Electrophysiological correlates of different anomic patterns in comparison with normal word production.

Different forms of anomia are observed in aphasia, which can be related to impaired semantic, lexical or phonological processes. In the present study, we analysed electrophysiological correlates of different patterns of anomia in six aphasic speakers. Event-related potentials (ERPs) were recorded during picture naming in each anomic speaker and in 15 healthy controls. Waveform analysis and temporal segmentation indicated a difference between high and low frequency words in the control group between 270 and 330 msec after picture onset. The ERPs recorded in the patients were compared to the control group. The time-windows of divergent ERP correlates were very similar between successful and erroneous naming, but they were differently distributed in the 6 patients. Two patients with conduction aphasia and impaired phonological encoding had normal electro-cortical activity during the first 300 msec and abnormal patterns between 300 and 450 msec. Two patients with lexical-semantic impairment had earlier ERP abnormalities starting immediately after visual processes. The two patients with less severe anomia and preponderance of omission errors displayed abnormal ERPs between 280 and 350 msec. These results indicate that abnormal electro-cortical correlates of anomic profiles can be observed in different time-windows, which seem to correspond to the time course of the impaired encoding processes.