A Primer on Interoception and its Importance in Psychiatry

Abstract

Interoception is the perception of signals from inside the body. It plays a significant role in the nervous, cardiovascular, respiratory, gastrointestinal, genitourinary, and endocrine systems. It is also closely related to the autonomic nervous system and inflammatory pathways and plays a significant role in our optimal functioning. Recently, interoception has gained more attention in neuropsychiatric research. Anatomical and physiological aspects of interoception like relevant brain areas, the role of the vagus nerve, and the autonomic nervous system are gradually being understood. Different facets of interoception like interoceptive attention, detection, magnitude, discrimination, accuracy, awareness, and appraisal have been proposed and their assessments and importance are being evaluated. Further, interoception is often dysregulated or abnormal in psychiatric disorders. It has been implicated in the psychopathology, etiopathogenesis, clinical features and treatment of mood, anxiety, psychotic, personality and addiction-related disorders. This narrative review attempts to provide a nuanced understanding of the pathway(s), components, functions, assessments, and problems of interoception and will help us to detect its disturbances and evaluate its impact on psychiatric disorders, leading to a better perspective and management. This will also advance interoception-related research.

INTRODUCTION

We receive and process various stimuli from the external world and within our bodies. These two processes are called “exteroception” and “interoception,” respect-ively. Their optimal functioning is essential [1]. Interocep-tion lacks rigorous understanding when compared to exteroception. This may be due to a lack of comprehensive definitions, well-defined boundaries, knowledge about the exact operating sensors, receptors, effectors, regulators and pathways, and objective measurements [1,2]. As a pathophysiological process (or processes), the role of interoception cuts across neurology and psychiatry. The majority of psychiatric disorders may often have impairment or dysregulation of interoception. So, psychiatrists need to be aware of interoception, its normal functions and its problems [3,4]. This will provide a better perspective and management. Broadening interoceptive psychiatric research is imperative and so is the need for its inclusion within the Research Domain Criteria (RDoC) paradigms [5]. In this narrative review, we provide a brief overview of interoception, its functioning, interoceptive pathways, measurement of interoception, and its dysfunction in various psychiatric disorders. We aim to present this as a comprehensive primer.

WHAT IS INTEROCEPTION?

The concept of interoception has evolved. Previously it was thought of as the perception of the inner-body physiological stimuli combined with proprioception. Proprio-ception is now not considered part of interoception [2]. Autonomic, hormonal and immunological components are currently included as afferent interoceptive signals [5]. Descending/efferent interoceptive pathways are being gradually understood. Thus, interoception is now considered a two-way “signal processing between the brain and the internal organs that generates a representation of the internal state of an organism.” The nervous, cardio-vascular, respiratory, gastrointestinal, genitourinary, and endocrine systems deal with interoception [2,6,7].

The concepts of interoception, proprioception and somatosensation have evolved together. Indeed, these are not mutually exclusive concepts, partly due to the conceptual underpinning - skin forming the anatomical boundary between the inner and outer body. Proprioception, thus arising from the inner skeletal muscles, joints and connective tissues was included in interoception, although with certain exceptions. The current approach in interoceptive research is to understand what the interoceptive sensations represent, rather than where these come from. Recent anatomical findings also show that brain areas (like the insula) involved in the detection and evaluation of proprioception are also involved in intero-ception. Proprioception represents inner body sensations and is therefore included within the broad concept of interoception and understanding only proprioception will leave out many aspects of interoception.

WHAT IS THE FUNCTION OF INTEROCEPTION?

Most of the models of interoception revolve around the brain’s ability to regulate emotions and respond to stress [8,9]. Internal bodily sensations are partly responsible for emotional feelings. Each individual reacts (emotionally or behaviourally) differently to a given situation. For example, those with higher interoceptive feelings have more intense emotional reactions [10-12]. To perform a range of behaviours, an individual must continuously monitor the external and internal changes during each behaviour. The changes are constantly evaluated and appraised, and the behaviour is modulated according to interoceptive feed-back. Interoceptive, including autonomous signals, provide a base for these subsequent emotionally mediated behavioural reactions [13,14]. However, the emotional and behavioural modifications do not necessarily depend on the brain’s ability to “regulate”; this may not be time and energy-efficient. Further, the brain not only regulates but may even predict the inner bodily sensation and detect deviance from a prediction which would then be signalled out [15-17].

