Have you ever been startled by someone suddenly talking to you when you thought you were alone? Even when they apologise for surprising you, your heart goes on pounding in your chest. You are very aware of this sensation. But what kind of experience is it, and what can it tell us about relations between the heart and the brain?
When considering the senses, we tend to think of sight and sound, taste, touch and smell. However, these are classified as exteroceptive senses, that is, they tell us something about the outside world. In contrast, interoception is a sense that informs us about our internal bodily sensations, such as the pounding of our heart, the flutter of butterflies in our stomach or feelings of hunger.
The brain represents, integrates and prioritises interoceptive information from the internal body. These are communicated through a set of distinct neural and humoural (ie, blood-borne) pathways. This sensing of internal states of the body is part of the interplay between body and brain: it maintains homeostasis, the physiological stability necessary for survival; it provides key motivational drivers such as hunger and thirst; it explicitly represents bodily sensations, such as bladder distension. But that is not all, and herein lies the beauty of interoception, as our feelings, thoughts and perceptions are also influenced by the dynamic interaction between body and brain.