Two-stage theory of conditioning: involvement of the cerebellum and the amygdala

Classical conditioning is thought to proceed through two successive stages: fast rate emotional conditioning followed by slower motor conditioning. Ta verify the involvement of the amygdala and the cerebellum in these two sta ges of learning, rats were subjected to paired tone-airpuff (CS-US) trials. Lick suppression to CS was used as an index of conditioned emotional respo nse (emotional CRs) and head movement was used as an index of motor CRs. Th e results showed that the fast acquisition of emotional CRs was dependent o n the integrity of the amygdala and the slow acquisition of motor CRs was d ependent on the integrity of the cerebellar interpositus nucleus. Cerebella r lesions had no effect on the acquisition of the emotional CRs but prevent ed the extinction of the emotional CRs seen in intact rats after massive co nditioning. These findings suggest that the amygdala and the cerebellum pro vide the neuronal substrates of the fast and slow conditioning systems, res pectively, and that conditioning-related cerebellar output interacts with t he amygdala-based emotional conditioning. (C) 2001 Elsevier Science B.V. Al l rights reserved.