The neurobiology of interoception and affect

Neuroimaging Meta-Analyses Reveal Convergence of Interoception, Emotion, and Social Cognition Across Neurodegenerative Diseases

BACKGROUND

Simultaneous interoceptive, emotional, and social cognition deficits are observed across neurodegenerative diseases. Indirect evidence suggests shared neurobiological bases underlying these impairments, termed the allostatic-interoceptive network (AIN). However, no study has yet explored the convergence of these deficits in neurodegenerative diseases or examined how structural and functional changes contribute to cross-domain impairments.

METHODS

A Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) activated likelihood estimate meta-analysis encompassed studies that met the following inclusion criteria: interoception, emotion, or social cognition tasks; neurodegenerative diseases (behavioral variant frontotemporal dementia, primary progressive aphasias, Alzheimer's disease, Parkinson's disease, multiple sclerosis); and neuroimaging (structural: magnetic resonance imaging voxel-based morphometry; functional: magnetic resonance imaging and fluorodeoxyglucose-positron emission tomography).

RESULTS

Of 20,593 studies, 170 met inclusion criteria (58 interoception, 65 emotion, and 47 social cognition) involving 7032 participants (4963 patients and 2069 healthy control participants). In all participants combined, conjunction analyses revealed AIN involvement of the insula, amygdala, orbitofrontal cortex, anterior cingulate, striatum, thalamus, and hippocampus across domains. In behavioral variant frontotemporal dementia, this conjunction was replicated across domains, with further involvement of the temporal pole, temporal fusiform cortex, and angular gyrus. A convergence of interoception and emotion in the striatum, thalamus, and hippocampus in Parkinson's disease and the posterior insula in primary progressive aphasias was also observed. In Alzheimer's disease and multiple sclerosis, disruptions in the AIN were observed during interoception, but no convergence with emotion was identified.

CONCLUSIONS

Neurodegeneration induces dysfunctional AIN across atrophy, connectivity, and metabolism, more accentuated in behavioral variant frontotemporal dementia. Findings bolster the predictive coding theories of large-scale AIN, calling for more synergistic approaches to understanding interoception, emotion, and social cognition impairments in neurodegeneration.

Interoceptive modulation of emotions

The metaphorical use of the heart to represent emotions has been documented since our earliest known writings, which reflects a historical recognition of the deep connection between bodily sensations and emotions. However, it remains an active topic of investigation to determine the degree to which bodily physiology modulates emotion states. Recent advances in the neuroscience of interoception-the process by which we sense, interpret, and integrate internal bodily signals and physiology-are uncovering neurobiological mechanisms by which visceral signals can influence emotions. Here we review interoceptive pathways that relay visceral signals to the brain and discuss how these signals influence emotion states as well as challenges and opportunities to better understand interoceptive modulation of emotions.

Heartbeat-related activity in the anterior thalamus differs between phasic and tonic REM sleep

Rapid eye movement (REM) sleep is a fundamental sleep state associated with diverse functions from elemental physiological processes to higher order neurocognitive functions. A growing body of research indicates that REM sleep with eye movements (phasic REM) differs from REM periods without ocular activity (tonic) in terms of spontaneous and evoked neural responses. Studies using auditory stimulation consistently observed enhanced evoked responses in tonic versus phasic REM, indicating that external processing is largely diminished when the eyes move during REM sleep. Whereas exteroceptive processing during sleep is widely studied, investigations on interoception (the processing of bodily signals) during sleep are scarce, and limited to scalp electroencephalographic recordings. Here we studied interoceptive processing in a group of epileptic patients (N = 11) by measuring their heartbeat-related neural activity in the anterior nuclei of the thalamus (ANT) during phasic and tonic REM sleep and resting wakefulness. Evoked potentials and beta-low gamma spectral power locked to the heartbeat were significantly different in phasic REM compared with tonic REM and wakefulness. Heartbeat-related neural signals exhibited pronounced inter-trial phase synchronization at lower (7-20 Hz) oscillatory activity in all vigilance states, but reduced gamma synchronization at later time points in phasic REM only. Tonic REM and wakefulness did not show significant differences in heartbeat-related activity in the ANT. Our findings indicate that heartbeat-related neural activity is detectable at the level of the ANT, showing distinct signatures of interoceptive processing in phasic REM compared with tonic REM and wakefulness. KEY POINTS: We studied interoceptive processing in the anterior the thalamus (ANT). The ANT tracks cardiac signals during wakefulness and rapid eye movement (REM) sleep. Phasic REM shows distinct patterns of heartbeat-related oscillatory activity. Interoceptive processing might be attenuated during REM periods with eye movements.

