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Abstract:
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 [1]. 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. 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 rst set of experiments we looked for cerebellar
BOLD responses evoked by moving large eld random dot kinematograms. Our preliminary
results indeed suggest that some of the previously proposed cerebellar regions are activated
by such pure visual stimulus. The visual responses were most pronounced in the posterior
vermis. However, visual responses were also elicited in another classical visual cerebellar
area, the dorsal paraocculus. In addition we also saw activation in the cerebellar hemispheres,
although much less pronounced. The differences in activation strength in different cerebellar
regions may be due to several factors: potentially larger physiological noise in the more caudal
cerebellar regions, larger distance of the caudal regions to the RF coil, and/or different density
distribution of activated afferent ber terminals in the different cerebellar regions. The function
of these sensory signals may subserve to optimize occulomotor performance [2] or sensory
performance [3] such as visual motion detection.
