I sync, therefore I am: brain-body synchrony in typical and disordered consciousness

Consciousness is often treated as a property of the brain alone, yet accumulating evidence suggests that it is shaped by a recurrent dialogue between the brain and body. In this review, we discuss how cognition associated with consciousness-processes that define the observer, their observations, and arising qualia-depend on structured rhythmic correspondences between bodily rhythms and brain signals. We first review how cardiac, respiratory, and gastric rhythms modulate neuroelectric and neurovascular fluctuations in support of interoception-perception of the bodily state-and functionally related faculties such as emotion and selfhood, which draw upon interoceptive representations. We then discuss how clinical and subclinical conditions are associated with dysrhythmia in underlying bodily rhythms and atypical increases or decreases in a bodily rhythm's modulation of brain processes. Across bodily systems, an emergent pattern suggests both an optimal window of brain-body synchrony, beyond which adverse effects are likely to occur, and that non-clinical, stress-related increases in brain-body synchrony may promote the utility of bodily rhythms for coordinating disparate entrained cognitive systems to facilitate functions such as multisensory integration. We conclude that these converging lines of research support a categorical difference between an embodied agent and the proverbial brain-in-a-vat because disturbing bodily rhythms or their coupling to the brain alters phenomenological experience-at times to such a degree as to warrant labeling the resulting states as meeting clinical criteria.