Manipulation of interoceptive signaling biases decision making in rhesus macaques

Several influential theories have proposed that interoceptive signals, sent from the body to the brain, contribute to neural processes that coordinate complex behaviors. We altered the physiological state of the body using compounds that have minimal effect on the brain and evaluated their effect on decision making in rhesus monkeys. We used glycopyrrolate, a nonspecific muscarinic (parasympathetic) antagonist, and isoproterenol, a beta-1/2 (sympathetic) agonist, to create a sympathetic-dominated state in the periphery, that was indexed by increased heart rate. Rhesus monkeys were trained on two variants of an approach-avoidance conflict task. The tasks offered a choice between enduring mildly aversive stimuli in exchange for a steady flow of rewards, or canceling the aversive stimuli, forgoing the rewards. The latency to interrupt the aversive stimuli was used as a measure of monkeys' tolerance for contact with a hot but not painful stimulus or airflow directed at their muzzle. Both drugs reduced tolerance for the aversive stimuli. To determine whether the drug-induced autonomic state reduced the subjective value of the reward, we tested the effects of glycopyrrolate on a food preference task. Food preference was unaltered, suggesting that the sympathetic dominated state in the periphery selectively reduces tolerance for aversive stimuli without altering reward-seeking behaviors. As the drugs used are expected to have little or no direct effect on the brain, the observed biases in decision making are likely induced by interoceptive afferents that signal to the brain the physiological state of the body.

The relationship between sleep and interoception

The present study aimed to characterise the relationship between sleep and interoception in two independent studies. Theoretical grounds for such a relationship include a weak relationship between subjectively- and objectively-measured sleep, the covariance of sleep with pain, as well as the mass regulation of a number of visceral biological systems. In addition, such a relationship is often reflected in our language (i.e., 'feeling' tired). In both studies (Study 1: N = 118, 73% female, mean age 20.98 years; Study 2: N = 830, 49% female, mean age 38.04 years) sleep over the last month was self-reported. Confidence in interoceptive accuracy, which is the precision with which a person can monitor visceral signals, was measured using the Interoceptive Accuracy Scale, while interoceptive attention, which is the dispositional tendency to attend to bodily signals, was measured using the Body Perception Questionnaire. Study 1 revealed a relationship between long sleep latency and low confidence in interoceptive accuracy (β = -0.222, p = 0.021) and poor sleep quality and less interoceptive attention (β = -0.226, p = 0.016). Study 2 replicated these results as well as made clear a more general pattern whereby poor sleep-characterised by short duration, poor quality, less efficiency, long latency, and more frequent nighttime awakenings-related to an interoceptive phenotype of less confidence in interoceptive accuracy and more interoceptive attention (all β ≥ 0.047, p ≤ 0.17). In conclusion, results from these two independent studies provide robust cross-sectional evidence for associations between various dimensions of poor sleep and greater interoceptive attention, but less confidence in interoceptive accuracy.

Development and validation of the Interoceptive States Vocalisations (ISV) and Interoceptive States Point Light Displays (ISPLD) databases

The ability to perceive others' emotions and one's own interoceptive states has been the subject of extensive research. Very little work, however, has investigated the ability to recognise others' interoceptive states, such as whether an individual is feeling breathless, nauseated, or fatigued. This is likely owing to the dearth of stimuli available for use in research studies, despite the clear relevance of this ability to social interaction and effective caregiving. This paper describes the development and validation of two stimulus sets for use in research into the perception of others' interoceptive states. The Interoceptive States Vocalisations (ISV) database and the Interoceptive States Point Light Displays (ISPLD) database include 191 vocalisation and 159 point light display stimuli. Both stimulus sets underwent two phases of validation, and all stimuli were scored in terms of their quality and recognisability, using five different measures. The ISV also includes control stimuli featuring non-interoceptive vocalisations. Some interoceptive states were consistently recognised better than others, but variability was observed within, as well as between, stimulus categories. Stimuli are freely available for use in research, and are presented alongside all stimulus quality scores, in order for researchers to select the most appropriate stimuli based on individual research questions.

