Effect of bilateral lesions of the dentate and interpositus cerebellar nuclei on conditioning of heart-rate and nictitating membrane/eyelid responses in the rabbit.

It has been shown that unilateral lesions of the medial dentate/lateral interpositus nuclear region of the cerebellum abolish the learned nictitating membrane (NM)/eyelid response of the eye ipsilateral to the lesion. The present study examined the effects of bilateral cerebellar lesions on acquisition of heart-rate conditioning (often viewed as a measure of 'conditioned fear') and both its short-and long-term effects on NM/eyelid learning and relearning. The results demonstrate that cerebellar lesions that completely and permanently abolish acquisition or retention of the somatic response (NM/eyelid) bilaterally have no effect on heart-rate conditioning. The neuronal circuits necessary for learning of the heart-rate response and for learning of the adaptive somatic response are thus in significant part different. Results are tentatively interpreted within the context of a two-process theory of aversive learning: an initial phase indexed by conditioned autonomic and 'non-specific' responses such as heart-rate and a subsequent phase of learning the specific adaptive responses.