To optimally adapt to constantly changing environments, our internal and external milieus are coupled: bodily signals (e.g., proprioceptive or interoceptive / viscerosensory) are continuously integrated with exteroceptive sensory input (e.g., visual or auditory). The bidirectional communication between the heart and the brain constitutes a major body-brain axis: Parasympathetic signals originating in the brain underlie adaptive beat-to-beat changes in the heart rate. This heart-rate variability (HRV) can be measured at rest or during a task. We found that patients with social anxiety disorder, compared to healthy controls, have reduced HRV at rest, which is associated with different brain activation during emotional face processing. In another study involving a task of social interactions, women with obesity showed increased HRV, which was influenced by how negative their body image was.

Not only does what we perceive influence our heart rate (e.g., threatening stimuli increase the heart rate) but the heartbeat also influences what/how we perceive. In a recent line of research, we investigate such cardiac cycle time effects in the visual and somatosensory domain. The cardiac cycle can be divided into systole, when the heart muscle contracts to eject blood into the arteries, and diastole, when the heart (re-)fills with blood.

We  found that people are more likely to prompt a (briefly presented) photo they’re asked to memorize during systole compared to diastole. However, whether they saw a picture during systole or diastole didn’t influence how well they remembered it (Kunzendorf et al., 2019, Psychophysiology; bioRxiv preprint; preregistration on OSF; code & data).

In several independent studies, we also observed that near-threshold somatosensory stimuli are more likely to be detected when they are presented at later phases of the cardiac cycle (diastole) – and that correctly detected stimuli lower the heart rate more strongly than non-detected ones (Motyka et al., 2019, Psychophysiology; code & data; Al et al., 2020, PNAS, Grund et al., 2021, bioRxiv).

People differ in how well they perceive signals from the body; and such inter-individual differences in interoceptive accuracy (IA) have been connected to several psychological and physiological parameters. For example, patients with social anxiety disorder show decreased IA.