EEG delta band as a marker of brain damage in aphasic patients after recovery of language

In this study spectral delta percentage was used to assess both brain dysfunction/inhibition and functional linguistic impairment during different phases of word processing. To this aim, EEG delta amplitude was measured in 17 chronic non-fluent aphasic patients while engaged in three linguistic tasks: Orthographic, Phonological and Semantic. Average mapping of aphasics' structural lesion showed core damage in the left cortical-subcortical perisylvian areas. Delta amplitude was overall significantly higher in aphasics with respect to matched controls, a result in line with the view that diaschisis/cortical inhibition persists to some extent also in the chronic phase. Analysis of regions of interest revealed a peak of delta activity in left perilesional EEG sites, posterior to the core damage where residual suffering tissue probably projects its dysfunctional activity. Time course of word processing showed in patients greater delta percentage/inhibition in the first interval after word offset in correspondence of which verbal working memory is engaged. The significant interaction including group and task factors points to greater left posterior inhibition in aphasics across all tasks and left vs. right anterior relative disinhibition only during the Phonological task, whereas controls showed greater left vs. right disinhibition at anterior sites in all tasks. Delta band, in addition to its ability to reflect structural damage, was effective in the assessment of functional impairment as well as of linguistic reorganization of aphasics at hemispheric level with a spatial scalp distribution consistent with lesion map.