Interoception Is Our Sixth Sense, and It May Be Key to Mental Health
Disruptions in interoception may underlie anxiety, eating disorders, and other mental health ailments
By the time Maggie May, an Arkansas resident in her 30s, was admitted to a psychiatric clinic in 2024, she had been struggling for years with atypical anorexia nervosa, an eating disorder that leads to severe food restriction and profound disturbances in body image. (Her name has been changed for privacy.) She had already tried traditional interventions with a psychotherapist and a dietitian, but they had failed to improve her condition. So when May heard about a trial of a new and unconventional therapy, she jumped at the opportunity.The treatment was unusual in that alongside talk therapy, May underwent several sessions in a sensory-deprivation chamber: a dark, soundproof room where she floated in a shallow pool of water heated to match the temperature of her skin and saturated with Epsom salts to make her more buoyant. The goal was to blunt May’s external senses, enabling her to feel from within—focusing on the steady thudding of her heart, the gentle flow of air in and out of her lungs, and other internal bodily signals.The ability to connect with the body’s inner signals is called interoception. Some people are better at it than others, and one’s aptitude for it may change. Life events can also bolster or damage a person’s interoceptive skills. Sahib Khalsa, a psychiatrist and neuroscientist at the University of California, Los Angeles, and his colleagues think a disrupted interoception system might be one of the driving forces behind anorexia nervosa. So they decided to repurpose a decades-old therapy called flotation-REST (for “reduced environmental stimulation therapy”) and launched a trial with it in 2018. They hypothesized that in people with anorexia and some other disorders, an underreliance on internal signals may lead to an overreliance on external ones, such as how one looks in the mirror, that ultimately causes distorted body image, one of the key factors underlying these conditions. “When they’re in the float environment, they experience internal signals more strongly,” Khalsa says. “And having that experience may then confer a different understanding of the brain-body relationship that they have.”On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.Studies have implicated problems with this inner sense in a wide variety of conditions, including anxiety disorders, post-traumatic stress disorder and borderline personality disorder. Some researchers and clinicians now think that problems in interoception might contribute to many mental illnesses. Alongside this research, which itself is complicated by challenges in testing design and by a less than clear understanding of interoception, other groups are also developing therapies that aim to target this inner sense and boost psychological well-being.This work is circling in on a central message: the body and mind are inextricably intertwined. “We have always thought about [mental health conditions] as being in the brain or the mind,” says Camilla Nord, a professor of cognitive neuroscience at the University of Cambridge. But clinicians have long noted that people with mental illness frequently report physical symptoms such as abnormalities in heartbeats, breathing and appetite, she adds.The idea that the body can influence the mind dates back centuries. In the 1800s two psychologists on opposite ends of the globe independently proposed a then novel idea: emotions are the result of bodily reactions to a specific event. Called the James-Lange theory after its founders, American psychologist William James and Danish doctor Carl Lange, this view ran counter to the long-dominant belief that emotions were the cause, not a consequence, of corresponding physiological changes.Although this notion has garnered critics, it inspired a slew of studies. The 1980s saw a surge of interest in the role of physiological signals in panic disorders. Researchers discovered that they could bring on panic attacks by asking people to inhale carbon dioxide–enriched air, which can increase breathing rates, or by injecting them with isoproterenol, a drug that increases heart rate.Breathing rate can affect how someone perceives the intensity and unpleasantness of pain.These findings led some psychologists to suggest that physical sensations were the primary trigger of panic attacks. In the early 1990s Anke Ehlers, a psychologist then at the University of Göttingen in Germany, and her team examined dozens of people with panic disorders and reported that these patients were better able to perceive their heartbeats than healthy individuals—and that this greater awareness was linked to more severe symptoms. On top of that, a small, preliminary study by Ehlers of 17 patients revealed that those who were more skilled at this task were more likely to relapse and start having panic attacks again. These observations hinted at a two-way dynamic: not only could physical sensations within the body cause psychological effects, but the ability to perceive and interpret those signals—in other words, one’s interoceptive ability—could have a profound influence on mental health.Over the years a growing body of evidence has indicated that interoception plays an important role in shaping both emotions and psychological health. A large chunk of this work has focused on the heart. With every heartbeat, blood rushes into the arteries and triggers sensors known as baroreceptors, which shoot off messages to the brain conveying information about how strongly and rapidly the heart is beating.In one pivotal 2014 study, Hugo Critchley, a