The Body That Knew First: Interoception, the Anterior Insula, and the Neuroscience of the Thumos

The anterior insular cortex is a strip of tissue buried in the lateral sulcus of the human brain, hidden beneath the temporal and frontal opercula, inaccessible to surface inspection. It is disproportionately enlarged in humans relative to other primates, approximately thirty percent larger than in the macaque (Craig, 2009). Within this tissue, raw physiological signals from every organ, every muscle, every visceral surface of the body converge into a single integrated representation: the conscious experience of how you feel right now. A.D. Craig calls this the “global emotional moment.” Antonio Damasio calls it the “feeling of what happens.” Lisa Feldman Barrett calls it your “body budget.” Homer called it the thumos.

For three thousand years, these descriptions have been running in parallel. The epic poet mapped the architecture of the felt interior through the vocabulary of breath, weight, and pressure. The neuroscientist maps the same architecture through functional magnetic resonance imaging and lamina I spinothalamocortical pathways. The convergence is not metaphorical. The anterior insula performs the precise function that Homer assigned to the thumos: it monitors the internal state of the organism, registers what matters, and generates the evaluative feeling that constitutes being alive.

What does the anterior insula actually do?

Craig’s landmark 2002 paper redefined interoception as the sense of the physiological condition of the entire body. Prior to Craig, interoception referred narrowly to visceral sensation: the gut, the heart, the organs of the trunk. Craig expanded the definition to include temperature, muscle tension, itch, air hunger, sensual touch, and all other signals conveyed by small-diameter C-fiber and A-delta afferents through the lamina I spinothalamocortical system (Craig, 2002). These afferents constitute a dedicated homeostatic pathway that parallels the efferent autonomic nervous system, providing the brain with a continuous, high-resolution image of what the body is undergoing.

The signals arrive first in the posterior insular cortex, where they are mapped topographically and modality-specifically: temperature here, cardiac rhythm there, gastric distension elsewhere. This is raw data, the physiological weight of the body’s current state, mapped without interpretation. As these representations move anteriorly, they undergo progressive integration. The mid-insula combines homeostatic signals with emotionally salient environmental input, modulated by the amygdala and the ventral striatum. The anterior insula then performs the decisive transformation: it integrates all of this information into a unified meta-representation of the sentient self at a single moment in time (Craig, 2009).

Craig describes a posterior-to-anterior gradient of increasing integration that culminates in awareness itself. The posterior insula registers that your heart is beating faster. The mid-insula links that acceleration to the sight of something threatening. The anterior insula produces the feeling — “I am afraid, right now, in this body.” This is not an abstract computation. It is the neural instantiation of subjective experience. Craig argues that the anterior insula, particularly in the right hemisphere, constitutes a plausible neural correlate of consciousness: the structure that generates the continuous feeling of being a self in time (Craig, 2009).

Functional imaging confirms the breadth of this claim. The anterior insula activates during thirst, heartbeat awareness, sexual arousal, pain, empathy, musical pleasure, maternal love, disgust, decision-making under uncertainty, error awareness, and the moment of perceptual recognition (Craig, 2009). The common denominator is not a specific emotion. It is the presence of subjective experience itself. Whatever you are feeling at this moment (calm, agitated, curious, bored), the anterior insula is representing it.

How did Damasio arrive at the same structure from the opposite direction?

Antonio Damasio began from the opposite direction: the catastrophic absence of interoception. In the early 1990s, Damasio studied neurological patients whose prefrontal cortices had been damaged, specifically in regions that connect to body-representing structures including the insular cortex. These patients retained their intelligence, their memory, their language, their capacity for abstract reasoning. What they lost was the capacity to make sound decisions about their own lives. They could not hold a job, sustain a relationship, or navigate social situations. The one consistent accompaniment to their decision-making failure was a “marked alteration of the ability to experience feelings” (Damasio, 1994).