A stressor is an external or internal factor that disrupts the equilibrium in the physiological or psychological sys-tems. Then a complex neuro-endocrine-immunological reaction involving the interoceptive system is set to curtail the effects of these factors and bring back the equilibrium. Two major processes are followed in achieving this objective [18]. One is homeostasis, which attempts to self- regulate the biological systems to defend stability in critical psychophysiological systems while adjusting to the changing external/internal conditions. The second is allostasis, which usually unfolds on chronic or repeated exposure to stressors [15]. In anticipation of a better adaptation to the new or changing conditions, the biological systems steadily redefine the internal setpoints of the psychophysiological parameter(s) that were earlier defended in a simple homeostatic process. This adjustment comes with a cost due to chronic or repeated neuro-endocrine-immunological reactive elevations called allostatic load.

The role of interoception in homeostasis may be prominent in Damasio’s Somatic Marker Hypothesis [19]. Damasio hypothesised that overt or covert bioregulatory signals influence the motivation and behaviour of a person. These signals arise when a problem in homeostasis is detected. According to the context, the body sends these signals to modify the behaviour and emotional response. This brings back stability to homeostatic mechanisms [11,20]. These internal changes (pH, oxygen levels and saturation, body temperature) are predominantly interoceptive signals. If interoception were absent or faulty, the transmitted stimuli would either be inadequate or altered. This would lead to poor homeostatic regulation and essentially would cause a threat to life.

Biological stress is hypothesised to be managed more efficiently if one detects interoceptive signals early. This requires interoceptive pathways to integrate the central and peripheral nervous system. Schulz and Vögele [21] proposed that very high/chronic/repeated stress may lead to dysfunctional interoception, altering their intensity, detection, monitoring, and feedback for regulation mechanisms [8].

Craig elaborated on functional anatomical afferent pathways between interoceptive signals and the brain, mapping all the body’s physiological conditions. These pathways are hypothesised to represent “I” ness and patch the gap in our understanding of the relation between self-awareness and emotions [22]. Further, Paulus proposed that decision-making is linked with homeostasis. Any significant inconsistency in homeostasis is signalled through interoception and is strategically and context-ually evaluated to form a decision [23,24]. Therefore, faulty decision-making could be related to homeostatic dysregulation.

The Embodied Predictive Interoception Coding (EPIC) model is a specific model proposed to understand the role and regulation of interoception based on prediction and errors [25]. Predictions predominantly drive the interoceptive response. From past experiences, the agranular visceromotor regions continuously try to estimate the body’s autonomic, immune and visceral signals (allostasis). When the actual signals match these predictions, the brain is more effective in maintaining the dynamic balance [25-28]. It may not employ extra resources for further regulation and continues to run in an auto-pilot mode. When there is a mismatch, the visceromotor cortices draw attention to the imbalance. This involves additional resource allocation until a dynamic balance is reached (current signals match the predicted ones as an active inference). The structures involved in reallocation involve the insula, cingulate cortex, and ventromedial prefrontal cortex [5,27,28].

The EPIC model is closely related to the computational modelling of interoception. Through hierarchical Bayesian models, interoception may generate a “generative model of interosensations” [1,17]. This not only monitors and solves interoceptive differences from a predesigned template (combining interoceptive body map and prior beliefs and expectations) but also predicts the subsequent differences. This seems to regulate homeostasis and allostasis effectively by reacting to changes immediately and predicting a prospective control [15,17]. Table 1 summarises the evolution of the concept of interoception and its functions and components.

Table 1.

The ever-growing realm of interoception: summarizing how our understanding of interoception has evolved over time [1,9]

