Long-term changes in the activity of superior colliculus neurons isolated from corticofugal influences

In acute experiments on nonnarcotized, immobilized cats, spike activity was studied in superior collicular neurons which were isolated from direct, descending cortical influences. Animals were taken for experimentation at various periods (from 3 to 20 months) after the operation which disconnected the cortical connections which projected from one hemisphere. An increase was noted in the regular forms of activity, and there was a decrease in the frequency of group discharges. Evoked activity of the cells was suppressed during the early periods after disconnection of corticocollicular connections. Later (after 9--12 months) its gradual restoration was observed. More than 70% of the neurons again began to respond to adequate stimuli. The sensitivity to moving photic stimuli was restored in only 17% of the neurons studied.