Working Memory and Inhibition in ASD

Background:  

Children with an autism spectrum disorder (ASD) have deficits in working memory (WM) and inhibition. However, studies on WM using the n-back task are inconclusive, partly because of small sample sizes and wide age ranges. The few studies on inhibition using the stop task, a pure measurement of inhibition, are also inconclusive. The only study using a classic stop task showed that children with ASD had an inhibition deficit, but so far this finding has not been replicated. Hence, it is unclear if school age children with ASD show WM deficits when measured with an n-back task, or inhibition deficits when measured with a stop task.

Objectives:  

We investigated WM (n-back) and inhibition (stop task) in a large sample of children with ASD. Besides regular group comparisons, we explored if children with ASD that experience WM and/or inhibition deficits showed different symptom severity, behavior, and cognitive ability than children without deficits.

Methods:

Seventy-seven children with ASD (67 male), and 45 typically developing (TD) children (27 male) performed an n-back task, and 74 children with ASD (64 male), and 43 TD children (26 male) performed a stop task (all children were 8-12 years, IQ>80). As the male/female ratio differed between groups, gender was taken into account in analyses. The ADI-R was administered to parents of the ASD group, and all parents filled out the social responsiveness scale, and the disruptive behavior disorder rating scale.

Results:  

N-back task accuracy of the ASD group increased more between the 0 and 1-back level than in the TD group, resulting in a worse 1-back level performance in ASD. Groups performed similarly poor at the 2-back level; apparently this level was too difficult for both groups. There were no significant group differences in reaction times.

Children with ASD also performed worse than TD children on the stop task. In both tasks there was no gender effect. Within the ASD group, children with WM and/or inhibition deficits had more conduct and oppositional defiant behavior than children without deficits.

Conclusions:  

The ASD group showed both WM and inhibition deficits, but these deficits were not present in all children with ASD. Parents of children with ASD that did show WM and/or inhibition deficits reported more conduct and oppositional defiant behavior than parents of children with no deficits.