Autism is associated with a greater than average rate of non-right-handedness, comprising both left- and mixed-handedness. Alongside deficits in left-hemisphere functions such as language and communication, this has given rise to the view that autism and some of its neurocognitive impairments might be due to an atypical pattern of cerebral lateralization.
Objectives:
To investigate whether left-handedness is (a) more common in adolescents with autism as compared to their unaffected siblings and typically developing controls, (b) associated with neurocognitive disadvantage and (c) correlated with clinical measures of impaired social communication and repetitive and stereotyped behaviour. We predicted that in view of the shared genetic risk for autism, adolescents with autism and their siblings would show a similar pattern in handedness and its cognitive correlates.
Methods:
Male adolescents with autism (n=35), their unaffected siblings (n=12) and typically developing controls (n=20; age: 12-18 years) were assessed for handedness using the Edinburgh Handedness Inventory. Raw handedness scores ranged from -100 to +100. The Stockings of Cambridge task from the Cambridge Neuropsychological Test Automated Battery (CANTAB) was applied to measure executive function in terms of planning as this has been linked to handedness in previous research. Communication abnormalities and stereotyped behaviours were measured using subdomains of the ADI-R and ADOS-G.
Results:
(a) Handedness showed a marked leftward shift in adolescents with autism in comparison to their siblings (p=.004), but not in comparison to controls. (b) Mean number of moves on the Stockings of Cambridge task was significantly related to a leftward handedness shift in the whole sample (r=-.355; p=.006) and in adolescents with autism (r=-.446; p=.013). (c) Communication abnormalities measured with the ADOS-A showed a trend towards correlation with a leftward handedness shift (r=-.331; p=.064). However, leftward raw handedness scores correlated significantly with higher scores on repetitive and stereotyped behaviour subdomains of the ADI-C (r=-.497; p=.004) and ADOS-D (r=-.502; p=.003). (d) Mean moves on the Stockings of Cambridge and the ADI-C (r=.398; p=.018) and ADOS-D (r=.379; p=.030) subscales showed a significant correlation.
Conclusions:
Functional asymmetry may be impaired in autism, but appears intact in siblings, suggesting that it may relate to autism itself rather than to the familial risk of the condition in the broader phenotype. Repetitive behaviour and not impaired communication abilities seems to be related to a leftward shift as well as to poorer executive function in males. Future research should also include brain structural correlates of asymmetry to corroborate these findings neuroanatomically, and to further test anomalous cerebral specialization in autism.
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