[Variability of neuronal activity of the parastriate cortex before and after callosotomy]

In acute experiments on anesthetized cats, variability of the unit activity in the field 18 of the visual cortex was studied. Both the spontaneous activity and the evoked activity by series of different light stimuli, were analysed. The data obtained show that callosotomy does not affect the variability of the spontaneous unit activity in the parastriate cortex. However, it does decrease the variability of the unit activity qualitative response (excitation--inhibition) to stimulation. The callosotomy increases variability of the predominant input (either ipsi--or contralateral) in regard to the mean spontaneous activity prior to and after a series of stimuli and decreases it in regard to the mean spontaneous unit activity for the whole period of study.