Associative fear learning and perceptual discrimination: A perceptual pathway in the development of chronic pain

Do Interoceptive Sensations Provoke Fearful Responses in Adolescents With Chronic Headache or Chronic Abdominal Pain? A Preliminary Experimental Study

Objective

To determine whether fear can be triggered when experiencing interoceptive sensations locally proximal to the primary pain region.  Two groups of adolescents (11-18 years) with chronic headache ( n  = 20) or chronic abdominal pain (CAP; n  = 20) completed three muscle tensing tasks to induce proximal versus distal sensations: (1) "frown" task (proximal for chronic headache; distal for CAP), (2) "tighten stomach" task (proximal for CAP; distal for chronic headache), and (3) safe comparison task (clench fist). Fear and avoidance were assessed via self-report. Adolescents with CAP reported greater fear and avoidance after the proximal compared with the distal task, while adolescents with chronic headache did not. Both groups reported similar levels of fear and avoidance in the frown and safe comparison task.  Results suggest that the perception of proximal interoceptive sensations appears to activate the fear system in adolescents with CAP. Future research is warranted.

The stress concept in gastroenterology: from Selye to today

More than eighty years after Hans Selye (1907-1982) first developed a concept describing how different types of environmental stressors affect physiological functions and promote disease development (called the "general adaptation syndrome") in 1936, we herein review advances in theoretical, mechanistic, and clinical knowledge in stress research, especially in the area of gastroenterology, and summarize progress and future perspectives arising from an interdisciplinary psychoneurobiological framework in which genetics, epigenetics, and other advanced ( omics) technologies in the last decade continue to refine knowledge about how stress affects the brain-gut axis in health and gastrointestinal disease. We demonstrate that neurobiological stress research continues to be a driving force for scientific progress in gastroenterology and related clinical areas, inspiring translational research from animal models to clinical applications, while highlighting some areas that remain incompletely understood, such as the roles of sex/gender and gut microbiota in health and disease. Future directions of research should include not only the genetics of the stress response and resilience but also epigenetic contributions.

Generalized Hyperalgesia in Children and Adults Diagnosed With Hypermobility Syndrome and Ehlers-Danlos Syndrome Hypermobility Type: A Discriminative Analysis

OBJECTIVE

Lowered pressure-pain thresholds have been demonstrated in adults with Ehlers-Danlos syndrome hypermobility type (EDS-HT), but whether these findings are also present in children is unclear. Therefore, the objectives of the study were to determine whether generalized hyperalgesia is present in children with hypermobility syndrome (HMS)/EDS-HT, explore potential differences in pressure-pain thresholds between children and adults with HMS/EDS-HT, and determine the discriminative value of generalized hyperalgesia.

METHODS

Patients were classified in 1 of 3 groups: HMS/EDS-HT, hypermobile (Beighton score ≥4 of 9), and healthy controls. Descriptive data of age, sex, body mass index, Beighton score, skin laxity, and medication usage were collected. Generalized hyperalgesia was quantified by the average pressure-pain thresholds collected from 12 locations. Confounders collected were pain locations/intensity, fatigue, and psychological distress. Comparisons between children with HMS/EDS-HT and normative values, between children and adults with HMS/EDS-HT, and corrected confounders were analyzed with multivariate analysis of covariance. The discriminative value of generalized hyperalgesia employed to differentiate between HMS/EDS-HT, hypermobility, and controls was quantified with logistic regression.

RESULTS

Significantly lower pressure-pain thresholds were found in children with HMS/EDS-HT compared to normative values (range -22.0% to -59.0%; P ≤ 0.05). When applying a threshold of 30.8 N/cm² for males and 29.0 N/cm² for females, the presence of generalized hyperalgesia discriminated between individuals with HMS/EDS-HT, hypermobility, and healthy controls (odds ratio 6.0).

