Mapping visually activated cerebellar regions in anaesthetised monkeys with fMRI

Visual input handed over to the cerebellum by way of the pontine nuclei plays a crucial role in the sensory guidance of movement in primates (Stein and Glickstein, Physiol. Rev., Vol. 72, 1992). Based on the demonstration of visual single unit activity and the results of tract tracing experiments, several cerebellar regions seem to be involved in the processing of visual signals. The list of cerebellar areas implicated in the processing of visual information comprises vermal lobules VI, VII, VIII and IX, the hemispheric lobules crus I, dorsal paraflocculus and flocculus. Although already long, this list may still not be complete. We therefore looked for visually evoked cerebellar BOLD activation with a vertical 4.7 Tesla MRI scanner in monkeys. This approach provides us with a direct visualisation of the complete multisynaptic cerebro-ponto-cerebellar pathway. Monkeys were scanned while being anaesthetised in order to rule out movement-related BOLD responses, induced by the visual stimuli. In a first set of experiments we looked for cerebellar BOLD responses, evoked by moving large field random dot kinematograms. Our preliminary results indeed suggest that some of the previously proposed cerebellar regions are activated by such pure visual stimulus. More detailed studies may enable us to further dissect these regions as to their differential preferences for different visual stimuli