THE CEREBELLUM AND RED NUCLEUS ARE NOT REQUIRED FOR IN-VITRO CLASSICAL-CONDITIONING OF THE TURTLE ABDUCENS NERVE RESPONSE

The role of the cerebellum during motor learning is a controversial is sue. Many authors have suggested that the cerebellum and its connectio ns with the red nucleus are essential for the acquisition of the condi tioned eye blink reflex. Although there is little argument that the ce rebellum is an important component to the generation of the conditione d response (CR), a number of studies have suggested that the cerebellu m is not essential for conditioning. Using an in vitro model of the cl assically conditioned turtle abducens nerve response, we investigated the effect of cerebellar and red nucleus lesions on the acquisition, e xtinction, and reacquisition of CRs. Neural discharge was recorded fro m the abducens nerve after a single shock unconditioned stimulus (US) was applied to the ipsilateral trigeminal nerve. When the US was paire d with a conditioned stimulus (CS) applied to the posterior eighth, or auditory, nerve, a positive slope of CR acquisition was recorded in t he abducens nerve. After extinction stimuli in which the CS and US wer e alternated, the number of CRs decreased to near zero. When the CS an d US were once again paired, reacquisition at a faster rate was record ed. The CRs showed unusual timing features compared with preparations in which the cerebellum was intact; they had significantly shorter lat encies and showed burstlike responses. These data demonstrate that it is possible to classically condition this in vitro preparation in the absence of the cerebellum and red nucleus. However, the latencies of C Rs were found to be dramatically altered in the cerebellar-lesioned pr eparations, suggesting that the cerebellum does play a role in the tim ing of the CR.