The behavioral phenomenon of blocking indicates that the informational relationship between the conditioned stimulus and the unconditioned stimulus is essential in classical conditioning. The eyeblink conditioning paradigm is used to describe a neural mechanism that mediates blocking, Disrupting inhibition of the inferior olive, a structure that conveys unconditioned stimulus information (airpuff) to the cerebellum prevented blocking in rabbits. Recordings of cerebellar neuronal activity show that the inferior olive input to the cerebellum becomes suppressed as learning occurs. These results suggest that the inferior olive becomes functionally inhibited by the cerebellum during conditioning, and that this negative feedback process might be the neural mechanism mediating blocking.