Reward responsiveness in patients with chronic pain

Reduced Gray Matter Volume and Cortical Thickness in Patients With Small-Fiber Neuropathy

Small-fiber neuropathy (SFN) is defined by degeneration or dysfunction of peripheral sensory nerve endings. Central correlates have been identified on the level of gray matter volume (GMV) and cortical thickness (CT) changes. However, across SFN etiologies knowledge about a common structural brain signature is still lacking. Therefore, we recruited 26 SFN patients and 25 age- and sex-matched healthy controls to conduct voxel-based- and surface-based morphometry. Across all patients, we found reduced GMV in widespread frontal regions, left caudate, insula and superior parietal lobule. Surface-based morphometry analysis revealed reduced CT in the right precentral gyrus of SFN patients. In a region-based approach, patients had reduced GMV in the left caudate. Since pathogenic gain-of-function variants in voltage-gated sodium channels (Nav) have been associated with SFN pathophysiology, we explored brain morphological patterns in a homogenous subsample of patients carrying rare heterozygous missense variants. Whole brain- and region-based approaches revealed GMV reductions in the bilateral caudate for Nav variant carriers. Further research is needed to analyze the specific role of Nav variants for structural brain alterations. Together, we conclude that SFN patients have specific GMV and CT alterations, potentially forming potential new central biomarkers for this condition. Our results might help to better understand underlying or compensatory mechanisms of chronic pain perception in the future. PERSPECTIVE: This study reveals structural brain changes in small-fiber neuropathy (SFN) patients, particularly in frontal regions, caudate, insula, and parietal lobule. Notably, individuals with SFN and specific Nav variants exhibit bilateral caudate abnormalities. These findings may serve as potential central biomarkers for SFN and provide insights into chronic pain perception mechanisms.

Obesity-mediated Lipoinflammation Modulates Food Reward Responses

Accumulation of white adipose tissue (WAT) during obesity is associated with the development of chronic low-grade inflammation, a biological process known as lipoinflammation. Systemic and central lipoinflammation accumulates pro-inflammatory cytokines including IL-6, IL-1β and TNF-α in plasma and also in brain, disrupting neurometabolism and cognitive behavior. Obesity-mediated lipoinflammation has been reported in brain regions of the mesocorticolimbic reward circuit leading to alterations in the perception and consumption of ultra-processed foods. While still under investigation, lipoinflammation targets two major outcomes of the mesocorticolimbic circuit during food reward: perception and motivation ("Wanting") and the pleasurable feeling of feeding ("Liking"). This review will provide experimental and clinical evidence supporting the contribution of obesity- or overnutrition-related lipoinflammation affecting the mesocorticolimbic reward circuit and enhancing food reward responses. We will also address neuroanatomical targets of inflammatory profiles that modulate food reward responses during obesity and describe potential cellular and molecular mechanisms of overnutrition linked to addiction-like behavior favored by brain lipoinflammation.

The role of expectations, control and reward in the development of pain persistence based on a unified model

Chronic, or persistent pain affects more than 10% of adults in the general population. This makes it one of the major physical and mental health care problems. Although pain is an important acute warning signal that allows the organism to take action before tissue damage occurs, it can become persistent and its role as a warning signal thereby inadequate. Although per definition, pain can only be labeled as persistent after 3 months, the trajectory from acute to persistent pain is likely to be determined very early and might even start at the time of injury. The biopsychosocial model has revolutionized our understanding of chronic pain and paved the way for psychological treatments for persistent pain, which routinely outperform other forms of treatment. This suggests that psychological processes could also be important in shaping the very early trajectory from acute to persistent pain and that targeting these processes could prevent the development of persistent pain. In this review, we develop an integrative model and suggest novel interventions during early pain trajectories, based on predictions from this model.

Relationship between behavioral and mood responses to monetary rewards in a sample of Indian students with and without reported pain

Physical pain has become a major health problem with many university students affected by it worldwide each year. Several studies have examined the prevalence of pain-related impairments in reward processing in Western, Educated, Industrialized, Rich, and Democratic (WEIRD) countries but none of the studies have replicated these findings in a non-western cultural setting. Here, we aimed to investigate the prevalence of physical pain symptoms in a sample of university students in India and replicate our previous study conducted on university students in Switzerland, which showed reduced mood and behavioral responses to reward in students with significant pain symptoms. We grouped students into a sub-clinical (N = 40) and a control group (N = 48) to test the association between pain symptoms and reward processes. We used the Fribourg reward task and the pain sub-scale of the Symptom Checklist (SCL-27-plus) to assess physical symptoms of pain. We found that 45% of the students reported high levels of physical symptoms of pain and interestingly, our ANOVA results did not show any significant interaction between reward and the groups either for mood scores or for outcomes related to performance. These results might yield the first insights that pain-related impairment is not a universal phenomenon and can vary across cultures.

Mindfulness-Oriented Recovery Enhancement for Addictive Behavior, Psychiatric Distress, and Chronic Pain: A Multilevel Meta-Analysis of Randomized Controlled Trials

Objectives

Methods

Results

Conclusions

Meta-analysis Pre-registration: PROSPERO #CRD42022319006

Supplementary Information

Changes in Touch Avoidance, Stress, and Anxiety During the COVID-19 Pandemic in Italy

In the present study we analyzed how attitudes toward touch have changed during the COVID-19 pandemic in an Italian sample, through two different studies: in the first we contacted participants of the Italian validation study of the Touch Avoidance Questionnaire, asking them to take part in a follow-up study (N = 31, 64.5% women, age 42.58 ± 15.15); in the second we recruited a new sample of 717 people (73.92% women, age 34.25 ± 13.11), comparing it to the full validation sample of the Touch Avoidance Questionnaire (N = 335, 64.48% women, age = 35.82 ± 14.32) to further investigate the relationship between the pandemic, stress responses, fear of contagion, anxiety, and attitudes toward touch. Overall, we found higher post-pandemic scores for touch avoidance toward strangers and family members and lower scores in touch avoidance toward friends of either gender, along with a slight increase in anxiety and stress. Touch avoidance was also positively related to anxiety and/or stress levels except for touch avoidance toward same-sex friends, for which the relationship with anxiety was negative. Surprisingly, we found that young people were the most anxious, despite older people being more at-risk of dying from COVID-19. Women were slightly more stressed out. COVID-19-related fears were significant predictors of touch avoidance toward partners, friends and strangers, but not of touch avoidance toward family. The results suggest that touch avoidance increased during the pandemic (except toward same-sex friends), together with anxiety and stress levels, but the change was relatively small.

