Normalisation and increase of abnormal ERP patterns accompany recovery from aphasia in the post-acute stage

Electrophysiological correlates of recovery from anomia were analysed in four aphasic patients in the post-acute stage. Event-related potentials (ERPs) were recorded during picture naming at baseline and after a period of therapy for anomia. All patients had severe anomia at baseline assessment and improved significantly in naming during the study period. Waveform analyses and temporal segmentation were carried out on the ERPs of each patient in comparison with 15 healthy control subjects. Normalisation as well as an increase of abnormal electrophysiological correlates accompanied recovery. An increase of abnormal amplitudes appeared in a patient with semantic impairment during the first 300 ms after picture onset, while only normalisation of amplitudes and topographic maps accompanied recovery in the three patients with lexical-phonological impairment in this early time-window. Abnormal amplitudes and topographic maps emerged during recovery in the patients with lexical-phonological impairment in later time-windows, starting between 250 and 300 ms. Follow-up ERP recordings carried out 6 months later in two of them showed normalisation of amplitudes and persistence of abnormal maps. The results suggest that electrophysiological changes accompanying recovery from anomia in the post-acute stage are observed in specific time-windows, probably corresponding to different encoding processes and that recovery correlates with normalisation of EEG patterns as well as with the emergence of abnormalities, which presumably indicates compensation mechanisms of specific encoding processes.