Left-hemispheric abnormal EEG activity in relation to impairment and recovery in aphasic patients.

Focal electromagnetic slow-wave activity is generated in the vicinity of brain lesions. The present study confirmed this for the EEG delta band (1-4 Hz): Activity in the waking state was pronounced over the hemisphere of the lesion in 11 stroke patients suffering from aphasia, but not in 10 healthy controls. Changes of abnormal slow waves patterns were tracked from 1-3 months to 2 years poststroke by recording the EEG five times at 4-month intervals. Across the first year poststroke, mean left-hemispheric delta amplitude and equivalent current dipole strength decreased in parallel with the spontaneous recovery of language function, whereas the regional distribution of delta activity sources was stabile across time. No changes were observed during the second year poststroke. Results suggest that abnormal slow waves in the vicinity of brain lesions may be related to impairment in brain function, and that their measurement may assist in depicting the course of functional recovery.