EEG Data Collection in Children with ASD: The Role of State in Data Quality and Spectral Power

Abstract

Background: Electroencephalography can elucidate neurobiological mechanisms underlying heterogeneity in ASD. Studying the full range of children with ASD introduces methodological challenges stemming from participants' difficulties tolerating the data collection process, leading to diminished EEGdataretentionandincreasedvariabilityin participant 'state' during the recording. Quantifying state will improve data collection methods and aide in interpreting results.

Objectives: Observationally quantify participant state during the EEG recording; examine its relationship to child characteristics, data retention and spectral power.

Methods: Participants included 5-11 year-old children with D (N=39) and age-matched TD children (N=16). Participants were acclimated to the EEG environment using behavioral strategies. EEG was recorded while participants watched a video of bubbles. Participant 'state' was rated using a Likert scale (Perceived State Rating: PSR).

Results: Participants with ASD had more elevated PSR than TD participants. Less EEG data were retained in participants with higher PSR scores, but this was not related to age or IQ. TD participants had higher alpha power compared with the ASD group. Within the ASD group, participants with high PSR had decreased frontal alpha power.

Conclusions: Given supportive strategies, EEG data was collected from children with ASD across cognitive levels. Participant state influenced both EEG data retention and alpha spectral power. Alpha suppression is linked to attention and vigilance, suggesting that these participants were less 'at rest'. This highlights the importance of considering state when conducting EEG studies with challenging participants, both to increase data retention rates and to quantify the influence of state on EEG variables.

Keywords: EEG; autism spectrum disorder; intellectual disability; spectral power.

Figure 1:. Conceptual outline of factors contributing to the EEG signal

Caption: As a measure of synchronized, post-synaptic neural activity, EEG is a method to assay neural mechanisms, which are thought to serve as intermediary between biological processes and observed behavioral characteristics. In order for the EEG signal to be interpretable, there needs to be a sufficient signal-to-noise ratio. Several studies have outlined specialized behavioral strategies suitable for acclimating participants to the EEG environment and therefor increasing successful EEG data acquisition. Participant ‘state’ during the EEG recording has the potential to contribute to the EEG signal as well, serving as a confound when drawing conclusions about underlying neurobiological traits. Although state may also be modulated through the use of behavioral strategies, measuring state during the recording is necessary in order to understand its relationship to data quality and contribution to the observed EEG signal.

Figure 2:. Histograms of verbal and non-verbal IQ scores in the ASD group

Caption: Histograms demonstrating the range of verbal and non-verbal IQ scores in the SD group. The ASD group included participants with a wide variety of verbal and non-verbal cognitive abilities.

Figure 3:. Percentage of EEG data retained by group

Caption: Scatterplot showing the percentage of EEG data retained (seconds remaining after artifact rejection/total seconds of recording x 100) by group (TD, ASD). Significantly more data was retained in the TD group (t=4.86, p<0.001). Additionally, there was more variability present in the ASD group.

Figure 4:. Frequency of Perceived State Ratings in the ASD group

Caption: Bar graph showing the frequency of Perceived State Ratings in the ASD group. PSR 1 indicates that the child showed no or very minimal signs of agitation during the recording. Higher ratings correspond to increasing levels of agitation. 67% of participants in the ASD group were rated as having a PSR of 1.

Figure 5:. Relationship between EEG data retention and IQ in the ASD group

Caption: Scatter plot showing EEG data retention (percent of data retained after artifact rejection) by IQ score in the ASD group. EEG data retention was not significantly related to IQ in the ASD group, after correcting for multiple comparisons (r=0.39, p=0.03).

Figure 6:. Power spectral density plots by region and group

Caption: Average relative power spectral density for ASD group (red), and TD group (blue), shown for frontal and occipital regions with the alpha band highlighted. Children in the TD group had significantly higher alpha power in both regions compared with children in the ASD group (Frontal t=3.41, p=0.003, d=1; Occipital t=2.37, p=0.02, d=0.7).

Figure 7:. Relative alpha spectral power by region and group

Caption: Bar graph showing relative alpha spectral power in frontal and occipital regions, in the TD group, ASD group with low PSR scores and ASD group with high PSR scores. Children in the TD group had significantly higher alpha power in both regions compared to children with ASD (regardless of PSR score; p-values 0.003–0.036). Within the ASD group, participants in the low PSR group had higher frontal alpha power compared to those in the high PSR group (t=2.49, p=0.02). Occipital alpha power did not differ between those in the high and low PSR groups (t=0.08, p=0.94).