Peculiarities of Visually Sensitive Neurons of the Extrastriate Associative Area 21b of the Cat Brain Cortex

On cats with pretrigeminal brainstem transection, we studied the properties of visually sensitive neurons of the extrastriate associative cortical area 21b. The dimensions and spatial distribution of the receptive fields (RF) of the neurons within the vision field were determined. It was found that large-sized RF prevailed within the area 21b (10 to 200 deg², 61%; greater than 200 deg², 22%), whereas small-sized RF (1 to 10 deg²) constituted 17% of all the studied RF. Stationary visual stimuli evoked on–off, off, and on responses in 43, 30, and 27% neurons of the area 21b, respectively. In the cases where moving stimuli were presented, 35% of the neurons demonstrated directional sensitivity; the rest of the neurons (65%) were directionally insensitive. We also found a group of neurons that were capable of differentiating not only the direction of the stimulus movement along the RF but also the dimension, shape, and orientation of a complicated moving stimulus. Taking into account the data obtained, we discuss the functional role of the neurons, which demonstrated a specific (specialized with respect to a set of the parameters of visual stimulus, and not to a single parameter) response in central processing of the sensory information.