Altered Reward Processing and Sex Differences in Chronic Pain

Chronic pain and reward processing are understood to be reciprocally related to one another. Previous studies of reward processing in chronic pain patients have reported incongruent findings. While several factors likely contribute to these disparate findings, these previous studies did not stratify their analyses by sex-a factor previously shown to robustly impact reward-related responses. Thus, we examined sex as a factor of interest in level of striatal activation during anticipation of monetary incentives among patients with chronic non-specific back pain and healthy controls (HC). This study utilized functional magnetic resonance imaging during a monetary incentive delay task to evaluate reward and loss responsivity in the striatum among males and females with and without chronic pain (N = 90). Group, sex, and group-by-sex interactions were analyzed via repeated measures analysis of variance. Among HC, males exhibited significantly greater blood oxygen level dependent (BOLD) signal in the striatum during reward anticipation, particularly during large reward trials. By contrast, no significant sex differences were observed among patients. A significant group-by-sex interaction was also observed, revealing diminished BOLD responses among males with chronic pain relative to control males. These results provide novel evidence of sex-specific reductions in anticipatory responses to reward in patients with chronic pain. Altered striatal reward responsivity among males, but not females, suggests that the reward systems of males and females are uniquely disrupted by chronic pain, and highlights the value of including sex as a factor of interest in future studies of reward responsivity in the context of persistent pain.

Updated Review of the Evidence Supporting the Medical and Legal Use of NeuroQuant® and NeuroGage® in Patients With Traumatic Brain Injury

Over 40 years of research have shown that traumatic brain injury affects brain volume. However, technical and practical limitations made it difficult to detect brain volume abnormalities in patients suffering from chronic effects of mild or moderate traumatic brain injury. This situation improved in 2006 with the FDA clearance of NeuroQuant®, a commercially available, computer-automated software program for measuring MRI brain volume in human subjects. More recent strides were made with the introduction of NeuroGage®, commercially available software that is based on NeuroQuant® and extends its utility in several ways. Studies using these and similar methods have found that most patients with chronic mild or moderate traumatic brain injury have brain volume abnormalities, and several of these studies found-surprisingly-more abnormal enlargement than atrophy. More generally, 102 peer-reviewed studies have supported the reliability and validity of NeuroQuant® and NeuroGage®. Furthermore, this updated version of a previous review addresses whether NeuroQuant® and NeuroGage® meet the Daubert standard for admissibility in court. It concludes that NeuroQuant® and NeuroGage® meet the Daubert standard based on their reliability, validity, and objectivity. Due to the improvements in technology over the years, these brain volumetric techniques are practical and readily available for clinical or forensic use, and thus they are important tools for detecting signs of brain injury.

Differences in Learning and Persistency Characterizing Behavior in Chronic Pain for the Iowa Gambling Task: Web-Based Laboratory-in-the-Field Study

Background

Chronic pain is a significant worldwide health problem. It has been reported that people with chronic pain experience decision-making impairments, but these findings have been based on conventional laboratory experiments to date. In such experiments, researchers have extensive control of conditions and can more precisely eliminate potential confounds. In contrast, there is much less known regarding how chronic pain affects decision-making captured via laboratory-in-the-field experiments. Although such settings can introduce more experimental uncertainty, collecting data in more ecologically valid contexts can better characterize the real-world impact of chronic pain.

Objective

We aim to quantify decision-making differences between individuals with chronic pain and healthy controls in a laboratory-in-the-field environment by taking advantage of internet technologies and social media.

Methods

A cross-sectional design with independent groups was used. A convenience sample of 45 participants was recruited through social media: 20 (44%) participants who self-reported living with chronic pain, and 25 (56%) people with no pain or who were living with pain for <6 months acting as controls. All participants completed a self-report questionnaire assessing their pain experiences and a neuropsychological task measuring their decision-making (ie, the Iowa Gambling Task) in their web browser at a time and location of their choice without supervision.

Results

Standard behavioral analysis revealed no differences in learning strategies between the 2 groups, although qualitative differences could be observed in the learning curves. However, computational modeling revealed that individuals with chronic pain were quicker to update their behavior than healthy controls, which reflected their increased learning rate (95% highest–posterior-density interval [HDI] 0.66-0.99) when fitted to the Values-Plus-Perseverance model. This result was further validated and extended on the Outcome-Representation Learning model as higher differences (95% HDI 0.16-0.47) between the reward and punishment learning rates were observed when fitted to this model, indicating that individuals with chronic pain were more sensitive to rewards. It was also found that they were less persistent in their choices during the Iowa Gambling Task compared with controls, a fact reflected by their decreased outcome perseverance (95% HDI −4.38 to −0.21) when fitted using the Outcome-Representation Learning model. Moreover, correlation analysis revealed that the estimated parameters had predictive value for the self-reported pain experiences, suggesting that the altered cognitive parameters could be potential candidates for inclusion in chronic pain assessments.

Conclusions

We found that individuals with chronic pain were more driven by rewards and less consistent when making decisions in our laboratory-in-the-field experiment. In this case study, it was demonstrated that, compared with standard statistical summaries of behavioral performance, computational approaches offered superior ability to resolve, understand, and explain the differences in decision-making behavior in the context of chronic pain outside the laboratory.

