Interoception refers to the way the brain senses signals coming from within the body. Some of these signals are rhythmic in nature, such as the beating of our hearts, the expanding of our lungs, or contractions of our stomach. These rhythms happen at different timescales and have different functions, but are all continuously sensed by the brain. Importantly, the last few years it has become clear that the way the brain is sensing these rhythms has a far reaching impact on cognition and large scale coupling of rhythms of the brain and the body exist. This has led to new theories which try to clarify the function which such a coupling might have. However, these theories mostly lump different types of bodily rhythms together, without specifying if for example coupling between the brain and the heart might serve a different function, or operate through different mechanisms, than coupling between the brain and the stomach.

This new work conducted by scientists from the Subjectivity, Brain, and Viscera team, investigated whether independent influences of the different visceral rhythms (from the heart, lungs, and stomach) might exist.

The experiment used a form of non-invasive brain stimulation (Transcranial Magnetic Stimulation, TMS) by which the corticospinal motor tract could be directly stimulated in healthy participants. Each time the stimulation occurs, a muscle response is evoked which intrinsically varies in amplitude. While this stimulation was performed, the cardiac, respiratory, and gastric rhythms were recorded, and thereby it could be tested if these variations in amplitude of the motor response, could be explained by the rhythms of the viscera, which was indeed found to be the case. Importantly however, it was demonstrated that the coupling between one of the internal organs to the brain did not necessarily correlate with the coupling between the brain and the other organs.

This means that participants could have unique profiles, showing for example strong heart-brain coupling without any strong coupling between the other organs and the brain.

These findings have important implications for theories giving functional interpretations between brain-body coupling, as both mechanisms and functions might differ for each of the organ systems.

Engelen T, Schuhmann T, Sack AT, Tallon-Baudry C (2025) Cardiac, respiratory, and gastric rhythms independently modulate motor corticospinal excitability in humans. PLoS Biol. 23(11): e3003478. https://doi.org/10.1371/journal.pbio.3003478