Sleep links hippocampal propensity for epileptiform activity to its viscerosensory inputs

The development of a seizure relies on two factors. One is the existence of an overexcitable neuronal network and the other is a trigger that switches normal activity of that network into a paroxysmal state. While mechanisms of local overexcitation have been the focus of many studies, the process of triggering remains poorly understood. We suggest that, apart from the known exteroceptive sources of reflex epilepsy such as visual, auditory or olfactory signals, there is a range of interoceptive triggers, which are relevant for seizure development in Temporal Lobe Epilepsy (TLE). The hypothesis proposed here aims to explain the prevalence of epileptic activity in sleep and in drowsiness states and to provide a detailed mechanism of seizures triggered by interoceptive signals.

The encoding of interoceptive-based predictions by the paraventricular nucleus of the thalamus D2+ neurons

Understanding how the brain integrates internal physiological states with external sensory cues to guide behavior is a fundamental question in neuroscience. This process relies on interoceptive predictions-internal models that anticipate changes in the body's physiological state based on sensory inputs and prior experiences. Despite recent advances in identifying the neural substrates of interoceptive predictions, the precise neuronal circuits involved remain elusive. In our study, we demonstrate that Dopamine 2 Receptor (D2+) expressing neurons in the paraventricular nucleus of the thalamus (PVT) play key roles in interoception and interoceptive predictions. Specifically, these neurons are engaged in behaviors leading to physiologically relevant outcomes, with their activity highly dependent on the interoceptive state of the mice and the expected outcome. Furthermore, we show that chronic inhibition of PVT D2+ neurons impairs the long-term performance of interoceptive-guided motivated behavior. Collectively, our findings provide insights into the role of PVT D2+ neurons in learning and updating state-dependent predictions, by integrating past experiences with current physiological conditions to optimize goal-directed behavior.

Predictive role of exteroceptive and interoceptive bodily dimensions to schizotypal personality traits

The phenomenological approach to schizophrenia emphasizes the role of bodily experiences in the onset and manifestation of positive, negative and disorganized psychotic symptoms. According to the dimensional approach to psychosis, there exists a continuum ranging from individuals with low levels of schizotypy to diagnosed schizophrenia patients, with schizotypy encompassing positive-like, negative-like, and disorganized-like symptoms of schizophrenia. Empirical evidence suggests that along this continuum, both exteroceptive (external sensory) and interoceptive (internal bodily) dimensions might be distorted. Understanding the contribution of these bodily dimensions in the manifestation of psychotic symptoms, even in schizotypy, might help target early interventions for individuals at risk of developing psychotic disorders. This study investigated the potential contribution of exteroceptive and interoceptive bodily dimensions to schizotypal personality traits, such as cognitive-perceptual traits (positive-like symptoms), interpersonal traits (negative-like symptoms), and disorganization traits (disorganized-like symptoms). Partial Least Squares Regression was used to integrate several bodily dimensions to understand their impact on schizotypy, revealing specific and non-specific contributions of exteroceptive and interoceptive dimensions to different traits. In particular, exteroceptive bodily dimensions generally predicted all schizotypal traits, with specific associations to positive-like symptoms, while interoceptive dimensions mostly predicted interpersonal-like and disorganized-like symptoms. These results suggest a difference in how exteroceptive and interoceptive bodily dimensions contribute to the three schizotypal traits. This highlights specific aspects of interoceptive and exteroceptive body representations that could serve as targets for early intervention. Particularly, interoception emerges as a potential prodromal marker, suggesting that early intervention in this area could be crucial.

Altered spatiotemporal brain dynamics of interoception in behavioural-variant frontotemporal dementia

BACKGROUND

Dysfunctional allostatic-interoception, altered processing of bodily signals in response to environmental demands, occurs in behavioural-variant frontotemporal dementia (bvFTD) patients. Previous research has not investigated the dynamic nature of interoception using methods like intrinsic neural timescales. We hypothesised that longer intrinsic neural timescales of interoception would occur in bvFTD patients, evidencing dysfunctional allostatic-interoception.

METHODS

One-hundred and twelve participants (31 bvFTD patients, 35 Alzheimer's disease patients, AD and 46 healthy controls) completed a well-validated task measuring cardiac-interoception and exteroception. Simultaneous EEG and ECG were recorded. Intrinsic neural timescales were measured via the autocorrelation window (ACW) of broadband EEG signals from each heartbeat and a time-lagged version of itself. Spatiotemporal clustering analyses identified clusters with significant between-group differences in each condition. Voxel-based morphometry was used to target the allostatic-interoceptive network. Neuropsychological tests of cognition and social cognition were assessed.

