Deficit in classical conditioning in patients with cerebellar degeneration.

There is evidence from animal experiments that the cerebellum and its associated brainstem circuitry are involved in the acquisition of the conditioned response. In order to obtain evidence for their involvement in humans, we studied classical delay conditioning, using the eye-blink conditioned response, in five patients with pure cerebellar cortical atrophy and seven patients with olivopontocerebellar atrophy. The results were compared with those obtained in a group of neurologically healthy volunteers matched with the patients for age and sex. The two groups of patients had similar abnormalities in the acquisition of the conditioned response and produced fewer conditioned responses than in the control subjects in any given block of trials. Many of the patients' conditioned responses were inappropriately timed with respect to the conditioned stimulus. These results support the role of the cerebellum in the expression and timing of the conditioned response.