Divergent effects of deep cerebellar lesions on two different conditioned somatomotor responses in rabbits.

Rabbits with bilateral lesions involving either the anterior interpositus nucleus or the superior cerebellar peduncle were subjected to appetitive Pavlovian conditioning training involving repeated pairings of a 2-s tone with an intraoral pulse of water. Such training resulted in the rapid development of robust, anticipatory jaw-movement responses (JM CRs) to the tone, and, in fact, the performance levels exhibited by lesioned animals did not differ significantly from those observed in sham-operated control animals. Additional experiments involving unpaired tone/water presentations confirmed the associative character of the JM CRs. On the other hand, lesioned animals exhibited severe bilateral performance deficits when later subjected to aversive eyeblink conditioning procedures, consistent with previous findings. The present results thus suggest that the interpositus nucleus is not an essential neural substrate for the development of appetitively conditioned masticatory responses.