Baseline EEG Recordings in Young Children with ASD: Stimulus Type Matters

Background: Baseline EEG has been increasingly studied as a biomarker of baseline brain activity in children with autism spectrum disorders (ASD). Characterization of baseline EEG in this population often requires the presentation of a visual stimulus to maintain a child’s attention; stimuli range from live examiners interacting with the child to abstract videos (Machado 2015, Gabard-Durnam 2015). Stimulus type may impact a child’s overall state and level of engagement with the testing environment, altering the child’s EEG oscillations, leading to variability in signal that reflects “state” and not “trait’ of a child.

Objectives: We asked if there were differences in baseline EEG power at specific frequency bands when children with ASD watched a video of abstract shapes compared to a segment of their favorite video. We hypothesized that neural correlates of attention and engagement, as quantified by higher theta power, would occur when children watched a more appealing stimulus like their favorite video.

Methods:  We examined data from 27 children with ASD ages 2-6 years old (37% female; mean age = 55.6±13.2 months, IQ 49-114), recruited from the Early Childhood Partial Hospitalization Program. Baseline EEG was recorded using a high density system (EGI Inc. 128-channels). Children watched a video of an abstract screen saver followed by their favorite cartoon video (varied based on each child’s preference). Each video was presented for 2 minutes. EEG data were processed per prior protocols (McEvoy 2015). Relative spectral power for delta (1-3 Hz), theta (4-7 Hz), alpha (8-12 Hz), beta (13-30 Hz), and gamma (31- 48 Hz) frequency bands were calculated using Welch’s method, in 9 regions of interest (ROIs) across the scalp. For statistical analysis, we used a general linear model with repeated measure design for 3 within-group comparisons (video, frequency, ROI); we further examined significant main effects using paired samples t-tests. 

Results: There was a significant interaction of stimulus type with group (F_{4, 23} = 4.878, P = 0.005). Post hoc analysis showed relative power in the delta frequency band was significantly higher (P_delta = 0.003) in the abstract video (mean = 0.495±0.087) compared with the favorite video (mean = 0.473±0.077). Relative power in the theta and beta frequency bands was significantly lower (P_theta = 0.019, P_beta = 0.043) in the abstract video (mean_theta= 0.252±0.067, mean_beta = 0.107±0.028) than in the favorite video (mean_theta = 0.271±0.078, mean_beta= 0.113±0.031). There were no significant differences in alpha or gamma power between stimulus types.

Conclusions: Baseline EEG power can change based on stimulus type, with greater theta and beta power that may reflect increased attention and engagement during a preferred video. Preferred video also has a social salience that may elicit greater attention. These findings support the importance of reporting stimulus type during baseline EEG recording and maintaining consistent testing parameters during recordings. In ongoing analyses, we will examine these findings in relation to the child’s IQ, age, ASD severity, and rating of a child’s behavior during the EEG session.