Pain, negative affective states and opioid-based analgesics: Safer pain therapies to dampen addiction

Across centuries and civilizations opioids have been used to relieve pain. In our modern societies, opioid-based analgesics remain one of the most efficient treatments for acute pain. However, the long-term use of opioids can lead to the development of analgesic tolerance, opioid-induced hyperalgesia, opioid use disorders, and overdose, which can ultimately produce respiratory depressant effects with fatal consequences. In addition to the nociceptive sensory component of pain, negative affective states arising from persistent pain represent a risk factor for developing an opioid use disorder. Several studies have indicated that the increase in prescribed opioid analgesics since the 1990s represents the root of our current opioid epidemic. In this review, we will present our current knowledge on the endogenous opioid system within the pain neuroaxis and the plastic changes occurring in this system that may underlie the occurrence of pain-induced negative affect leading to misuse and abuse of opioid medications. Dissecting the allostatic neuronal changes occurring during pain is the most promising avenue to uncover novel targets for the development of safer pain medications. We will discuss this along with current and potential approaches to treat pain-induced negative affective states that lead to drug misuse. Moreover, this chapter will provide a discussion on potential avenues to reduce the abuse potential of new analgesic drugs and highlight a basis for future research and drug development based on recent advances in this field.

Reward Responsiveness in Patients with Opioid Use Disorder on Opioid Agonist Treatment: Role of Comorbid Chronic Pain

OBJECTIVE

Evidence suggests that blunted reward responsiveness may account for poor clinical outcomes in both opioid use disorder (OUD) and chronic pain. Understanding how individuals with OUD and comorbid chronic pain (OUD+CP) respond to rewards is, therefore, of clinical interest because it may reveal a potential point of behavioral intervention.

METHODS

Patients with OUD (n = 28) and OUD+CP (n = 19) on opioid agonist treatment were compared on: 1) the Probabilistic Reward Task (an objective behavioral measure of reward response bias) and 2) ecological momentary assessment of affective responses to pleasurable events.

RESULTS

Both the OUD and the OUD+CP groups evidenced an increase in reward response bias in the Probabilistic Reward Task. The rate of change in response bias across blocks was statistically significant in the OUD group (B = 0.06, standard error [SE] = 0.02, t = 3.92, P < 0.001, 95% confidence interval [CI]: 0.03 to 0.09) but not in the OUD+CP group (B = 0.03, SE = 0.02, t = 1.90, P = 0.07, 95% CI: -0.002 to 0.07). However, groups did not significantly differ in the rate of change in response bias across blocks (B = 0.03, SE = 0.02, t = 1.21, P = 0.23, 95% CI: -0.02 to 0.07). Groups did not significantly differ on state measures of reward responsiveness (P's ≥0.50).

CONCLUSIONS

Overall, findings across objective and subjective measures were mixed, necessitating follow-up with a larger sample. The results suggest that although there is a reward response bias in patients with OUD+CP treated with opioid agonist treatment relative to patients with OUD without CP, it is modest and does not appear to translate into patients' responses to rewarding events as they unfold in daily life.

The Association Between Smoking Abstinence and Pain Trajectory Among Veterans Engaged in U.S. Department of Veterans Affairs Mental Health Care

OBJECTIVE

To prospectively examine associations between smoking and nicotine abstinence and pain trajectory over 12 months among smokers with low, moderate, and severe pain and to assess whether these associations differ over time.

DESIGN

A secondary analysis of the "Proactive Outreach for Smokers in VA Mental Health" study, a randomized controlled trial of proactive outreach for veteran smokers engaged in U.S. Department of Veterans Affairs (VA) mental health care.

METHODS

Participants were categorized into "low" (n = 616), "moderate" (n = 479), and "severe" pain (n = 656) groups according to baseline pain score. Associations between self-reported abstinence from smoking and nicotine at 6 and 12 months and pain trajectory, measured via the PEG scale (Pain intensity, Enjoyment of life, General activity) composite score, were assessed through the use of general linear mixed models. Interaction tests assessed whether these associations differed at 6 and 12 months. Analyses were conducted within the overall sample and within the separate pain groups.

RESULTS

There were significant interactions in the overall sample and the low and moderate pain groups, such that 7-day point prevalence smoking abstinence was associated with lower pain scores at 6 but not 12 months. In the severe pain group, 7-day abstinence from both smoking and nicotine was associated with lower pain scores across both time points. Six-month prolonged abstinence was not associated with pain scores.

CONCLUSIONS

In this prospective analysis conducted among veteran smokers engaged in mental health services, 7-day abstinence from smoking and nicotine was associated with significantly lower levels of pain. Education efforts could help better inform smokers on the relationship between smoking and pain.

Understanding Pain Catastrophizing: Putting Pieces Together

The present narrative review addresses issues concerning the defining criteria and conceptual underpinnings of pain catastrophizing. To date, the concept of pain catastrophizing has been extensively used in many clinical and experimental contexts and it is considered as one of the most important psychological correlate of pain chronicity and disability. Although its extensive use, we are still facing important problems related to its defining criteria and conceptual understanding. At present, there is no general theoretical agreement of what catastrophizing really is. The lack of a consensus on its definition and conceptual issues has important consequences on the choice of the pain management approaches, defining and identifying problems, and promoting novel research. Clinical and research work in absence of a common theoretical ground is often trivial. It is very surprising that clinical and experimental work has grown extensively in the past years, without a common ground in the form of a clear definition of pain catastrophizing and overview of its conceptual basis. Improving the efficacy and efficiency of pan catastrophizing related treatments requires an understanding of the theoretical construct. So far, most interventions have only demonstrated modest effects in reducing pain catastrophizing. Therefore, clarifying the construct may be an important precursor for developing more targeted and effective interventions, thereby easing some of the burden related to this aspect of pain. In our review, we have extracted and de-constructed common elements that emerge from different theoretical models with the aim to understand the concept of catastrophizing, which components can be modulated by psychological interventions, and the general role in pain processing. The analysis of the literature has indicated essential key elements to explain pain catastrophizing: emotional regulation, catastrophic worry (as repetitive negative thinking), rumination, behavioral inhibition and behavioral activation (BIS/BAS) systems, and interoceptive sensitivity. The present paper attempts to integrate these key elements with the aim to re-compose and unify the concept within a modern biopsychosocial interpretation of catastrophizing.

Anhedonia in chronic pain and prescription opioid misuse

BACKGROUND

Both acute and chronic pain can disrupt reward processing. Moreover, prolonged prescription opioid use and depressed mood are common in chronic pain samples. Despite the prevalence of these risk factors for anhedonia, little is known about anhedonia in chronic pain populations.

