Classical conditioning in rabbits using pontine nucleus stimulation as a conditioned stimulus and inferior olive stimulation as an unconditioned stimulus.

Classical conditioning of skeletal muscle responses was accomplished by pairing microstimulation of the pontine nuclei as a conditioned stimulus (CS) with microstimulation of the dorsal accessory olive as an unconditioned stimulus (US). A conditioned response identical in form to the behavioral response elicited by the olivary stimulation was established when the CS was forward paired with the US, and behavioral extinction occurred with CS-alone presentations or unpaired CS-US presentations. Conditioned responding could not be established or maintained when the CS and US were simultaneously presented or when the US preceded the CS (i.e., backward paired). Complete lesions of the interpositus nucleus abolished both conditioned and unconditioned responses. These findings support the idea that plasticity associated with classical conditioning of skeletal muscle responses occurs in regions of the cerebellum that receive convergent CS and US input.