Neurophysiological correlates of word and pseudo-word processing in well-recovered aphasics and patients with right-hemispheric stroke.

Neurophysiological correlates of language recovery after stroke were investigated. Neurological patients with single focal lesions in their left or right hemisphere and healthy control subjects made lexical decisions on written words and pseudo-words while EEG responses were recorded. At the time of testing, patients did not show clinically apparent language dysfunction, although those with left-hemisphere lesions had suffered from aphasia in the first months after their stroke. A P3-like positive deflection of the event-related potential (ERP) was reduced in the patients relative to healthy controls, this reduction being most pronounced over the hemisphere affected by stroke. Consistent with earlier research, healthy control subjects showed more positive ERPs to words than to pseudo-words. This pattern was reversed in both patient groups, where words elicited more negative-going ERPs than pseudo-words already 160-320 ms after stimulus onset. Because ERPs showed between-group differences only for words, these word-specific neurophysiological signatures altered in stroke patients with well-recovered language functions may be a correlate of cortical lesions or an index of reorganization of language after stroke.