Executive Functions in ASD
There are three key theories that attempt to explain the links between brain and behaviour in Autistic spectrum disorders (ASD): the Theory of Mind Deficit Hypothesis (for a review see Baron-Cohen, 2001), the Weak Central Coherence (Happé & Frith, 2006) and that of Executive Dysfunction (Hill, 2004).
Executive functions is an umbrella term for a number of cognitive and behavioural capacities such as planning, working memory, inhibition, mental flexibility, multitasking, initiation and monitoring of action (Gilbert & Burgess, 2008). Executive functions are usually impaired in patients with frontal lobe damage and in many neurodevelopmental disorders like ADHD, OCD, schizophrenia and ASD. These disorders are likely to involve deficits in the frontal lobes.
Autistic people seem to be impaired only in some tests of executive functions, especially those involving multitasking (“Six Element Test”, Hill & Bird, 2006), planning (“Tower of London”, Ozonoff et al, 1991) and Inhibition (“Go/No-Go task” , Ozonoff & Strayer, 1997). Deficits have also been shown in planning and abstract problem solving tasks (Hill & Bird, 2006). On other tests their performance is equal or superior to control groups (Minshew, Goldstein & Siegel, 1997). It’s worth noting that ASD individuals are mostly impaired in newer tests rather than classical tests of executive functions (Hill & Bird, 2006, Gilbert et al., 2008). These findings could be due to the heterogeneity of different tests of executive function (Gilbert et al., 2008).
Most of the tasks in which ASD individuals show deficits are thought to be mediated by the frontal lobes. A number of studies have identified several several cortical, subcortical abnormalities and functional differences (Kawakubo et al., 2009; Schmitz et al., 2005).
The theory of cortical underconnectivity posits a deficit in integration of information at the neural and cognitive levels (Just et al., 2006). Findings from neuroimaging studies such as the thinning of the corpus callosum and the reduced connectivity, especially with the frontal areas and also the fusiform face area in ASD people support the theory of underconnectivity (Hughes, 2007). Recently, increased activation in medial rostral prefrontal cortex (BA 10) during tasks of stimulus-oriented versus stimulus-independent attention has been found in people with ASD (Gilbert et al., 2008). Previous studies has shown the importance of rPFC in selection between stimulus-oriented and stimulus-independent thought (Gilbert, Frith & Burgess, 2005; Ramnani & Owen, 2004). On the same task the control group showed greater activity primarily in bilateral occipital cortex. According to Gilbert et al.:
“This suggests that the control group were able to modulate activity in early visual cortex according to the attentional demands of the task to a greater degree than the ASD group. The stimuli were matched between the two conditions, suggesting attentional modulation rather than an effect of stimulus-category. This finding is consistent with the suggestion of functional underconnectivity in ASD”
Happé, F., Booth, R., Charlton, R. & Hughes, C. (2006) Executive function deficits in Autism Spectrum Disorders and Attention-Deficit/Hyperactivity Disorder: Examining profiles across domains and ages. Brain and Cognition.
Baron-Cohen, S., & Swettenham, J. (1998) Theory of mind in autism: Its relationship to executive function and central coherence. In D.J. Cohen & F.R. Volkmar (Eds.), Handbook of autism and pervasive developmental disorders (2nd ed., pp. 880–893). New York: Wiley.