Executive function (EF) in dyslexia: examining an EF profile associated with dyslexia and comorbid dyslexia-ADHD and exploring the near and far transfer effects of EF training in dyslexia alone.

Although there are several competing theories to explain dyslexia, no clear causal pathway has been established. Current theories also fail to address associated socio-emotional difficulties and high co-occurrence of dyslexia with ADHD. Executive function (EF), an umbrella term for a triad of high-level cognitive processes associated with pre-frontal brain regions – response inhibition (RI), working memory updating and switching, is a candidate factor for explaining the overlap between dyslexia and ADHD and co-occurring socio-emotional issues. EF appears to be a modifiable trans-diagnostic factor differentially implicated in neurodevelopmental conditions and therefore may offer novel routes for targeted interventions. Yet, it is unclear if EF is an overlapping impairment associated with dyslexia and comorbid dyslexia-ADHD, and which aspects of EF are important for explaining severity of reading and socio-emotional outcomes. Addressing methodological issues from previous EF profiling studies, this PhD aimed to (a) examine EF in both dyslexia conditions using Miyake’s 3-factor model (inhibition-common EF, updating and switching – specific EFs) (study 1), (b) explore the ability of EF to predict dyslexia diagnosis and severity of symptoms expressed in core reading and non-core socio-emotional domains (study 1), and (c) explore the near (EF, brain activity) and far (reading, self-regulation, socio-emotional problems) transfer effects of low and high doses of targeted common EF (inhibition) training in dyslexia (study 2). Study 1 established that response inhibition (RI) and updating are overlapping transdiagnostic impairments associated with dyslexia and comorbid dyslexia-ADHD. Logistic and linear regression analyses suggest that RI and updating impairments are predictive of dyslexia diagnosis and core reading outcomes (study 1). The predictive role of RI in dyslexia diagnosis and severity of reading outcomes was further confirmed in a secondary sample (study 2). A 6-week RI targeted training intervention led to pre-post changes across both doses in RI (cognitive and neural levels), other EF abilities (updating and switching), reading ability, socio-emotional problems and self-regulation in dyslexia alone (study 2). However, no interaction effects were observed, making it difficult to determine if RI training transfer was achieved in both cases. Overall findings suggest, for the first time, that RI is an overlapping impairment in dyslexia and comorbid dyslexia-ADHD that is implicated in reading and socio-emotional issues. Nevertheless, further research with passive and active placebo groups is needed to determine whether RI training can transfer to improvements in RI, other EFs and associated issues in children with dyslexia