Cortical Response Field Dynamics in Cat Visual Cortex

Abstract

Little is known about the "inverse" of the receptive field--the region of cortical space whose spatiotemporal pattern of electrical activity is influenced by a given sensory stimulus. We refer to this activated area as the cortical response field, the properties of which remain unexplored. Here, the dynamics of cortical response fields evoked in visual cortex by small, local drifting-oriented gratings were explored using voltage-sensitive dyes. We found that the cortical response field was often characterized by a plateau of activity, beyond the rim of which activity diminished quickly. Plateau rim location was largely independent of stimulus orientation. However, approximately 20 ms following plateau onset, 1-3 peaks emerged on it and were amplified for 25 ms. Spiking was limited to the peak zones, whose location strongly depended on stimulus orientation. Thus, alongside selective amplification of a spatially restricted suprathreshold response, wider activation to just below threshold encompasses all orientation domains within a well-defined retinotopic vicinity of the current stimulus, priming the cortex for processing of subsequent stimuli.