EVOKED POTENTIALS IN AUDITORY CORTEX AFTER BILATERAL TRANSECTION OF THE BRACHIUM OF THE INFERIOR COLLICULUS IN THE CAT

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Abstract
The effects of mesencephalic lesions of the auditory pathways on cortical potentials evoked by clicks were studied in 6 cats. In 4 cats the following procedures were performed bilaterally under pentobarbital anesthesia: (a) auditory cortex was exposed and surveyed for evoked potentials, (b) attempts were made to section the brachium of the inferior colliculus, and (c) as many as 6 pairs of chronic transcortical electrodes were implanted on each side in auditory cortex. Two months elapsed between steps (b) and (c) in a single animal. Step (c) preceded (b) in another animal. Multiple attempts were made to record evoked potentials with animals anesthetized with pentobarbital, and unanesthetized. After sacrifice, electrode positions were confirmed and brain stems prepared for histological study. The brachium was sectioned completely on one or both sides in 5 of the 6 cats. Evoked potentials with onset latencies less than 10 msec, never were obtained ipsilateral to complete brachium lesions, but were recorded in unanesthetized and anesthetized animals ipsilater to incomplete lesions.