Phenotyping in clinical EEG research – Considering effects of motor activity on functional lateralization in the electrophysiological signal

Objective: To investigate whether EEG asymmetries are primarily driven by cognitive or motor processes, and to establish normative patterns across different task conditions.Methods: We analyzed resting-state and task-related EEG asymmetry data from 610 healthy adults aged 20 to 70, from the Dortmund Vital Study (ClinicalTrials.gov: NCT05155397). Participants completed three tasks with increasing cognitive and motor demands: Psychomotor Vigilance, Simon, and Stroop tasks. EEG asymmetries were examined during pre-stimulus, post-stimulus, and resting-state across multiple frequency bands.Results: Timepoint had the strongest impact on EEG asymmetry, particularly in alpha and theta bands, with significant differences between resting-state and task-related conditions. Age had minimal effect on asymmetry patterns. Non-right-handers displayed more dynamic shifts in asymmetry, while right-handers maintained more stable lateralization. Correlations of asymmetry indexes revealed strong interhemispheric coupling in frontal and weaker connectivity in central regions. Post-stimulus frontal asymmetries showed stronger correlations compared to resting-state and pre-stimulus, highlighting dynamic, task-specific lateralization.Conclusions: EEG asymmetry is not static but dynamically modulated by task engagement and stimulus novelty.Significance: This study highlights EEG asymmetry as a dynamic biomarker of brain function, offers standards in EEG-asymmetry research, and may serve as a reference for clinical and non-clinical studies.