The extent of the functions of interoception (from early to recent)	Domains included	The direction of information flow	Interoceptive components involved	Functions added
Recognition of the sensations originating from the “internal surface” of the body	Anatomical, physiological	Unidirectional – viscera to the brain	Attention, detection, magnitude	Pain, proprioception, visceral sensations
Recognition of the internal state of the body	Anatomical, physiological	Unidirectional – viscera to the brain	Attention, detection, magnitude	Hunger, thirst, kinesthetic, vestibular, need for excretion
Recognition, evaluation and integration of multimodal sensory processes of the inner body	Anatomical, physiological	Unidirectional – viscera to the brain	Attention, detection, magnitude, discrimination, accuracy	Mapping of the inner physiological conditions
Recognition, evaluation, integration and monitoring of the inner state of the body	Anatomical, physiological (autonomic nervous and inflammatory systems)	Unidirectional – viscera to the brain	Attention, detection, magnitude, discrimination, accuracy, awareness, appraisal	Homeostasis, allostasis, sleep, physiological decision making
Recognition, evaluation, integration, monitoring and regulation of the internal states - require information exchange	Anatomical, physiological, emotional	Bidirectional	Attention, detection, magnitude, discrimination, accuracy, awareness, appraisal, sensibility	Stress regulation and response, resource allocation, emotional decision making
Recognition, evaluation, integration, monitoring, regulation and prediction of internal states	Anatomical, physiological, emotional, cognitive	Bidirectional with predictive capacity	Attention, detection, magnitude, discrimination, accuracy, awareness, appraisal, sensibility	Cognition, motivation, drive, memory, cognitive decision making
Recognition, evaluation, integration, monitoring, regulation and prediction of oneself	Anatomical, physiological, emotional, cognitive, philosophical	Bidirectional, predictive, metaphysical	Attention, detection, magnitude, discrimination, accuracy, awareness, appraisal, sensibility insight	Understanding “I”-ness

WHAT ARE THE COMPONENTS OF INTEROCEPTION?

Interoception has several components. These are attention, detection, magnitude, discrimination, accuracy, aware-ness, sensibility, appraisal, insight, and self-report [5,16, 29,30].

Interoceptive attention is observing one’s inner body states or sensations with a deliberate conscious focus on visceral and/or somatic signals or responses. It is often modulated by emotions [31]. Interoceptive detection refers to whether a person can consciously determine whether or not an interoceptive sensation is present. Interoceptive magnitude refers to the intensity of the bodily sensation. It answers questions like “How strong/fast/ hard was my heart beating?”. It is called interoceptive discrimination when one can delineate the bodily symptoms from different organs or systems and distinguish two different interoceptive sensations. This was one of the earliest interoceptive domains to be understood experi-mentally by training subjects to differentiate the vibration from their heart and external sources. This component lies close to proprioception [32,33]. Interoceptive accuracy is an accurate and precise perception of bodily sensations and evaluation of their changes. Thus, it is the ability to detect and monitor interoceptive sensations. It may often require an objective assessment of interoceptive signals like the heartbeat. Interoception accuracy is also known as interoceptive sensitivity [1,5,11].

Interoceptive awareness is a broad domain that includes any kind of conscious interoceptive feature that is self-reported [1,34]. However, it also means that a person is actively aware of bodily sensations. Thus, metacog-nition regarding interoceptive perception depends on interoceptive accuracy [30,35]. Interoceptive sensibility is the self-perceived ability to sense internal physical sensations. Another facet of interoception is the appraisal of internal bodily sensations, which ultimately help in its regulation. This component seems important in mindfulness and body-oriented therapies [11]. Interoceptive insight is proposed to include confidence and accuracy, which is also metacognitive. Interoceptive self-reports are psychometric assessments that combine various degrees of interoceptive awareness, sensibility, appraisal, and insight. Interoceptive self-reports evaluate “the ability to reflect upon one’s autobiographical experiences of interoceptive states, make judgments about their outcomes, and describe them through verbal or motor responses” [1]. Table 2 uses the heartbeat as the prototype interoceptive sensation to evaluate these facets.

Table 2.

Understanding the different components of interoception [5,16,29,30]

Component	Question for evaluation
Attention	Can I focus on my heartbeat?
Detection	Can I feel my heartbeat?
Magnitude	How much is my heartbeat?
Discrimination	Can I differentiate my heartbeat from other inner body sensations?
Accuracy	Can I accurately and correctly count my heartbeats?
Awareness	Can I feel my heartbeat and report it?
Sensibility	Am I sensitive to my heartbeat?
Appraisal	Is my heartbeat unusual?
Insight	Can I be confident in accurately counting my heartbeat?

WHAT IS THE PATHWAY OF INTEROCEPTION (Fig. 1)?

Fig. 1.

Interoceptive pathways. The afferent (light-shaded arrows) and efferent (dark-shaded arrow) inter-oception pathways are shown here.

