Classical heart rate conditioning and affective behavior: the role of the cerebellar vermis.

The involvement of the cerebellar vermis in the control of affective behaviors and in the coordination of fear-related somatic and autonomic conditioned responses is reviewed in this paper. In particular, the review focuses on the role of the midline cerebellum (vermis) on the acquisition and/or expression of classically conditioned bradycardia in the rabbit. The results of both lesioning and electrophysiological experiments indicate that the cortex of lobule III through VII is important, although not essential, in the acquisition and retention of this response, but it is not the site of its memory trace. The time course of the development of the conditioned bradycardia in neonatal rabbits is also described. The results obtained are consistent with the possibility that the expression of conditioned bradycardia may depend on the complete maturation of cerebellum. Moreover, preliminary data on the effects of the ablation of cerebellar vermis, performed at early stages of development, on the characteristics of conditioned bradycardia showed by adult rabbits are presented. These results indicate that cerebellar vermis is essential for the correct maturation of the response and that the timing of the lesion is critical for determining the characteristics of conditioned bradycardia in the adult.