Rabbit classically conditioned eyelid responses do not reappear after interpositus nucleus lesion and extensive post-lesion training.

The left eyelid responses of four rabbits were classical conditioned by pairing a tone conditioned stimulus and air puff unconditioned stimulus. After conditioned responses were well-established, the left interpositus nucleus was lesioned and 150-200 post-lesion training sessions, distributed over 10 months, were given. In three of the rabbits, no anticipatory conditioned responses were observed on paired trials and responses were at or below spontaneous blinking rates on 2,500 ms CS-alone trials that were also presented. Post-lesion conditioned responses were present when the right side was trained. The fourth rabbit showed few post-lesion conditioned responses on paired trials but eventually showed 80% conditioned responses on tone-alone trials. Histological analysis of the lesion extents indicate that a portion of the anterior interpositus nucleus was spared in this rabbit. These results argue that unlike other cerebellar lesion effects reported in the literature, where some recovery of function is normally noted, the effects of interpositus nucleus lesions are somewhat unique in that conditioned response abolition is seen as long as 10 months after the lesion.