The surround of a visually recognized target modulates visual recognition. Surround modulation is stronger in the periphery than in the center of the visual field. A previous study of the early visual cortex of cats showed that surround modulation is stronger in the cortical regions corresponding to the periphery of the visual field than in those corresponding to the center. To date, the neural mechanisms underlying surround modulation is poorly understood. In the present study, an electrode array with 5×5 recording points was inserted into the cortex corresponding to the peripheral visual field. In this manner, the spiking activities of the neurons responding to the center and to the periphery of the stimulus were recorded. Two types of visual stimuli were used:(1)center-surround stimuli with a center spot of 5° diameter and a differently controlled grating in the periphery, and(2)full-field stimuli with a uniform grating. Cross-correlations of the spikes were analyzed in a total of 436 cell pairs, and 26 pairs correlated significantly. Significance was defined as a cross-correlation value exceeding 5 SD of the mean values between time lag of ±25ms and ±50ms. Of these 26 pairs, 11 showed significant cross-correlation in response to center-surround stimuli, but not to full-field stimuli. Time lag of the significant cross-correlation indicated the direction of information flow between the neurons. In 8 of the 11 pairs, the information flow was directed from the periphery to the center of the stimuli, and in 3 pairs from the center to the periphery. Of the 11 pairs, 5 pairs showed time lag of 1-5ms and fewer pairs showed time lag of <1ms, 5-10ms and >10ms. These results suggest that the information flow caused by center-surround stimuli is detectable using multichannel recording electrodes and analysis of cross-correlation of spiking activities originating from single neurons.
