The role of the human thalamus in processing corollary discharge.

Corollary discharge signals play an important role in monitoring self-generated movements to guarantee spatial constancy. Recent work in macaques suggests that the thalamus conveys corollary discharge information of upcoming saccades passing from the superior colliculus to the frontal eye field. The present study aimed to investigate the involvement of the thalamus in humans by assessing the effect of thalamic lesions on the processing of corollary discharge information. Thirteen patients with selective thalamic lesions and 13 healthy age-matched control subjects performed a saccadic double-step task in which retino-spatial dissonance was induced, i.e. the retinal vector of the second target and the movement vector of the second saccade were different. Thus, the subjects could not rely on retinal information alone, but had to use corollary discharge information to correctly perform the second saccade. The amplitudes of first and second saccades were significantly smaller in patients than in controls. Five thalamic lesion patients showed unilateral deficits in using corollary discharge information, as revealed by asymmetries compared with the other patients and controls. Three patients with lateral thalamic lesions including the ventrolateral nucleus (VL) were impaired contralaterally to the side of damage and one patient with a lesion in the mediodorsal thalamus (MD) was impaired ipsilaterally to the lesion. The largest asymmetry was found in a patient with a bilateral thalamic lesion. The results provide evidence for a thalamic involvement in the processing of corollary discharge information in humans, with a potential role of both the VL and MD nuclei.