CONCLUSION

Children and adults with HMS/EDS-HT are characterized by hypermobility, chronic pain, and generalized hyperalgesia. The presence of generalized hyperalgesia may indicate involvement of the central nervous system in the development of chronic pain.

Learning by experience? Visceral pain-related neural and behavioral responses in a classical conditioning paradigm

BACKGROUND

Studies investigating mechanisms underlying nocebo responses in pain have mainly focused on negative expectations induced by verbal suggestions. Herein, we addressed neural and behavioral correlates of nocebo responses induced by classical conditioning in a visceral pain model.

METHODS

In two independent studies, a total of 40 healthy volunteers underwent classical conditioning, consisting of repeated pairings of one visual cue (CS^High ) with rectal distensions of high intensity, while a second cue (CS^Low ) was always followed by low-intensity distensions. During subsequent test, only low-intensity distensions were delivered, preceded by either CS^High or CS^Low . Distension intensity ratings were assessed in both samples and functional magnetic resonance imaging data were available from one study (N=16). As a consequence of conditioning, we hypothesized CS^High -cued distensions to be perceived as more intense and expected enhanced cue- and distension-related neural responses in regions encoding sensory and affective dimensions of pain and in structures associated with pain-related fear memory.

KEY RESULTS

During test, distension intensity ratings did not differ depending on preceding cue. Greater distension-induced neural activation was observed in somatosensory, prefrontal, and cingulate cortices and caudate when preceded by CS^High . Analysis of cue-related responses revealed strikingly similar activation patterns.

CONCLUSIONS & INFERENCES

We report changes in neural activation patterns during anticipation and visceral stimulation induced by prior conditioning. In the absence of behavioral effects, markedly altered neural responses may indicate conditioning with visceral signals to induce hypervigilance rather than hyperalgesia, involving altered attention, reappraisal, and perceptual acuity as processes contributing to the pathophysiology of visceral pain.

Classical Conditioning Differences Associated With Chronic Pain: A Systematic Review

Prominent clinical models of chronic pain propose a fundamental role of classical conditioning in the development of pain-related disability. If classical conditioning is key to this process, then people with chronic pain may show a different response to pain-related conditioned stimuli than healthy control subjects. We set out to determine whether this is the case by undertaking a comprehensive and systematic review of the literature. To identify studies comparing classical conditioning between people with chronic pain and healthy control subjects, the databases MEDLINE, PsychINFO, PsychARTICLES, Scopus, and CINAHL were searched using key words and medical subject headings consistent with 'classical conditioning' and 'pain.' Articles were included when: 1) pain-free control and chronic pain groups were included, and 2) a differential classical conditioning design was used. The systematic search revealed 7 studies investigating differences in classical conditioning between people with chronic pain and healthy control participants. The included studies involved a total of 129 people with chronic pain (fibromyalgia syndrome, spinal pain, hand pain, irritable bowel syndrome), and 104 healthy control participants. Outcomes included indices of pain-related conditioning such as unconditioned stimulus (US) expectancy and contingency awareness, self-report and physiological measures of pain-related fear, evaluative judgements of conditioned stimulus pleasantness, and muscular and cortical responses. Because of variability in outcomes, meta-analyses included a maximum of 4 studies. People with chronic pain tended to show reduced differential learning and flatter generalization gradients with respect to US expectancy and fear-potentiated eyeblink startle responses. Some studies showed a propensity for greater muscular responses and perceptions of unpleasantness in response to pain-associated cues, relative to control cues.

PERSPECTIVE

The review revealed preliminary evidence that people with chronic pain may exhibit less differential US expectancy and fear learning. This characteristic may contribute to widespread fear-avoidance behavior. The assumption that altered classical conditioning may be a predisposing or maintaining factor for chronic pain remains to be verified.

Outcomes following non-life-threatening orthopaedic trauma: Why are they considered to be so poor?

