Executive dysfunction in autism

'Executive function' is traditionally used as an umbrella term for functions such as planning, working memory, impulse control, inhibition and shifting set as well as the initiation and monitoring of action. These functions share the need to disengage from the immediate environment to guide actions. Executive functions are typically impaired in patients with acquired damage to the frontal lobes as well as in a range of neurodevelopmental disorders that are likely to involve congenital deficits in the frontal lobes. Such clinical disorders include attention deficit hyperactivity disorder (ADHD), obsessive compulsive disorder, Tourette syndrome, phenylketonuria, schizophrenia and autism spectrum disorder. It should be noted that executive dysfunction can be observed in those with acquired damage to non-frontal brain areas.

Autism spectrum disorder is a developmental disorder characterised by impaired social interaction and communication as well as repetitive behaviours and restricted interests. It is a lifelong disorder and affects at least 0.6% of the population with males being affected three times more often than females. Estimates of learning disability vary. In a recent review of epidemiological studies the percentage of individuals with a learning disability is given as 70%.

In recent years three key cognitive theories have been investigated in an attempt to understand the link between the brain and behaviour in autism. The most well-known of these is the theory of mind deficit hypothesis, and another account is that of weak central coherence. Although these two accounts together can explain many of the deficits and assets associated with autism, repetitive behaviours and restricted interests might best be explained by a third cognitive theory: that of executive dysfunction.

Mental flexibility

Poor mental flexibility is illustrated by perseverative, stereotyped behaviour and difficulties in the regulation of motor acts. This indicates problems in the ability to shift to a different thought or action according to changes in a situation. One task in which poor mental flexibility has been shown in autism is the Wisconsin Card Sorting Task (WCST). On this and similar tasks, individuals with autism experience a difficulty in mental flexibility in relation to normally developing individuals and those with other neurodevelopmental disorders (Figure 1). The deficit on the WCST is maintained over time and is not restricted to Western cultures. (For detailed information of studies of flexibility see http://archive.bmn.com/supp/tics/Hill_Suppl_tables.pdf )

Figure 1 . Mean group performance of children with autism (blue) and normally developing children (red). Groups were matched for chronological age. The performance of children with autism was significantly worse than that of the normally developing children on the WCST (p , 0.01), but not on the Stroop test (high scores indicate poorer performance). Data redrawn from [21] . (See also Supplementary information online at: http://archive.bmn.com/supp/tics/Hill_Suppl_tables.pdf ).

Inhibition

The story regarding inhibition is somewhat different . On a classic test of inhibition, the Stroop task, autistic children and adolescents are unimpaired (Figure 1). This is in contrast to other neurodevelopmental disorders clearly associated with executive dysfunction such as ADHD and phenylketonuria . Furthermore, autistic performance is normal on some other tests of inhibition, in particular a test of negative priming and neutral inhibition conditions of a Go/No-Go task.

Autistic children have also been shown to perseverate significantly more than a mental age matched control group on the Windows and Detour-Reaching tasks. This difficulty is seen in situations with and without a social component, as well as when the rules of the 'game' are both arbitrary or non-arbitrary.

Overall, these findings have been taken to indicate a difficulty in the inhibition of a prepotent response. However, as performance on the Stroop test - involving the inhibition of a prepotent response - is unimpaired in autism, how can these results be reconciled? Russell (2002) has postulated that the rules of some executive function tests appear arbitrary to autistic individuals and that it is this that causes the observed difficulties. He argues that executive function tests that do not lack a rationale are passed by those with autism. (For detailed information of studies of inhibition see http://archive.bmn.com/supp/tics/Hill_Suppl_tables.pdf )

Conclusion

Our understanding of executive dysfunction in autism has progressed over the past decade and it has been possible to identify components of intact executive function as well as dysfunction in the disorder. Overall, school-aged and adult autistic individuals of all ability ranges are impaired in the executive function of planning and show a certain type of perseverative behaviour, taken to indicate a deficit in mental flexibility. These individuals do not exhibit impaired inhibitory control per se, although they do show impaired inhibition of a prepotent response in certain cases, perhaps reflecting the forced application of an arbitrary rule.

Click to read the entire article

Taken from: Elizabth L. Hill. (2004). Executive Dysfunction is Autism, TRENDS in Cognitive Sciences, 8(1), pp. 26-32.