ROLE OF CEREBELLUM IN ADAPTIVE MODIFICATION OF REFLEX BLINKS

We investigated the involvement of the cerebellar cortex in the adapti ve modification of corneal reflex blinks and the regulation of normal trigeminal reflex blinks in rats, The ansiform Crus I region contained blink-related Purkinje cells that exhibited a complex spike 20.4 msec after a corneal stimulus and a burst of simple spike activity correla ted with the termination of orbicularis oculi activity, This occurrenc e of the complex spike correlated with trigeminal sensory information associated with the blink-evoking stimulus, and the burst of simple sp ike activity correlated with sensory feedback about the occurrence of a blink, Inactivation of the inferior olive with Lidocaine prevented a ll complex and significantly reduced simple spike modulation of blink- related Purkinje cells, but did not alter orbicularis oculi activity e voked by corneal stimulation, In contrast, both acute and chronic lesi ons of the cerebellar cortex containing blink-related Purkinje cells b locked adaptive increases in orbicularis oculi activity of the lid ips ilateral but not contralateral to the lesion, These data are consisten t with the hypothesis that the cerebellum is part of a trigeminal refl ex blink circuit, Changes in trigeminal signals produce modifications of the cerebellar cortex, which in turn, reinforce or stabilize modifi cations of brainstem blink circuits, When the trigeminal system does n ot attempt to alter the magnitude of trigeminal reflex blinks, cerebel lar input has little or no effect on reflex blinks.