Global and Local Scale Gamma-Band Activity within a Perceptual Organization Task in Individuals with and without Autism Spectrum Disorder

Background: In autism spectrum disorders (ASD), a bias to process local rather than global facial information (e.g., relations between face parts) has been proposed to be an underlying cause of impaired face processing. The temporal synchronization within and between cortical micro circuits, as measured by oscillatory gamma-band activity (GBA; > 25 Hz), offers an opportunity to examine how the brain integrates visual information into a coherent whole (“binding problem”). GBA findings are heterogeneous in ASD when compared to controls. Novel analytic approaches suggest coherence measures such as the inter-trial variability within subjects (inter-trial phase coherence; ITPC) and phase synchrony between electrodes (phase-locking value; PLV) to study processing efficiencies.

Objectives: We examined GBA amplitude, ITPC and PLVs in ASD individuals (n=20) and age- and IQ-matched neurotypical controls (N=25) during a perceptual organization task to investigate the hypothesis of an imbalance of local and global processing of faces.

Methods: Participants saw upright and inverted Mooney stimuli, which are degraded, two-tone pictures of human faces, and indicated face perception behaviorally (Face or No-Face). EEG was time-locked to the presentation of the stimuli.

Results: The pattern for Face and No-Face responses indicated significantly larger GBA for controls compared to individuals with ASD. ITPC analyses did not reveal any Group differences. Compared to ASD individuals, controls displayed larger phase synchrony for Face responses at posterior sites. For No-Face responses, synchrony pairs at frontal sites showed larger synchrony in controls compared to ASD individuals.

Conclusions: We detected lower levels of GBA for Face and No-Face responses in individuals with ASD, potentially indicative of a less effective activation of cortical micro circuits or impaired binding processes. Since ITPC did not differ between groups, ASD individuals do not seem to be inefficient in their local response to visual stimuli. Larger PLVs for controls (higher phase synchrony between electrodes) may suggest more elaborated communication on the global scale. In line with the framework provided by Kessler et al. (2016), our results suggest that local neural activity is similar in both ASD and neurotypical controls, but that the global, neural communication is less effective in ASD.