The purpose of this review article is to assess the current literature on the outcomes of simple orthopaedic trauma. Simple trauma is defined as the fracture or injury of one limb due to an acute event. Fractures are the most common cause of hospitalized trauma in Australia and associated with multiple social, psychological and physical consequences for patients. The literature to date suggests that there are multiple factors leading to relatively poor outcomes following simple trauma, modifiable and non-modifiable. The most oft cited are older age, lower educational status, being injured at work, injury severity score, pre-existing disease, workers compensation, litigation and pain at initial assessment. Additional psychological risk factors quoted attribute to the injury to an external source and the use of passive coping strategies. This review aims to summarise the relevant literature relating to these risk factors and give direction to improving outcomes and future research into this important area.

Using visuo-kinetic virtual reality to induce illusory spinal movement: the MoOVi Illusion

Background

Illusions that alter perception of the body provide novel opportunities to target brain-based contributions to problems such as persistent pain. One example of this, mirror therapy, uses vision to augment perceived movement of a painful limb to treat pain. Since mirrors can’t be used to induce augmented neck or other spinal movement, we aimed to test whether such an illusion could be achieved using virtual reality, in advance of testing its potential therapeutic benefit. We hypothesised that perceived head rotation would depend on visually suggested movement.

Method

In a within-subjects repeated measures experiment, 24 healthy volunteers performed neck movements to 50^o of rotation, while a virtual reality system delivered corresponding visual feedback that was offset by a factor of 50%–200%—the Motor Offset Visual Illusion (MoOVi)—thus simulating more or less movement than that actually occurring. At 50^o of real-world head rotation, participants pointed in the direction that they perceived they were facing. The discrepancy between actual and perceived direction was measured and compared between conditions. The impact of including multisensory (auditory and visual) feedback, the presence of a virtual body reference, and the use of 360^o immersive virtual reality with and without three-dimensional properties, was also investigated.

Results

Perception of head movement was dependent on visual-kinaesthetic feedback (p = 0.001, partial eta squared = 0.17). That is, altered visual feedback caused a kinaesthetic drift in the direction of the visually suggested movement. The magnitude of the drift was not moderated by secondary variables such as the addition of illusory auditory feedback, the presence of a virtual body reference, or three-dimensionality of the scene.

Discussion

Virtual reality can be used to augment perceived movement and body position, such that one can perform a small movement, yet perceive a large one. The MoOVi technique tested here has clear potential for assessment and therapy of people with spinal pain.

Symptoms and the body: Taking the inferential leap

The relationship between the conscious experience of physical symptoms and indicators of objective physiological dysfunction is highly variable and depends on characteristics of the person, the context and their interaction. This relationship often breaks down entirely in the case of "medically unexplained" or functional somatic symptoms, violating the basic assumption in medicine that physical symptoms have physiological causes. In this paper, we describe the prevailing theoretical approach to this problem and review the evidence pertaining to it. We then use the framework of predictive coding to propose a new and more comprehensive model of the body-symptom relationship that integrates existing concepts within a unifying framework that addresses many of the shortcomings of current theory. We describe the conditions under which a close correspondence between the experience of symptoms and objective physiology might be expected, and when they are likely to diverge. We conclude by exploring some theoretical and clinical implications of this new account.

Opioid suppression of conditioned anticipatory brain responses to breathlessness

Opioid painkillers are a promising treatment for chronic breathlessness, but are associated with potentially fatal side effects. In the treatment of breathlessness, their mechanisms of action are unclear. A better understanding might help to identify safer alternatives. Learned associations between previously neutral stimuli (e.g. stairs) and repeated breathlessness induce an anticipatory threat response that may worsen breathlessness, contributing to the downward spiral of decline seen in clinical populations. As opioids are known to influence associative learning, we hypothesized that they may interfere with the brain processes underlying a conditioned anticipatory response to breathlessness in relevant brain areas, including the amygdala and the hippocampus.