From this clinical observation, Damasio developed the somatic-marker hypothesis: the proposal that emotions mark certain aspects of a situation or certain outcomes of possible actions by generating body-state changes that are then represented in body-mapping brain regions. A “gut feeling” is not a metaphor in Damasio’s framework. It is a literal interoceptive signal generated by autonomic activity in the viscera, mapped by the insular and somatosensory cortices, and presented to consciousness as an evaluation. Patients who lost this capacity lost the ability to evaluate. They could still think. Thinking without feeling simply does not produce the signal that marks one option as better than another (Damasio, 1994).

The implications for the history of Western thought are severe. Descartes separated mind from body. Plato ranked reason above feeling. The entire tradition from Socrates forward assumed that rational deliberation operates best when uncontaminated by emotion. Damasio titled his book Descartes’ Error because the neuroscience demonstrates the opposite: “Emotion and feeling, along with the covert physiological machinery underlying them, assist us with the daunting task of predicting an uncertain future and planning our actions accordingly” (Damasio, 1994). The body that Plato demoted and Descartes exiled is the same body whose signals make rational evaluation possible.

In The Feeling of What Happens, Damasio extended the argument to consciousness itself. Feelings, he proposed, are the brain’s captive-audience representation of the body in “full biological swing,” a continuous, updated landscape of visceral, muscular, and metabolic activity that constitutes the ground reference for all higher cognition (Damasio, 1999). By 2018, in The Strange Order of Things, he traced this principle to its cultural implications: feelings and homeostatic regulation are foundational to the emergence of human civilizations. Cultural phenomena arise from the same biological imperatives that govern cellular survival (Damasio, 2018). The body does not merely support the mind. It teaches it what matters.

What did Panksepp discover below the cortex?

While Craig mapped the cortical architecture of interoception and Damasio traced its consequences for reason, Jaak Panksepp worked from below. His 1998 Affective Neuroscience identified seven primary emotional circuits in the subcortical brain (SEEKING, RAGE, FEAR, LUST, CARE, PANIC/GRIEF, and PLAY) that operate across all mammalian species. Panksepp’s central argument was that these ancient emotional systems are not cognitive constructions or cultural products. They are genetically dictated operating systems embedded in structures that predate the neocortex by hundreds of millions of years (Panksepp, 1998).

Panksepp distinguished between what he called ROM functions (read-only memory, the subcortical emotional operating systems) and RAM functions (the flexible, cortical cognitive programs that develop through experience). The ROM functions reside in lower, subcortical regions. The RAM functions concentrate in the neocortex. This distinction matters because it establishes that raw affective experience is the deepest substrate of cognition, preceding it by hundreds of millions of years. Panksepp wrote that “it is this ancient animal heritage that makes us the intense, feeling creatures that we are” (Panksepp, 1998). The human cortex, for all its cognitive sophistication, has not altered the deep functional architecture of the ancient brain systems that generate emotional life.

The relevance to the thumos is direct. Homer did not locate feeling in the head. He located it in the chest, in the phrenes, in the seething organ that precedes and often overrides rational deliberation. Panksepp’s neuroscience confirms that Homer’s intuition was architecturally accurate: the deepest emotional systems operate below the level of cortical cognition, in structures that generate the raw feeling states upon which all higher evaluation depends. The cortex interprets these signals. It does not create them.

How does Barrett complete the picture?

Lisa Feldman Barrett’s theory of constructed emotion, articulated in How Emotions Are Made (2017), introduces a final element: prediction. Barrett argues that the brain does not wait passively for sensory input and then react. It predicts, constantly, what the body will need next. The interoceptive network — which Barrett’s lab demonstrated to be an intrinsic brain network analogous to those for vision and hearing, issues predictions about body-state changes, simulates the sensory consequences of those changes, and then compares the simulations against incoming interoceptive signals (Barrett, 2017).

Barrett calls the regulatory dimension of this process “body budgeting.” Every prediction the brain makes about a motor action simultaneously adjusts the body’s metabolic allocation: speeding the heart, releasing cortisol, dilating blood vessels, metabolizing glucose. These adjustments produce interoceptive sensations that Barrett identifies as the neural basis of affect: the continuous background feeling of pleasantness or unpleasantness, agitation or calm, that accompanies every waking moment (Barrett, 2017). Affect is not a response to the world. It is a summary of the body’s current metabolic state, generated by the interoceptive network’s predictions and prediction errors.

