Neuronal activity and attention in the primary visual cortex

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To study mechanisms for an integration of stimulus information distributing wide area in the visual field, we examined modulatory effects of visual responses of neurons by grating stimuli presented outside of receptive field in the primary visual cortex of anesthetized cats. Responses to the optimally oriented grating patch in the receptive field were suppressed by surrounding stimulus particularly in complex cells of the superficial layer. Effectiveness of surrounding stimulus was dependent on relationship between the cell's preferred spatial frequency (SF) and the SF of surrounding grating. Among the 21 cells which exhibited significant suppression with a presence of surrounding stimulus, the most effective SF of surrounding stimulus for the suppressive modulation was same as that of the optimal SF for the receptive field stimulus in 12 cells and different in 6 cells. In remaining 3 cells, SF dependency of the response modulation by SF was not observed. Our results suggest that neural connection among SF domains sharing similar SF preference is one of the basis of the contextual modulation of responses in the visual cortex.