The impact of pre-stroke formal education on language test performance in aphasic and non-aphasic stroke survivors.

Background: A greater amount of education is known to positively impact language skills in neurotypical populations, but its influence on language outcomes and recovery after stroke remains unclear. Aims: This study of 749 stroke survivors, with and without aphasia, investigated (A) which aphasia assessment tasks benefitted most from more pre-stroke education; and whether the effect of education (B) differs for aphasic and non-aphasic participants or other stroke and non-stroke-related variables, and/or (C) facilitates recovery from post-stroke aphasia. Methods: Participants ranged from one month to 42 years post-stroke. They were assessed using (i) the Comprehensive Aphasia Test (CAT), and (ii) self-report questionnaires that measured speech production, comprehension, reading, and writing at one week and one year post-stroke. Multiple regression analyses investigated the effect of education amount, and its interaction with other variables, on language outcomes and recovery. Bayesian statistics assessed the strength of the evidence for any observed effects. Many variables including lesion size, age at stroke, and initial severity were controlled for. Results: (A) More years of formal education were associated with better overall language skills, with significant, albeit small effects found for semantic and letter fluency (β = 0.123 and 0.166) and spoken picture description, specifically, the number of words produced (β = 0.085) and grammatical well-formedness (β = 0.087). (B) The benefit of more pre-stroke education was mostly additive with the effects of other variables including initial aphasia severity and left hemisphere lesion size, but was reduced in older participants who had large lesions with severe initial symptoms. Finally, (C) no significant effect of education on language recovery was observed. Conclusion: More pre-stroke formal education is associated with higher post-stroke language scores on a wide range of tasks for both aphasic and non-aphasic participants, but, in participants with large lesions that cause severe aphasia, this advantage diminishes with age. These results suggest a generic benefit of education on language test performance rather than a specific role of pre-stroke education in aiding language outcomes and recovery. An individual's educational background should therefore be considered when interpreting assessment scores.