TIME-SLICE ANALYSIS OF INHIBITION IN CAT STRIATE CORTICAL-NEURONS

A PROMINENT feature of visual cortical neurones is orientation specifi city. The underlying mechanisms and the possible contributions of intr acortical inhibition are continuously the subject of intense debate. W e analysed orientation tuning in relation to time after stimulus onset and the effects of blockade of GABAergic inhibition with microiontoph oretically applied bicuculline in single cells in area 17. The majorit y of the cells had sharp and temporally stable orientation specificity ; however, changes of receptive field structure, widening of orientati on tuning and changes in preferred orientation were observed between 3 0 and 150 ms after stimulus onset when inhibition was blocked. This in dicates that under normal conditions in most striate cortical cells in tracortical inhibition sculptures receptive field structure and keeps orientation tuning narrow and constant in time.