Involvement of the cerebellar thalamus in human saccade adaptation

Saccade adaptation can be experimentally induced by systematically displaci ng a visual cue during a targeting saccade. Nonhuman primate studies have h ighlighted the crucial role of the cerebellum for saccade adaptation, but i ts neural substrates in humans are poorly understood. Recent physiological experiments suggest that, in addition to cerebellar structures, cortical ar eas may be involved as well. We have therefore hypothesized that saccade ad aptation may rely on a cerebello-cerebral network, in which the cerebellar thalamus may link cerebellar and cerebral structures. To test this hypothes is, we studied saccade adaptation in a group of four patients with a thalam ic lesion, with (n=2) or without (n=2) involvement of the cerebellar thalam us. Compared to healthy subjects, saccade adaptation was reduced in patient s with associated cerebellar syndrome, but normal in patients without cereb ellar syndrome. These results are consistent with the hypothesis that cereb ello-thalamic pathways contribute to saccade adaptation in humans and sugge st that the thalamus relays adaptation-related information from the cerebel lum to cerebral cortical oculomotor areas.