Interoception

Abstract

Interoception, a form of perception, is the sensing of the internal physiological state of the body, the afferent signals from the heart, lungs, gut, and other viscera and their central representation as felt bodily states. This article traces the concept from Sherrington's original division of the senses through Craig's account of a dedicated pathway that re-represents bodily condition in the insular cortex. It sets out the three-dimensional model separating interoceptive accuracy, sensibility, and awareness, the heartbeat tasks that measure them, and the predictive-processing view on which felt states are inferred rather than read off the signal. It closes with the long link between interoception and emotion, from the James-Lange theory to the roadmap tying interoceptive disturbance to anxiety, depression, and eating disorders. Three demonstrations model the heartbeat-counting score, the three dimensions, and interoceptive inference.

Keywords: interoception, heartbeat perception, insula, interoceptive accuracy, predictive processing

A person sitting quietly can often report whether their heart is pounding or steady, whether their stomach is full or empty, whether their breath is tight or easy. These reports do not come from the five outward-facing senses; they come from a separate afferent stream that carries the condition of the body's own tissues to the brain. Interoception is the reception, representation, and awareness of that stream, the sense by which the physiological state of the body becomes available to perception and feeling (Craig, 2002). It is distinct from somatosensory perception of the body surface, which reports events at the boundary with the outside world, and from proprioception, which reports the position of the limbs; interoception reports the inner milieu. The term has widened over its history from the strict sense of visceral afferents to a broad notion covering all signals that inform the brain of the body's internal state, and that widening is itself a matter of live debate (Ceunen et al., 2016).

What Interoception Is

Interoception is the sensing of the internal state of the body, as opposed to the sensing of the external world or of the position of the body in space. The threefold division is Sherrington's: he distinguished exteroceptors, which face the outside world; proprioceptors, which report the mechanical state of the musculoskeletal system; and interoceptors, the receptors of the viscera and internal surfaces that report events within the body (Sherrington, 1906). On this original scheme interoception was strictly visceral. The modern usage is broader, taking in signals of temperature, pain, cardiac and respiratory activity, blood chemistry, hunger, and other bodily states, on the grounds that all of them inform the brain about the condition of the body rather than about the outside world; where exactly to draw the boundary, and whether the enlarged concept remains coherent, is a question the field has repeatedly reopened (Ceunen et al., 2016).

The reframing that made interoception a central topic in cognitive neuroscience was Craig's. He argued that the classical picture, on which visceral afference is a diffuse, poorly localized background sense, understates a specific and richly organized system. A dedicated pathway, beginning in small-diameter afferent fibres and ascending through lamina I of the spinal cord, carries information about the physiological condition of all the tissues of the body to the brainstem and thalamus, and from there to the insular cortex, where it is mapped and re-represented (Craig, 2002). On this account interoception is not merely the detection of visceral events but the basis of a felt sense of the body as a whole, and its cortical representation in the insula is where that sense becomes subjective feeling. This is the sense in which interoception underwrites embodied cognition: the mind's models of itself are grounded in a continuously updated representation of the body's interior.

The Three Dimensions of Interoception

A persistent confusion in the early literature was to treat interoception as a single quantity, so that a questionnaire asking people how well they sense their bodies and a laboratory test of how accurately they actually do so were assumed to measure the same thing. They do not correlate well, and Garfinkel and colleagues resolved the tangle by separating interoception into three dissociable dimensions (Garfinkel et al., 2015). Interoceptive accuracy is objective performance on a behavioural test, such as how closely counted heartbeats match recorded ones. Interoceptive sensibility is the subjective, self-reported belief about one's own interoceptive ability, whether measured by questionnaire or by the confidence a person expresses on a task. Interoceptive awareness is a metacognitive quantity: the correspondence between accuracy and confidence, that is, whether a person's confidence tracks their actual performance, high when they do well and low when they do not.

The three can come apart in instructive ways. A person may be objectively accurate yet not know it, reporting low confidence, or objectively poor yet serenely confident, a dissociation between accuracy and sensibility with low awareness in both cases. Only when confidence rises and falls with performance is awareness high. The distinction matters because different dimensions relate to different outcomes: trait anxiety, for instance, has been linked more closely to the interaction of these dimensions than to accuracy alone, and lumping them together obscures the relationships (Garfinkel et al., 2015). The first demonstration lets the reader set accuracy and confidence independently and see how the awareness dimension, their correspondence, emerges from the pair.

