Indirect White Matter Pathways Are Associated With Treated Naming Improvement in Aphasia

Abstract

Background: White matter disconnection of language-specific brain regions associates with worse aphasia recovery. Despite a loss of direct connections, many stroke survivors may maintain indirect connections between brain regions.

Objective: To determine (1) whether preserved direct connections between language-specific brain regions relate to better poststroke naming treatment outcomes compared to no direct connections and (2) whether for individuals with a loss of direct connections, preserved indirect connections are associated with better treatment outcomes compared to individuals with no connections.

Methods: We computed structural whole-brain connectomes from 69 individuals with chronic left-hemisphere stroke and aphasia who completed a 3-week-long language treatment that was supplemented by either anodal transcranial direct current stimulation (A-tDCS) or sham stimulation (S-tDCS). We determined differences in naming improvement between individuals with direct, indirect, and no connections using 1-way analyses of covariance and multivariable linear regressions.

Results: Independently of tDCS modality, direct or indirect connections between the inferior frontal gyrus pars opercularis and angular gyrus were both associated with a greater increase in correct naming compared to no connections (P = .027 and P = .039, respectively). Participants with direct connections between the inferior frontal gyrus pars opercularis and middle temporal gyrus who received S-tDCS and participants with indirect connections who received A-tDCS significantly improved in naming accuracy.

Conclusions: Poststroke preservation of indirect white matter connections is associated with better treated naming improvement in aphasia even when direct connections are damaged. This mechanistic information can be used to stratify and predict treated naming recovery in individuals with aphasia.

Keywords: aphasia; brain connectomics; magnetic resonance imaging; rehabilitation; stroke; white matter.

Fig. 1.

Lesion overlay of all 69 participants. The warmer the color, the more participants had a lesion in this area. L=left hemisphere, R=right hemisphere.

Fig. 2.

A) Results of the significant analysis of covariance (ANCOVA) post hoc tests for connection type between the inferior frontal gyrus pars opercularis (IFGop) and angular gyrus (AG). B) Results of the significant interaction between treatment type and connection type between the inferior frontal gyrus pars opercularis (IFGop) and middle temporal gyrus (MTG) on change in naming accuracy after treatment. Line graphs were chosen to visualize the interaction between treatment type and connection type. Error bars display 95%-confidence intervals. Covariates appearing in the model are evaluated at the following values: Western Aphasia Battery (Aphasia Quotient) at baseline = 58.18, Age = 60.00, highest year of school completed = 14.82.

Fig. 3.

Signal propagation between each of the three region pairs. Fig. 3A IFGop and AG, Fig. 3B: IFGop and MTG, Fog, Fig 3C: AG and MTG. Colors of regions represent the percentage of patients passing these regions on the indirect connection from one region to the other. The greener the color the more patients passed this region.