The role of the thalamus in conveying efference copy information

Abstract

It is commonly believed that spatial stability of our retinal image is achieved by monitoring an efference copy of the command to move the eyes. Recent work suggests that the thalamus conveys efference copy information passing from the superior colliculus (SC) to the frontal eye field (FEF) in macaques. The aim of this study was to investigate, if thalamic lesions in humans lead to deficits in using efference copy information. Twelve patients with selective thalamic lesions and twelve healthy, age-matched controls were examined with 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 were different. Thus the subject could not rely on retinal information, but had to use efference copy information to perform a correct second saccade. The amplitudes of first and second saccades were significantly smaller in patients than in controls. Individual patients were, however, impaired in using efference copy information. Four patients showed unilateral deficits, revealed by asymmetries in their performance in comparison to the other patients and to normal controls. Two patients with dorsolateral thalamic lesions were impaired contralateral to the side of their lesions, one patient with a lesion in the mediodorsal thalamus was impaired ipsilateral to the lesion. The largest asymmetry was found in a patient with a bilateral thalamic lesion. The results indicate that thalamic patients may show impairments in using efference copy information. Interestingly, the ipsilateral deficit observed in one patient is inconsistent with the findings in macaques.

Footnotes

 This research was funded by the International Graduate School for Neuroscience (IGSN), Bochum, Germany