Brain Network Involved in Response Inhibition Shows Delayed Recruitment in Adults with ASD

Background: There are varying reports of inhibitory control skills in adults with autism spectrum disorder (ASD), with some showing that their ability to exercise inhibition is on par with controls, while others find a significant deficit. Neuroimaging studies have demonstrated that despite performing similarly to controls, adults with ASD have atypical activation of and connectivity between brain regions subserving inhibition, such as the bilateral inferior frontal gyri (IFG) and anterior cingulate cortex (ACC). A thorough characterization of these brain differences is still lacking, however, as little is known regarding the timing of recruitment of these brain areas and networks and in which frequency bands of neuronal firing they occur in ASD.

Objectives: We determined the temporal, spatial, and frequency-specific dynamics of brain connectivity in adults with and without ASD during an inhibitory control task using magnetoencephalography (MEG).

Methods: We recruited 47 adults with ASD (32 M; 27.0±5.9 years old) and 43 age- and sex-matched control adults (30 M; 27.3±5.7 years old). In the MEG scanner, participants performed a go/no-go task comprising two blocks of differing proportions of ‘no-go’ trials, inhibition (25%) and vigilance (75%), allowing us to compare ‘no-go’ trials with high vs. low inhibition demands, rather than compare ‘no-go’ to ‘go’ trials, the latter being contaminated by motor responses. For the MEG analyses, we estimated time series of activity across the brain using a beamformer. We calculated connectivity between regions within each canonical frequency band using the weighted phase lag index. We compared connectivity values in the ‘no-go’ trials of the inhibition vs. vigilance blocks between 100-500ms, post-stimulus onset. Significant results are reported at a FWE-corrected p < 0.05. Participants also completed the self-report version of the Behavior Rating Inventory of Executive Function, Adult Version (BRIEF-A). Inhibition subscale scores were compared between groups and correlated with brain connectivity values.

Results: Results indicate that adults with ASD reported more difficulties with inhibition on the BRIEF-A, but this difference was only a trend (t(46)=1.93, p=0.06). Despite equivalent performance on the go/no-go task (F(1,83)=0.10, p=0.76), adults with ASD showed decreased connectivity (p=0.047) in a network containing the right IFG and right insula between 200-300 ms in the high gamma frequency band. Subsequently, between 300-400 ms in the same frequency band, adults with ASD exhibited increased connectivity (p=0.042) in a similar network, which included the right IFG, right insula, ACC, and left supplementary motor area (SMA). Connectivity between the right IFG and the bilateral SMA was negatively correlated with Inhibition scores on the BRIEF-A in controls (β=-9.80, p=0.02), but not in adults with ASD (β=4.10, p = 0.21).

Conclusions: Adults with ASD appear to show delayed recruitment of an inhibitory control brain network compared to controls, as well as atypical connectivity between inhibitory and motor areas, both of which may contribute to the inhibition difficulties reported in their everyday life, but less apparent in laboratory tasks.