Cerebellar cortical lesions and reacquisition in classical conditioning of the nictitating membrane response in rabbits

Portions of cerebellar cortex, particularly Larsell's hemisphere VI, have been identified as involved but not essential for the acquisition and retention of classical conditioning of the nictitating membrane (NM) response in rabbit. The present experiment was undertaken to examine the effect of lesions of cerebellar cortical regions projecting to anterior dorsolateral interpositus nucleus. Lesions of relatively equal size, including hemisphere VI and additionally more medial, anterior, or lateral cerebellar cortex were made after rabbits were classically conditioned. The effect of these cerebellar cortical lesions on retention to tone versus light conditioned stimulus (CS) and the timing of the conditioned response was evaluated. In spite of relatively large cerebellar cortical lesions, reacquisition of the conditioned NM response occurred quite rapidly. Whether the lesion was more medial and anterior or more lateral did not affect retention. Retention was significantly poorer with light CS than with tone CS. Timing of CRs was not affected by these lesions of cerebellar cortex, but the lesions spared most of the anterior lobe. The parasagittal zone C3 covering the longitudinal band of tissue from anterior lobe to the paramedian lobule and projecting to dorsolateral anterior interpositus requires additional exploration for its role in classical NM conditioning.