METHODS

We conducted a large-scale, systematic study of anhedonia in chronic pain, focusing on its relationship with opioid use/misuse, pain severity, and depression. Chronic pain patients across four distinct samples (N = 488) completed the Snaith-Hamilton Pleasure Scale (SHAPS), measures of opioid use, pain severity and depression, as well as the Current Opioid Misuse Measure (COMM). We used a meta-analytic approach to determine reference levels of anhedonia in healthy samples spanning a variety of countries and diverse age groups, extracting SHAPS scores from 58 published studies totaling 2664 psychiatrically healthy participants.

RESULTS

Compared to healthy samples, chronic pain patients showed higher levels of anhedonia, with ~25% of patients scoring above the standard anhedonia cut-off. This difference was not primarily driven by depression levels, which explained less than 25% of variance in anhedonia scores. Neither opioid use duration, dose, nor pain severity alone was significantly associated with anhedonia. Yet, there was a clear effect of opioid misuse, with opioid misusers (COMM ⩾13) reporting greater anhedonia than non-misusers. Opioid misuse remained a significant predictor of anhedonia even after controlling for pain severity, depression and opioid dose.

CONCLUSIONS

Study results suggest that both chronic pain and opioid misuse contribute to anhedonia, which may, in turn, drive further pain and misuse.

Italian Validation of the Touch Avoidance Measure and the Touch Avoidance Questionnaire

Social touch is essential in relationships and well-being, but the unique personal experience of touch is not assessed and taken into account in health and social care services. The pleasantness of gentle stroking is influenced by gender, toucher genre, toucher familiarity, culture, and age. Moreover, pleasantness is influenced by touch avoidance, the attitude toward interpersonal touch. The aim of this article is to present the translation, adaptation, and validation in Italian of two scales to measure touch avoidance. For translation and validation, we selected the most used scale, the Touch Avoidance Measure (TAM) and a more recent scale, the Touch Avoidance Questionnaire (TAQ). Confirmatory factor analyses reported good model fit for the TAM [comparative fit index (CFI) = 0.947, Tucker-Lewis index (TLI) = 0.940, root-mean-square error of approximation (RMSEA) = 0.065] and excellent model fit for the TAQ (CFI = 0.954, TLI = 0.950, RMSEA = 0.058). Internal consistency was high for all subscales, except the TAQ "Stranger" subscale. One-month test-retest reliability ranged from 0.67 to 0.90 for each subscale. Lastly, convergent validity between the TAM and TAQ was also found to be high. We conclude that the TAM and TAQ can be used to assess touch avoidance with Italian samples. The instrument can be used to support healthcare professionals and to assess attitudes toward touch in individuals with interpersonal difficulties.

Initial Responsiveness to Reward Attainment and Psychopathology in Children and Adults: An RDoC Study

The Research Domain Criteria (RDoC) initiative of the National Institute of Mental Health (NIMH) established a dimensional framework for understanding psychiatric constructs. Initial Responsiveness to Reward Attainment (IRRA) was identified as a dimensional construct relevant to several psychiatric disorders. The current study aimed to (1) examine IRRA as a predictor of psychopathology and impairment in children and their parents, and (2) examine the potential effects of sex and ancestry on the relationship between IRRA and psychopathology. Participants included 1127 children ages 6 to 12, and 1018 of their parents. Parents and children completed self-report measures of IRRA. Psychopathology and impairment were measured using self-report for adults, and parent-report and semi-structured interview for children. In adults, IRRA was significantly, but modestly, related to adaptive functioning. In children, IRRA was significantly, but modestly, related to overall, school, spare time, home, and peer functioning. Findings suggest IRRA may be a helpful construct for understanding adaptive functioning in adults and children, however it may be less helpful for understanding specific dimensions of psychopathology. Additionally, ancestry should be taken into consideration when examining how IRRA relates to psychopathology and functioning.

Differential effects of state and trait social anhedonia on suicidal ideation at 3-months follow up

BACKGROUND

Recent work suggests that the social component of anhedonia is more associated with suicide ideation than the other component of pleasure. The present study investigated the differential effects of state and trait social anhedonia on suicidal ideation across two undergraduate samples based on the Interpersonal Theory and Three-Step Theory of Suicide.

METHODS

State social anhedonia was assessed with a single item (Loss of Interest in People) extracted from the Beck Depression Inventory, while trait social anhedonia was assessed using the Anticipatory and Consummatory Interpersonal Pleasure Scale. Suicidal ideation was re-administered at a 3-month follow-up.

RESULTS

In Study 1, higher state social anhedonia was associated with greater levels of suicidal ideation, while trait social anhedonia moderated the relationship between thwarted belongingness, perceived burdensomeness and suicidal ideation. In Study 2, state social anhedonia was margin significant predictor of suicidal ideation, while trait social anhedonia moderated the relationship between psychological pain and suicidal ideation.

CONCLUSIONS

These findings confirmed the presence of two different effects on suicidal ideation in state and trait social anhedonia: state social anhedonia directly was associated with suicidal ideation, while trait social anhedonia was indirectly related through their effects on other risk factors of suicidality.

Anxiety, Reinforcement Sensitivity and Social Context in Accepting the Experience of Pain Among Rheumatoid Arthritis Patients

Background: Acceptance has become one of the most widely studied processes regarding chronic pain because of its ability to influence participants' adaptation and coping responses. Leading researchers have found relationships between variables such as anxiety, reinforcement sensitivity, and the responses of the participants' environment to their behavior and acceptance. In contrast, few studies have been found that investigate the variables that predict the acceptance of pain. This study has set out to explore the relationships between pain-related anxiety, sensitivity to contingencies, and the punishment responses of significant people toward pain behaviors regarding pain acceptance. Methods: With a view to fulfilling this purpose, a cohort of 62 participants with rheumatoid arthritis was chosen, and the subjects were assessed through the following self-report measures: Chronic Pain Acceptance Questionnaire, CPAQ; Pain Anxiety Symptoms Scale, PASS-20; The Sensitivity to Punishment and Sensitivity to Reward Questionnaire, SPSRQ, and The West Haven-Yale Multidimensional Pain Inventory, WHYMPI. The study's initial objectives were achieved by means of a stepwise multiple linear regression analysis. Results: The linear regression analyses revealed a negative and significant correlation between anxiety, reinforcement sensitivity, and the significant persons' responses to pain behaviors and pain acceptance. Conclusion: The results suggest that the identification of these variables might be important for addressing these participants' pain. Finally, the discussion focuses on our findings' implications as regards their use in clinical practice.

