Bilateral cerebellar lesions disrupt conditioned eyelid responses in unrestrained rats

Electromyographic eyelid responses in unrestrained rats were classically conditioned in a Pavlovian delay paradigm by using a tone conditioned stimulus (CS) and periorbital shock unconditioned stimulus (US). After eyelid conditioning was complete, bilateral electrolytic lesions were made in the dentate-interpositus region of the cerebellar nuclei. Initial eyelid conditioning was reliable and very similar to that previously observed in the rabbit, although the asymptotic eyelid responses contained a short-latency startle response in addition to the usual conditioned and unconditioned responses (CR and UR). Substantial decrements in CRs were observed in 13 of the 14 rats with accurately placed lesions. In contrast, startle responses and URs were unaffected. The results replicate the effects of cerebellar lesions on eyelid CRs in the rabbit and suggest that the anatomical basis of eyelid conditioning in both species is similar.