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.     

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.     

Temporal course of disinhibition of the visual cortex neurons and their sensitivity to cross-like figures

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

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.     

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.     

Disinhibitory zone of the striate neuron receptive field and its sensitivity to the cross-like shape]

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.     

Dynamics of tuning to orientation of cross-like figures in neurons from the cat visual cortex

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.