MODIFICATION OF NEUROMAGNETIC CORTICAL SIGNALS BY THALAMIC INFARCTIONS

Auditory evoked responses and spontaneous cortical activity were recor ded with a whole-scalp 122-channel neuromagnetometer from 7 patients, who had small thalamic infarctions in the region of the left anterior tuberothalamic artery and associated memory defects. In contrast to he althy control subjects, with dominant rhythmic activity at 10.6 +/- 0. 6 Hz in the parieto-occipital region, the spectral maximum in the pati ents was at 8.9 +/- 0.4 Hz. Abnormal acceleration of rhythmic activity was also observed bilaterally in rolandic areas. Our findings imply t hat lesions of non-specific thalamic nuclei may disturb human brain rh ythms in widespread cortical areas. 'Mismatch responses' to deviant to nes (1.1 kHz) among standards (1.0 kHz), suggested to reflect sensory auditory memory in healthy subjects, were absent in 2 patients, marked ly decreased in 3, and normal in 2, implying that pathways passing thr ough the anteromedial thalamus contribute to modulation of these respo nses. We conclude that local unilateral lesions in the anteromedial th alamus may cause extensive, bilateral alterations in the brain's elect ric activity. (C) 1998 Elsevier Science Ireland Ltd.