FINDINGS

In bvFTD patients, longer interoceptive-ACWs than controls were observed in the bilateral fronto-temporal and parietal regions. In AD patients, longer interoceptive-ACWs than controls were observed in central and occipitoparietal brain regions. No differences were observed during exteroception. In bvFTD patients only, longer interoceptive-ACW was linked to worse sociocognitive performance. Structural neural correlates of interoceptive-ACW in bvFTD involved the anterior cingulate, insula, orbitofrontal cortex, hippocampus, and angular gyrus.

INTERPRETATION

Our findings suggest a core allostatic-interoceptive deficit occurs in people with bvFTD. Further, altered interoceptive intrinsic neural timescales may provide a neurobiological mechanism underpinning the complex behaviours observed in bvFTD patients. Our findings support synergistic models of brain disease and can inform clinical practice.

FUNDING

All funding sources are reported in the Acknowledgements.

The Vagus Nerve as a Gateway to Body Ownership: taVNS Reduces Susceptibility to a Virtual Version of the Cardiac and Tactile Rubber Hand Illusion

Transcutaneous auricular vagus nerve stimulation (taVNS) has been shown to influence cognitive and emotional function and enhance interoceptive awareness. This study investigates if taVNS effects extend to the experience of body ownership, as measured via susceptibility to the rubber hand illusion (RHI) in a virtual reality setting. The experiment involved 27 participants who underwent real and sham stimulation in two separate sessions while experiencing synchronous or asynchronous visuo-cardiac and visuo-tactile feedback on a virtual arm in place of their own. Results indicated that active compared to sham taVNS decreased sensitivity to the illusion in both cardiac and tactile trials. Specifically, a greater proprioceptive drift difference (PDD) toward the rubber hand was observed for synchronous compared to asynchronous trials only during sham (t(26) = -4.58, pbonf < 0.001) but not during active (pbonf = 1.00) stimulation. A similar pattern was also observed for subjective ownership, where synchronous trials led to greater subjective ownership than asynchronous trials only during sham (t(26) = -3.52, pbonf = 0.010) but not during active (pbonf = 1.00) stimulation. These findings suggest that stimulation might enhance body ownership, making individuals more attuned to their real bodily signals and less susceptible to bodily illusions. Additionally, physiological measures such as heart rate (HR), heart rate variability (HRV), and skin sympathetic nervous activity (SKNA) were assessed to explore the autonomic effects of taVNS. We observed a decrease in HR during active stimulation (t(26) = 4.30, pbonf < 0.001), and an increase in SKNA during both sham (t(26) = -4.40, pbonf < 0.001) and active stimulation (t(26) = -4.85, pbonf < 0.002). These findings contribute to the understanding of the vagus nerve's role in integrating visceral and somatosensory signals, with implications for clinical applications in conditions characterized by altered interoception and body ownership.

Computational Approaches for Uncovering Interoceptive Mechanisms in Psychiatric Disorders and Their Biological Basis

Interoception, the process of detecting, perceiving, and interpreting signals from within the body, is essential for physiological regulation and adaptive behavior. A growing body of research underscores important potential links between interoceptive dysfunction and psychiatric disorders. Parallel advancements in the field of computational psychiatry have led to the development of biologically plausible models of information processing in the brain. This review surveys the current state of traditional and computational research approaches to study interoceptive processes in psychiatry. We also provide a foundational description of predominant computational approaches and theoretical models of interoception. Finally, we discuss the potential molecular foundations of interoceptive computation and consider future directions for incorporating computational models to enhance clinical insights and inform personalized treatments. We conclude that combining interoception and computational modeling approaches holds considerable promise in moving the field forward, both in addressing unresolved mechanistic questions and identifying novel potential therapeutic targets.

Boredom signals deviation from a cognitive homeostatic set point

Boredom is the feeling of wanting but failing to engage the mind and can be conceived as one among many signals of suboptimal utilization of cognitive and neural resources. Using homeostasis as an analogy, this perspective argues that boredom represents a signal indicating deviation from optimal engagement-that is, deviation from a cognitive homeostatic set point. Within this model, allostasis accounts for chronic boredom (i.e., trait boredom proneness), according to which faulty internal models are responsible for why the highly boredom prone may set unrealistic expectations for engagement. In other words, the model characterizes boredom as a dynamic response to both internal and external exigencies, leading to testable hypotheses for both the nature of the state and the trait disposition. Furthermore, this perspective presents the broader notion that humans strive to optimally engage with their environs to maintain a kind of cognitive homeostatic set-point.

