An MEG Study of Inhibition in Adolescents with Autism Spectrum Disorders

Background: Self-control depends upon cognitive processes such as response inhibition, which is the ability to withhold a prepotent, or competing, response.  Inhibition enhances adaptive functioning (Halperin et al. 1994), which is necessary for both social interactions and cognitive flexibility. As impairments in social functioning and the presence of restricted or repetitive behaviour (DSM-IV) are core criteria of an autism spectrum disorder (ASD) diagnosis, the study of inhibition is critical in this clinical population.  Furthermore, inhibition undergoes considerable development during the adolescent years and understanding the deficits in this process in ASD may help inform interventions.

Objectives: To determine spatial and temporal aspects of neural processing associated with response inhibition task in adolescents with ASD using magnetoencephalography (MEG).

Methods: Whole-head MEG data were acquired from 10 teenagers with an ASD diagnosis (ages 13.3 to 17.9; mean age 15.7) (8 males; 2 females); and 10 age and gender matched control teenagers (mean age 15.8).  Individuals with ASD (with an IQ above 80) met criteria specified by the Autism Diagnostic Observation Schedule-Generic (ADOS-G) and the Autism Diagnostic Interview Revised (ADI-R).  Subjects performed a visual go/no-go task that required participants to press a button to ‘go’ stimuli or withhold their response (no-go) if an "x" was overlaid on the visual stimuli. The experimental condition consisted of 33% no-go trials and tested the ability to withhold a prepotent tendency to respond, whereas the baseline condition consisted of 66% no-go trials.  The baseline condition was subtracted from the inhibition condition and then the MEG data were averaged.  Principal component analysis (PCA) was then applied to these data, examining the within-group variance of task related brain activity.  As well, beamformer analyses were applied to the data to localize brain activation, co-registered to each participant’s anatomical MRI scan. 

Results: Our preliminary analyses revealed a greater overall global field power (GFP) for controls in comparison to the ASD group.  Beamformer analyses revealed activation in the right middle frontal gyrus in a time window of 210 to 250 ms in only the control group when thresholded to 95% of peak activation.  A virtual sensor placed in the right middle frontal gyrus displayed peak activity in controls during a 200 to 250 ms time window, but no comparable activity in the ASD group.   

Conclusions: The lower overall power measured during the inhibition task in the ASD group compared to controls may be due to a lack of synchronization in neural firing within the ASD group.  Our preliminary analyses also indicate a greater activation of the right middle frontal gyrus in typical teenagers in comparison to teenagers with ASD.   Inhibition in healthy adults is commonly associated with activation of the right frontal lobe.  Thus, it appears that typically developing teenagers are perhaps utilizing the appropriate functional network responsible for inhibition, whereas adolescents with autism are not.