The interoceptive pathway is complex and not yet fully understood [36]. The path starts from interoceptive signals. These are biochemical, mechanical, thermal and/or electromagnetic signals. Interoceptive signals are interpreted by specialised sensors called interoceptors. These are centrally and peripherally located and detect chemical, osmotic, mechanical, gustatory, humoral, thermal and nociceptive changes [2]. Details of their locations are given in Table 3 [37-39]. From here, the afferent pathway can be classified as neural and non-neural. These divisions are not mutually exclusive. The Vagus Nerve (VN) and the dorsal root ganglia form the neural part of the afferent pathway. The afferent VN fibres transmit the signals to the nucleus tractus solitarius (NTS), while the dorsal root involves the spinal cord. Those involving the VN are mainly parasympathetic afferents (dealing with chemical and mechanical signals), while those relayed by the spinal cord are sympathetic afferents (dealing with thermal and nociceptive signals). Apart from this pathway, interoception is also regulated by the hypothalamus, pituitary, gonads, adrenals, and thyroid (hypothalamic–pituitary–adrenal [HPA] axis, the hypothalamic-pituitary-gonadal axis, and the hypothalamic-pituitary-thyroid axis). Circula-tory and lymphatic systems are also included in the afferent pathway [2,6,36].

Table 3.

Central and peripheral interoceptors [37-39]

Interoceptor type	Central	Peripheral
Chemoreceptors	Hypothalamus, hindbrain	Oral cavity, gastrointestinal tract, portal vein, mesenteric vein, carotid body
Osmoreceptors	Anterior hypothalamus, organum vasculosum lamina terminalis, subfornical organ	Spread throughout the vascular system, viscera (such as carotid body, upper GI tract, portal vein)
Mechanoreceptors	Motor cortex	Joints, ligaments, tendons, muscles, skin. Stretch: carotid body, viscera
Gustatory receptors	NTS, insula, hypothalamus, thalamus	Tongue, palate epithelium
Thermoreceptors	Hypothalamus	Skin, viscera
Nociceptors	Prefrontal cortex, anterior cingulate cortex, amygdala, ventromedial medulla	Free nerve endings (A-delta and C), Schwann cells

These signals are then projected to subcortical areas of the brain. The NTS is the most prominent of these. Locus coeruleus (LC), parabrachial nucleus and thalamus (ventro-medial nucleus) are also involved. From here, the signals are relayed to cortical areas such as the insula, hypothalamus, anterior cingulate cortex, somatosensory cortex, occipital cortex, and limbic regions. The insula is thought to be specifically crucial in interoception, with a viscerotropic/anatomical interoceptive map. The posterior insula receives signals from the thalamus and integrates these, along with the central region. The anterior insula regulates interoception’s emotional, cognitive and perhaps social aspects by forming circuits with the prefrontal cortex, orbitofrontal cortex, and limbic structures [7,31,40].

The descending pathway of interoception is more com-plex. At the cortical level, this is called the central autonomic network (CAN) [2,41,42]. It broadly involves similar cortical areas which are involved in afferent function-ing. It also includes subcortical regions like NTS and LC. The efferent pathways can also be divided into neural and non-neural pathways—the former acts through the VN/ cranial nerves to the sympathetic and parasympathetic ganglia as the effectors. The non-neural part acts on the peripheral organs through humoral, vascular and lymphatic systems. The efferent pathways can also be divided by their function, involving the autonomic, immune and endocrine systems. The neural part of the autonomic system involves the descending efferent sympathetic spinal and parasympathetic vagus fibres. These mainly regulate cardio-respiratory and gastrointestinal functioning. The non-neural part of the autonomic system is then predominantly controlled by the HPA axis [2,6,36].

Similarly, the immune system has neural and non-neural parts. The autonomic system partly influences the efferent neural pathways of the immune system. This represents the cholinergic anti-inflammatory pathway mediated through the VN. Cytokines and monocytes regulate the non-neural part through humoral and lymphatic pathways. The endocrine system is controlled predominantly by the hypothalamus. It holds food and fluid intake, thermoregulation, and stress mechanisms [2,43]. Further, a proposal has been made to add motor functions in the interoceptive pathway [44].

HOW TO ASSESS INTEROCEPTION?

