Abstract

The cerebellar lobule HVI was investigated in terms of plastic structure mediating the classical conditioning of the rabbit's nictitating membrane response(NMR). In experiment 1, animals were received tone stimulus(80㏈, 1㎑, sine wave, without white noise) continually during the intertrial interval(ITI). The tone stimulus was turned off during the CS period. This withdrawal of tone stimulus was adopted as <TEX>${\bar{CS}}$</TEX>. Animals received the <TEX>${\bar{CS}}$</TEX> and corneal airpuff US parings in delay conditioning paradigm rapidly reached criterion like animals received CS-US pairings. Moreover, the electrolytic leisions of the interpositus nucleus selectively disrupted the CR aquired by <TEX>${\bar{CS}}$</TEX>-US pairings. The result suggests that this type of conditioning is mediated by the cerebellum as well and the cerebellum can associate the changes of stimuli itself. In addition, there was no transfer effect between <TEX>${\bar{CS}}$</TEX>-US and CS-US learning. The findings are discussed in terms of the convergence of the climbing and the mossy fibers on the Purkinje cells and the associative functions of the cerebellar neural network. In experiment 2, the long ISI was adopted(800msec CS duration, delay conditioning paradigm) in order to investigated the timing regulation function of the cerebellar cortex on motor learning. After the NMR conditioning(<TEX>${\bar{CS}}$</TEX>-US, group1 and CS-US, group2) reached the criterion, the cerebellar lobule HVI was electrolytically lesioned with four electrodes. The result showed that the CR was reduced about 50% in both groups and the effects were due to the disruption of timing regulation of the CR onset. Results indicated that the cerebellar lobule HVI is essential for the timing regulation of the CR onset. However, to understand the detailed neural mechanism of the conditioning of NMR, it was suggested that neural network approach including several structures resided in the cerebellum and in the brain stem(especially inferior olive) is more desirable than finding only one essential structure approach.