Thalamotomy and thalamic stimulation: effects on cognition.

Before, during and after ventrolateral thalamotomy, patients were subjected to neuropsychological tests with emphasis on verbal perception and memory. In the first study, the patients were tested with a dichotic listening task before surgery, during thalamic stimulation, and after the lesion. Left thalamic stimulation increased the number of correct responses from the right ear, whereas a left thalamotomy abolished the expected right ear superiority. Stimulation and lesions of the right thalamus did not have similar effects. In a second study, Parkinsonian patients were tested with an extended neuropsychological test battery before and after thalamotomy. The operation did not reduce the cognitive capacity in this group of patients. In the last study, the effects of thalamic stimulation on verbal memory was tested. High-intensity stimulation of the left thalamus resulted in fewer words being recalled as compared with right thalamic and low-intensity stimulation.