Interoception, Action and Relaxation – InterAX

Interoception, defined as the conscious or unconscious perception of internal bodily signals, encompasses many different systems (cardio-respiratory, gastro-intestinal, genito-urinary, …) with very distinct physiological functions. By contrast in cognitive neuroscience interoception is referred to as the “sense of the body” and considered holistically, in cognitive theories (e.g., self) or mechanistic frameworks (e.g., body-brain oscillatory coupling). Besides, theories and frameworks tend to draw on experimental results obtained in a specific organ and hence might over-generalize. The aim of InterAX is to resolve this tension between global, holistic views of interoception on the one hand, and both anatomo-functional pathways and organ-specific experimental results on the other hand. We will tease apart organ-specific and organ-general properties in the coupling between visceral rhythms (cardiac, respiratory and gastric) and the motor system in humans. The motor system is an ideal candidate since it is a central component of the perception-cognition-action loop, and recent years have revealed coupling between either action timing or motor cortex activity for each of the three visceral rhythms, but in separate experiments. Here, we will systematically record the cardiac, respiratory and gastric rhythms in young healthy male and female participants, and to quantify the links between visceral rhythms and action timing, corticospinal excitability, and passive relaxation.

In a first series of experiments, we will quantify the respective contribution of all three visceral rhythms contribute to the timing of actions performed either with the hand or the eye, in different experimental situations. We will determine whether results are best explained by a global neuromodulatory mechanism, affecting all visceral rhythms – effector couplings, or by the convergence of somatotopically organized and viscerotopically organized pathways, and to which extent each visceral-action coupling is dependent on the cognitive features of the task performed.
In a second series of experiment, we will use transcranial magnetic stimulation to elicit motor evoked potentials in a hand muscle, or a cortical evoked motor potential, to further quantify interoception in a task-independent manner and probe underlying neural pathways and mechanisms. These experiments will reveal the extent to which visceral rhythms influence the corticospinal system, whether the influence is of cortical origin and influences the functional integration and complexity of neural dynamics.
The two sets of experiments also provide new objective and non-invasive measures of visceral interoception through the influence of visceral rhythm on the motor system, unbiased by participants’ beliefs about their own interoceptive sensitivity. This is a major improvement on current interoceptive measures, which rely on tasks that are biased by beliefs and/or target only one visceral rhythm at a time.
In a third experiment, we will investigate the link between visceral rhythms and relaxation. Indeed, many relaxation practices use attention to, or control of, interoceptive rhythms, and practitioners believe to have better access to internal bodily sensations. Inspired by experiments showing that modulating external stimuli by the cardiac rhythm has an effect on perception and cognition, we will modulate relaxing auditory landscapes by the cardiac, respiratory or gastric rhythm of participants, unbeknownst to them. We hypothesize that if patterns of muscle contraction/relaxation are more likely at some phases of the cardiac/respiratory/gastric cycle, as explored in the first and second series of experiments, then the alignment of external sensory inputs with visceral rhythms might enhance this pattern and foster relaxation. The results obtained here can be used to develop evidence-based strategies for the optimization of relaxation strategies, with a strong societal impact to improve well-being.