Reduced Resting Gamma Power Is Associated with Symptom Severity in Autism

Background: In addition to the triad of impairments observed in autism, sensory processing abnormalities have also been reported.  Recent studies have suggested that abnormal electroencephalography (EEG) frequency oscillations may indicate impaired sensory processing in psychiatric disorders, including Autism Spectrum Disorders (ASD).  Specifically, abnormal oscillations in the gamma frequency band have been found in ASD and proposed as a potential biomarker; however, these findings have been mixed depending on whether evoked versus resting gamma oscillations were examined.  While many studies have investigated gamma oscillations in ASD, none have reported an association between gamma and ASD symptom severity. Examining the relationship between the degree of ASD symptomatology and gamma abnormalities may be a first step towards better understanding the extent to which gamma oscillations function as a potential biomarker in ASD.  

Objectives: 1) To investigate resting gamma power in high functioning males with ASD compared to age and IQ matched typically developing controls (TDC) using EEG and 2) to explore associations between the gamma frequency band and ASD symptom severity as measured by the Social Responsiveness Scale (SRS). 

Methods: Resting scalp EEG was recorded from 15 boys diagnosed with ASD and 18 typically developing boys (TDC) ranging in age from 9 to 18 years (M=14.5 years, SD=2.8 years).  Total gamma power was calculated for 9 electrodes, averaged across frontal (F5, Fz, F6), central (C5, Cz, C6) and parietal (P5, Pz, P6) regions and a repeated measures ANOVA was used to determine significant differences by group and brain region. Groups were matched on age and IQ.  Exploratory analyses included Pearson correlations to examine associations between resting gamma power and SRS total across all subjects. 

Results: In the gamma frequency band, significant main effects of topography (p<0.001) and a topography by subject group (diagnosis) interaction (p=0.012) were found.  A t-test confirmed that at central electrodes, resting gamma power was reduced in ASD compared to TDC (p =0.014).  Exploratory analyses yielded a significant negative correlation between gamma power at central electrodes and the SRS total (Pearson r = -0.4; p = 0.021).

Conclusions: To our knowledge, this is the first study to report an association between abnormal power oscillations in the gamma frequency band and ASD symptom severity.  Our findings provide a foundation for future studies to investigate the relationships between physiological measures and ASD symptomatology in order to increase our understanding of the fundamental neural deficits observed in ASD and provide further support of gamma oscillations as a possible biomarker.  Future studies should include males and females with lower-functioning ASD relative to other clinical comparison groups (e.g., ADHD) to further elucidate this finding.