Measuring Cardiac Interoception

The heartbeat is the workhorse signal of interoception research, because it is internal, involuntary, and can be recorded objectively for comparison with a person's perception. Two tasks dominate. In the heartbeat-counting task introduced by Schandry, a person silently counts the heartbeats they feel over several timed intervals without taking their pulse, and an accuracy score is computed from how closely the counted number matches the number actually recorded; better perceivers, on this measure, also reported more intense emotional experience (Schandry, 1981). In the heartbeat-discrimination task, a person judges whether a train of tones is synchronous with their own heartbeat or lags it, a two-alternative judgement scored like a signal detection problem. The counting task is simpler and more widely used, though it is open to a serious validity challenge. Because the score rewards a count that matches the recorded number of beats, it is confounded with the person's prior knowledge of their own heart rate: scores correlate with actual heart rate and with time estimation, so a good score need not reflect felt beats at all (Zamariola et al., 2018). Brener and Ring argued on psychophysical grounds that establishing genuine heartbeat detection demands methods that isolate the felt signal from such inference, which the counting task does not (Brener & Ring, 2016).

Whatever the counting task's limits, individual differences in cardiac interoceptive accuracy are consequential, and they have a clear neural signature. Using the heartbeat-discrimination task inside a scanner, Critchley and colleagues found that people with more accurate interoception showed greater activity in the right anterior insula and adjacent cortex, and that the grey-matter volume of that region predicted both interoceptive accuracy and self-reported visceral awareness (Critchley et al., 2004). Converging evidence tied heartbeat perception and cardiovascular arousal to the same insular and cingulate structures (Pollatos et al., 2007). Table 1 sets out the principal measurement tasks and the dimension of interoception each one is best suited to tap.

Cardiac tasks dominate because the heartbeat is convenient to record, but the same logic extends to other channels, including respiratory load, gastric rhythm, and thermal and pain signals, and the consensus roadmap urges measurement across them rather than reliance on the heart alone (Khalsa et al., 2018). The second demonstration implements the Schandry counting score for a single interval, letting the reader set a heart rate, an interval, and a counted number of beats, and reporting the per-interval accuracy score the formula returns; the full score averages this term over several intervals, as the Worked Example does.

The Neural Basis: From Lamina I to the Insula

The anatomy Craig described gives interoception a cortical destination as specific as those of vision or hearing. Small-diameter afferents reporting the state of the tissues synapse in lamina I of the dorsal horn, which projects, in primates, through a distinct thalamic relay to the dorsal posterior insula; this posterior insular region behaves as a primary interoceptive cortex, a topographic map of the body's physiological condition (Craig, 2002). From there the representation is re-mapped forward along the insula to the anterior insular cortex, and it is this anterior re-representation, Craig argued, that transforms a mapped bodily state into a subjective feeling, and that is uniquely elaborated in humans (Craig, 2009). The vagus nerve and its brainstem target, the nucleus of the solitary tract, provide a parallel route for signals from the heart, lungs, and gut, converging on the same insular and cingulate territory; the earlier synthesis of these afferent routes and their relevance to psychosomatic medicine is Cameron's (Cameron, 2001).

The functional imaging bears out the anatomy. The anterior insula is the region whose activity scales with interoceptive accuracy and whose structure predicts it, and it is co-activated with the anterior cingulate cortex in a pairing that recurs across studies of feeling and its expression in action (Critchley et al., 2004; Pollatos et al., 2007). Craig's proposal that the anterior insula supports a felt, moment-to-moment awareness of the bodily self connects interoception directly to consciousness: on this view the sentient self is built, in the first instance, from the representation of the body's own condition (Craig, 2009). Figure 1 traces the ascending pathway from the viscera to the anterior insula.

Interoception as Inference

The account so far is a feedforward one, in which bodily signals ascend and are read out. The predictive-processing turn inverts it. On the interoceptive-inference view, the brain does not passively receive the state of the body but continuously predicts it, generating expectations about the causes of its interoceptive input and updating them only by the prediction error that survives (Seth, 2013). A felt state such as anxiety or calm is then not a direct readout of visceral afference but a perceptual inference, the brain's best explanation of its bodily signals given its prior expectations, weighted by how reliable each is taken to be. This aligns interoception with the same predictive coding framework applied to the outward senses, and it locates the embodied, feeling self within it: the sense of being a self with a body is, on Seth's proposal, a controlled hallucination constrained by interoceptive prediction.

