Involvement of the cerebellar thalamus in human saccade adaptation

Saccade adaptation can be experimentally induced by systematically displacing a visual cue during a targeting saccade. Nonhuman primate studies have highlighted the crucial role of the cerebellum for saccade adaptation, but its neural substrates in humans are poorly understood. Recent physiological experiments suggest that, in addition to cerebellar structures, cortical areas may be involved as well. We have therefore hypothesized that saccade adaptation may rely on a cerebello-cerebral network, in which the cerebellar thalamus may link cerebellar and cerebral structures. To test this hypothesis, we studied saccade adaptation in a group of four patients with a thalamic lesion, with (n=2) or without (n=2) involvement of the cerebellar thalamus. Compared to healthy subjects, saccade adaptation was reduced in patients with associated cerebellar syndrome, but normal in patients without cerebellar syndrome. These results are consistent with the hypothesis that cerebello-thalamic pathways contribute to saccade adaptation in humans and suggest that the thalamus relays adaptation-related information from the cerebellum to cerebral cortical oculomotor areas.