The practical consequence is that any event that significantly impacts the body budget becomes personally meaningful. Barrett’s laboratory demonstrated that body-budgeting regions adjust metabolic resources in response to photographs of animals, food, car crashes, and money — even when the subject is lying completely motionless in a scanner. The brain predicts the body’s response to these images and adjusts the budget accordingly. The resulting interoceptive sensations constitute what the subject feels about what they see (Barrett, 2017). This is evaluation in its most elemental form: the body’s metabolic response to a situation, registered as feeling, before any conscious judgment occurs.

Barrett insists that every brain region claimed to be a “home of emotion” is in fact a body-budgeting region within the interoceptive network. These regions do not react. They predict. Affect is therefore continuous, present from birth to death, and constitutive of consciousness itself: “Affect is a fundamental aspect of consciousness, like brightness and loudness” (Barrett, 2017). When the brain represents wavelengths of light, you experience brightness. When it represents air pressure changes, you experience loudness. When it represents interoceptive changes, you experience feeling.

What did Homer already know?

The Homeric thumos performs every function that Craig, Damasio, Panksepp, and Barrett have identified through independent research programs. It monitors the internal state of the organism. It registers what matters through a physics of accumulation — experience settles into the thumos, fills it, weighs it down. It generates autonomous evaluative responses that the hero consults as a second self. And it operates through a posterior-to-anterior gradient of increasing integration that maps precisely onto Craig’s insular architecture.

The Homeric formula kata phrena kai kata thumon — “down through the phrenes and down through the thumos” — appears twenty-one times in the epics, twenty of those for mortal deliberation (Caswell, 1990). The preposition kata encodes a gravitational physics: thought moves downward, through layered organs, from raw sensation to integrated evaluation. The phrenes (the sealed chest-cavity, the container) receive the initial impact. The thumos processes it into meaning. The gradient is not metaphor. Michael Clarke demonstrated that Homeric language operates through “a coherent somatic phenomenology” in which the chest functions as a literal forge where feeling is tempered, hardened, or liquefied under pressure (Clarke, 1999).

Craig’s posterior insula receives raw interoceptive data — the physiological weight of the body’s condition. His anterior insula integrates this data into a unified evaluative moment. Homer’s phrenes receive the blow. Homer’s thumos converts it into the evaluative voice that speaks back to the hero. The structural parallel is exact.

Panksepp’s subcortical emotional systems correspond to what Homer encoded as the autonomous agency of the thumos — the organ that barks, seethes, advises, and resists before the hero’s rational mind has formed an opinion. Damasio’s somatic markers correspond to what Homer depicted when Odysseus deliberates with his thumos rather than against it: the body’s signals are not noise to be filtered out of rational deliberation but the evaluative substrate upon which deliberation depends. Barrett’s body budget corresponds to the Homeric physics of accumulation and depletion: the thumos is a vessel that fills under grief, empties under joy, and hardens under sustained pressure into iron (Peterson, in press).

Shirley Darcus Sullivan’s comprehensive analysis confirmed the thumos as the most prominent psychic entity in Homer, appearing over 750 times — functioning as “a vibrant source of activity within the person” that encompasses feeling, deliberation, perception, desire, and moral evaluation (Sullivan, 1995). Ruth Padel insisted that the thumos behaves simultaneously as breath, agent, organ, and force, and that imposing modern distinctions between physical and psychological onto these terms is anachronistic (Padel, 1992). The neuroscience agrees. The anterior insula does not observe a distinction between body and mind. It generates the feeling state that constitutes both.

Why does this convergence matter?

The Interoception Summit of 2016, organized by Sahib Khalsa at the Laureate Institute for Brain Research, gathered the leading interoception researchers in the world and produced a consensus definition: interoception is “the process by which the nervous system senses, interprets, and integrates signals originating from within the body, providing a moment-by-moment mapping of the body’s internal landscape across conscious and unconscious levels” (Khalsa et al., 2018). Dysfunction of this process is now recognized as a component of anxiety disorders, mood disorders, eating disorders, addictive disorders, and somatic symptom disorders.