Healthy volunteers viewed visual cues (neutral stimuli) immediately before induction of experimental breathlessness with inspiratory resistive loading. Thus, an association was formed between the cue and breathlessness. Subsequently, this paradigm was repeated in two identical neuroimaging sessions with intravenous infusions of either low-dose remifentanil (0.7 ng/ml target-controlled infusion) or saline (randomised).

During saline infusion, breathlessness anticipation activated the right anterior insula and the adjacent operculum. Breathlessness was associated with activity in a network including the insula, operculum, dorsolateral prefrontal cortex, anterior cingulate cortex and the primary sensory and motor cortices.

Remifentanil reduced breathlessness unpleasantness but not breathlessness intensity. Remifentanil depressed anticipatory activity in the amygdala and the hippocampus that correlated with reductions in breathlessness unpleasantness. During breathlessness, remifentanil decreased activity in the anterior insula, anterior cingulate cortex and sensory motor cortices. Remifentanil-induced reduction in breathlessness unpleasantness was associated with increased activity in the rostral anterior cingulate cortex and nucleus accumbens, components of the endogenous opioid system known to decrease the perception of aversive stimuli.

These findings suggest that in addition to effects on brainstem respiratory control, opioids palliate breathlessness through an interplay of altered associative learning mechanisms. These mechanisms provide potential targets for novel ways to develop and assess treatments for chronic breathlessness.

•

The mechanisms of how low-dose opioids relieve breathlessness are unknown.

•

We tested whether low-dose opioids affect conditioned anticipation and perception of breathlessness.

•

Low-dose opioids reduced unpleasantness, but not intensity of breathlessness.

•

Reduced breathlessness unpleasantness was associated with activation of the endogenous opioid system.

•

Breathlessness relief was predicted by decreased anticipatory activity in amygdala/hippocampus.

Learned Fear of Gastrointestinal Sensations in Healthy Adults

BACKGROUND & AIMS

Gastrointestinal symptom-specific fear and anxiety are important determinants of gastrointestinal symptom perception. We studied learning of fear toward innocuous gastrointestinal sensations as a putative mechanism in the development of gastrointestinal symptom-specific fear and anxiety.

METHODS

Fifty-two healthy subjects (26 women) received 2 types of esophageal balloon distention at a perceptible but nonpainful intensity (conditioned stimulus [CS], the innocuous sensation) and at a painful intensity (unconditioned stimulus [US]). Subjects were assigned randomly to 1 of 2 groups. During the learning phase, the innocuous CS preceded the painful US in the experimental group (n = 26). In the control group (n = 26), on the contrary, the US never followed the CS directly. During a subsequent extinction phase, both groups received only CS distention-the painful US was no longer administered. Indexes of fear learning toward the innocuous CS distention included the skin conductance response, fear-potentiated startle (measured by the eye-blink electromyogram), and self-reported expectancy of the US.

RESULTS

During the learning phase, only the experimental group learned to fear the innocuous gastrointestinal CS, based on the increase in US expectancy (compared with the control group, P = .04), increased skin conductance response (compared with the control group, P = .03), and potentiated startle reflex (compared with the control group, P = .001) in response to the CS. The differences between the experimental and control groups in US expectancy and skin conductance, but not fear-potentiated startle, disappeared during the extinction phase.

CONCLUSIONS

Fear toward innocuous gastrointestinal sensations can be established through associative learning in healthy human beings. This may be an important mechanism in the development of fear of gastrointestinal symptoms, implicated in the pathophysiology of functional gastrointestinal disorders.

