Early subacute frontal callosal microstructure and language outcomes after stroke

The integrity of the frontal segment of the corpus callosum, forceps minor, is particularly susceptible to age-related degradation and has been associated with cognitive outcomes in both healthy and pathological ageing. The predictive relevance of forceps minor integrity in relation to cognitive outcomes following a stroke remains unexplored. Our goal was to evaluate whether the heterogeneity of forceps minor integrity, assessed early after stroke onset (2-6 weeks), contributes to explaining variance in longitudinal outcomes in post-stroke aphasia. Both word- and sentence-level tasks were employed to assess language comprehension and language production skills in individuals with first-ever left-hemisphere stroke during the early subacute and chronic phases of recovery (n = 25). Structural and diffusion neuroimaging data from the early subacute phase were used to quantify stroke lesion load and bilateral forceps minor radial diffusivity. Multiple linear regression models examined whether early subacute radial diffusivity within the forceps minor, along with other factors (stroke lesion load, age, sex and education), explained variance in early subacute performance and longitudinal recovery (i.e. change in behavioural performance). Increased early subacute radial diffusivity in the forceps minor was associated with poor early subacute comprehension (t = -2.36, P = 0.02) but not production (P = 0.35) when controlling for stroke lesion load, age, sex and education. When considering longitudinal recovery, early subacute radial diffusivity in the forceps minor was not linked to changes in performance in either comprehension (P = 0.11) or production (P = 0.36) under the same control variables. The examination of various language components and processes led to novel insights: (i) language comprehension may be more susceptible to white matter brain health than language production and (ii) the influence of white matter brain health is reflected in early comprehension performance rather than longitudinal changes in comprehension. These results suggest that evaluating baseline callosal integrity is a valuable approach for assessing the risk of impaired language comprehension post-stroke, while also underscoring the importance of nuanced analyses of behavioural outcomes to enhance our understanding of the clinical applicability of baseline brain health measures.