neuropsychiatrist at Brighton and Sussex Medical School in England, and his team reported that this process can affect a person’s sensitivity to fear. By monitoring volunteers’ heartbeats while they viewed fearful or neutral faces, they found that people detected fearful faces more easily and judged them as more intense when their heart was pumping out blood than when it was relaxing and refilling. But participants with higher levels of anxiety often perceived fear even when their hearts relaxed.Researchers have also demonstrated that bodily signals such as breathing patterns and gut rhythms can influence emotional reactions. People are quicker to react to fearful faces while breathing in than while breathing out, and breathing rate can affect how someone perceives the intensity and unpleasantness of pain.In more recent work, some neuroscientists have turned their attention to the gastrointestinal system. In 2021 Nord and her colleagues discovered that people given a dose of an antinausea drug that affects gut rhythms—processes within the stomach that help digestion—were less likely to look away from pictures of feces than they normally would have been. These disgust-related visceral signals, Nord speculates, may be relevant to eating disorders. “It’s possible that some of these signals contribute to feeling aversion to signals of satiety, making satiety very uncomfortable, a feeling you don’t want to feel,” she says.But how, exactly, do disruptions in interoception come about? Many researchers suspect it may have to do with our brain’s predictions going awry. Interoception, like our other senses, feeds information to the brain, which some neuroscientists suggest is a prediction machine: it constantly uses our prior knowledge of the world to make inferences about incoming signals. In the case of interoception, the brain attempts to decode the cause of internal sensations. If its interpretations are incorrect, they may lead to negative psychological effects—for example, if a person erroneously assumes their heart rate is elevated, they may begin to feel anxious in the absence of a threat. And if a person has learned to associate pangs of hunger with disgust, they might severely restrict how much food they consume.Inner signals can be much more ambiguous than the external input from other senses such as sight and hearing. So the brain’s prior information about these internal signals becomes especially important, says André Schulz, a professor of psychology at the University of Luxembourg.To better understand and assess potential mismatches in subjective and objective measures of our bodily signals, researchers have developed a framework that captures the different dimensions in which interoceptive processing occurs. In 2015 Sarah Garfinkel, then a postdoctoral researcher in Critchley’s group at Brighton and Sussex, and her colleagues proposed a model to clearly differentiate three categories of interoceptive processing: interoceptive accuracy (how well someone performs, objectively, on relevant tasks such as heartbeat detection), interoceptive sensibility (a person’s subjective evaluation of their interoceptive abilities), and interoceptive awareness (how well that self-assessment matches their actual abilities).Along with their collaborators, Garfinkel, now at University College London, and Critchley have found that in autistic adults there is a link between anxiety and a poor ability to predict one’s interoceptive skill—in this case, one’s sensitivity to heartbeat. In a study of 40 people (20 of whom had autism), they and their colleagues discovered that individuals with autism performed worse on a heartbeat-detection task and were more likely to overestimate their interoceptive abilities than those without autism. This disconnect was more pronounced in people with higher levels of anxiety, suggesting that errors in the ability to predict bodily signals may contribute to feelings of anxiety, Critchley says.In recent years the list of psychiatric conditions linked to interoceptive dysfunctions has grown. Some, such as panic and anxiety disorders, are associated with heightened attention to one’s internal processes; others, such as borderline personality disorder and schizophrenia, may be tied to a blunting of one’s ability to connect with these signals. In a review of interoception research, published in 2021, Nord and her colleagues examined 33 studies that collectively involved more than 1,200 participants. They found that people with a range of psychiatric disorders, including anxiety disorders and schizophrenia, shared similar alterations in the insula, a key brain region linked with interoception during body-sensing-related tasks.Overall, though, studies show mixed results. “If you look across the literature, [however many] studies have found an association with, say, anxiety, [a roughly] equal amount will have not found a relationship or found it in the other direction,” says Jennifer Murphy, a psychologist at the University of Surrey in England.The varying results could stem from the challenges associated with studying interoception, which can be difficult to both manipulate and measure. Take cardiac interoception. In most early studies in this domain, participants counted their pulses, but this test may measure people’s estimate of their heart rate rather than how well they can feel their heartbeat. This flaw was perhaps most clearly demonstrated in a 1999 study in which people with pacemakers reported their heart rates while experimenters (with the participants’ consent) secretly tuned their pacemakers’ timing up or down. Participants’ self-reported heart rates didn’t follow the shifts in the actual