EEG–ECG/HRV associations under multi-stage cognitive stress: characterization and mechanisms

OBJECTIVE: Mental stress affects cognitive, emotional, and cardiovascular function, but subjective stress scales are susceptible to individual bias. Brain-heart coupling offers a potential approach to stress assessment. This study examined stage-dependent EEG-ECG/HRV associations during mental arithmetic and Stroop tasks. APPROACH: Sixty healthy adults were recruited, EEG and ECG were recorded during baseline rest, four mental-arithmetic stages, inter-task rest, and four Stroop stages. Stage-specific Spearman correlations characterized between-participant associations between five EEG band-power measures and seven ECG/HRV indices. Mixed-effects models separating within- and between-participant effects tested whether within-participant associations varied across difficulty stages and tasks. MAIN RESULTS: Significant EEG-HRV correlations decreased in number after task onset and partially recovered during inter-task rest. Mental arithmetic showed more pronounced negative high-frequency EEG-vagal HRV correlations, whereas Stroop showed Theta/Beta-HR associations at onset and sustained Alpha-RMSSD associations during middle-to-late stages. Neither task showed FDR-significant stage-averaged within-participant associations. Within-participant EEG × difficulty-stage interactions were FDR-significant for 12 of 35 whole-frontal associations during mental arithmetic and none during Stroop. Combined models identified five significant within-participant EEG × difficulty × task interactions. No linear difficulty interactions survived FDR correction in sensitivity analyses. SIGNIFICANCE: These findings support stage-dependent EEG-ECG/HRV associations in this fixed-order cognitive-stress paradigm. They may inform physiologically interpretable candidate measures for objective mental stress assessment and wearable monitoring.