Awareness of one’s body is intimately linked to self-identity, the sense of being “me” . A key question is how the brain integrates different sensory signals from the body to produce the experience of this body as mine, known as sense of body-ownership. Converging evidence suggests that the integration of exteroceptive signals related to the body, such as vision and touch, produces or even alters the sense of body-ownership . However, multisensory integration conveys information about the body as perceived from the outside, and hence, represents only one channel of information available for self-awareness. Interoception, defined here as the sense of the physiological condition of the body, is a ubiquitous information channel used to represent one’s body from within. While the effects of exteroception on the physiological regulation of the body have been recently documented, little is known on whether interoceptive awareness may influence exteroceptive representations of one’s body. We, therefore, sought to understand the interaction between interoceptive and exteroceptive awareness of the body using interoceptive sensitivity measures and bodily illusions.

Interoception – The Sense of Internal Organ Function

Overview of the Interoceptive sense

Interoception is a relatively unheard of sensory system. It is the sense responsible for detecting internal regulation responses, such as respiration, hunger, heart rate, and the need for digestive elimination. It is detected through nerve endings lining the respiratory and digestive mucous membranes. It completes the internal picture of how the human body is perceived, along with the vestibular and proprioceptive senses.

If interoception is well modulated, these sensations will be detected normally, and will not be overly agitating or needed in large quantities for regulation. A pounding heartbeat won’t feel great, but it won’t be traumatizing and it won’t be craved. The same is true for hunger and thirst, as well as the feeling of the need to urinate or have a bowel movement.

Interoceptive Defensiveness

For those who are hypersensitive to interoceptive input, these sensations can be irritating and distracting. A pounding heartbeat might be overly painful or inspire fear. Hunger pains might be intense and cause a person to eat more often than usual to avoid the feeling. They may also use the restroom frequently to avoid painful bowel and bladder sensations, or they may withhold from using the bathroom, as the removal process itself is painful. These feelings may also last longer than they would for most people.

Interoceptive Under-Responsiveness

If a person is under-responsive to interoception, they may not feel or respond to these sensations appropriately, quickly enough, or at all. They may rarely feel themselves breathing or their hearts beating. They may not feel hungry or thirsty often, so they may not perform these everyday tasks as often as others because they do not sense the need to. They will often be slow potty trainers and may end up developing enuresis because they do not feel the need to eliminate bowel waste or urine before the body begins to perform the task anyway. They may not breathe or sweat when their bodies should because they do not feel the need to. They also are commonly diagnosable for interoceptive discrimination dysfunction, as well.

Interoceptive Seeking

Sensory seekers may crave interoceptive input. One of the reasons they need to keep moving is that they may also be seeking a pounding or racing heartbeat, as well as a fast rate of respiration. They may frequently take large, deep breaths. Hunger and thirst sensations might actually feel good, causing them to not desire to eat or drink, not wanting the feeling to go away. This can also lead to withholding bowel and bladder waste, as the sensation of needing to eliminate them may be craved.

Interoceptive Discrimination Disorder

For those who suffer from an Interoceptive Discrimination Disorder, determining what their body needs at any given moment can be quite a challenge. Often, they have difficulty interpreting their own body signals. They may not be able to determine just how hungry or thirsty they are. They may only feel a slight need to use the restroom, when in fact, the matter is urgent! They will have difficulty in knowing when they are feeling better or worse, warmer or colder, and tired or energetic. They simply can’t make sense out of what their bodies are telling them.

Converging evidence indicates that primates have a distinct cortical image of homeostatic afferent activity that reflects all aspects of the physiological condition of all tissues of the body. This interoceptive system, associated with autonomic motor control, is distinct from the exteroceptive system (cutaneous mechanoreception and proprioception) that guides somatic motor activity. The primary interoceptive representation in the dorsal posterior insula engenders distinct highly resolved feelings from the body that include pain, temperature, itch, sensual touch, muscular and visceral sensations, vasomotor activity, hunger, thirst, and ‘air hunger’. In humans, a meta-representation of the primary interoceptive activity is engendered in the right anterior insula, which seems to provide the basis for the subjective image of the material self as a feeling (sentient) entity, that is, emotional awareness.

How do you feel? Interoception: the sense of the physiological condition of the body

As humans, we perceive feelings from our bodies that relate our state of well-being, our energy and stress levels, our mood and disposition. How do we have these feelings? What neural processes do they represent? Recent functional anatomical work has detailed an afferent neural system in primates and in humans that represents all aspects of the physiological condition of the physical body. This system constitutes a representation of ‘the material me’, and might provide a foundation for subjective feelings, emotion and self-awareness.