Examining the Executive Function Profile of Children with Autism, Autism Plus Significant Symptoms of Attention Deficit Disorder, and Typical Development

Background: Attention deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) are very common early onset neurodevelopmental disabilities. ADHD co-occurs in 28-53% of children with ASD (Sinzig et al., 2009, Simonoff et al., 2008; Leyfer et al., 2006). Executive function (EF), or the ability to manage complex or conflicting information in the service of a goal, is significantly impaired in both ASD and ADHD. EF encompasses inhibition, shifting and working memory by mid childhood. Executive function impairments are particularly problematic because poor EF is related to: (1) lower academic performance, and (2) higher rates of aggression and disruptive behavior. In 2013, the DSM-5 first permitted the dual diagnosis of ASD and ADHD. As a result, there is relatively little information about the behavioral profiles of children with both disorders in contrast to ASD alone.

Objectives: To examine the executive function profile of 7 to 11-year-old children with ASD, ASD+ADHD and typical development. 

Methods: To date, participants include 20 children with ASD, 8 children with ASD+ADHD and 33 children with typical development (TD) all between 7-11 years of age. Enrollment of children with ASD is ongoing. ASD was confirmed via the ADOS-2 and ADI-R. Symptoms of ADHD were measured via the Child Behavior Checklist (CBCL). The three groups did not differ on age, sex, verbal IQ, or performance IQ. Executive function was measured by four separate tasks, each completed using a laptop computer: The Color-Word Stroop and the Child ANT Flanker Task measured inhibition of interfering information, the Change Task assessed inhibition of responses and set-shifting, and the Backward Digit Span Task examined verbal working memory skills. 

Results: For the two measures of inhibition that involved suppressing interfering information (Stroop and Flanker), the overall effect of group approached significance (ps=.06). The groups significantly differed on the inhibitory measure that required suppression of a dominant response (Change Task), F(2,53)=7.96, p=.001 (ASD+ADHD < ASD, TD). Shifting (Change Task) also differed by group, F(2,54)=5.23, p=.008 (ASD < ASD+ADHD, TD).  Finally, groups differed in verbal working memory skills, F(2,58)=5.57, p=.006 (ASD+ADHD < ASD, TD).

Conclusions: We found that children with ASD+ADHD were distinguished from children with TD and ASD alone using a behavioral battery of EF tasks by measures of inhibition of dominant responses and working memory. Children with ASD were distinguished by a measure of shifting. Results suggest that the type of inhibitory task demands may be particularly informative in distinguishing children with ASD from children who have both ASD and ADHD. Additionally, results suggest that other EF domains such as working memory and shifting contribute to the unique profile of ASD versus ASD+ADHD.