Executive Function: Cognition and Behaviour in Adults with Autism

Background: Executive function (EF) is a complex cognitive construct incorporating a number of processes associated with higher-level thought and behaviour across the life-span. EF has been much studied in Autism Spectrum conditions with inconsistent findings reported in terms of impairment across the different facets of EF. It is thus not clear if impairments in EF are truly characteristic of ASD in respect of cognition and if cognitive deficits are consistently related to behavioural features. Co-morbidity and individual heterogeneity are important factors to take account of in study design.

Objectives:  The study aimed to investigate the performance of high functioning adults without intellectual disability with robust diagnosis of Autism Spectrum Disorder (ASD) across a range of EF tasks, and particularly to consider the issue of heterogenity. The study also explored whether EF impairments impact on (a) everyday function and (b) ASD symptomatology including repetitive behaviours.

Methods:  Participants with ASD (n=110) were compared with age and IQ matched healthy controls (n=31) on a battery of well validated clinical neuropsychology tasks assessing planning, cognitive flexibility, inhibition, generativity/fluency and speed of task completion. Information about the behavioural characteristics associated with EF difficulties was collected using standardised informant and self-report. Participants with co-morbid ADHD, psychosis and neurological disability were excluded from the study. Group differences across the main test indices were investigated. Exploratory factor analysis was employed to consider the universality of impairment across EF function.

Results:  Participants with ASD were significantly more likely to score in the impaired range across all the EF tasks, although notably approximately 1/3 of the ASD group were not impaired on any of the EF test indices. Significantly higher levels of behavioural, cognitive and emotional characteristics associated with EF were reported in the ASD group. Exploratory factor analysis confirmed a single underlying construct or 'EF factor' consistent with the theoretical account in the literature of a single over-arching executive process. This 'EF factor' was not related to ASD symptoms or behavioural characteristics. Behavioural characteristics associated with ASD could also not be accounted for by co-morbid psychiatric difficulties such as anxiety.

Conclusions:  The majority of high functioning adults with ASD are impaired across a number of tests of executive function when compared to adults without ASD. Performance across EF tests was found to represent a single underlying construct. Everyday difficulties associated with EF impairment are common in adults with ASD but on the basis of these findings are not accounted for by performance on neuropsychological tests, ASD symptoms or psychiatric co-morbidity. The findings of this study suggest executive function is an important domain to consider when assessing adults with ASD in respect of formulating difficulties and modifying interventions to reduce executive demands. Further investigation into 'dysexecutive' difficulties in everyday function in ASD is warranted. Notably one third of adults with ASD in this study were not impired on any of the EF measures.