This means that the organ Homer described as the thumos — the somatic site of feeling, value, and evaluation — is the same organ whose dysfunction underlies the most prevalent mental health conditions of the modern world. When convergence psychology, as articulated through Seba Health and in Cody Peterson’s published scholarship, identifies the thumos, the feeling function, and the anterior insula as a single functional architecture operating across three millennia, it is not drawing an analogy. It is naming a fact.

Jung defined feeling as the psychological function of evaluation — the capacity that tells us what a thing is worth, what its meaning is for us (Jung, 1921, cited in Sullivan, 1995). Von Franz emphasized that when feeling operates as the inferior function, it appears “primitive, childish, often completely out of proportion.” Hillman radicalized the claim: the entire West privileges clarity and spirit, thinking and intuition, while feeling is the repressed, the excessive, the out-of-proportion — and that is the soul (Hillman, 1975). Damasio’s neuroscience confirms Hillman’s diagnosis. The West’s twenty-four-century campaign to subordinate feeling to reason, launched by Plato in the Republic and extended through Stoic apatheia, Christian asceticism, Cartesian dualism, and Enlightenment rationalism, has systematically devalued the organ that generates the capacity to evaluate.

The body was never waiting for philosophy to grant it epistemic authority. The anterior insula was mapping the physiological condition of the organism and producing conscious feeling long before Socrates sent Xanthippe away. Panksepp’s subcortical emotional systems were generating raw affect long before Plato ranked the soul into a command structure. Barrett’s body-budgeting regions were issuing predictions and computing metabolic costs long before Descartes severed mind from body. The neuroscience of interoception does not discover a new faculty. It rediscovers the one that Western culture has spent twenty-four centuries attempting to suppress.

Bruno Snell wrote in 1953 that the Homeric hero’s psychology is indistinguishable from his physiology (Snell, 1953). He meant this as a mark of the archaic — evidence that the Greeks had not yet “discovered the mind.” Craig, Damasio, Panksepp, and Barrett demonstrate that Snell had the direction of travel reversed. The Homeric fusion of psychology and physiology is not a primitive condition that civilization outgrew. It is the accurate description of how the evaluative organ works. The anterior insula does not distinguish between bodily sensation and emotional awareness. It integrates them into a single felt moment. The thumos did the same.

The body knew first. The neuroscience is arriving late.

Sources Cited

Barrett, Lisa Feldman (2017). How Emotions Are Made: The Secret Life of the Brain. Houghton Mifflin Harcourt.

Caswell, Caroline P. (1990). A Study of Thumos in Early Greek Epic. Brill.

Clarke, Michael (1999). Flesh and Spirit in the Songs of Homer. Oxford University Press.

Craig, A.D. (2002). “Interoception: The Sense of the Physiological Condition of the Body.” Nature Reviews Neuroscience, 3(8), 655-666.

Craig, A.D. (2009). “How Do You Feel — Now? The Anterior Insula and Human Awareness.” Nature Reviews Neuroscience, 10(1), 59-70.

Damasio, Antonio (1994). Descartes’ Error: Emotion, Reason, and the Human Brain. Penguin Books.

Damasio, Antonio (1999). The Feeling of What Happens: Body and Emotion in the Making of Consciousness. Harcourt Brace.

Damasio, Antonio (2018). The Strange Order of Things: Life, Feeling, and the Making of Cultures. Pantheon.

Khalsa, Sahib S. et al. (2018). “Interoception and Mental Health: A Roadmap.” Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, 3(6), 501-513.

Panksepp, Jaak (1998). Affective Neuroscience: The Foundations of Human and Animal Emotions. Oxford University Press.

Padel, Ruth (1992). In and Out of the Mind: Greek Images of the Tragic Self. Princeton University Press.

Peterson, Cody (in press). “The Iron Thumos and the Empty Vessel.” Jung Journal: Culture & Psyche.

Snell, Bruno (1953). The Discovery of the Mind. Harvard University Press.

Sullivan, Shirley Darcus (1995). Psychological and Ethical Ideas: What Early Greeks Say. Brill.