Assessing executive functions in post-stroke aphasia—utility of verbally based tests

Schumacher, Rahel; Halai, Ajay D.; Ralph, Matthew A. Lambon · 2022 · Crossref

DOI: 10.1093/braincomms/fcac107

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Summary

This study investigates the utility of verbally based executive function tests in patients with chronic post-stroke aphasia. While such tests are often avoided in this population due to language impairments, the authors hypothesize that they may reveal distinct cognitive deficits beyond language loss. The research aimed to determine if these tests measure independent executive functions, how performance correlates with language and nonverbal abilities, and what neural structures underlie these performances. The observational study included 32 patients with left-hemispheric strokes and varying aphasia severity. Participants completed three standardized verbal executive tests: verbal fluency (category and letter switching), the Hayling sentence completion test (initiation and suppression), and the Stroop colour-word interference test. Performance was analyzed using principal component analysis (PCA) to identify underlying cognitive dimensions. These components were correlated with a broad battery of language and nonverbal cognitive tests. Additionally, voxel-based correlational methodology (VBCM) was applied to structural MRI data to identify brain-behavior relationships, linking performance components to specific lesion patterns or tissue integrity. Results indicated that a substantial number of patients could perform the verbal executive tests. PCA revealed that performance in each test was driven by two independent components rather than a single factor reflecting overall language impairment. For the Stroop test, components reflected "language" (naming/reading speed) and "control" (interference errors). Hayling test components reflected "initiation" and "suppression," while fluency components reflected "generation" and "switching." Crucially, these components showed distinct correlations with background tests; for instance, Stroop control correlated with nonverbal impairment severity, while Hayling suppression did not correlate significantly with overall impairment severity. VBCM analyses demonstrated that each component had unique neural correlates. Stroop language and Hayling initiation correlated with left parietal and temporal regions, whereas Stroop control correlated with left hippocampal and brainstem areas. Hayling suppression was associated with left frontal and right paracingulate regions, and fluency switching correlated with right cerebellar structures. The findings demonstrate that verbally based executive tests capture multidimensional cognitive deficits in aphasia that are not solely explained by language impairment. Each executive component has distinct behavioral correlates and separate neural substrates, often involving frontal, parietal, and cerebellar regions. This suggests that administering these tests provides valuable clinical and theoretical insights into the specific executive dysfunctions present in aphasia, supporting their use in comprehensive neuropsychological assessments despite language deficits.

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• cognitive impairment