# Age‐Related Differences and Effects of Internalizing Symptoms on Aperiodic Neural Activity in Adolescents

## TL;DR

This study explores how aperiodic brain activity in adolescents relates to age and internalizing symptoms like depression and anxiety.

## Contribution

It is among the first to examine aperiodic EEG activity in adolescents with internalizing symptoms, revealing age-related interactions.

## Key findings

- Adolescents with depressive disorders showed steeper age-related declines in aperiodic exponent.
- Depressive symptoms strengthened the inverse association between aperiodic activity and age, while anxiety symptoms weakened it.
- No group differences in aperiodic activity were observed, but symptom-related moderation effects were found.

## Abstract

The power spectrum derived from electroencephalography (EEG) recordings has been shown to include both periodic (e.g., delta, theta, alpha, beta) and aperiodic (e.g., 1/f exponent shape, vertical offset) components. Although internalizing disorders have been characterized by alterations in several periodic EEG measures, aperiodic activity has typically been treated as noise and unexamined in clinical neuroscience. Importantly, recent evidence has shown that aperiodic activity may reflect fundamental biological constructs such as excitatory‐inhibitory (E‐I) neural balance and neuronal cell spiking which are implicated in internalizing disorders. While previous research has found some evidence for blunted aperiodic parameters in adults with depression, few studies have probed the association between anxiety symptoms and aperiodic activity, and no work has probed these associations in adolescence when both mood and anxiety disorders commonly onset. Here, adolescents with current depressive disorders (n = 53), at high risk for depression due to maternal depressive history (n = 49), and at low risk for depression due to no maternal or personal depressive history (n = 51) completed an eyes‐closed resting state EEG paradigm to estimate aperiodic parameters. No group differences in aperiodic activity were observed, but age‐related declines in aperiodic exponent were moderated by depressive diagnosis such that those with a current depressive disorder diagnosis showed a steeper decline in the aperiodic exponent with age. Further, age‐related declines in aperiodic activity were moderated in opposite directions by internalizing symptoms such that elevated depressive symptoms steepened the inverse association between aperiodic activity and age, while elevated anxiety symptoms weakened this association. Results suggest unique alterations of aperiodic activity with internalizing symptoms and highlight the importance of considering aperiodic activity as a unique construct from periodic activity in investigating internalizing symptoms and brain development.

Aperiodic neural activity has historically been treated as noise despite its associations with excitatory‐inhibitory neural balance and neuronal cell spiking implicated across development and depressive disorders. This study is among the first to examine associations between aperiodic activity and internalizing symptoms and disorders in adolescents, finding evidence of interactions between age and depressive and anxiety symptoms, and highlighting the need to consider aperiodic EEG activity in clinical neuroscience.