🍄 The Eighth Sense

Interoception—the brain’s capacity to detect bodily sensations such as heartbeat—could be the answer to anxiety and the key to consciousness. Is this the wonder sense we’ve all been waiting for?

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Hello, we’re Alice, and we are always in a state of wander. Finally, a new season of the senses is out! The eighth human sense, “interoception” is piquing the interest of the neuroscientists researching it, and psychologists putting it into play. While exteroception is sensing of the outside world through vision, touch, sound and smell, interoception is the study of the inside world. It’s the information from our hearts and our organs, which tell us about the state of the body.  

“I think one of the fascinating things about the senses is not only is each intrinsically interesting in and of itself, it also profoundly influences and is influenced by the other senses and also our own thoughts.”—Biologist Ashley Ward, author of Sensational: A New Story of our Senses [2023], speaking on The Spectator podcast.

The inner-fluencer

“As scientists, we focus so much on the brain and how that governs the mind and tells us how we think and how we feel,” neuroscientist Sarah Garfinkel, Professor of Cognitive Neuroscience at University College London (UCL) tells BBC Sounds. “But our brains and our minds are dynamically coupled to our bodily states, and our thoughts, feelings and perceptions can be influenced by internal signals from the body.” Garfinkel, who specializes in interoception, leads UCL’s Clinical and Affective Neuroscience group, investigating how emotion is expressed in body and brain. “Bodily organs are in constant communication with our brain, so they shape neural activity and interoception is the formal study of this.”

These studies—first pioneered by Prof Antonio Damasio at the University of Southern California in the 1990s—are swelling. “We are seeing an exponential growth in interoceptive research,” Prof Manos Tsakiris, a psychologist at Royal Holloway, University of London, tells The Guardian. He explains how interoception is not just sensations we are aware of, but also the unconscious and automatic feedback between body and brain. “There’s a constant communication dialogue between the brain and the viscera,” says Tsakiris, who is also the Director of the Centre for the Politics of Feelings, University of London. Interoception helps to keep your blood pressure level, for example, and stabilize blood sugar levels. It includes all the signals from your internal organs, including your cardiovascular system, your lungs, your gut, your bladder and your kidneys.

Introspection on interoception

Some scientists see interoception at the potential core of our consciousness. ‘Researchers have come to recognize that our sense of interoception, which monitors internal body signals—such as heart rate, pain, thirst and pleasure—plays a major role in creating our thoughts and emotions,’ reports the New Scientist. Now, many consider interoception to be a fundamental feature of consciousness, too. “The brain on its own isn’t enough to generate subjective experience, says Catherine Tallon-Baudry, a neuroscientist at the Ecole Normale Supérieure in Paris. Without the body, the self simply wouldn’t exist. “Just as the notion of ‘car’ exists only if a certain number of components are present and interacting with each other.”

Mind-body muddle

But if interoception is your brain's representation of sensations from your body, then getting it wrong can be a biological catastrophe. “Interoception helps us to form our most basic sense of self,” Prof Hugo Critchley, Chair of Psychiatry at Brighton and Sussex Medical School, tells The Guardian. He explains that poor interoceptive awareness can lead to the sense of “depersonalisation” and dissociation, which are early symptoms of psychosis. It can also contribute to symptoms in psychiatric conditions such as anxiety, PTSD and schizophrenia.

The predictive mind and catastrophizing

… is at play here. “A fast-beating heart will have a very different emotional impact on a person who ascribes the cause as recent exercise versus one who fears they are having a sudden heart attack,” writes neuroscientist Andy Clark in The Experience Machine: How Our Minds Predict and Shape Reality [2023]. “The very same bodily information can thus feel very different according to how we represent the larger context in which the bodily signals arise.”

Clark, a Professor of Cognitive Philosophy at the University of Sussex and at Macquarie University, Australia, explains In the “racing heart” case, that interoceptive information about heart rate and shortness of breath is integrated with information about the larger context (working out in the gym), delivering new predictions that may cause us to take a break or grab an energy drink. “But alter the context and the very same raw bodily information might cause us to suspect something far more sinister and to dial 911.”

Mind-body muscle training

“Interoception-training” is being considered to treat conditions such as anxiety and PTSD. “Researchers and clinicians are recognizing interoception as a key mechanism to mental and physical health, where understanding our body’s signals helps us understand and regulate emotional and physical states,” Dr Helen Weng at the University of California San Francisco, tells The Guardian.

