Cerebellum mediates modality-specific modulation of sensory responses of midbrain and forebrain in rat

Evidence of a sensory role of the cerebellum, mediating a modulation of effectiveness of afferent input at other parts of the brain, has been reported previously for certain sense modalities but has not been evaluated across several in a mammal. After a conditioning train of stimuli applied to the cerebellar surface in unanesthetized rats, diffuse flashes, acoustic clicks, and shocks to the sciatic nerve evoked multiunit and field potential responses that were recorded at three levels: midbrain, thalamus, and cerebral cortex. At a best interval between end of conditioning train (cerebellar) and test (sensory) stimuli, all three levels show modulation of the evoked responses, each in a specific direction (enhancement or depression), with a characteristic time course. Visual responses in the tectum are enhanced; those in the cortex are depressed. Tectal responses that have been nearly abolished by increasing background illumination are partially restored by the conditioning cerebellar train. Auditory brainstem responses (short latency, less than 10 ms, far-field waves I to III, attributed to medullary levels) are depressed; wave IV from the inferior colliculus is relatively enhanced at short intervals and is depressed at longer intervals. Somatosensory responses in thalamus and cortex are depressed. Lobulae V, VI, and VII of the vermis are more effective sites of stimulation than other areas tested. Most of the modulations are ascribed to central sites; a few are ascribed to peripheral sites.