The research will analyze brain circuits and neuronal mechanisms which are involved in mammalian motor learning. The nictitating membrane (NMR) response of rabbits will be conditioned by pairing a neutral conditional stimulus (CS; light or white noise) with a mild shock to the orbit unconditional stimulus (US). After several CS-US pairings the animals learn to respond to the CS alone. The effects on the conditioning of lesions of the dorsolateral pons and the middle cerebellar peduncle will be tested. Such lesions should block the CS signal from reaching the cerebellar cortex and abolish the conditioned but not the unconditional response. Physiological studies will analyze the somatotopic organization of the rabbit dorsal accessory olive (DAO). The inferior olive may be the source of US information in NMR conditioning. This idea will be confirmed and extended by conditioning limb flexion in rabbits and testing the effects of appropriately placed lesions in the DAO and the cerebellar cortex. If the DAO and anterior lobe are somatotopically mapped, conditioning should be impaired or abolished when lesions are placed in that portion of the DAO or cerebellar cortex which receives US information from the trained limb. Conditioning will be established in decerebrate rabbits to determine the minimal amount of brain tissue necessary for conditioning, and to provide a preparation in which the activity of single neurons can be recorded during conditioning. In anatomical experiments auditory and visual pathways will be traced from the forebrain, diencephalon and midbrain to the pontine nuclei. Orthograde and retrograde labelling techniques will be combined to determine which pontine cells relay CS information to the critical regions of the cerebellar cortex. Results will help to clarify the locus and mechanisms involved in motor learning and some of the possible circuits which can still function in people with traumatic or degenerative lesions of the forebrain.
