Slow Event-Related Brain Activity of Aphasic Patients in Word Comprehension and Rhyming Tasks

Abstract:
Slow event-related potentials were examined in healthy and aphasic subjects in two-stimulus designs comprising a Word Comprehension (stressing lexical access) and Rhyming (testing, in addition, for phonological encoding) tasks. Aphasics performed more poorly than controls on both tasks. Responses were analysed only for trials leading with correct response and for subjects who performed well above chance. A discriminant analysis of ERP amplitudes differentiated significantly between the groups for the Slow Wave (0.5-1.0 s post-S1 onset) in the Word Comprehension, for the Slow Wave and the iCNV (1.0-2.0 s post-S1 onset) in the Rhyming task. ERP topography showed left-anterior predominance of the negative Slow Wave and iCNV in controls, while aphasics showed smaller anterior and larger left- posterior amplitudes. The tCNV (1 s pre-S2) with centro-parietal focus in both groups was smaller in aphasics than in controls. Results indicate left-hemispheric activation for language processes such as lexical access, phonological encoding, and short-term storage of verbal stimuli and impaired (less left-anterior) and compensatory processes (more left-posterior activity) in aphasics. Canonical correlations between performance measures and ERP amplitudes did not reveal any statistical relationship.