The interaction between stress and chronic pain through the lens of threat learning

Stress and pain are interleaved at multiple levels - interacting and influencing each other. Both are modulated by psychosocial factors including fears, beliefs, and goals, and are served by overlapping neural substrates. One major contributing factor in the development and maintenance of chronic pain is threat learning, with pain as an emotionally-salient threat - or stressor. Here, we argue that threat learning is a central mechanism and contributor, mediating the relationship between stress and chronic pain. We review the state of the art on (mal)adaptive learning in chronic pain, and on effects of stress and particularly cortisol on learning. We then provide a theoretical integration of how stress may affect chronic pain through its effect on threat learning. Prolonged stress, as may be experienced by patients with chronic pain, and its resulting changes in key brain networks modulating stress responses and threat learning, may further exacerbate these impairing effects on threat learning. We provide testable hypotheses and suggestions for how this integration may guide future research and clinical approaches in chronic pain.

Mapping the Affective Dimension of Embodiment With the Sensation Manikin: Validation Among Chronic Pain Patients and Modification by Mindfulness-Oriented Recovery Enhancement

OBJECTIVE

Mindfulness-based interventions target novel pain relief mechanisms not captured by legacy pain scales, including 1) cultivating awareness of pleasant and neutral sensations proximal to unpleasant sensations and 2) interoceptively mapping sensation location and spatial distribution.

METHODS

We created a digital sensation manikin (SM) by overlaying a human figure silhouette with a grid of 469 "sensation" pixels. A series of five research questions examined the SM's discriminant validity, construct validity, incremental validity, convergence with an objective measure of pain attentional bias, and sensitivity to a mindfulness-based psychological treatment, Mindfulness-Oriented Recovery Enhancement (MORE). A sample of opioid treated chronic pain patients (n = 108; age, 53.79 (12.94) years; female, 65%) was recruited to answer research questions 1 to 5, and a sample of healthy controls (n = 91; age, 36.47 (13.50) years; female, 55%) was recruited as the comparison group for research question 1.

RESULTS

Chronic pain patients reported significantly more unpleasant sensations than did healthy controls (p < .001, d = 1.23) and significantly fewer pleasant sensations (p = .001, d = 0.50). The SM also evidenced expected relationships with multiple measures of pain (r = 0.26-0.29) and well-being (r = -0.21 to 0.28), uniquely predicted pain interference (β = -0.18), and exhibited a significant association with pain attentional bias (r = 0.25). Finally, mindfulness-based intervention via MORE significantly increased the ratio of pleasant to unpleasant sensations reported by chronic pain patients relative to an active control condition (p = .036, d = 0.51).

CONCLUSIONS

This study supports the SM's validity and indicates that assessing both pleasant and unpleasant sensations broadens the scope of pain measurement. Although the SM would benefit from further optimization, its continued use is likely to contribute to improved assessment and treatment options for chronic pain patients.

Reward Processing under Chronic Pain from the Perspective of "Liking" and "Wanting": A Narrative Review

The therapeutic goals of patients with chronic pain are not only to relieve pain but also to improve the quality of life. Chronic pain negatively affects various aspects of daily life, such as by decreasing the motivation to work and reward sensitivity, which may lead to difficulties in daily life or even unemployment. Human and animal studies have shown that chronic pain damages reward processing; the exploration of associated internal mechanisms may aid the development of treatments to repair this damage. Incentive salience theory, used widely to describe reward processing, divides this processing into “liking” (reward-induced hedonic sensory impact) and “wanting” (reward-induced motivation) components. It has been employed to explain pathological changes in reward processing induced by psychiatric disorders. In this review, we summarize the findings of studies of reward processing under chronic pain and examine the effects of chronic pain on “liking” and “wanting.” Evidence indicates that chronic pain compromises the “wanting” component of reward processing; we also discuss the neural mechanisms that may mediate this effect. We hope that this review aids the development of therapies to improve the quality of life of patients with chronic pain.

Exploring the potential role of mesocorticolimbic circuitry in motivation for and adherence to chronic pain self-management interventions

Adherence to pain self-management strategies is associated with favorable psychobehavioral outcomes among individuals with chronic pain. Substantive adherence to treatments teaching these adaptive skills often proves challenging, resulting in poor individual and societal outcomes. Evidence demonstrates motivation for behavior change as a key predictor of treatment adherence. Despite behavioral techniques that target motivation, however, nonadherence persists as a barrier to positive clinical outcomes in chronic pain. Understanding the neurobiological mechanisms underlying treatment motivation might highlight novel avenues for augmentative therapies. The purpose of this review is to present theory and evidence that the mesocorticolimbic system (i.e., brain circuitry associated with reward processing and motivation) contributes to treatment motivation among chronic pain patients, ultimately influencing adherence. We review evidence for motivation as a key adherence determinant, detail neuroimaging findings relating mesocorticolimbic circuitry and motivation, and discuss data supporting mesocorticolimbic dysfunction among chronic pain patients. We propose a neurobehavioral model for adherence to pain self-management interventions, listing testable hypotheses. Finally, we discuss potential research and intervention implications from the proposed model.

The behavioural inhibition system, behavioural activation system and experiential avoidance as explanatory variables of comorbid chronic pain and posttraumatic stress symptoms

Background: The variables that underlie comorbid chronic pain and posttraumatic stress symptoms (PTSS) are not yet clearly established. Objective: The aim of the present study was to analyse the role of the behavioural inhibition system (BIS), behavioural approach system (BAS) and experiential avoidance (EA) in pain adjustment (i.e. pain intensity, daily functioning and pain-related impairment) in patients with chronic pain and PTSS. Methods: A battery of instruments was administered to 388 chronic pain patients. The sample was divided into those with PTSS (n = 194) and those without PTSS (n =194). Results: Significant differences were found between groups in the BIS, EA, impairment and daily functioning. No differences were found between groups in the BAS. Structural equation modelling showed that the BIS and EA were associated with worse adjustment in the 194 patients with both chronic pain and PTSS. The BAS was associated with a lower level of pain and greater daily functioning. Conclusion: The findings provide evidence that BIS and BAS activation and EA play a role in adjustment to chronic pain in patients with concurrent PTSS. These results may help guide the development of psychological treatments for patients with both conditions.