Why Harmless Sensations Might Hurt in Individuals with Chronic Pain: About Heightened Prediction and Perception of Pain in the Mind

In individuals with chronic pain harmless bodily sensations can elicit anticipatory fear of pain resulting in maladaptive responses such as taking pain medication. Here, we aim to broaden the perspective taking into account recent evidence that suggests that interoceptive perception is largely a construction of beliefs, which are based on past experience and that are kept in check by the actual state of the body. Taking a Bayesian perspective, we propose that individuals with chronic pain display a heightened prediction of pain [prior probability p(pain)], which results in heightened pain perception [posterior probability p(pain|sensation)] due to an assumed link between pain and a harmless bodily sensation [p(sensation|pain)]. This pain perception emerges because their mind infers pain as the most likely cause for the sensation. When confronted with a mismatch between predicted pain and a (harmless bodily) sensation, individuals with chronic pain try to minimize the mismatch most likely by active inference of pain or alternatively by an attentional shift away from the sensation. The active inference results in activities that produce a stronger sensation that will match with the prediction, allowing subsequent perceptual inference of pain. Here, we depict heightened pain perception in individuals with chronic pain by reformulating and extending the assumptions of the interoceptive predictive coding model from a Bayesian perspective. The review concludes with a research agenda and clinical considerations.

Interoceptive cues predicting exteroceptive events

The growing body of research on interoceptive conditioning has predominantly focused on associative learning paradigms that investigated the formation of intero-interoceptive or extero-interoceptive associations. Yet, little research has explored whether interoceptive sensations can enter an intero-exteroceptive association. Therefore, in an interoceptive conditioning paradigm, healthy participants experienced a respiratory resistance for 8s, causing mild dyspnea (interoceptive conditioned stimulus, CS), that was either paired to an aversive electrocutaneous stimulus (unconditioned stimulus, US) (experimental condition, n=25), or presented in an unpaired fashion (control condition, n=25) during the acquisition phase. In a subsequent extinction phase, the US was not delivered anymore. US-expectancy, skin conductance responses (SCR), and eyeblink startle EMG were used as indices of associative learning. During acquisition, we observed stronger US expectancies during the CS as compared to the intertrial interval in the experimental group, but not in the control group, nor during extinction. In line, only in the experimental group did skin conductance responses to the CS increase across acquisition. The pattern of the eyeblink startle data did not reach statistical significance. In sum, interoceptive sensations can become associated with exteroceptive events.

Neck Pain and Proprioception Revisited Using the Proprioception Incongruence Detection Test

BACKGROUND

Proprioceptive imprecision is believed to contribute to persistent pain. Detecting imprecision in order to study or treat it remains challenging given the limitations of current tests.

OBJECTIVES

The aim of this study was to determine whether proprioceptive imprecision could be detected in people with neck pain by testing their ability to identify incongruence between true head motion and a false visual reference using the Proprioception Incongruence Detection (PID) Test.

DESIGN

A cross-sectional study was conducted.

METHODS

Twenty-four people with neck pain and 24 matched controls repeatedly rotated to specific markers within a virtual world and indicated if their true head rotation was more or less than the rotation suggested by the visual feedback. Visual feedback was manipulated at 6 corrections, ranging from 60% of true movement to 140% of true movement. A standard repositioning error (RPE) test as undertaken for comparison.

RESULTS

Healthy controls were better able to detect incongruence between vision and true head rotation (X̅=75.6%, SD=8.5%) than people with neck pain were (X̅=69.6%, SD=12.7%). The RPE test scores were not different between groups. The PID Test score related to self-reported pain intensity but did not relate to RPE test score.

LIMITATIONS

Causality cannot be established from this cross-sectional study, and further work refining the PID Test is needed for it to offer clinical utility.

CONCLUSIONS

Proprioceptive precision for neck movement appears worse in people with neck pain than in those without neck pain, and the extent of the deficit appears to be related to usual pain severity. The PID Test appears to be a more sensitive test than the RPE test and is likely to be useful for assessment of proprioceptive function in research and clinical settings.

Influence of Interoceptive Fear Learning on Visceral Perception

OBJECTIVES

Interoceptive fear learning and generalization have been hypothesized to play a key role in unexplained abdominal and esophageal pain in patients with functional gastrointestinal disorders. However, there is no experimental evidence demonstrating that fear learning and generalization to visceral sensations can be established in humans and alter visceral perception.

