Direction-selective cells in complex family in cat striate cortex.

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Abstract
Neurons (31) out of a population of 112 quantitatively studied cells in the cat striate cortex were classified as belonging to the complex family (complex, 16; hypercomplex II, 15). Approximately half the cells in the complex family were completely selective for the direction of stimulus motion. In contrast to cells not completely directional (mean resting discharge < 6 spikes/s), these cells had a higher mean resting (spontaneous) discharge (> 6 spikes/s), were more commonly hypercomplex II (9) than complex (5) and had wider receptive fields. With stimulus motion in the nonpreferred direction, all the completely directional cells showed evidence of inhibition over the greater part, or all, of the receptive field. The inhibition was indicated by the suppression of the resting discharge (12) or of the driven discharge when there was no spontaneous firing. Except of the direction of stimulus motion, inhibition in the nonpreferred direction is augmented by all the same stimulus parameters that increase the excitatory response in the preferred direction. Direction-selective inhibition is maximal at the same location in the receptive field where the excitatory response in the preferred direction is maximal. The inhibition is maximal for the optimal stimulus orientation and stimulus length in the preferred direction. Irrespective of the presence or absence of end-zone inhibition, cells in the complex family tend to be dominated equally by the 2 eyes (ocular-dominance class 4). Cells in the complex family are largely confined to cortical layers 3 and 5, with cells deep to layer 4 having a higher resting discharge (mean, 12 spikes/s) than those superficial to that layer (mean, 2 spikes/s).