Abstract

The present experiment purports to examine effects of the cerebellar cortical simple lobule(HVI) on the classical conditioning of rabbit's nictitating membrane responses(NMR). The study examined whether the lobule HVI is an essential structure for NMR conditioning and whether it is the localized site where the critical memory trace related to classical NMR conditioning is formed. Many of the previous studies which explored the function of the lobule HVI in the MNR neural circuit have employed aspiration lesion techniques. But the aspiration may also damage inferior olive, pontine nuclus and deep cerebellar nucleus by retrograde degenerations of neural fibers as well as the simple lobule. In this study, kainic acid was micro-injected into the lobule HVI in order to overcome such porblems because the kainic acid destroys selectively the cell bodies and leave the fibers intact. Subjects were 16 rabbits. All animals were trained using standard procedures for NMR conditioning. The conditioning involves a tone(1㎑, 85㏈ SPL, 350㎳) as the conditioned stimulus(CS) with a coterminating periorbital electric shock(3㎃, 100㎳) delivered at the right eye as the unconditioned stimulus(US). Following the conditioning, the simple lobule of the right side cerebellum was lesioned. After recovery, animals received 5 days training on the right side to test for retention and reacquisition of conditioned responses. Then, animals received an additional session in which training was switched to the left side. Results show that complete lesions of the lobule HVI abolished previously established conditioning and prevented subsequent reacqusition, while unconditioned responses to US were intact. Lesions of the other cerebellar lobules did not impair the conditioning. The results suggested that the simple lobule is an essential part for classical NMR conditioning and that neural plasticity related to memory trace during the conditioning occurs in the simple lobule rather than in the dentate-interpositus nucleus.