Slow power-envelope associations among brain, heart, and gut signals during sleep: an exploratory multivariate transfer entropy study

Sleep and the brain-gut axis both involve the coordinated regulation of the central nervous system (CNS), autonomic nervous system (ANS), and enteric nervous system. Although the role of the brain-gut axis in sleep regulation is increasingly recognized, the dynamic information flow and its directionality among the brain, heart, and gut systems during sleep remain unclear as statistical associations. In this study, based on overnight sleep data from 24 healthy subjects, we simultaneously collected occipital electroencephalogram (EEG), electrocardiogram, and bowel sound signals, constructed a multimodal physiological signal analysis framework, and employed a multivariate transfer entropy method based on non-uniform embedding and k -nearest neighbor estimation to systematically quantify directed statistical associations at the level of slow power envelope co-modulations among the brain, heart, and gut systems within the framework of sleep staging. The results reveal a consistent pattern of directed statistical associations: information transfer from heart to brain, brain to gut, and heart to gut consistently exceeds that in the reverse directions across all sleep stages. Sleep-stage dynamics further dissociate within-system from inter-system information flow: internal information exchange within the brain and gut intensifies with sleep depth and weakens during REM, whereas inter-system pathways show divergent stage-dependent patterns: heart-to-brain flow increases from light to deep sleep, while heart-to-gut and brain-to-gut flow are suppressed during deep sleep. At the frequency-band level, the brain, heart, and gut each exhibit dynamically reorganized source–receiver roles across sleep stages, with specific frequency bands contributing differentially to each inter-system pathway depending on sleep stage. This study identifies exploratory statistical patterns of directional information flow among the brain, heart, and gut systems during sleep, providing hypothesis-generating observations for future studies on sleep and multi-organ interactions. These directed associations do not establish anatomical pathways, causal regulation, or clinical biomarkers, and should be regarded as exploratory.