Precise burst synchrony in the superior colliculus of the awake cat duringmoving stimulus presentation

This study aimed to characterize the synchrony that occurs between cell dis charges in the superior colliculus of the awake cat. We trained cats to per form a visual fixation in the presence of a visual moving stimulus and then recorded 686 pairs of neighboring cells in the superior colliculus during task performance. A new method to assess the significance of precise discha rge synchronization is described, which permits analysis of nonstationary d ata. Of 181 pairs with sufficient data for quantitative analysis, 125 showe d a cross-correlation histogram (CCH) with features assessed as significant using this approach. CCHs frequently showed an isolated central peak (41 o f 125) or a peak flanked by one or two troughs (68 of 125), and in a few ca ses an oscillatory pattern of similar to 65 Hz (16 of 125). This is in cont rast to the oscillation frequency reported for the visual cortex and shows that oscillations in the superior colliculus probably arise from a cortex-i ndependent mechanism. Our method also permits direct quantification of the correlation shift pred ictors, assessing precise time locking of spikes to the stimulus. Only 1 of 125 cross-correlation shift predictors had a significant central peak, mea ning that most of the CCH features were not related to cell discharges time -locked to the stimulus presentation. Further investigation using a burst-jittering method showed that synchrony in the superior colliculus is attributable to precise synchronization of sh ort bursts of spikes. Such synchrony could be related to the network dynami cs and the common inhibitory feedback from local interneurons, which would act as temporal selectors of the cells with greatest or fastest response.