Barrett and Simmons pressed the point to its physiological conclusion. They argued that the agranular visceromotor regions of the cortex, including the anterior insula and anterior cingulate, do not merely receive interoceptive predictions but issue them, driving the body's regulation in advance of need rather than in reaction to it (Barrett & Simmons, 2015). On this view interoception is in the service of allostasis, the anticipatory regulation of the body's resources, and perception of the body's state is a by-product of a system built to control it; this reframes emotional self-regulation as a form of predictive bodily control. The third demonstration makes the inference concrete, combining a prior expectation of bodily arousal with an incoming sensory signal, weighted by their precisions, to yield the perceived state and the prediction error that would revise it.

Interoception, Emotion, and Health

The tie between interoception and feeling is the oldest thread in the subject. James proposed that an emotion just is the perception of bodily changes as they occur, so that the felt fear is the perception of a racing heart and a tightened chest rather than their cause (James, 1884). Cannon's critique was sharp and enduring: visceral responses, he argued, are too slow, too uniform across different emotions, and too insensitive to be the substance of the rapid and differentiated feelings people report, and severing them need not abolish emotion (Cannon, 1927). Schachter and Singer's two-factor theory offered the classic compromise: bodily arousal supplies the intensity of an emotion while a cognitive appraisal of the situation supplies its quality, so that one physiological state can be felt as different emotions according to how it is interpreted (Schachter & Singer, 1962). The modern position is neither the pure James-Lange view nor its wholesale rejection. Bodily signals are read as one ingredient of emotion, weighted against context and expectation, and individual differences in interoceptive accuracy modulate the intensity and use of feeling: more accurate perceivers show stronger emotional responses and, in one influential result, made better use of bodily signals in intuitive decision making (Dunn et al., 2010). That bodily signals can guide choice is the core of Damasio's somatic-marker hypothesis, on which emotional reactions tied to the past outcomes of decisions are re-evoked as bodily states that bias present choice, often ahead of deliberate reasoning (Damasio, 1996). The contemporary account of how interoception enters emotion is Critchley and Garfinkel's, on which feelings arise from the integration of interoceptive prediction with the state of the body (Critchley & Garfinkel, 2017).

Because interoception supplies the bodily component of feeling, its disturbance has been implicated across a wide range of conditions. Heightened or misread cardiac signals feature in the vicious circle of panic and anxiety; blunted interoception has been reported in depression; distorted signals from the gut and body are central to eating disorders; and altered bodily awareness appears in addiction and in some functional and dissociative disorders. A large consensus statement mapped these connections and set an agenda for interoception as a transdiagnostic target, arguing that a common disturbance of the brain's modelling of the body may run beneath conditions that look unrelated on the surface (Khalsa et al., 2018). Whether interoceptive training can move clinical outcomes remains open, but the framing has reorganized how a swathe of psychopathology is understood.

Worked Example

The heartbeat-counting task can be scored exactly, and the second demonstration reports, for a single interval, the same number the formula gives. Schandry's heartbeat perception score averages, over the timed intervals, one minus the absolute difference between recorded and counted beats divided by the recorded beats: a score of one is perfect, and it falls toward zero as the count departs from the truth in either direction. Consider a person at rest with a heart rate of 72 beats per minute, which is 1.2 beats per second, tested over three intervals of 25, 35, and 45 seconds. The recorded number of beats is the rate times the duration: 1.2 times 25 is 30 beats, 1.2 times 35 is 42 beats, and 1.2 times 45 is 54 beats.

Suppose the person, as most do, undercounts, reporting 27, 33, and 40 beats. The first interval contributes one minus the quantity the absolute value of 30 minus 27, which is 3, divided by 30, that is one minus 0.100, or 0.900. The second contributes one minus 9 divided by 42, one minus 0.214, or 0.786. The third contributes one minus 14 divided by 54, one minus 0.259, or 0.741. The score is the mean of the three, 0.900 plus 0.786 plus 0.741 divided by three, which is 2.427 divided by three, about 0.809. A score of roughly 0.81 is typical of a moderately accurate perceiver; scores climb toward 0.90 and above in the best perceivers and fall below 0.60 in the poorest. The systematic undercounting in the example is itself characteristic, and it is one reason the counting task is thought to be contaminated by beliefs about resting heart rate: a person who assumes their heart beats about once a second will count toward that assumption rather than toward the beats they feel.

