BILATERAL CONTROL OF THE ORBICULARIS OCULI MUSCLE BY ONE CEREBELLAR HEMISPHERE IN THE FERRET

REPORTS that lesions of the anterior interpositus nucleus in the cereb ellum or of the cerebellar cortex abolish classically conditioned eyeb link responses were originally taken to indicate that the cerebellum i s the locus of learning. This interpretation has recently been questio ned by reports that conditioned responses may recover after ipsilatera l cerebellar lesions. It cannot be excluded, however, that the recover ed responses were produced by the intact contralateral hemisphere. In order to determine if cerebellar outflow to the orbicularis oculi musc le is bilateral, we stimulated both the brachium conjunctivum and a co rtical area in the c3 zone of the cerebellar cortex which controls eye blink. Both kinds of stimulation elicited EMG activity in both the ips i- and the contralateral eyelids. The results thus show that that ther e is a bilateral control of eyeblink from each cerebellar hemisphere a nd they raise the possibility that recovery of conditioning after ipsi lateral cerebellar lesions is due to the intact hemisphere. Reports of such recovery after unilateral lesions are therefore inconclusive.