Neuronal activity in the cerebellar interpositus and lateral pontine nuclei during inhibitory classical conditioning of the eyeblink response.

Single-unit neuronal activity was recorded from the cerebellar interpositus nucleus and lateral pontine nuclei during conditioned inhibition of the eyeblink response in rats. Conditioned inhibition training sessions included 100 trials/day for 12 days. During each training session, the rats were given 50 presentations of a tone conditioned stimulus (CS) that was paired with a brief periocular shock unconditioned stimulus (US). They were also given 50 presentations of a compound stimulus that included the tone-CS and a light-CS. The compound-CS was not paired with the US. The two types of trials were mixed throughout the session and presented in an irregular sequence. This training procedure resulted in significant inhibition of the eyeblink response during the compound-CS. Neurons in the interpositus and lateral pontine nuclei exhibited significantly less activity during the compound-CS relative to the tone-CS. The suppression of cerebellar and pontine learning-related neuronal activity during the inhibitory CS may be critical for inhibiting the conditioned eyeblink response.