Functional structuration of the cerebellar efferent network involved in forelimb control, during processing of an associative conditioning.

A simplified sensorimotor pathway was subjected to an associative conditioning in fully awake cats. It was defined by the location of electrodes for applying the conditional stimulation (CS) in the cerebellar interpositus nucleus (IN) and the unconditional stimulation (UCS) on the skin of the forelimb. Electrodes chronically implanted all along the pathway allowed the simultaneous study of the motor and the neurobiological effects of conditioning. Persistent motor changes were observed in parallel with interposito-rubral and thalamocortical synaptic efficiency changes. The two kinds of event evolved similarly and significant correlations were found between them. Changes appeared to be induced according to modalities similar to those underlying elementary mechanisms of neuronal plasticity. The modulations of thalamocortical synaptic efficiency inside the primary motor cortex (MI) determined a new pattern of distribution of cerebellar effects on musculature, indicating that in adult brains the functional organization of central motor pathways is not definitely rigid it can still be subject to adaptive modifications.