Cardiac activity is associated with changes in microstates of the electroencephalogram in healthy adults: A resting state study

The brain and the heart communicate bidirectionally, primarily through the autonomic nervous system. Among the available tools for investigating this interaction, electroencephalographic (EEG) microstates-quasi-stable scalp topographies reflecting global brain integration-can offer novel insights into brain-heart dynamics. Although two previous studies assessed the relationship between cardiac function and EEG microstates, they were primarily focused on directionality and time-based heart rate variability indices. Therefore, in this study, we investigated the relationship between EEG microstates and cardiac cycle by simultaneously recording EEG and electrocardiograms from 103 healthy participants during an open eyes resting state. Circular statistics were used to characterize phase-EEG microstate coupling by computing participant-level phase angles for each EEG microstate. Our analysis revealed temporal associations between specific EEG microstates and cardiac events: EEG microstates A, D, and E showed distinct probabilities of occurrence throughout the cardiac cycle, with EEG microstate A exhibiting increased probability during R and T waves of the electrocardiogram. Furthermore, the occurrence probabilities of EEG microstates A and E varied with the phase of low-frequency heart rate variability (LF-HRV). The findings of this exploratory study provide evidence for the coupling between peripheral cardiac processes and central brain activity, suggesting that EEG microstate patterns reflect cardiac-related activity.