pulses; their beliefs about how their heart rates should be changing had a much stronger influence.To address these limitations, scientists have been devising better study methods. Micah Allen, a neuroscientist at Aarhus University in Denmark, and his team have developed a heart-rate-discrimination task in which people are asked to report whether a series of tones is faster or slower than their current pulse, allowing researchers to quantify how sensitive an individual is to their heartbeats. Allen and his colleagues are now testing breath interoception in a similar way. Using a computer-controlled device, the researchers can make precise changes to the air resistance someone feels when they inhale through a tube. By doing so, they can quantify how well the person can detect changes in their breathing.Using these new techniques, Allen’s team has learned that an individual’s interoceptive chops don’t translate across all domains. In a recent preprint study of 241 people, they found that a person’s ability to perceive their heart rate wasn’t correlated to their performance in a breathing-resistance task.Researchers have also been combining these behavioral tests with measurements of brain activity. One example is the heartbeat-evoked potential, a spike in brain signaling that occurs each time the heart beats. Scientists have found that changes in these signals, which can be detected with noninvasive brain-imaging techniques such as electroencephalography, are linked to accuracy in heartbeat-detection tasks and to the ability to process emotions. Similar brain signals related to organs such as the gut and those of the respiratory system have been linked to the ability to perceive sensations within those organs.These studies indicate that interoception abilities don’t align across a person’s bodily functions, from breathing to heart rate to gut rhythms. It’s therefore difficult to know whether the conflicting findings about the role of interoception disruptions in mental disorders mean there is no meaningful relation to be found or whether the issue is that researchers have simply not been using the right task or studying the most relevant system or level of interoception, Murphy says. “It’s very unlikely that every condition will have the same bit of interoception disrupted.”Untangling how, exactly, interoception is disrupted in people with mental illness remains an active area of investigation. Some experts say answers may come from treatment trials investigating whether interventions that target disturbances in this inner sense might boost mental health. Many such studies are currently underway.“To understand what interoception is, we need to manipulate it,” Allen says. “And to understand its role as a biomarker, as something that is related to mental health, we also need to manipulate it.”Jane Green knows stressful situations can have immediate effects on her body. For Green, who has autism, reading a piece of bad news or dealing with a face-to-face confrontation may set off a chain reaction in her body: a rush of adrenaline followed by a pounding heart, bloating and itchiness, among other physical reactions.Such responses may be linked to an inability to read one’s inner body. In 2019 she took part in a clinical trial in which Critchley, Garfinkel and their colleagues sought to test just that—how resolving a discrepancy between a person’s perceived interoceptive abilities and reality could improve anxiety levels in adults with autism spectrum disorder. The intervention in the study focused on tasks that involved heartbeat detection.After training and testing 121 participants (half of whom were randomly assigned to receive a noninteroception-based control task) across six sessions, the team reported in a 2021 paper that this treatment successfully reduced anxiety in their participants and that this effect persisted for at least three months.Participating in the trial was a “real turning point” in Green’s ability to deal with anxiety, she says. “I recognize now that when I’m stressed, whether I like it or not, my body reacts,” she explains. Although she still experiences physical reactions to emotionally charged situations, they are often less severe than they were prior to the treatment. And her knowledge of what’s happening in her body has made it easier to cope, she adds. Green is chair and founder of SEDSConnective, a charity dedicated to neurodivergent people with connective tissue disorders such as Ehlers-Danlos syndromes. These conditions tend to overlap with anxiety disorders, and Green is now advocating for interoception-based therapies to help affected people.A person’s interoceptive capabilities might be especially malleable during early childhood or adolescence.For May, who participated in the flotation-REST trial, what she learned from being cut off from the external world helped her to get through an inpatient stay at an eating-disorder clinic where she was being forced to eat—and, as a result, gain weight. “You’re working on the things that drove you to come in the first place, but at the same time, your distress with your body is getting worse and worse,” she says. When she was in the flotation chamber, however, May’s awareness of her physical body would slip away, reducing some of the negative feelings she had about herself and quieting the worries that swirled in her mind. “You can’t tell where your body stops and the water begins,” May says. “Because you’re completely buoyant, you also have no sense of the ways that your body distresses you.”Flotation-REST shows promise: in a clinical trial of 68 people hospitalized for anorexia nervosa who were randomly assigned to the therapy or a