Discussion

Interoception has moved in two decades from the margins of physiology to a central place in accounts of emotion, the self, and mental health, and the reason is a convergence of anatomy, measurement, and theory. Craig's demonstration of a dedicated afferent pathway with a cortical map in the insula gave the sense a specific neural home, and the imaging that followed tied individual differences in interoceptive accuracy to that home in the anterior insula (Craig, 2002; Critchley et al., 2004). The three-dimensional model then disciplined a literature that had been conflating a person's bodily sensitivity with their belief about it, and made clear that accuracy, sensibility, and awareness must be measured and reasoned about separately (Garfinkel et al., 2015).

The predictive-processing reframing is the current organizing idea, and its force is that it makes interoception continuous with the rest of perception rather than a special case: felt bodily states are inferences, and the visceromotor cortex issues predictions in the service of anticipatory regulation (Seth, 2013; Barrett & Simmons, 2015). Two tensions keep the field active. The first is methodological: the most-used measure, heartbeat counting, is open to the charge that it indexes beliefs about the heart as much as felt heartbeats, its scores confounded with heart rate itself and with time estimation, and disentangling genuine interoceptive accuracy from prior knowledge is an unsolved problem that colours every result built on the task (Zamariola et al., 2018; Brener & Ring, 2016). The second is conceptual: the enlargement of interoception to cover nearly every bodily signal risks draining the term of content, and drawing a principled boundary remains contested (Ceunen et al., 2016). What is no longer in doubt, running back through Cannon's critique to James's original claim, is that the body's internal state is not a silent backdrop to the mind but a signal the brain continuously reads, predicts, and feels (James, 1884; Khalsa et al., 2018).

Common Misconceptions

Interoception is the same as touch, the sense of the body.

It is not. Touch and the other somatosensory senses report events at the body surface, the boundary with the outside world, and proprioception reports limb position; interoception reports the internal physiological condition of the viscera and tissues, and travels a distinct afferent pathway to the insula (Craig, 2002).

A high score on a heartbeat-counting test proves a person truly feels their heartbeats.

Not necessarily. Because the score rewards matching the recorded number, a person whose beliefs about their resting heart rate happen to be accurate can score well without feeling individual beats, which is why the counting task is separated from confidence and from discrimination measures, and why interoception is split into distinct dimensions rather than one (Garfinkel et al., 2015).

Emotion is simply the direct perception of bodily changes, as James proposed.

The pure form of that claim did not survive Cannon's critique, that visceral responses are too slow and too undifferentiated to be the whole of emotion. The modern view treats bodily signals as one weighted ingredient, integrated with context and expectation through interoceptive inference rather than read off directly (Cannon, 1927; Critchley & Garfinkel, 2017).

Glossary

Allostasis.

The anticipatory regulation of the body's internal resources, adjusting physiology in advance of need rather than only in reaction to it; interoceptive prediction is held to serve it.

Anterior insula.

The forward part of the insular cortex where the interoceptive map is re-represented; proposed by Craig to be where bodily state becomes subjective feeling, and where activity tracks interoceptive accuracy.

Exteroception.

The sensing of the external world through receptors that face outward, such as vision, hearing, and touch; Sherrington's contrast class to interoception.

Heartbeat-counting task.

Schandry's measure in which a person silently counts felt heartbeats over timed intervals; the accuracy score compares the counted number with the number actually recorded.

Heartbeat-discrimination task.

A measure in which a person judges whether tones are synchronous with, or delayed from, their own heartbeat, scored like a signal-detection problem.

Interoception.

The sensing, representation, and awareness of the internal physiological state of the body, from the viscera and internal tissues, as distinct from exteroception and proprioception.

Interoceptive accuracy.

Objective performance on a behavioural test of bodily perception, such as the correspondence between counted and recorded heartbeats.

Interoceptive awareness.

The metacognitive correspondence between accuracy and confidence: whether a person's confidence in their bodily judgements tracks how well they actually perform.

Interoceptive inference.

The account on which felt bodily states are the brain's precision-weighted predictions about the causes of its interoceptive signals, updated by prediction error, rather than a direct readout.

Interoceptive sensibility.

The subjective, self-reported belief about one's own interoceptive ability, measured by questionnaire or by expressed confidence, independent of objective accuracy.

Lamina I.

The most superficial layer of the spinal dorsal horn, where small-diameter interoceptive afferents synapse and begin the ascending spinothalamic pathway that reports the body's physiological condition.

Prediction error.

The mismatch between a predicted bodily signal and the one received; the quantity that, weighted by precision, drives revision of the brain's interoceptive model.