METHODS

In a novel fear learning-generalization paradigm, an innocuous esophageal balloon distension served as conditioned stimulus (CS), and distensions at three different pressure levels around the pain detection threshold were used as generalization stimuli. During fear learning, the CS was paired with a painful electrical stimulus (unconditioned stimulus) in the conditioning group (n = 30), whereas in the control group (n = 30), the unconditioned stimulus was delivered alone. Before and after fear learning, visceral perception thresholds for first sensation, discomfort, and pain and visceral discrimination sensitivity were assessed.

RESULTS

Fear learning was established in the conditioning group only (potentiated eye-blink startle to the CS (t(464.06) = 3.17, p = .002), and fear generalization to other stimulus intensities was observed (t(469.12) = 2.97, p = .003; t(464.29) = 4.17, p < .001). The thresholds for first sensation habituated in the control group, whereas it remained constant in the conditioning group (F(1,43) = 9.77, p = .003).

CONCLUSIONS

These data show that fear learning using visceral stimuli induces fear generalization and influences visceral perception. These findings support the idea that in functional gastrointestinal disorder, fear learning and generalization can foster gastrointestinal-specific anxiety and contribute to visceral hypersensitivity.

Could Stress Contribute to Pain-Related Fear in Chronic Pain?

Learning to predict pain based on internal or external cues constitutes a fundamental and highly adaptive process aimed at self-protection. Pain-related fear is an essential component of this response, which is formed by associative and instrumental learning processes. In chronic pain, pain-related fear may become maladaptive, drive avoidance behaviors and contribute to symptom chronicity. Pavlovian fear conditioning has proven fruitful to elucidate associative learning and extinction involving aversive stimuli, including pain, but studies in chronic pain remain scarce. Stress demonstrably exerts differential effects on emotional learning and memory processes, but this has not been transferred to pain-related fear. Within this perspective, we propose that stress could contribute to impaired pain-related associative learning and extinction processes and call for interdisciplinary research. Specifically, we suggest to test the hypotheses that: (1) extinction-related phenomena inducing a re-activation of maladaptive pain-related fear (e.g., reinstatement, renewal) likely occur in everyday life of chronic pain patients and may alter pain processing, impair perceptual discrimination and favor overgeneralization; (2) acute stress prior to or during acquisition of pain-related fear may facilitate the formation and/or consolidation of pain-related fear memories; (3) stress during or after extinction may impair extinction efficacy resulting in greater reinstatement or context-dependent renewal of pain-related fear; and (4) these effects could be amplified by chronic stress due to early adversity and/or psychiatric comorbidity such depression or anxiety in patients with chronic pain.

Perceptual discrimination in fear generalization: Mechanistic and clinical implications

For almost a century, Pavlovian conditioning is the imperative experimental paradigm to investigate the development and generalization of fear. However, despite the rich research tradition, the conceptualization of fear generalization has remained somewhat ambiguous. In this selective review, we focus explicitly on some challenges with the current operationalization of fear generalization and their impact on the ability to make inferences on its clinical potential and underlying processes. The main conclusion is that, despite the strong evidence that learning influences perception, current research has largely neglected the role of perceptual discriminability and its plasticity in fear generalization. We propose an alternative operationalization of generalization, where the essence is that Pavlovian conditioning itself influences the breadth of fear generalization via learning-related changes in perceptual discriminability. Hence a conceptualization of fear generalization is incomplete without an in-depth analysis of processes of perceptual discriminability. Furthermore, this highlights perceptual learning and discriminability as important future targets for pre-clinical and clinical research.

Interoception and the uneasiness of the mind: affect as perceptual style

Autonomous system models of interoception describe perception of bodily sensations as an active process in which the brain generates and tests hypotheses about the body on the basis of proximal information. This view of perception as inference allows a new perspective on the role of affect in perception. Affect and interoception are closely linked, but processes underlying this link are poorly understood. We suggest that a predictive coding perspective allows acknowledging affect as integral part of information processing. We outline how affect may intrinsically modify processes of interoception by acting as threshold mechanism in stimulus grouping and information compression. We outline how well-established methods, for example, from categorization research may allow quantifying this influence of affect on perception in empirical tests of predictive coding models. We discuss how this may enrich the study of the relationship between affect and interoception and may have important clinical relevance.

