Time-slice analysis of inhibition in cat striate cortical neurones.

A prominent feature of visual cortical neurones is orientation specificity. The underlying mechanisms and the possible contributions of intracortical inhibition are continuously the subject of intense debate. We analysed orientation tuning in relation to time after stimulus onset and the effects of blockade of GABAergic inhibition with microiontophoretically applied bicuculline in single cells in area 17. The majority of the cells had sharp and temporally stable orientation specificity; however, changes of receptive field structure, widening of orientation tuning and changes in preferred orientation were observed between 30 and 150 ms after stimulus onset when inhibition was blocked. This indicates that under normal conditions in most in most striate cortical cells intracortical inhibition sculptures receptive field structure and keeps orientation tuning narrow and constant in time.