a lower cross/bar ratio and selectivity of tuning in the units with small receptive fields. The functional implication of neuronal sensitivity to cross and corner and possible meaning of correlation between their functional characteristics are discussed.

[The sensitivity of the cat visual cortex neurons to cruciform figures during stimulation of the central and peripheral receptive fields]. / Chuvstvitel'nost' neironov zritel'noi kory koshki k krestoobraznym figuram pri stimuliatsii tsentra i periferii retseptivnogo polia.

The role of the central and peripheral zones of the receptive field (RF) in sensitivity to cruciform figures was studied in 29 neurons of the cat primary visual cortex. Separated or combined stimulation of these zones revealed summation, reciprocity response interaction, or the absence of their interaction by the sensitivity index (ratio between response magnitudes to a cruciform figure and a bar). Stimulation of only central or only peripheral zone of the RF in nearly equal number of cases increased or decreased the sensitivity index in comparison with full cruciform figure. The neurons were found which did not change their sensitivity to cruciform figure under conditions of its partial masking. Mechanisms and functional significance of the interaction between the central and peripheral zones of RF for selection of line crossing in the striate cortex are discussed.

Selective and invariant sensitivity to crosses and corners in cat striate neurons.

Many neurons (56/174, or 32.2%) studied in the cat striate cortex (area 17) increased significantly (by 3.3 times on average) their responses under stimulation by cruciform or corner figures of specific or non-specific shape and orientation flashing in receptive field as compared with single light bar of preferred orientation. Most of these neurons (71.4%) were found to be highly selective to both the shape (the angle between the figure's lines) and orientation of these figures. In the neuronal selection studied we have also found all possible types of invariance of the cross and corner tuning to orientation and/or shape of these figures. We found neurons with selectivity to the form of the figures and invariance to their orientation and, on the contrary, units invariant to shape but selective to orientation. Some cells were found invariant to both the form and orientation of the cruciform or corner figure but highly sensitive to appearance of any such figure in the receptive field. Two main hypotheses about the mechanisms of selective sensitivity to crosses and angles can be considered. They are as follows: an excitatory convergence of two units with different preferred orientations, and intracortical inhibitory interactions. The cells with double orientation tuning for a single bar are found relatively rarely (about 20%), thus making the first suggestion the most unlikely. This circumstance is of special importance since it provides evidence against the hierarchic formation of the higher-order cortical units from a set of lower-order cells that is still under discussion. The units with high sensitivity to cross or corner seem to be ideally suitable for their selection, rather than to serve as classical orientation detectors only.

Sensitivity to cross-like figures in the cat striate neurons.

The responses and orientation tuning in 48 out of 62 (77.4%) neurons of the cat striate cortex (area 17) significantly, but with different sign, changed at stimulation by specific cross-like figure flashing in receptive field as compared with single light bar of preferred orientation. Neurons of the first group (19 units from 62, 30.6%) were found to increase the responses by 3.3 times if stimulated by a certain cross-like figure, specific for each cell configuration and orientation. Under the same conditions, neurons of the second group (29 or 46.8% revealed a three-fold decrease of responses and all tuning characteristics worsened. Among them 8% of total number of cells showed bimodal or double orientation tuning when stimulated by some configurations of crosses due to an angle specific inhibition. Dependence of the revealed effects on excitatory convergence from neurons with different orientation tuning, on inhibitory influences from end-stop and side-zones of receptive field, as well as possible functional implication of the first group neurons for an angle and line-crossing detection are discussed.

Dynamics of orientation tuning in the cat striate cortex neurons.

Dynamics of orientation tuning was studied by a flashing light bar in 233 single units of cat primary visual cortex. Orientation tuning was plotted by the criterion of spike number in successive fragments of responses with a step of 10 or 20 ms. Preferred orientation and the width of orientation tuning were measured for each of such curves. It was found that successive dynamic change of preferred orientation during response was typical for 63% of units under study, while such change of orientation tuning width was typical for 93%. Neurons with or without shift in preferred orientation differed in their response characteristics: latency and duration of discharge, its frequency and response rise time, as well as quality of orientation tuning. Possible functional significance of two groups of cortical units, "scanners" (with systematic preferred orientation shift) and "timers" (without it), is discussed in accordance with the idea of spatiotemporal orientation coding in the primary visual cortex.