From feeling chilly to burning up: How thermal signals shape the physiological state of the body and impact physical, emotional, and social well-being

This review examines the role of thermal interoception-awareness of body temperature-in shaping physiological states and its impact on physical, emotional, and social well-being. We describe the neural pathways and mechanisms involved in thermal processing and environmental heat exchange and how thermal interoception influences both autonomic and behavioral responses, contributing to survival and homeostasis. Additionally, the review highlights the significance of thermal signals and thermoregulation in determining higher-order cognitive and emotional functions, such as regulating sleep patterns and activity levels, monitoring physical well-being, regulating emotions, and even social interactions. We describe the existing instruments for assessing body temperature and thermal awareness and call for further research to investigate the role of thermal interoception in emotional and social domains. We also discuss potential therapeutic applications, particularly in the context of psychosomatic and neurological disorders characterized by emotional dysregulation, disrupted sleep and mood patterns, social difficulties, and alterations in self-consciousness.

Common threads: Altered interoceptive processes across affective and anxiety disorders

There is growing attention towards atypical brain-body interactions and interoceptive processes and their potential role in psychiatric conditions, including affective and anxiety disorders. This paper aims to synthesize recent developments in this field. We present emerging explanatory models and focus on brain-body coupling and modulations of the underlying neurocircuitry that support the concept of a continuum of affective disorders. Grounded in theoretical frameworks like peripheral theories of emotion and predictive processing, we propose that altered interoceptive processes might represent transdiagnostic mechanisms that confer common vulnerability traits across multiple disorders. A deeper understanding of the interplay between bodily states and neural processing is essential for a holistic conceptualization of mental disorders.

Intergenerational Transaction of Emotional Health in Collective Family Context: Family Functioning, Parental and Children's Gratitude, and Their Depression

Background: The current study is intended to examine how positive family functioning, collectively constructed by parents and children in the family context, may contribute to their gratitude and depression, two pivotal human emotions closely related to human health, in which the gratitude and depression of parents and children are assumed to affect each other bidirectionally and parental and children's gratitude is expected to link the relations between positive family functioning and their depression. Methods: The data for analysis came from a community sample of 310 Chinese parent-child dyads, which were measured by the Family Functioning Style Scale (FFSS), Gratitude Questionnaire (GQ), and depression subscale of the Brief Symptom Inventory (BSI) from both the parent and child participants. Results: The results indicated that positive family functioning contributed to higher parental and children's gratitude and their less depression, and parental and children's gratitude and depression affected each other positively. Furthermore, serial mediation analyses discovered the complex processes from positive family functioning to the actor's depression in parents or children through their gratitude or the links from the partner effect to the actor effect of parental and children's gratitude or from the partner effect of parental or children's gratitude to their partner effect of depression. Conclusions: Findings of the current study prove the collective effects of family functioning on the emotional development of gratitude and depression among parents and children, in which parental and children's gratitude and depression bidirectionally impact each other and lead to the actor's depression in them through the complex serial mediated effects. For this, pro-family and health-related policies and services should be provided to promote family functioning and emotional management in a home context to enhance family and emotional health among parents and children.

Interoception primes negative emotion processing during cognitive reappraisal: Electroencephalographical evidence

Interoception, which refers to sensing, interpreting, and integrating internal bodily signals, has been suggested to be associated with emotion regulation. Previous research has demonstrated individual differences in interoception and its impact on emotion regulation. However, the priming effect of interoception on emotion regulation and the underlying neural mechanisms remain unknown. This study aims to examine how interoception primes different strategies of cognitive reappraisal, using electroencephalography (EEG). Thirty-seven healthy participants completed an interoceptive priming task. We found that interoception increased the amplitudes of the late positive potential (LPP) during both interpretation and detachment strategies. The priming effect of interoception in enhancing LPP amplitudes lasted longer for interpretation than for detachment. A decrease in alpha power during reinterpretation was observed after interoceptive priming, but not during detachment. The results revealed that interoception enhanced attention to bodily signals associated with negative emotions during cognitive reappraisal. Interoception showed distinct effects on different strategies of cognitive reappraisal, with different underlying neural mechanisms. Interoception-based programs may be an effective way to enhance the capacity for cognitive reappraisal.

