# Oscillatory and Aperiodic Contributions to EEG Event‐Related Time‐Frequency Metrics During Cognitive Control and Reinforcement Processing: A Registered Report

## TL;DR

This study examines how brain rhythms and non-rhythmic activity contribute to cognitive tasks using EEG data, revealing that some patterns are due to oscillations while others reflect aperiodic changes.

## Contribution

The study introduces a method to distinguish oscillatory and aperiodic EEG components during cognitive tasks, revealing new insights into their distinct roles.

## Key findings

- Mediofrontal theta synchronization and parietal alpha desynchronization are primarily oscillatory.
- Aperiodic power changes are stimulus-locked and correlate with cognitive control and reinforcement processing.
- Baseline correction does not fully eliminate aperiodic correlations with time-frequency power.

## Abstract

Brain oscillations, or rhythms, coordinate communication across distributed brain networks. These rhythms provide a foundation for the brain network interactions required for cognition. Oscillations coexist with non‐rhythmic background aperiodic activity that forms a characteristic 1/f pattern in power spectra. Aperiodic brain activity is associated with cognition and can confound the detection of oscillations. In this Registered Report, we applied time‐resolved spectral parameterization to EEG recordings during two common cognitive tasks. Neural dynamics recorded during many cognitive paradigms show similar patterns, including synchronization of mediofrontal theta (4–8 Hz) and desynchronization of posterior alpha (9–13 Hz) and central beta (15–30 Hz). Our results indicate that common task time‐frequency signatures, including mediofrontal theta synchronization and parietal alpha desynchronization, can be attributed primarily to neural oscillatory phenomena. Intriguingly, we uncover evidence of stimulus‐locked aperiodic power changes, which are responsive to the need for cognitive control and to reinforcement processing. Furthermore, aperiodic power correlated strongly with non‐baseline‐corrected total power estimates, and whereas oscillatory power correlated strongly with portions of baseline‐corrected power estimates, it failed to correlate with other portions of baseline‐corrected power. Finally, after baseline correction, aperiodic correlations with TF power remain high. These results indicate two primary outcomes. First, task TF signatures in theta and alpha bands reflect primarily parameterized oscillations. Second, aperiodic activity is time‐dependent during cognitive processing, and these dynamics are not accounted for by baseline correction.

Event‐related EEG time‐frequency is assumed to reflect brain oscillations, but aperiodic activity can confound measuring neural oscillations. We show that spectral features in theta and alpha bands are essentially oscillatory while revealing aperiodic event‐related dynamics and condition differences during the need for control and reinforcement processing. Event‐related EEG features are not fully oscillatory, even after baseline correction, showing the need for enhanced analyses to study oscillations without aperiodic confounds.