Comparing Inhibitory Profiles of Children with ASD, ASD and Inattention Symptoms, and ASD and ADHD Symptoms

Background: Children with autism spectrum disorders (ASD) often have comorbid attention-deficit/hyperactivity disorder (ADHD) symptoms (Rommelse et al., 2010). Additionally, children with comorbid ASD and ADHD also have deficits in inhibition (Sinzig et al., 2007). Whether profiles of children with ASD and symptoms of inattention (ASD+inattention) differ from those of children with ASD+ADHD (symptoms of hyperactivity/as well as symptoms of inattention) is unknown. Understanding differences in ADHD symptom presentation in children with ASD may improve interventions and clinical outcomes in these stratified populations.

Objectives: To investigate the presentation of inhibition deficits in children with ASD, ASD+inattention, and ASD+ADHD.

Methods: Caregivers of 75 children with ASD (10 females; M=9.07±1.37 years) completed the CBCL, which was used to create three subgroups: ASD (n=31), ASD+ADHD (n=26), and ASD+inattention (n=18). T-scores on the BRIEF Inhibition subscale were a subjective, parent-report measure of inhibition. Higher scores on these measures reflect greater impairment in functioning. Children also completed objective measures of inhibition. From the Stroop Task, correct reaction time (cRT) on incongruent-congruent trials indexed interference suppression (i.e., bigger differences reflect worse inhibition). From the Change Task, proactive slowing on the dominant task (i.e., how much children are able to slow themselves down during the dominant task compared to their speed during practice trials) indexed better inhibition (working more slowly and carefully on the dominant task compared to baseline speed). Accuracy on change trials indexed the ability to suppress the dominant response to make the non-dominant response.

Results: Separate univariate ANOVAs compared measures of inhibition between children with ASD, ASD+inattention, and ASD+ADHD. Group was entered as a between-subjects factor and post-hoc comparisons were Bonferroni corrected.

In the model comparing BRIEF Inhibition T-Scores, there was a significant main effect of group, F(2,72)=9.82, p<.05. Post-hoc tests showed that T-Scores of children with ASD+ADHD were significantly higher than children with ASD+inattention, p=.027, and children with ASD, p=.001. However, T-scores did not differ between children with ASD and ASD+inattention, p=.765.

On the Stroop Task: the main effect of group was also significant, F(2,66) =4.80, p<.05, with the same pattern by group: children with ASD+ADHD differed from those with ASD+inattention, p= .037, and ASD, p=.024. The ASD and ASD+inattention groups did not differ, p=1.0.

In the model comparing proactive slowing during the Change Task, the main effect of group was significant, F(2,66)=2.949, p<.05. Children with ASD+ADHD marginally worse than those with ASD, p=.055, but not ASD+inattention, p= .484. Proactive slowing did not differ between ASD and ASD+Inattention, p=1.00.

Groups did not differ on accuracy during change trials, F(2,66)=.435, p<.05.

Conclusions: Collectively, these analyses suggest that in the domain of inhibition, children with ASD and inattention are more similar to children who have ASD than children who have comorbid ASD and ADHD. A better understanding of these differences may further inform effective interventions and improve clinical outcomes. Future analyses will compare these subgroups on additional measures of executive functioning as well as measures of social functioning given that social problems are more strongly correlated with inattention than hyperactivity (Maton et al., 2010).