Generalization of Fear to Respiratory Sensations

Interoceptive fear conditioning (IFC), fear generalization and a lack of safety learning have all been hypothesized to play a role in the pathogenesis of panic disorder, but have never been examined in a single paradigm. The present study aims to investigate whether healthy participants (N=43) can learn both fear and safety to an interoceptive sensation, and whether such learning generalizes to other, similar sensations. Two intensities of inspiratory breathing impairment (induced by two pressure threshold loads of 6 and 25 cm H2O) served as interoceptive conditional stimuli (CSs) in a differential conditioning paradigm. An inspiratory occlusion was used as the unconditioned stimulus (US). Generalization was tested 24h after conditioning, using four generalization stimuli with intensities in-between CS+ and CS- (GSs: 8-10.5-14-18.5 cm H2O). Measures included US-expectancy, startle blink EMG responses, electrodermal activity and respiration. Perceptual discrimination of interoceptive CSs and GSs was explored with a discrimination task prior to acquisition and after generalization. Results indicate that differential fear learning was established for US-expectancy ratings. The group with a low intensity CS+ and a high intensity CS- showed the typical pattern of differential fear responding and a similarity-based generalization gradient. In contrast, the high intensity CS+ and low intensity CS- group showed impaired differential learning and complete generalization of fear. Our findings suggest that interoceptive fear learning and generalization are modulated by stimulus intensity and that the occurrence of discriminatory learning is closely related to fear generalization.

Placebo effects and their determinants in gastrointestinal disorders

Placebo effects in clinical trials have sparked an interest in the placebo phenomenon, both in randomized controlled trials (RCTs) and in experimental gastroenterology. RCTs have demonstrated similar short-term and long-term placebo response rates in gastrointestinal compared to other medical diagnoses. Most mediators and moderators of placebo effects in gastrointestinal diseases are also of similar type and size to other medical diagnoses and not specific for gastrointestinal diagnoses. Other characteristics such as an increase in the placebo response over time and the placebo-enhancing effects of unbalanced randomization were not seen, at least in IBS. Experimental placebo and nocebo studies underscore the 'power' of expectancies and conditioning processes in shaping gastrointestinal symptoms not only at the level of self-reports, but also within the brain and along the brain-gut axis. Brain imaging studies have redressed earlier criticism that placebo effects might merely reflect a response bias. These findings raise hope that sophisticated trials and experiments designed to boost positive expectations and minimize negative expectations could pave the way for a practical and ethically sound use of placebo knowledge in daily practice. Rather than focusing on a 'personalized' choice of drugs based on biomarkers or genes, it might be the doctor-patient communication that needs to be tailored.

Interoception, contemplative practice, and health

Interoception can be broadly defined as the sense of signals originating within the body. As such, interoception is critical for our sense of embodiment, motivation, and well-being. And yet, despite its importance, interoception remains poorly understood within modern science. This paper reviews interdisciplinary perspectives on interoception, with the goal of presenting a unified perspective from diverse fields such as neuroscience, clinical practice, and contemplative studies. It is hoped that this integrative effort will advance our understanding of how interoception determines well-being, and identify the central challenges to such understanding. To this end, we introduce an expanded taxonomy of interoceptive processes, arguing that many of these processes can be understood through an emerging predictive coding model for mind–body integration. The model, which describes the tension between expected and felt body sensation, parallels contemplative theories, and implicates interoception in a variety of affective and psychosomatic disorders. We conclude that maladaptive construal of bodily sensations may lie at the heart of many contemporary maladies, and that contemplative practices may attenuate these interpretative biases, restoring a person’s sense of presence and agency in the world.