Reacquisition of classical conditioning after removal of cerebellar cortex.

We trained rabbits with white noise and light conditioned stimuli and a face shock unconditioned stimulus for classical conditioning of the nictitating membrane response and then removed the ipsilateral cerebellar cortex by aspiration. Larsell's hemisphere lobule VI was completely removed in 5 rabbits; the pattern of degeneration in the inferior olive matches the projections to HVI reported in experiments with horseradish peroxidase. All rabbits showed an initial abolition of conditioned responses but then relearned within two days. This indicates that cerebellar cortical lobule HVI normally is involved but is not necessary for classical conditioning.