Beyond the DSM-5: Examining the effects of processing speed and working memory on ADHD symptoms and adaptive functioning

Abstract

Children with Attention Deficit Hyperactivity Disorder (ADHD) not only exhibit significant variability in the impulsive and hyperactive symptoms that characterise the diagnosis, but also in the presence and severity of impairment necessary to meet diagnostic criteria, such as adaptive functioning. An investigation of the mechanisms underlying this heterogeneity is paramount to provide effective interventions. Impaired working memory and processing speed have been shown to be associated with both ADHD symptoms and adaptive functioning. As such, the present study investigated the association between symptoms of ADHD, adaptive functioning, processing speed and working memory, before examining whether the latter two variables mediate the relationship between ADHD symptoms and adaptive functioning. Participants in this study included 103 children aged 6 – 12 years, 35 of whom were formally diagnosed with ADHD. ADHD symptom severity was assessed using the KSADS-PL, adaptive functioning was measured using combined teacher and parents’ ratings on the BASC-3, and the WISC-V assessed processing speed and working memory. In line with the hypotheses, the results showed that a greater percentage of children with ADHD displayed impairment in adaptive functioning, processing speed, and working memory compared to typically developing children. Significant correlations were found between all study variables, except between processing speed and hyperactive symptoms, adaptability, social skills, and functional communication. Bias-corrected, bootstrapped mediation analyses showed that working memory, but not processing speed, partially mediated the relationship between ADHD symptoms and adaptive functioning, suggesting that working memory should be assessed and addressed within the treatment of ADHD to reduce adaptive functioning impairment.