Executive Function in Autism: A Systematic Review and Meta-Analysis

Background: Executive function (EF) is an umbrella term for functions such as working memory, impulse control, planning, mental flexibility and fluency. Deficits in EF are common in autism but not present in all individuals. Numerous studies investigated EF among the spectrum but have yielded varying findings according to the age of the participants and the type of task used (Hill, 2004). Some studies revealed global deficits in overall functions, some more specifically in planning and flexibility (Ozonoff et al., 1999) while some indicated no difference with typically developing (TD) individuals (Russell, 1999). Furthermore, greater deficits seem present in children compared to adults (Happé, 2006). The nature of EF difficulties in autism remains unclear due to an important heterogeneity among previous results and the lack of systematic review. 

Objectives: The main goal of this meta-analysis was to determine the pattern and magnitude of executive deficits in autism spectrum disorder. 

Methods: A systematic literature search was performed (PubMed, PsycINFO; 1970-2015) using key word such as “autism”, “ASD”, “PDD”, “Asperger”, “working memory” and “executive function”. A total of 1770 studies were identified. 100 cognitive behavioural studies met the inclusion criteria (presence of an age and IQ-matched control group; FSIQ≥70; use of standardized test), involving 2706 ASD and 2778 typically developed (TD) individuals. Results were analyzed with comprehensive meta-analysis software according to the different executive functions (inhibition, flexibility, planning / organization, fluency and working memory) for ASD and TD individuals. Effect sizes were calculated (Cohen’s d, standardized mean difference) for each executive function and supplementary analysis were computed for each type of measure and more recurrent test used.  

Results: Analyzes showed inferior results for autistic individuals, relative to TD individuals, in all areas of executive functions (d = 0.25 to 0.54; all p ≤ .001). ASD individuals showed the strongest and most consistent difficulties in set‐shifting and planning (d = respectively 0.54, 0.49, both p ≤ .001). Significantly lower performances in working memory are found exclusively in visuospatial tasks (d=0.25, p=.001), not in verbal working memory tasks. Lastly, moderate group differences were found on measures of inhibition (d = 0.45, p ≤.001) and fluency (d= .46, p≤.001) relative to controls. Data analysis is still undergoing for the effect of intellectual level and the developmental aspect.

Conclusions: This systematic review reveals that while autism is associated with global executive difficulties, executive function difficulties are most consistent for measures of planning and mental flexibility. A better understanding of the executive functions profile of autistic individuals will support 1) a better understanding of the nature of some symptoms seen in autism and 2) development of appropriate intervention and educational strategies, especially since the development of executive functions in autism seems to follow a different pathway. However, detailed research is needed to define the role of some comorbidities in the autism spectrum executive profile, especially the role of ADHD.