Disrupted eyelid conditioning in a patient with damage to cerebellar afferents.

A 54-year-old woman with damage to cerebellar circuitry resulting from a cerebrovascular accident underwent classical conditioning of the eye-blink response to a tone conditioned stimulus and an air-puff unconditioned stimulus. In contrast to 5 age-matched controls who readily acquired the conditioned response (CR), emitting a mean of 56.7 CRs over 70 trials, the patient emitted only 6 CRs in 100 trials and never emitted 2 consecutive CRs. There were no differences in spontaneous blink rate, sensitivity to the air puff, or sensitivity to the tone between the experimental subject and the control subjects. That conditioning of the eye-blink response is disrupted in a human with damage to cerebellar circuitry is consistent with an accumulating body of literature indicating that the cerebellum is the essential site of plasticity for classically conditioned somatic responses.