Proprioception.

The sensing of the mechanical state of the musculoskeletal system, the position and movement of the limbs; Sherrington's third division, distinct from both exteroception and interoception.

Somatic-marker hypothesis.

Damasio's proposal that bodily-emotional states associated with the past outcomes of choices are re-evoked to bias decision making, often before conscious deliberation.

Two-factor theory.

Schachter and Singer's account on which an emotion is the joint product of undifferentiated bodily arousal and a cognitive appraisal that gives that arousal its specific quality.

Vagus nerve.

The major parasympathetic nerve carrying afferent signals from the heart, lungs, and gut to the nucleus of the solitary tract in the brainstem, a parallel route into the interoceptive system.

Key Researchers

Lisa Feldman Barrett. University Distinguished Professor of Psychology at Northeastern University; with W. Kyle Simmons she recast interoception as active prediction, arguing that visceromotor cortex issues interoceptive predictions in the service of allostasis rather than passively receiving bodily signals. Faculty Page - Google Scholar - Wikipedia - ORCID

Arthur D. Craig (1951-2023). Neuroanatomist at the Barrow Neurological Institute; he traced the lamina I pathway that re-represents the body's physiological condition in the insular cortex and argued that the anterior insula is the substrate of a felt awareness of the bodily self. Wikipedia - Wikidata

Hugo D. Critchley. Chair in Psychiatry at Brighton and Sussex Medical School; his imaging work showed that interoceptive accuracy tracks anterior insular activity and grey-matter volume, and he developed the modern account linking interoception to emotion. Faculty Page - Google Scholar - Wikipedia - ORCID

Sarah N. Garfinkel. Professor of Cognitive Neuroscience at University College London; she introduced the three-dimensional model that separates interoceptive accuracy, sensibility, and awareness, clarifying a construct that had been conflated across measures. Faculty Page - Google Scholar - Wikipedia - ORCID

Rainer Schandry. Professor Emeritus of Biological Psychology at Ludwig-Maximilians-Universität München; he devised the mental heartbeat-tracking task, the standard behavioural measure of cardiac interoceptive accuracy, and showed that better perceivers report more intense emotion. Faculty Page - Wikipedia - Wikidata

Anil K. Seth. Professor of Cognitive and Computational Neuroscience at the University of Sussex; he extended predictive processing to the body's interior with the theory of interoceptive inference, on which felt states and the embodied self arise from the brain's predictions about its bodily signals. Faculty Page - Google Scholar - Wikipedia - ORCID

Frequently Asked Questions

What is interoception?
Interoception is the sense of the internal physiological state of the body, the reception and representation of signals from the heart, lungs, gut, blood vessels, and other tissues, and their emergence as felt bodily states (Craig, 2002).

How is interoception different from the other senses?
The outward-facing senses report the external world and proprioception reports the position of the limbs, whereas interoception reports the condition of the body's own interior, traveling a distinct afferent pathway to the insular cortex (Sherrington, 1906).

What are the three dimensions of interoception?
They are accuracy, objective performance on a bodily-perception task; sensibility, a person's self-reported belief about their own sensitivity; and awareness, the metacognitive correspondence between the two, which can dissociate from each other (Garfinkel et al., 2015).

How is interoception measured?
Most often through cardiac tasks: the heartbeat-counting task, in which a person silently counts felt beats over timed intervals, and the heartbeat-discrimination task, in which a person judges whether tones match the heartbeat (Schandry, 1981).

Which part of the brain supports interoception?
The insular cortex: a primary interoceptive map lies in the posterior insula, and the anterior insula re-represents it, with activity and grey-matter volume there tracking how accurately a person perceives their heartbeat (Critchley et al., 2004).

What is interoceptive inference?
It is the view that felt bodily states are not read directly from afferent signals but inferred, as the brain's precision-weighted predictions about the causes of its interoceptive input, updated by prediction error (Seth, 2013).

How is interoception related to emotion?
Bodily signals are one weighted ingredient of emotion, integrated with context and expectation; more accurate interoceptive perceivers tend to show more intense emotional responses and make more use of bodily signals in intuitive judgement (Dunn et al., 2010).

Why does interoception matter for mental health?
Disturbed interoception has been implicated across anxiety, depression, eating disorders, and addiction, and a consensus statement proposed it as a transdiagnostic target, a shared disturbance in how the brain models the body (Khalsa et al., 2018).

References