Activation of mesolimbic reward system via laterodorsal tegmental nucleus and hypothalamus in exercise-induced hypoalgesia

Ventral tegmental area (VTA) dopamine (DA) neurons are the primary source of dopamine in target structures that constitute the mesolimbic reward system. Previous studies demonstrated that voluntary wheel running (VWR) by neuropathic pain (NPP) model mice produces exercise-induced hypoalgesia (EIH), and that activation of mesolimbic reward system may lead to EIH. However, the neuronal mechanism by which the mesolimbic reward system is activated by VWR is unknown. Here, we found that VWR produces EIH effects and reverses the marked reduction in activated lateral VTA (lVTA)-DA neurons induced by NPP. The proportions of activated laterodorsal tegmental nucleus (LDT)-cholinergic and lateral hypothalamus-orexin neurons were significantly enhanced by VWR. Retrograde tracing and dual immunostaining revealed that VWR activates lVTA-projecting LDT-cholinergic/non-cholinergic and lateral hypothalamic area (LHA)-orexin/non-orexin neurons. Therefore, EIH effects may be produced, at least in part, by activation of the mesolimbic reward system via activation of LDT and LHA neurons.

Emotion dysregulation as a transdiagnostic mechanism of opioid misuse and suicidality among chronic pain patients

BACKGROUND

Chronic pain is a prevalent condition that causes functional impairment and emotional suffering. To allay pain-induced suffering, opioids are often prescribed for chronic pain management. Yet, chronic pain patients on opioid therapy are at heightened risk for opioid misuse-behaviors that can lead to addiction and overdose. Relatedly, chronic pain patients are at elevated risk for suicidal ideation and suicidal behaviors.

MAIN BODY

Opioid misuse and suicidality are maladaptive processes aimed at alleviating the negative emotional hyperreactivity, hedonic hyporeactivity, and emotion dysregulation experienced by chronic pain patients on opioid therapy. In this review, we explore the role of emotion dysregulation in chronic pain. We then describe why emotionally dysregulated chronic pain patients are vulnerable to opioid misuse and suicidality in response to these negative affective states.

CONCLUSION

Emotion dysregulation is an important and malleable treatment target with the potential to reduce or prevent opioid misuse and suicidality among opioid-treated chronic pain patients.

Volume and shape of subcortical grey matter structures related to headache: A cross-sectional population-based imaging study in the Nord-Trøndelag Health Study

BACKGROUND

The relationship between subcortical nuclei and headache is unclear. Most previous studies were conducted in small clinical migraine samples. In the present population-based MRI study, we hypothesized that headache sufferers exhibit reduced volume and deformation of the nucleus accumbens compared to non-sufferers. In addition, volume and deformation of the amygdala, caudate, hippocampus, pallidum, putamen and thalamus were examined.

METHODS

In all, 1006 participants (50-66 years) from the third Nord-Trøndelag Health Survey, were randomly selected to undergo a brain MRI at 1.5 T. Volume and shape of the subcortical nuclei from T1 weighted 3D scans were obtained in FreeSurfer and FSL. The association with questionnaire-based headache categories (migraine and tension-type headache included) was evaluated using analysis of covariance. Individuals not suffering from headache were used as controls. Age, sex, intracranial volume and Hospital Anxiety and Depression Scale were used as covariates.

RESULTS

No effect of headache status on accumbens volume and shape was present. Exploratory analyses showed significant but small differences in volume of caudate and putamen and in putamen shape between those with non-migrainous headache and the controls. A post hoc analysis showed that caudate volume was strongly associated with white matter hyperintensities.

CONCLUSION

We did not confirm our hypothesis that headache sufferers have smaller volume and different shape of the accumbens compared to non-sufferers. No or only small differences in volume and shape of subcortical nuclei between headache sufferers and non-sufferers appear to exist in the general population.

Enhancing Natural Reward Responsiveness Among Opioid Users Predicts Chronic Pain Relief: EEG Analyses From a Trial of Mindfulness-Oriented Recovery Enhancement

OBJECTIVE

Although opioid-treated chronic pain patients evidence blunted responsiveness to natural rewards, focusing on naturally rewarding stimuli can produce analgesia in these patients. A prior randomized controlled trial (RCT) demonstrated that a social work intervention-Mindfulness-Oriented Recovery Enhancement (MORE)-enhanced natural reward processing as indicated by event-related brain potentials (ERPs). The aim of the present study was to perform a secondary data analysis on ERPs collected in this RCT to explore whether improvements in electrocortical response to natural reward predicted pain relief.

METHOD

The sample for this secondary analysis included opioid-treated chronic pain patients with complete ERP data (N = 29). Participants were randomized to 8 weeks of MORE or a support group control condition, and ERPs to images representing naturally rewarding stimuli were measured before and after 8 weeks of treatment. We explored associations between changes in brain reward response, chronic pain symptoms, and pain coping.

RESULTS

Increases in ERP reward response were significantly associated with decreased pain severity from pretreatment to posttreatment (β = -.48, p = .007) and improvements in pain catastrophizing (β = -.36, p = .05) and diverting attention as a means of pain coping (β = .38, p = .043). Increased ERP reward response predicted decreased pain interference by 3-month follow-up (β = -.37, p = .048).

CONCLUSIONS

Chronic pain may be alleviated by enhancing brain response to natural rewards.