Creative puppet therapy reduces hallucinations in patients diagnosed with schizophrenia: Preliminary findings

Anomalous experiences and hallucinations characterize schizophrenia. This study aimed at determining the efficacy of creative puppet therapy (CPT; creation of a puppet with malleable DAS) to reduce severe anomalous experiences and hallucinations among patients diagnosed with schizophrenia. Double-blinded, controlled trials were performed on a convenience sample of 24 patients from a mental health center. The intervention group of 12 patients (who created puppets) and the pseudo-treatment group of 12 patients (who were involved in outdoor leisure trips) were compared to the control group of 12 control participants (who created puppets). Cardiff Anomalous Perceptions Scale (CAPS) assessed hallucinations; Emotional Expression Inventory (EEXI) assessed the emotional expression of one's own puppet. Puppet facial features were measured. Results showed that CPT effectively reduced (d = -4.00) hallucination frequency in patients. Hallucination reduction occurred across all sensory modalities, but touch and bodily interoception. Exteroceptive vs. interoceptive hallucinations was the most valuable classification in patients. Compared to controls, puppets created by patients expressed more negative emotions and had larger eye diameters, shorter noses, and larger whole face width. Eye diameter was correlated with fear, sadness, anger, and disgust, and whole face width with boredom. Fragmented-self integration of schizophrenia through CPT treatment might exploit aggregative dominance of the patient's own body.

Heart-Brain Axis: A Narrative Review of the Interaction between Depression and Arrhythmia

Arrhythmias and depression are recognized as diseases of the heart and brain, respectively, and both are major health threats that often co-occur with a bidirectional causal relationship. The autonomic nervous system (ANS) serves as a crucial component of the heart-brain axis (HBA) and the pathway of interoception. Cardiac activity can influence emotional states through ascending interoceptive pathways, while psychological stress can precipitate arrhythmias via the ANS. However, the HBA and interoception frameworks are often considered overly broad, and the precise mechanisms underlying the bidirectional relationship between depression and arrhythmias remain unclear. This narrative review aims to synthesize the existing literature, focusing on the pathological mechanisms of the ANS in depression and arrhythmia while integrating other potential mechanisms to detail heart-brain interactions. In the bidirectional communication between the heart and brain, we emphasize considering various internal factors such as genes, personality traits, stress, the endocrine system, inflammation, 5-hydroxytryptamine, and behavioral factors. Current research employs multidisciplinary knowledge to elucidate heart-brain relationships, and a deeper understanding of these interactions can help optimize clinical treatment strategies. From a broader perspective, this study emphasizes the importance of considering the body as a complex, interconnected system rather than treating organs in isolation. Investigating heart-brain interactions enhance our understanding of disease pathogenesis and advances medical science, ultimately improving human quality of life.

Interoceptive Processing in Functional Gastrointestinal Disorders

Functional gastrointestinal disorders (FGIDs) are characterized by chronic gastrointestinal symptoms in the absence of overt pathology and affect a significant percentage of the worldwide population. They are commonly accompanied by co-morbid psychiatric symptomatology and are associated with significant suffering and great healthcare services utilization. There is growing evidence that dysregulation of the gut-brain axis and disturbances in the processing of afferent interoceptive signals lie at the heart of these disorders. In this context, the aim of the current review was to detect and critically review original articles focusing on the role of interoception in the pathophysiology of FGIDs. Our search yielded 38 relevant studies. FGID patients displayed increased visceral sensitivity, enhanced attention to gastrointestinal interoceptive cues, and greater emotional arousal when coping with gut-derived sensations. Neuroimaging studies have shown significant structural and functional changes in regions of the interoceptive network, while molecular and genetic studies have revealed significant associations between interoceptive signaling and deficits in excitatory neurotransmission, altered endocrine and immune physiological pathways, and aberrant expression of transient receptor potential channel genes. Finally, there were emerging data suggesting that interoception-based interventions may reduce physical symptoms and improve quality of life and should be integrated into FGID clinical management practices.

When Studying Affective Responses to Exercise, the Definition of "Intensity" Must Reference Homeostatic Perturbations: A Retort to Vollaard et al

In articles on the methodology of studies investigating affective and enjoyment responses to high-intensity interval training, we noted that, occasionally, exercise conditions described as involving "high" intensity exhibited heart rates that were only as high as, or even lower than, heart rates recorded during comparator conditions described as being of "moderate" intensity. Drs. Vollaard, Metcalfe, Kinghorn, Jung, and Little suggest instead that exercise intensity in high-intensity interval-training studies can be defined in terms of percentages of peak workload. Although we maintain that defining exercise intensity in terms of percentages of maximal heart rate is a suboptimal way to quantify the degree of homeostatic perturbations in response to exercise, we are unconvinced that definitions of intensity relying solely on workload are appropriate for studies investigating affective and enjoyment responses to exercise. The reason is that affect is theorized to have evolved to relay information about homeostatic perturbations to consciousness.