Executive Function and Social Cognition Impairments in Autism Spectrum Disorder, Attention-Deficit/Hyperactivity Disorder and Comorbid Presentation

Background: Attention-deficit/hyperactivity disorder (ADHD) frequently co-occurs among people with autism spectrum disorder (ASD), prompting studies of individuals with the “pure” disorders and their “combined” (i.e., ASD+ADHD) form. Social cognition (SC) deficits were often reported in ASD. Furthermore, executive function (EF) deficits were often reported in individuals with ADHD and with ASD, although the latter finding might be associated with the co-occurring ADHD symptoms in the population. ^1,2 To date, only one study of EF and SC in adults in this population have been conducted,³ the findings of which were confounded by uneven distributions of sex and ADHD subtypes across groups.

Objectives: This study compared the EF and SC impairments of young adult males with ASD, ADHD, ASD+ADHD against those with typical development (TD). Medication intake and ADHD subtypes were balanced across groups with ADHD diagnoses. We expected the ADHD and the ASD+ADHD groups to be impaired primarily in EF, and the ASD in SC, relative to the TD group.

Methods: We tested 105 young adult males (age 20-27 years, FSIQ ≥ 70) with ASD (n = 26), ADHD (n = 27), ASD+ADHD (n = 27) against TD controls (n = 25) on a battery of computerized EF (response inhibition, sustained attention, visuospatial working memory, cognitive flexibility, temporal discounting) and SC tasks (theory of mind [ToM] and facial emotion recognition [FER]). Behavioral data were analyzed using omnibus MANOVAs and further explored using univariate ANOVAs with Group as a predictor. Analyses were conducted with and without IQ added as a covariate and contrasts were planned between each clinical group against TD.

Results: Omnibus MANOVAs revealed an effect of Group in EF (p = .001) and SC performance (p = .002). Univariate ANOVAs revealed that, relative to TD, the ASD, ASD+ADHD and ADHD groups were impaired on primary measures of response inhibition (commission errors), sustained attention (omission errors) and working memory (ps ≤ .03), but these findings did not survive in the ASD group after IQ was covaried. Impairments in temporal discounting were specific to ADHD (p = .03), and remained when IQ was covaried. Cognitive flexibility did not differ across groups. The ASD and ASD+ADHD groups committed more errors during both SC tasks than the ADHD and TD groups, but only the FER errors in the ASD group (p < .001) remained after IQ was covaried.

Conclusions: Response inhibition, sustained attention, and working memory were not only impaired in the ADHD and ASD+ADHD, but also in the ASD group, although in the latter only when IQ was not included. Temporal discounting deficits was specific to ADHD and suggested the pervasive executive dysfunction in this population. SC impairments were found in the ASD and ASD+ADHD groups, although mostly did not survive when IQ was covaried. These demonstrate the associations between EF deficits and ADHD, SC deficits and ASD symptoms. There was some support for additivity of impairments in the combined diagnosis and the role of IQ as an explanatory factor for the variation of cognitive findings in adults in the populations.