Hemispheric Lateralisation of Neural Responses to Faces in Individuals with Autism: a Magnetoencephalographic Study

Background: It is commonly agreed that laterality is a fundamental feature associated with brain functioning under normal conditions. Recent findings obtained from electrophysiological and neuroimaging studies provide evidence for lateralised anomalies in the neural response in individuals with autism spectrum disorders compared to typically developing individuals. However, it is unresolved whether such anomalies reflect qualitative changes in laterality rather than quantitative modulation of neural activity without affecting hemispheric patterns in general.

Objectives: To investigate hemispheric differences in the neural response associated with face processing using magnetoencephalography.

Methods: 8 male individuals with autism and 8 typically developing male subjects participated in this study. Participants were matched on age (mean 12 years) and IQ. All measurements were taken at the Brain Research Unit, Helsinki University of Technology, using a VectorView(TM) system providing first-order gradiometers most sensitive to directly underlying neuronal currents. The participants performed a matching task that required attention to be paid to the identity of images, where pairs of images of adolescents with varying gaze direction and motorbikes were presented sequentially. This study was approved by the ethics committee of Tampere University, and all participants and their parents gave informed consent before experimentation.

Results: At 100 ms after stimulus onset, all image categories evoked stronger responses over right compared to left extra-striate cortices in both groups, however the responses detected over the right hemisphere were significantly stronger in individuals with autism compared to typically developing subjects. In typically developing individuals, straight gaze evoked significantly stronger activity over left anterior cortices at around 340 ms compared to averted gaze. The opposite pattern, averted stronger than straight, was found in individuals with autism over approximately the same region and latency. These findings will be compared to results obtained from an analysis of asymmetry of alpha-band power.

Conclusions: These data suggest that laterality changes in autism are bound to be multifaceted, being both quantitative and qualitative dependent on stimulus type and processing stage. This may have implications for inferring the functional neuroanatomy in autism based on known correlation of brain activity and task parameter established in typically developing individuals.