TEMPORAL INFLUENCES OF RECEPTIVE FIELD SURROUND ON CENTER RESPONSES IN AWAKE-MONKEY V1 J. Sharma*; V. Dragoi; M. Sur Dept Brain & Cognitive Sci, MIT, Cambridge, MA, USA The responses of V1 neurons to stimuli presented within their classical receptive field are influenced by stimuli present outside the center. Furthermore, prior exposure to a stimulus in the surround affects the center response.We have previously reported that center responses are influenced in an orientation-specific manner by an adapting surround stimulus: an iso-oriented surround suppresses responses, whereas an orthogonal surround either facilitates or suppresses responses, though to a lesser extent (Sharma et al.,2000). We have now investigated the temporal effects of the adapting surround. We first determined orientation tuning and time course of response of a cell to drifting sinusoidal gratings(3 degree patch covering the CRF). Next, the surround was adapted by a grating for 1 second (10deg., center blocked out), followed by the center stimulus, with or without stimulus in the surround. In many cases, the suppressive effect of the surround was preceded by an initial facilitation, lasting up to 200 msec. In addition,in a subset of cells that we recorded (18/63),the presence of a surround influences the temporal modulation of the cell's response by the drifting gratings. In general,the ratio of the spatial phase specific component (F1)to the spatial phase invariant component (F0) for these cells is reduced. The spatial phase selective responses are orientation specific and the surround modulation is pronounced in cells with high direction selectivity.Thus, the influence of the surround on the center can be quite specific in time and space, and the surround can cause a reduction not only in overall center responses but also in their temporal modulation. Supported by: Supported by NIH grants EY07023 and NS39022