# Confirmation of a Useful Dark‐Room Resting‐State Procedure: Periodic and Aperiodic MEG Activity in Children

## TL;DR

This study confirms that a resting-state MEG procedure with children's eyes open in a dark room is a viable alternative to the traditional eyes-closed method.

## Contribution

The study expands the use of the dark-room resting-state procedure to a larger age range and introduces aperiodic MEG activity analysis.

## Key findings

- The dark-room procedure reliably captures parietal-occipital alpha frequency and aperiodic measures in children.
- Aperiodic measures (offset and exponent) showed good reliability across 15 brain regions in both typical and autism spectrum disorder groups.
- Regional differences in aperiodic measures suggest the need for source space analysis rather than scalp sensor space.

## Abstract

In a previous paper, we showed in children 6–12 years old that a resting‐state (RS) eyes‐open dark room (DR) task provides RS parietal‐occipital alpha measures similar to those obtained using the standard RS eyes‐closed (EC) exam. Results provided initial evidence that the RS DR procedure is feasible and useful with populations often excluded from electrophysiology RS studies, such as participants who cannot remain awake with their eyes closed or cannot remain still for an extended period. The present study extended the DR and EC comparisons to a much larger sample of children spanning a wider age range and expanded the analysis strategy to examine RS aperiodic measures (offset and slope [exponent] of the power spectrum) and to evaluate 15 distinct brain regions rather than just the previously examined parieto‐occipital RS periodic alpha activity. RS activity was recorded using MEG, here reporting on 147 DR and EC datasets obtained from children (including 23 with evaluable datasets at multiple timepoints) with typical development (TD; N = 69) and children with autism spectrum disorder (ASD; N = 53) 7.7–17.1 years old. Findings showed good reliability in both TD and ASD for the EC and DR parietal‐occipital peak alpha frequency (frequency with highest alpha power; interclass correlation [ICC] = 0.84, p < 0.001). The ICC for periodic parieto‐occipital PAF power was lower (ICC = 0.65). For offset and exponent, the two RS aperiodic measures, fair to good reliability for both groups was observed between DR and EC at all 15 brain regions (mean and median ICC values 0.77–0.80). Offset and exponent values differed significantly across the 15 brain regions, as did associations between age and both aperiodic measures. Findings confirm that the DR exam is a viable way to obtain RS periodic and aperiodic measures. The lack of TD/ASD differences in the EC and DR periodic and aperiodic ICCs supports the generalizability of the DR procedure. Finally, regional differences in aperiodic measures demonstrate the need to assess aperiodic activity in brain source space rather than scalp sensor space.

Resting‐state (RS) brain activity, when an individual is not pursuing a specific goal, provides a foundation for basic and higher‐order brain processes relied on when people are focused on a goal. RS activity is typically examined in an eyes‐closed (EC) condition. Unfortunately, the RS EC exam can only be used with individuals who can follow instructions to stay awake with their eyes closed for an extended period. That excludes groups such as infants, toddlers, and individuals who have intellectual disability. Comparison of RS neural measures obtained in an EC condition and in a dark‐room (DR) eyes‐open condition in children with typical development and children with autism spectrum disorder (7.1–17.1 years old) showed that the DR eyes‐open exam is a viable way to obtain RS measures, with some caveats about how the brain activity should be measured.