Receptive fields of neurons in the cats visual cortex after a change of alertness level.

Exact and reliable changes in receptive fields (RF) of neurons in the primary visual cortex were revealed after the action of extravisual stimuli such as air-puff to the corner of a closed eye which leads to an enhancement of alertness level. Such stimulus evoked a change in the configuration and size of RFs in most investigated units. This lasted from 15 to 30 min and in most cases the size of RFs excitatory zones decreased, while the size of inhibitory surround increased. This effect could be seen at different levels of visual adaptation. Under light and short anesthesia (sombrevin) the main picture of RF change was different: increase of excitatory zones and nearly equal probability of the opposite changes in inhibitory RF parts lasting from 5 to 30 min. The role of intracortical inhibitory systems in the modulation of RF size and form is discussed. The possible behavioral meaning of the observed effects may consist in the fine description of signal properties in the small RFs at high alertness level, while under opposite conditions enlarged RFs can serve to improve signal detection and organization of orienting reaction even to a weak new stimulus.