MEG Measures of Inhibition in Adults with Autism Spectrum Disorders

Background:  Self-control depends upon cognitive processes such as response inhibition, which is the ability to withhold a dominant response. Poor inhibitory control is seen in autism spectrum disorders (ASD), and can have serious social ramifications. There have been conflicting results pertaining to the brain networks involved in inhibition in ASD.

Objectives:  To determine the spatial and temporal aspects of neural processing associated with inhibition in adults with and without ASD using magnetoencephalography (MEG).

Methods:  Whole-head MEG data were obtained from 20 adults (ages 20-34): 10 (8 males; 2 females) with ASD diagnoses from clinicians and 10 healthy controls matched on age and gender. IQ scores were obtained. Subjects performed a go/no-go task that required participants to press a button to visual ‘go’ stimuli or withhold their response (no-go) if an "x" was superimposed on the stimuli. The experimental condition consisted of 33% no-go trials and tested the ability to withhold a prepotent tendency to respond. The control condition consisted of 66% no-go trials, thus not producing a prepotent tendency to respond. Data were analysed with independent component analysis and trials with artefacts were removed. The control condition was then subtracted from the experimental condition and principal component analysis (PCA) applied to the averaged data, to assess differences between groups for the no-go trials in the two conditions (which did or did not require inhibition). Beamformer analyses were also run on the data, within the time windows determined by analysis of the sensor data, to locate the brain regions activated during inhibition.

Results:  Measurements of global field power (GFP) showed a broad peak for both the control and ASD groups between 200ms – 300ms, with lower amplitudes in the ASD group. PCA analyses revealed significant peak activation between 212ms and 228ms for the control group and between 220ms and 262ms for the ASD group. In control adults, significant activity was found with beamformer analyses in the right inferior frontal gyrus (IFG) that peaked around 223ms on the source time course. For adults with ASD activation in the IFG did not pass threshold.

Conclusions:  These preliminary results suggest a delay in the neural processing associated with response inhibition as well as a lower activation of the IFG, in adults with ASD; past research has also found IFG activity associated with inhibition in healthy adults.  These findings also provide insight into the neural mechanisms that underlie inhibition in individuals with ASD.