An electrophysiological contribution to the study of language lateralization and prognosis of aphasia

Abstract

The study is aimed at identifying hemispheric language dominance in both the right-handed and left-handed participants. Eighteen right-handed and 18 left-handed young volunteers were invited to listen for 80 times to a 720 ms duration Italian word. Signals from 16 electrodes were averaged and displayed both as traces and maps. When the word was delivered to the participant, a positive component at 340 ms was recorded, following the N100-P200 complex. The potential was significantly lateralized to the left hemisphere in 50% of the right-handers. The left-handed group was less homogeneous. Six out of 18 participants (33%) had a right lateralization, six participants (33%) had the positive potential shifted to the left hemisphere. Finally, the remaining participants had a bilateral representation. The maps show that there are no two participants alike, independently of either sex or handedness. A 300 Hz tone of the same duration failed to evoke the P340. Results indicate the utility of event-related potentials in studying the language processing. The possibility to identify cortical localization permits a better prognosis of acquired aphasia. The method is relatively cheap and noninvasive. Application is suggested in those participants who are at risk of stroke or in patients to be submitted to a neurosurgical intervention nearby possible language areas.