Brain-heart interactions in the neurobiology of consciousness

Abstract

Recent experimental evidence on patients with disorders of consciousness revealed that observing brain-heart interactions helps to detect residual consciousness, even in patients with absence of behavioral signs of consciousness. Those findings support hypotheses suggesting that visceral activity is involved in the neurobiology of consciousness, and sum to the existing evidence in healthy participants in which the neural responses to heartbeats reveal perceptual and self-consciousness. More evidence obtained through mathematical modeling of physiological dynamics revealed that emotion processing is prompted by an initial modulation from ascending vagal inputs to the brain, followed by sustained bidirectional brain-heart interactions. Those findings support long-lasting hypotheses on the causal role of bodily activity in emotions, feelings, and potentially consciousness. In this paper, the theoretical landscape on the potential role of heartbeats in cognition and consciousness is reviewed, as well as the experimental evidence supporting these hypotheses. I advocate for methodological developments on the estimation of brain-heart interactions to uncover the role of the heart in the origin, levels, and contents of consciousness. The ongoing evidence depicts interactions further than the cortical responses evoked by each heartbeat, suggesting the potential presence of non-linear, complex, and bidirectional communications between brain and heartbeat dynamics. Further developments on methodologies to analyze brain-heart interactions may contribute to a better understanding of the physiological dynamics involved in homeostatic-allostatic control, cognitive functions, and consciousness.

Dynamic fluctuations in ascending heart–to–brain communication under mental stress

“…The study of mental stress elicited in other paradigms, such as mental arithmetic, could give a broader view of the physiological processes involved in brain–heart information exchange. Our study confirms the advantages of analyzing the interactions between brain and heart, instead of studying heart rate and brain dynamics separately [19,67], to understand the origin and potential pathways of the observed physiological changes. The understanding of brain–heart dynamics and the neurophysiological substrates of stress has clinical relevance.…”

“…The existing EEG evidence is described as neural correlates, which does not imply causality between the observed parallel changes in brain and autonomic activities [19]. For instance, acute stress triggers parallel fluctuations in heart rate variability and functional connectivity between central executive and default mode networks [20].…”

“…However, the existing experimental evidence has not yet described the mutual and bidirectional interplay between central and autonomic nervous systems under stress. The existing EEG evidence is described as neural correlates, which does not imply causality between the observed parallel changes in brain and autonomic activities [19]. For instance, acute stress triggers parallel fluctuations in heart rate variability and functional connectivity between central executive and default mode networks [20].…”

Confounding effects of heart rate, breathing rate, and frontal fNIRS on interoception

“…In recent years, there has been a substantial increase in the number of studies on interoception that aim to describe the mechanisms involved in the sensing of inner bodily signals and their influence on brain dynamics. [1][2][3] Interoception includes the sensing of cardiac, respiratory, and gut signaling. 4 More in general, interoception has been defined as the sense of physiological condition of the entire body, 5 which can potentially include other interoceptive submodalities, such as thermosensation, pain, or affective touch.…”

“…[7][8][9] The functions associated with interoceptive processes include homeostatic and allostatic regulation as well as the integration of information that enables bodily awareness and consciousness. 1,3,[10][11][12][13] Evidence has demonstrated that neural responses to heartbeats contribute to visual, 14 somatosensory, 15 auditory, 16,17 and self-perception. [18][19][20] Further, recent evidence has suggested that breathing is aligned with the perception of sensory inputs, 21,22 suggesting that it is involved in perceptual sensitivity modulation and, possibly, shaping neural dynamics.…”