A complex system like interoception has inherent difficulties in its measurement. Theoretically, interoception should be amenable for measurement at each step th-roughout its pathway [2,5,36,45]. With advances in technology, interoceptive signals and interoceptors may be identified. Their electric potentials and other neural substrates can become a base for measuring their activities. Brain networks specifically involved in interoception can also be evaluated through functional imaging. The ascending and descending neural pathways of interocep-tion can be crudely measured by indirect or direct assessment of the VN and the autonomic nervous system. Non- neural elements such as hormones may also be quan-tified.

The most common methods to measure interoception are the electric brain signals and ANS parameters during specific tasks, which are thought to detect interoception, and by self-reports [5,45,46]. Controversies remain about which task measures what domain of interoception. Heart-beat is the most common interoceptive signal that has been measured. The most common tasks are heartbeat counting and heartbeat detection tasks. These evaluate cardiac interoception [32,47]. However, other systems, especially the gastrointestinal (GI) system, may deal more extensively with interoception (through the gut-brain axis). Research is underway to develop new methods for interoception measurement pertinent to the gastrointestinal system [48,49].

The behavioural tasks seem to detect heartbeat-related evoked potentials (HEP) in the brain electroencephalo-graphy (EEG) [50]. HEP is the most common EEG measure applied in interoceptive studies. The HEP is measured in relation to the R-wave in ECG and is thought to reflect the brain’s processing of cardiac activity. The ANS-related measures which are most commonly used are heart-rate variability, pupil dilation and salivary amylase measure-ment. ANS measures are relatively easy to acquire, but these are indirect measurements of VN activity, which is thought to regulate interoception [2,51]. Further, functional imaging studies focus on circuits between the insula and other related brain areas to understand which brain circuits are involved when the subject performs the interoceptive tasks [52].

Self-reports measure various domains of interoception. The most common self-reports are the Body Perception Questionnaire [53], the Multidimensional Assessment of Interoceptive Awareness [54], the Body Awareness Que-stionnaire [55], the Private subscale of the Body Conscious-ness Questionnaire and Self-Awareness Questionnaire [56]. Few scales, such as Visceral Sensitivity Index [57], Five Facet Mindfulness Questionnaire [58] and Emotional Susceptibility Scale [59], do not use the term “interocep-tion” in their names but measure similar constructs. Self-reports are easy to administer. However, most scales show low convergence when combined and assessed. Thus, choosing the correct scale is essential per the clinical or research requirements [60,61].

PROBLEMS OF INTEROCEPTION IN PSYCHIATRY

Most psychiatric disorders are related to the problems of the “inner self” or “inner feelings” [1,4]. While pathophysiological processes underlying qualitative “inner self” are less understood, these are better delineated with disturbances of emotions and feelings. Here we try to represent interoceptive problems by dividing these into two groups: quantitative and qualitative. An inherent clue of this can be found in anxiety, depression and impulse control disorders to be highly comorbid. However, this division does not render these groups mutually exclusive.

Quantitative interoceptive problems have been reported in panic and anxiety disorders, depression, somatoform/pain-related disorders, and eating disorders. Anxiety spectrum disorders, particularly panic disorders, deal with interoceptive dysfunction [62,63]. Common anxiety symptoms such as palpitations, dizziness, flushing, inner sinking sensation, derealisation, nausea, urge to micturate, muscle tension, fatigue, and “edgy feeling” can all be due to interoceptive dysfunction. Signs of anxiety such as increased heart rate, blood pressure, ANS, and higher mental functions predominantly regulate fight-flight res-ponses. This involves interoceptive pathways. Chronic or heightened stress may lead to dysfunctional interoceptive path(s) at various levels. For example, when a person panics, the origin of tachycardia, breathlessness, blurring of vision, and dizziness may be at the interoceptors level, where increased interoceptive sensitivity picks such signals and multiplies these. The signals then reach an already primed or dysregulated ANS and are further transmitted limbic system, thalamus, LC and hippocampus. These areas then bring neurochemical changes like an increased release of norepinephrine. Signals are then relayed to the cortical regions where faulty assessment and appraisal of the situation and aberrant metacognitive beliefs may further increase anxiety. The efferent arm of interoception then acts accordingly, which can be measured, for example, by abnormal cortisol levels, raised blood pressure, and increased inflammatory markers. Various therapies for anxiety spectrum disorders such as cognitive-behavioural, exposure, biofeedback, relaxation, mindfulness, floatation, yoga, respiratory training, and thermo-modulation are essentially based on syncing the exteroception and interoception. Interoceptive manipulation becomes especially important in post-traumatic stress disorder symptoms like exaggerated startle and hyper-vigilance [23,63-65].

