Neglect induced by thalamotomy in humans: a quantitative appraisal of the sensory and motor deficits.

Stereotactic lesions for the treatment of tremor and rigidity in patients with Parkinson's disease are occasionally followed by neglect of the use of contralateral extremities for spontaneous movement when there are no specific sensory or motor deficits. A group of patients with neglected extremities was compared with a group of patients in which thalamotomy did not produce neglect. Neglect was shown by changes in motor performance, somatosensory evoked potentials (SEP) and electroencephalographic frequency induced by the lesion, as well as radiological evidence of brain atrophy and place and extension of lesions. Reaction time to both auditory and somatosensory stimuli was significantly increased only in the extremities contralateral to the lesion of patients with neglect; tremor decreased equally in both groups, and other motor abilities remained unchanged. P-200 component of SEP decreased in amplitude and increased in latency only in cases with neglect, particularly ipsilateral to the lesion; early components and mean electroencephalographic frequency remained unchanged. Brain atrophy was significant in patients with neglect, particularly for the posterior portion of the 3rd ventricle. No differences in size and location of the lesions were found between the groups. Results indicate that this type of neglect is not secondary to lesions in specific sensory of motor pathways, but to lesions of structures coupling sensorimotor functions and the process of attention and that midline thalamic nuclei atrophy precipitates the neglect, perhaps by critically decreasing the amount of reticulothalamocortical projections engaged in selective attention.