placebo, Khalsa’s team found that six months after treatment, those who received therapy reported less body dissatisfaction than those who did not. The researchers have also created a version of this therapy for anxiety and depression. In early-stage clinical trials, this intervention appeared to reduce the symptoms of those disorders. Now they are investigating whether this therapy might also benefit people with amphetamine use disorder.Other interoception-based treatments are also under investigation. At Emory University, a group led by clinical psychologist Negar Fani has been examining the effects of combining a mindfulness-based intervention with a wearable device that delivers vibrations corresponding to a person’s breaths. In a group of trauma-exposed individuals, this intervention increased the participants’ confidence in their bodily signals more than the mindfulness-based intervention alone. Even long after these sessions, people report being able to recall the feeling of breath-synced vibrations, Fani says. “It helps to ground them, brings them back into the present moment. They can access their body signals and figure out what they want to do with them.” The team is now conducting a follow-up study to see whether this treatment can improve mental well-being in people who have experienced trauma.In yet another ongoing trial, Nord is collaborating with Garfinkel on a series of studies aimed at understanding in which body systems—and in which of the three dimensions (accuracy, sensibility and awareness)—interoception is altered in people with various mental disorders, among them anxiety and depression. As part of that effort, the researchers are testing interventions, including interoceptive training, mindfulness therapy—to help improve the mind-body connection—and stimulation of the insula with focused ultrasound.Scientists still have plenty of questions to answer about interoception. One major open question is how differences in interoception arise. Some of our interoceptive abilities may begin taking shape during early infanthood. Scientists have discovered that babies as young as three months show differences in the amount of time they spend looking at colored shapes moving either in or out of sync with their heartbeats—a finding that suggests our ability to sense heart rhythms is present at this young age.Interactions with caregivers during one’s first years may play a crucial role in determining how in tune a person becomes with their body. The way a parent responds to an infant’s cues about being hungry, tired or in pain, for instance, may shape how well the child is able to interpret those signals later in life. Although direct evidence for this hypothesis is still lacking, studies have shown that an individual’s early caregiving environment can shape how their body responds to stress.Other factors such as a person’s sex or various environmental conditions, including adversity in early life, may also influence how interoception develops. Some research suggests that adverse experiences, especially chronic, interpersonal trauma early in life, may be key contributors. Clinicians have long observed that traumatic events can lead people to detach or “dissociate” from the body, and some researchers have proposed that this disconnect can disrupt interoceptive processes over time. For a subset of people, these alterations might be linked to an increased likelihood of self-harm and suicide: one 2020 study, for example, found that people with a history of suicide attempts and a diagnosed mental illness, such as anxiety, PTSD or depression, were worse at an interoceptive heartbeat-detection task than those who had the same ailments but had not attempted to take their own life.A person’s interoceptive abilities may change over time. Interoceptive capabilities might be especially malleable during certain life stages: periods such as early childhood, when a person is just learning how to interpret their bodily signals, or adolescence, when puberty is creating a whirlwind of physical changes. It might be one mechanism, among many, that explains why “these times tend to be risk periods for the development of mental illness,” Murphy says.The boundaries of interoception are also only beginning to be understood. In recent years some scientists have become interested in probing the links between the immune system and the brain, which are in constant conversation. An emerging body of work suggests that the brain both keeps tabs on and influences what happens in the immune system, and the immune system can in turn affect the brain. Studies have linked dysfunction in the immune system—namely, inflammation—to mental illnesses such as depression, psychosis and trauma-related disorders. The immune system may affect our mental states over much longer time scales than, say, the heart, which can influence our emotional experiences in real time.Understanding the mysteries of interoception may lead to better therapies for illnesses of the mind—and the body. Some researchers believe that understanding interoception may ultimately be helpful for treating physical symptoms as well. Schulz and his team, for instance, are currently evaluating interoception-based treatments for chronic fatigue syndrome (also known as myalgic encephalomyelitis), a complicated disorder that causes a range of symptoms, including severe tiredness. “Interoception has so much relevance to health in general,” Fani says. “We can’t ignore it anymore.”IF YOU NEED HELPIf you or someone you know is struggling or having thoughts of suicide, help is available. Call or text the 988 Suicide & Crisis Lifeline at 988 or use the online Lifeline Chat at chat.988lifeline.org.
