Classical conditioning of the eyeblink reflex in the decerebrate-decerebellate rabbit.

The purpose of these experiments was to test the hypothesis that a conditioned nictitating membrane reflex can be acquired in decerebrate rabbits in the absence of the cerebellum. Experiments examining the effects of large cerebellar lesions on the acquisition and performance of the conditioned reflex were performed in acutely prepared decerebrate rabbits. Most lesions encompassed all of the cerebellar nuclear regions ipsilateral to the eye receiving the unconditioned stimulus. In all rabbits included in this study the continuity between the cerebellar nuclei and the brainstem was interrupted, even in those preparations in which small regions of the nuclei were present in the lateral hemisphere. The findings demonstrate that these animals could acquire the conditioned reflex independent of whether conditioning had occurred prior to the cerebellectomy. Strong associativity was found between the latency of the conditioned response and the interstimulus interval between the conditioned and unconditioned stimuli. The behavior of the conditioned reflex observed in the decerebrate-decerebellate animals differed from that reported for awake intact rabbits in two ways. Once the conditioned behavior had been acquired, the percent of trials showing conditioned responses was somewhat less in decerebrate-decerebellate rabbits and was also more variable in these animals. The data demonstrate that the nictitating membrane reflex can be classically conditioned in the absence of the cerebellum, indicating that this structure is neither necessary nor sufficient for the acquisition of this type of conditioned behavior. In addition, an hypothesis is presented which addresses the difference between the data reported here and those previously reported by other laboratories based on observations in awake intact animals.