Hemispatial somatosensory and motor extinction after stereotactic thalamic lesions

Several authors have reported marked hemispatial visual neglect following ventrolateral (VL) thalamotomy for the relief of dyskinesia. However, few patients who undergo this procedure show clinical neglect. Characteristics of patients and precise localization of the lesions associated with post-operative hemispatial neglect, and the course of neglect, have not been documented. The objective of this study was to identify the precise location of surgical lesions and characteristics of patients who show hemispatial neglect or extinction following stereotactic thalamotomy, and to identify the nature and course of the hemispatial deficit. Twelve consecutive patients underwent stereotactic thalamotomy, restricted to the nucleus ventralis intermedialis (Vim), for the relief of tremor or dystonia. No patient showed visual neglect or extinction, but three patients showed somatosensory and/or motor extinction contralateral to thalamotomy. One patient showed significant hemispatial deficits beyond 2 weeks; no patient had the deficit beyond 1 month. All patients who developed post-operative extinction had non-thalamic, subcortical or cortical lesions prior to thalamotomy. A minority of patients show evidence of hemispatial neglect or extinction as a consequence of selective unilateral or bilateral lesions to Vim. Those who did show neglect had additional cortical and/or subcortical lesions, and their neglect recovered rapidly. The results are discussed in the context of evidence from previous lesion studies, cerebral blood flow studies, PET studies and animal studies, that indicate a role of the thalamus in spatial attention. Our results indicate that the Vim nucleus of the thalamus may play a redundant, rather than an essential role, in a cortical/subcortical network underlying spatially specific, sensory guided movements.