Interoception is also evaluated in depression [4,23]. Mostly, interoceptive abilities seem to be diminished in depression. This finding related to various theories of depression, such as poor body awareness from an inaccurate understanding of own bodily symptoms, impaired detection of exteroception including social cues, imbalance of thoughts and feelings followed by a poor situational appraisal, and therefore, deficient emotional expression, dissociation, cognitive distortions, mind-body mismatch, increased rumination and dysfunctional immune reaction [11,23,66,67]. The interpersonal and social rhythm therapy used in bipolar disorder gives prime importance to the detection and accurate contextual appraisal of interoceptive signals like body temperature, blood pressure, bowel movements, cardiovascular efficiency, and muscle strength [68].

Dysfunctional interoceptive appraisal and subsequent mismatch also contribute to increased attention with poor accuracy to bodily symptoms and nociception, as seen in somatoform and pain-related disorders [69,70]. Similarly, “internalised” cues of body parts being “distorted” are frequent in body dysmorphic disorder. An internalised build- up of tension before pulling out hair in trichotillomania reflects interoceptive signalling dysfunction [4,5]. These built tensions may be recorded verbatim by the patient or through physiological measures by assessing highly negative (stress) or inadequate arousal (boredom) [71].

Dysfunctional interoception is also found in Anorexia Nervosa (AN) and Bulimia Nervosa (BN). Symptoms like bloating, fullness, nausea, anxiety after eating, and body image distortion may be due to aberrant interoceptive encoding. Inability to differentiate inner bodily signals from outside “noise,” biased interoceptive anticipatory responding, and emotional dysregulation are commonly associated with eating disorders [5,72].

Qualitative disturbances of interoception probably merge autism, schizophrenia, substance use, and personality disorders. Significantly, alexithymia, as a concept, cuts across these psychiatric diagnostic boundaries. Inventories and questionnaires about eating disorders often focus on interoception and alexithymia [56,73]. In autism, interoceptive awareness seems to correlate with alexithymia and, in turn, adversely affects social functioning (Theory of Mind) [74]. Symptoms such as “made phenomenon,” thought alienation, and somatic passivity have links to interoception through poor ego boundary delineation and experience of body ownership. Personality theories (extraversion and introversion, Myers-Briggs hypothesis, five-factor model) emphasise individual interoceptive differences. Interoception may indeed be hard- wired and considered to be a trait marker. Personality traits like borderline, emotionally unstable, and schizoid personality are also partly related to interoceptive malfunction and dysregulation [75-77].

Craving, withdrawal, and intoxication in drug dependence often depend on inner bodily cues. Various domains of drug dependence, such as arousal, selective attention, novelty-seeking, reward processing, prediction error, conditioning, and cue reactivity, are theoretically related to interoceptive functioning. Likewise, the processing of these domains includes the insula as a critical brain region, which is again the seat of interoception. Alcohol, nicotine, cocaine, cannabis, and amphetamine dependence have been hypothesised and evaluated for deviant interoceptive pathways leading to faulty appraisal [1,78].

HOW CAN FUTURE RESEARCH HELP?

We are gradually gaining more perspective regarding interoception in psychiatric disorders. Randomised control trials of interoceptive interventions are conducted in panic disorder, eating disorders, and depression [4]. Various methods like interoceptive exposure, panic control therapy, CBT with interoceptive training, mindfulness-based CBT, self-help training, and body awareness training have shown improvement in self-reports and physiological assessments. Alternative treatment options such as meditation, yoga, and qigong have also been evaluated [79]. Newer neuromodulation techniques, such as transcutane-ous vagal nerve stimulation, may have clinical effects mainly by modulating interoception [80]. As the research increases, interoception may be understood in the RDoC framework. This suits interoception well, as the basic division of RDoC relies not only on self-reports and behaviours but also on neural circuits, cells and molecules [5,34]. Delineating these components will require advanced technologies but will increase knowledge of specific areas like the Gut-Brain axis, regulation of attention between exteroception and interoception, and insular visceral topography. It will also be challenging to separate cognition and emotion from interoceptive studies, as these play essential roles in homeostasis and allostasis. Perhaps, neurophysiological assessments will help how cortical influences change interoception, predominantly subcortical. These understandings will improve future neuropsychiatric research related to interoception.