It’s also being trialled for substance use addiction, where sufferers often have poor emotional regulation, and a sense of disembodiment, which can make it harder to avoid relapse. Prof Cynthia Price at the University of Washington, Seattle tested a yearlong training program that encouraged participants to focus on the internal sensations within sequential body areas, reports The Guardian. Preliminary results suggest that the therapy successfully reduces symptoms of depression and cravings—and significantly increased abstinence. “These skills should be helpful for anyone, regardless of whether they have a health condition,” says Price.

Heart of the matter

“Interoceptive training regimes are already being explored as treatments for anxiety,” writes Clark. “My one-time University of Sussex colleague Professor Sarah Garfinkel has been exploring interventions that improve cardiac self-awareness as a treatment for various forms of anxiety. She found that people with anxiety are often very internally focused, while at the same time surprisingly bad at knowing their own heartbeat. In other words, they focus hard on their internal state but do so without much accuracy or precision.”

How does she know? “We now have actual tests by getting people, for example, to count their number of heartbeats over a specified timeframe and their correct responses are essentially a ratio of how many heart beats they report relative to how many heartbeats they actually had,” Garfinkel, who worked on interoception studies with Critchley at the University of Sussex, tells BBC Radio 4.  

Clark explains that “Garfinkel found that anxiety was most strongly associated with the combination of low accuracy regarding your own internal state and an inflated sense of that accuracy. This means that you are more likely to suffer anxiety if you are interoceptively inaccurate and yet falsely believe yourself to be very accurate.”

Inner sense

Garfinkel’s latest work seems to show just that, finding reduced anxiety as interoceptive accuracy increases, writes Clark. “An extreme example of such accuracy emerged while she was working with a leading hostage negotiator—their interoceptive self-accuracy on the heartbeat task was 100 percent. Garfinkel speculates that this extreme self-accuracy plays some yet-to-be-fully-understood role in the hostage negotiator’s ability to pick up ‘empathically’ on how others are feeling so as to judge when and how best to intervene.”

“Not only can you understand your own physiological state and emotions, it allows you insight into their emotional state as well,” Garfinkel tells Chris White, a former hostage negotiator with New Scotland Yard and the UK government, during their study, heard on BBC Radio 4.

When Clark asked if Garfinkel thought there was a possibility that “my heartbeat or a negotiators heartbeat would match the other individual, and if it did, do you think that enhances the ability to connect?” Garfinkel replied:

“Our bodies have an incredible capacity to align with the bodies of others, where we can feel and socially connect with others, our hearts beat together.”

Autism and interoception

Interoception-training is also being used to to assist those with autism, to observe and communicate their body’s needs. “Interoception refers to sensing and processing of signals that come from within the body, to let us know how our body is feeling,” Kelly Mahler, an occupational therapist, tells Uniquely Human: The Podcast. “Our bodies are designed through the sense of interoception to give us messages about what our body needs for comfort. So for example, noticing a certain feeling in your body, a growling feeling in my stomach lets me know I am hungry and that I need to eat, or when I am sleepy I feel it in my eyes and my muscles.”

Research shows that interoception is an important factor to the development of effective self-regulation skills within children, teens, and adults. Mahler, the author of The Interoception Curriculum, A Step-by-Step Guide to Developing Mindful Self-Regulation, explains that neurodivergent people, including autistics, ADHDers, or people with anxiety, often report interoceptive differences. “For example, they may have difficulty noticing body signals resulting in missing clues that inform their emotional or physical experience. Or they may notice body signals but are not sure exactly what the body signals mean uniquely for them, resulting again in unreliable information regarding their emotions or physical health needs. Alternatively, many neurodivergents are often clear on their inner experience but have it misunderstood and/or mislabelled by often well-intentioned people.”

We all have very different inner bodily sensations providing a process that allows for discovery and validation of each person’s unique experience, and this is what becomes important. It’s the individual interpretation that helps self-regulation. “Therefore, interoceptive activities can be very helpful to many neurodivergent people, specifically when offered in a way that emphasizes individuality,” explains Mahler.

Research by Garfinkel and colleagues has shown what seems to be a positive effect in individuals with autism spectrum condition. “In this work, participants with better interoceptive self-awareness were also better able to detect the emotional information ‘hidden’ in other people’s speech intonations,” writes Clark. “This suggests that training that improves interoceptive self-awareness in people with autism spectrum condition may thereby improve their ability to discern subtle emotional information.”

