Our five senses are seeing, hearing, smelling, tasting, and touching.
Proprioception is frequently called “the sixth sense”, which helps us with body position, movement and action. This sense allows for walking in the darkness without losing balance. The finger nose proprioception test is a bedside test to check if a patient can touch their nose with the finger while the eyes are closed. Patients with proprioceptive impairment will miss the tip of the nose.
The vestibular system is a sensory system occasionally called “the seventh sense”. This system helps us with balance, spatial awareness, and orientation. Babies holding up their heads or learning how to walk are great examples of the vestibular system. While skateboarding or sliding down a slide, we don’t get dizzy or disoriented because of the vestibular system.
And then we have the eighth sense, interoception, the sense of the body’s internal state. From a contemporary point of view, interoception includes the perception of bodily signals arising from the viscera (lungs, heart, stomach, bladder), brain, skin, or muscles. The interoception receptors located throughout our body continually retrieve information about how the body is feeling (heartbeat low or up, muscle soreness, the level of fullness in the stomach or the bladder, electrolytes levels in cells, and so on).
This enormous and detailed information composed of “feelings” in the body is translated into millions of electrical pulses. While decoding these electrical pulses, the brain builds our perception of reality and uses guiding concepts to make sense of all this sensory input noise. Most of the time, we are unaware of this processing: when our brain tries to stabilize our sugar levels, we don’t feel which cells are affected. However, we notice some fragments of sensations here and there: heart beating, stomach clenching, or tensioned muscles.
The guiding concepts come in the form of names, labels, or memories of similar experiences from the past: “Two weeks ago, the mouth felt dry as it does now. I did drink some water last time, and that sensation went away. Perhaps I need to drink water this time too.” Suppose a specific bodily sensation happens for long periods or is intense enough. In that case, the brain’s prediction mechanism of what should happen next becomes encoded as a much quicker process: “thirst – drink water”. However, it does happen that this predictive process misinterprets and mislabels bodily feelings.
Brains didn’t evolve for rationality. They did not evolve for you to think or to perceive the world accurately. They didn’t even really evolve for you to see or hear or feel. Brains evolved to regulate a body so that it could move around the world efficiently.
The core task of a brain working in service to the body is allostasis: regulating the body’s internal systems by anticipating needs and preparing to satisfy them before they arise. Interoception — your brain’s representation of sensations from your own body — is the sensory consequence of this activity […], and is central to everything from thought, to emotion, to decision making, and our sense of self.
Your body is part of your mind, not in some gauzy mystical way, but in a very real biological way.
Maintaining allostasis is a lot like managing a budget for the body, in which glucose, water, salt, and other biological compounds constitute the currency […]; as with any budget, it’s possible to run a metabolic deficit. When this happens, the brain will reduce spending on two “expensive” things: moving the body and learning new information. This can result in fatigue, confusion, and anhedonia and, in the long run, depression.
Allostatic disruption is just one of many factors that contribute to depression […]. Appreciating the physical basis of symptoms can be helpful for people suffering with the disorder, who often feel that they can’t control their negative thoughts and feelings.
Psychology professor Lisa Feldman Barrett
Interoception is part of embodied cognition, a research field that states that the organism’s body shapes many cognitive features. This cognitive science field draws research from “psychology, neuroscience, ethology, philosophy, linguistics, robotics, and artificial intelligence”. It is in stark contrast to the Cartesian mind-body dualism, where the body is at the mercy of our emotions and is an insignificant carcass for “the seat of cognition”, the all-mighty brain. For the embodied cognition theoreticians, we are not brains that have an attached body. We are bodies.
It is as though this body is a tree alive with scurrying feelings, rustling ideas, chattering thoughts, chirping intuitions.
Stephen Batchelor – Buddhism without Beliefs
No wonder we invented metaphors to link body clues (how we feel our stomach, muscles, heart) and our emotions: heartbreaking, gut-wrenching, visceral reactions, hangry (a blend of hungry and angry), sick to the stomach. Taking a deep breath in the face of anger or fear is a sign to use our interoception awareness. And behind our “intuition” sense, or going with the gut, we find interoception.
When interoception is working correctly, we feel when our balance is skewed, and we are motivated to act. Through self-regulation techniques, we relieve the discomfort caused by that imbalance, be it by going to the toilet or becoming aware that we are starting to get angry or anxious. A lack of interoception awareness means that we struggle in interpreting correct the body’s internal signals: watching Netflix when we are dead tired, eating a large meal and still feeling hungry, overreacting to minor injuries or not noticing significant injuries. Autism, anxiety, depression, trauma, or sensory processing disorders, are often related to poor interoceptive systems.
If a person’s interoception is not fully developed, they may find it difficult to manage their emotions and social interactions. If someone does not recognise the signals for an emotion, they are not able to respond to it. This can result in anger becoming rage, sadness becoming distress and so on. Other people can perceive this as dysregulation or a lack of emotional maturity.
Perhaps we all have stories about when we felt inclined to overeat when we didn’t sleep enough. When we feel overwhelmed, even the slightest sensory input can disrupt us. Or when we feel our stomach in knots, we label this bodily sensation as anxiety or fear (when perhaps, we are dehydrated or didn’t sleep enough).
Interoception activities that could help: breathing exercises, toe curls, water bottles with prompts to drink, smart watches for heart rate, sleep trackers, yoga, mindfulness, body scan meditations, exercise.
However, people with anxiety disorders experience heightened interoceptive awareness. Focusing on the millions of little things inside might become triggers for such people who need to reach out to clinicians in dealing with interoceptive exposure. Further research: Interoceptive Exposure and Interoceptive Exposure for Anxiety: Does It Work?
In the end, we would be wise to remember Jonathan Swift’s words:
May you live every day of your life.