Pain Therapy Guided by Purpose and Perspective in Light of the Opioid Epidemic

Prescription opioid misuse is an ongoing and escalating epidemic. Although these pharmacological agents are highly effective analgesics prescribed for different types of pain, opioids also induce euphoria, leading to increasing diversion and misuse. Opioid use and related mortalities have developed in spite of initial claims that OxyContin, one of the first opioids prescribed in the USA, was not addictive in the presence of pain. These claims allayed the fears of clinicians and contributed to an increase in the number of prescriptions, quantity of drugs manufactured, and the unforeseen diversion of these drugs for non-medical uses. Understanding the history of opioid drug development, the widespread marketing campaign for opioids, the immense financial incentive behind the treatment of pain, and vulnerable socioeconomic and physical demographics for opioid misuse give perspective on the current epidemic as an American-born problem that has expanded to global significance. In light of the current worldwide opioid epidemic, it is imperative that novel opioids are developed to treat pain without inducing the euphoria that fosters physical dependence and addiction. We describe insights from preclinical findings on the properties of opioid drugs that offer insights into improving abuse-deterrent formulations. One finding is that the ability of some agonists to activate one pathway over another, or agonist bias, can predict whether several novel opioid compounds bear promise in treating pain without causing reward among other off-target effects. In addition, we outline how the pharmacokinetic profile of each opioid contributes to their potential for misuse and discuss the emergence of mixed agonists as a promising pipeline of opioid-based analgesics. These insights from preclinical findings can be used to more effectively identify opioids that treat pain without causing physical dependence and subsequent opioid abuse.

Behavioral Inhibition and Activation Systems, and Emotional Regulation in Individuals With Chronic Musculoskeletal Pain

Gray's Reinforcement Sensitivity Theory postulates two distinct neurophysiological systems that underlie thoughts, emotions, and behavior: the Behavioral Inhibition System (BIS) and the Behavioral Approach System (BAS). Preliminary research suggests that both systems may play relevant roles in the adjustment of individuals with chronic pain. However, there is a lack of research on the extent to which emotional regulation (i.e., cognitive reappraisal and expressive suppression) mediates the associations between BIS and BAS activation and emotional responses in individuals with chronic pain. The aim of this study was to test a model of the associations between the BIS and BAS, cognitive reappraisal and expressive suppression, and positive and negative affect in individuals with chronic musculoskeletal pain. In total, 516 participants were interviewed. Structural Equation Modeling was used to estimate the associations between variables. The empirical model showed a good fit to the data (χ²/df = 1.95; RMSEA = 0.04; GFI = 0.99; AGFI = 0.98; CFI = 0.99). The hypothesized model received partial support. The BIS was associated with cognitive reappraisal and expressive suppression; cognitive reappraisal was associated with negative and positive affect; expressive suppression was positively associated with affect; and the BAS was not associated with the emotional regulation strategies assessed. However, the BIS and BAS were both directly associated with negative and positive affect. The results suggest that individuals with chronic pain with higher BIS activation appear to use greater expressive suppression. Cognitive reappraisal strongly mediated the BIS-negative affect association. The results also suggest that BAS activation may have a weak or inconsistent association with emotional regulation approaches in individuals with chronic pain. These data provide new and relevant information on the potential role of the BIS and BAS as predictors of psychological functioning in individuals with chronic pain. They suggest that the BIS-BAS model of chronic pain may need to be modified to take into account the potential negative effects of BAS activation. The findings suggest that treatments for emotional regulation could potentially reduce the negative impact of chronic pain via BIS.

Mindfulness is Associated With Increased Hedonic Capacity Among Chronic Pain Patients Receiving Extended Opioid Pharmacotherapy

OBJECTIVES

Chronic pain and long-term opioid use may lead to a persistent deficit in hedonic capacity, characterized by increased sensitivity to aversive states and insensitivity to natural rewards. Dispositional mindfulness has been linked with improved emotion regulation and pain coping. The aim of the current study was to examine associations between dispositional mindfulness, hedonic capacity, and pain-related interference in an opioid-using chronic pain sample.

METHODS

Data were obtained from a sample of 115 chronic pain patients on long-term opioid therapy (68% females, M age=48.3, SD=13.6) who completed the Five Facet Mindfulness Questionnaire (FFMQ), the Snaith-Hamilton Anhedonia and Pleasure Scale (SHAPS), the Brief Pain Inventory, and a psychiatric assessment of major depression. Bivariate correlations, hierarchical multiple regression, and path analysis were used to determine whether dispositional mindfulness scores (FFMQ) predicted variance in hedonic capacity (SHAPS), and whether hedonic capacity mediated the association between mindfulness and pain interference.

RESULTS

We observed a significant positive correlation between dispositional mindfulness and hedonic capacity scores (r=0.33, P<0.001). Hierarchical regression indicated that after controlling for pain interference and major depressive disorder diagnosis, dispositional mindfulness explained a significant portion of variance in hedonic capacity (β=0.30, P<0.01). The association between dispositional mindfulness and pain interference was mediated by hedonic capacity (b=-0.011, SE=0.005; 95% CI, -0.004 to -0.024, full model R=0.39).

DISCUSSION

Findings indicate that dispositional mindfulness was associated with hedonic capacity among this chronic pain sample. In light of this association, it is plausible that interventions that increase mindfulness may reduce pain-related impairment among opioid-using patients by enhancing hedonic capacity.

Hedonic and motivational responses to food reward are unchanged in rats with neuropathic pain

Rewards influence responses to acute painful stimuli, but the relationship of chronic pain to hedonic or motivational aspects of reward is not well understood. We independently evaluated hedonic qualities of sweet or bitter tastants and motivation to seek food reward in rats with experimental neuropathic pain induced by L5/6 spinal nerve ligation. Hedonic response was measured by implantation of intraoral catheters to allow passive delivery of liquid solutions, and "liking/disliking" responses were scored according to a facial reactivity scale. Spinal nerve ligation rats did not differ from controls in either "liking" or "disliking" reactions to intraoral sucrose or quinine, respectively, at postsurgery day 21, suggesting no differences in perceived hedonic value of sweet or bitter tastants. To assess possible motivational deficits during acute and chronic pain, we used fixed- and progressive-ratio response paradigms of sucrose pellet presentation in rats with transient inflammatory or chronic neuropathic pain. Assessment of response acquisition and break points under the progressive ratio schedule revealed no differences between sham and spinal nerve ligation rats for up to 120 days after injury. However, rats with inflammation showed decrements in lever pressing and break points on days 1 and 2 after complete Freund adjuvant injection that normalized by day 4, consistent with transient ongoing pain. Thus, although acute ongoing inflammatory pain may transiently reduce reward motivation, we did not detect influences of chronic neuropathic pain on hedonic or motivational responses to food rewards. Adaptations that allow normal reward responding to food regardless of chronic pain may be of evolutionary benefit to promote survival.