🦋 Awakened senses

We have unlimited range of sensory possibilities, blending and blurring in different ways. And becoming aware of these possibilities can help us tap into subtle information. “Sensory experience happens at that meeting point between what is me and what is not me, between the self and what is not myself,” David Abram, Cultural Ecologist, Philosopher told ALICE. “With awakened senses we would look out in the landscape and experience a field of imagination. It is the way of bringing imagination alive and discovering that we live inside of a grand imagination, a big outrageous story that is unfolding all around us.”

What else we are wandering…

🔍 True sense?
Well, Aristotle (384-322 BC) is credited with first numbering the five senses in his work De Anima, and neurologists have now numbered and generally agreed on nine senses. “A broadly acceptable definition of a sense for neurologists would be a group of sensory cells that responds to a specific physical phenomenon, and that corresponds to a particular region of the brain where the signals are received and interpreted,” according to the Sensory Trust UK. “Some things that we lay-folks might refer to as ‘senses’, such as the sense of direction for instance, are defined by neurologists as post-sensory cognitive activities and don’t count in this definition.”

🧠 Never knew you had it in you
We’re all on first name terms with the famous five: hearing, taste, touch, sight and smell. Some of the others include the “vestibular” sense, which is input from the inner ear, and our centre for balance. “Proprioception”, meanwhile, is the sense that lets us perceive the location, movement, and action of parts of the body. It’s how we sense where our head is if our eyes are closed, for example. It doesn’t stop there. Due to some overlap between different senses, different methods of neurological classification can yield as many as 21 senses, and eco-psychologist Michael J Cohen, says humans have 53 senses at our disposal!

🧠 The Proust effect
Have you ever had a “Proustian moment”? asks philosopher Alain de Botton on the Happy Place podcast. “It’s when your involuntary memory is jogged by a sight of a smell or something, like concrete after rain, or the light at dusk and suddenly you’re catapulted back to another period of your life and suddenly you’re back in touch with what something was really like.”

The expression stems from a passage in Marcel Proust’s À La Recherche Du Temps Perdu: “No sooner had the warm liquid mixed with the crumbs touched my palate than a shudder ran through me and I stopped, intent upon the extraordinary thing that was happening to me. An exquisite pleasure had invaded my senses, something isolated, detached, with no suggestion of its origin.”

🧠 Gut instinct just got real
“Now as scientists we’re understanding the biological basis of gut instinct,” Garfinkel tells the BBC. “It isn’t just an instinct, it’s actually potentially founded on your capacity to accurately detect internal bodily sensations.”

🧠 The social self
Interoceptive signals act as constant reminders of our existence as a bodily self, distinguishing the 'self' from the 'other. ' How do we do this? Self-awareness. Going with your gut. Connect body feelings. Reappraise what you are feeling and press pause between sensation and your emotion state. Interoception, which extends beyond emotion and decision-making, creates our sense of self.

“It’s one thing to develop a trusting relationship with your body at home, in private. It’s quite another to develop it in a social environment,” writes Saga Briggs for Psyche. Briggs explains that we have a ‘social interoception’, basically switching between internal and external experience, which interoception expert and psychologist Andrew J. Arnold and neuroscientist Karen Dobkins call ‘attentional switching.’ “Awareness needs to switch between internal and external experience, in a moment-by-moment fashion, so that the two may be integrated for adaptive learning in social situations,” Dobkins explains. For example, reflecting on how the inside of your body feels when talking with another person, versus being on your own, is important to know your ‘social body’ so you can use it as a guide.

🧠 Heart-eyes
Let’s finish with finding emo. “Our bodies have a wonderful capacity to also reflect the emotional state of others, so physiological signatures of emotion that you have, I may also have” says Garfinkel. ‘For example if you’re sad, then your pupils get small, and if I look at you, my pupils also get small. So now this physiological signature of sadness that you have, I have as well, and we think this is maybe the biological basic of empathy that my body state matches your body state so I don’t just say, I’m so sorry, this is awful, I actually embody that feeling myself.”

🧠 Embodied Consciousness
If consciousness is embodied, that could affect how we think about death, which is currently defined by the World Health Organization as the irreversible loss of brain (but not body) function. The research also has implications for the consciousness of other animals and how we treat them. And if consciousness is embodied, it would mean that a machine or robot with no way of integrating signals from its body will never be truly conscious.  

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