Subtle executive impairment in children with autism and children with ADHD

Background: The executive functions of inhibition, planning, flexible shifting of actions, and working memory are commonly reported to be impaired in neurodevelopmental disorders. Method: We compared these abilities in children (8-12 years) with high functioning autism (HFA, n = 17), attention deficit-hyperactivity disorder (ADHD, n = 21) and healthy controls ( n = 32). Response inhibition was assessed using the Stroop Color and Word Test ( Golden, 1978). Problem solving, set- shifting, and nonverbal memory were assessed using three tasks, respectively, from the CANTAB (R) ( Cambridge Cognition, 1996): the Stockings of Cambridge task; the Intra-Dimensional/Extra-Dimensional set- shifting task; and the Spatial Working Memory task (SWM) with tokens hidden behind 3, 4, 6, and 8 boxes. Results: There were no group differences on the response inhibition, planning, or set- shifting tasks. On the SWM task, children with HFA made significantly more between-search errors compared with controls on both the most difficult problems (8-box) and on the mid-difficulty problems (6-box); however, children with ADHD made significantly more errors compared to controls on the most difficult (8-box) problems only. Conclusion: Our findings suggest that spatial working memory is impaired in both ADHD and HFA, and more severely in the latter. More detailed investigation is needed to examine the mechanisms that differentially impair spatial working memory, but on this set of tasks there appears to be sparing of other executive functions in these neuropsychiatric developmental disorders.