Towards a science and practice of resilience in the face of pain

The primary objective of this paper is to discuss how a resilience approach to (chronic) pain may advance our current understanding of (mal)adaptation to pain. Different resilience perspectives are described, and future challenges for research, prevention and treatment of (chronic) pain are discussed. Literature searches were performed in Web of Science and PubMed to identify relevant literature on risk and resilience in the context of pain. Resilience can be best defined as the ability to restore and sustain living a fulfilling life in the presence of pain. The Psychological Flexibility Model, the Broaden-and-Build Theory, and Self-Determination Theory are described as theories that may provide insight into resilience within the context of (chronic) pain. We describe how a resilience paradigm shifts the outcomes to pursue in pain research and intervention and argue the need for including positive outcomes in addition to negative outcomes. Psychological flexibility, positive affect and basic psychological needs satisfaction are described as potentially important resilience mechanisms with the potential to target both sustainability and recovery from pain. A resilience approach to chronic pain may have important implications for the prevention and treatment of chronic pain problems, as it may give specific indications on how to empower patients to continue living a fulfilling life (in the presence of pain).

SIGNIFICANCE

The resilience approach put forward in this review spotlights sustainability of positive outcomes (e.g. engagement in meaningful activities) in the presence of pain as an outcome to pursue beyond recovery of negative outcomes. We illuminate the evidence-base and practical application of promising resilience mechanisms (positive emotions, psychological flexibility, needs satisfaction). For this article, a commentary is available at the Wiley Online Library.

A Trigger for Opioid Misuse: Chronic Pain and Stress Dysregulate the Mesolimbic Pathway and Kappa Opioid System

Pain and stress are protective mechanisms essential in avoiding harmful or threatening stimuli and ensuring survival. Despite these beneficial roles, chronic exposure to either pain or stress can lead to maladaptive hormonal and neuronal modulations that can result in chronic pain and a wide spectrum of stress-related disorders including anxiety and depression. By inducing allostatic changes in the mesolimbic dopaminergic pathway, both chronic pain and stress disorders affect the rewarding values of both natural reinforcers, such as food or social interaction, and drugs of abuse. Despite opioids representing the best therapeutic strategy in pain conditions, they are often misused as a result of these allostatic changes induced by chronic pain and stress. The kappa opioid receptor (KOR) system is critically involved in these neuronal adaptations in part through its control of dopamine release in the nucleus accumbens. Therefore, it is likely that changes in the kappa opioid system following chronic exposure to pain and stress play a key role in increasing the misuse liability observed in pain patients treated with opioids. In this review, we will discuss how chronic pain and stress-induced pathologies can affect mesolimbic dopaminergic transmission, leading to increased abuse liability. We will also assess how the kappa opioid system may underlie these pathological changes.

[Chronic pain : Perception, reward and neural processing]

Many chronic pain syndromes are characterized by enhanced perception of painful stimuli as well as alterations in cortical processing in sensory and motor regions. In this review article the alterations in muscle pain and neuropathic pain are described. Alterations in patients with fibromyalgia and chronic back pain are described as examples for musculoskeletal pain and also in patients with phantom limb pain after amputation and complex regional pain syndrome as examples for neuropathic pain. In addition to altered pain perception, cumulative evidence on alterations in the processing of reward and the underlying mechanisms in chronic pain has been described. A description is given of what is known on how pain and reward interact and affect each other. The relevance of such interactions for chronic pain is discussed. The implications of these findings for therapeutic approaches are delineated with respect to sensorimotor training and behavioral therapy, focusing on the effectiveness of these approaches, mechanisms and future developments. In particular, we discuss operant behavioral therapy in patients with chronic back pain and fibromyalgia as well as prosthesis training in patients with phantom limb pain and discrimination, mirror and imaginary training in patients with phantom limb pain and complex regional pain syndrome. With respect to the processing of reward, the focus of the discussion is on the role of reward and associated learning in pain therapy.

The Neurobiology Shaping Affective Touch: Expectation, Motivation, and Meaning in the Multisensory Context

Inter-individual touch can be a desirable reward that can both relieve negative affect and evoke strong feelings of pleasure. However, if other sensory cues indicate it is undesirable to interact with the toucher, the affective experience of the same touch may be flipped to disgust. While a broad literature has addressed, on one hand the neurophysiological basis of ascending touch pathways, and on the other hand the central neurochemistry involved in touch behaviors, investigations of how external context and internal state shapes the hedonic value of touch have only recently emerged. Here, we review the psychological and neurobiological mechanisms responsible for the integration of tactile “bottom–up” stimuli and “top–down” information into affective touch experiences. We highlight the reciprocal influences between gentle touch and contextual information, and consider how, and at which levels of neural processing, top-down influences may modulate ascending touch signals. Finally, we discuss the central neurochemistry, specifically the μ-opioids and oxytocin systems, involved in affective touch processing, and how the functions of these neurotransmitters largely depend on the context and motivational state of the individual.

Anxiety and Depression in Bidirectional Relations Between Pain and Smoking: Implications for Smoking Cessation

Pain and tobacco smoking are highly prevalent and comorbid conditions that impose considerable burdens on individuals and health care systems. A recently proposed reciprocal model suggests that these conditions interact in a bidirectional manner, resulting in greater pain and the maintenance of tobacco addiction. Anxiety and depression are common among smokers in pain and have been identified as central mechanisms of interest. There is emerging evidence that smokers with anxiety/depression may experience more severe pain and functional impairment, greater pain-induced motivation to smoke, and increased sensitivity to pain during periods of smoking abstinence. Based on empirical findings, we hypothesize that these experiences may engender expectations that abstaining from smoking will exacerbate both pain and negative affect, thus eroding self-efficacy for smoking cessation and increasing perceived barriers to quitting. The goal of this narrative review is to examine the role of anxiety/depression in complex pain-smoking relations so as to advance evolving theoretical perspectives and inform the development of tailored interventions.