Restricted Repetitive Behaviors Related to Increased Activity at Ends of the Power Spectrum: Results from the ABC-CT Interim Analysis

Background: Individuals with autism spectrum disorder (ASD) exhibit high variability across symptom domains. To better understand the neural mechanisms behind clinical heterogeneity, it is important to investigate whether symptoms are associated with specific facets of brain activity. While there have been many studies assessing brain function in ASD, relatively few have examined how brain activity correlates with specific symptoms of ASD independent of a task. Previous research has found that increased behavioral rigidity, a common symptom in ASD, is correlated with increased alpha power in typically developing individuals. However, this relationship has not been directly investigated in individuals with ASD.

Objectives: To investigate whether a relationship exists between behavioral rigidity and alpha power in a sample including individuals with ASD.

Methods: 215 children between the ages of 6 and 11 years 7 months were recruited. 152 met criteria for ASD and 63 were typically developing (TD). EEG data was recorded using an EGI 128 channel net at a sampling rate of 1000Hz for three minutes while participants viewed an abstract screensaver (changing colors). Restricted repetitive behaviors (RRBs) were measured using subscales of the Autism Diagnostic Observation Schedule 2 (ADOS-2) and the Social Responsiveness Scale (SRS).

Results: T-tests were run comparing power bands of the EEG frequency spectrum; delta (1 to 3Hz), theta (4 to 7 Hz), alpha (8 to 12 Hz) beta (13 to 35 Hz) and gamma (>35 Hz) bands between diagnostic groups. No group differences were found (p>0.05). However, RRB symptoms as measured by the ADOS-2 and SRS were correlated with the EEG measures. Increased ADOS-2 RRB symptoms were significantly associated with greater absolute delta power (r=0.12,p=0.019), absolute theta power (r=0.12,p=0.017), absolute beta power (r = 0.11, p=0.024) and absolute gamma power (r=0.18, p=0.00032) but not absolute alpha power (r=0.066,p=0.19). Correlations with the SRS measure of behavioral rigidity were likewise significant for delta (r=0.11, p=0.030), theta (r=0.11, p=0.029), beta (r=0.12, p=0.014), and gamma (r=0.18, p=0.00050) bands but not for the alpha band.

Conclusions: Compared to findings from prior research in TD adults, in this study, increased activity at the ends of the power spectrum (delta, theta, gamma, and beta bands), but not in alpha, were associated with RRBs in participants with ASD. Other studies that have found that the extremes of the power spectrum are increased in ASD while alpha power is reduced, and postulate that this difference is partially related to abnormal GABAergic inhibitory tone in ASD (Wang et al 2013). Our results suggest that RRBs are a behavioral correlate of this phenomenon. GABA is thought to reduce power in the extremes of the spectrum and increase power in the alpha band (Gabard-Durnham et al 2012). Increased RRBs may indicate increased dysregulation in GABA tone in individuals with ASD. These results are a step towards specific linkages between cortical mechanisms and clinical symptomology.