Red nucleus lesions impair acquisition of the classically conditioned nictitating membrane response but not eye-to-eye savings or unconditioned response amplitude.

Following a single electrocoagulating RF lesion aimed at left red nucleus, rabbits received classical conditioning of the nictitating membrane (NM) response. A tone was the conditioned stimulus (CS) and electrostimulation of the eye was the unconditioned stimulus (US). The US was applied to the right eye during the initial phase of training. It was then switched to the left eye to assess transfer of learning and ultimately switched back to the right eye. NM responses were recorded simultaneously from both eyes during each phase of training. Consistent with reports implicating a cerebellar-rubro circuit in this behavior, RN lesions disrupted acquisition of CRs in the eye contralateral to the lesion. Animals with disrupted NM CRs of the right eye resembled controls in showing transfer of conditioning to the left eye. CR-disrupting lesions did not affect UR amplitude.