Spatiotemporal structure of complex cell receptive fields and influence of GABAergic inhibition

Spatiotemporal receptive field (RF) profiles were mapped with reverse correlation technique for complex cells in the striate cortex of cat. The RFs were constituted with ON and OFF subfields that overlapped much extensively in space and also largely in time. The subfields had spatial width of 1.0-4.3 degrees and temporal duration of 33-139 ms, whereas late responses were absent in most cases. When microiontophoresis of gamma-aminobutyric acid type A (GABAA) antagonist bicuculline was performed on the cells, little change occurred in width and onset time of the subfields, but the duration was prolonged in a subset of cells. These results suggest that intracortical inhibition may contribute to improve the accuracy of visual signals encoded in neuronal activities, but is unlikely critical for determining the primary structure of complex cell RF.