Risky monetary behavior in chronic back pain is associated with altered modular connectivity of the nucleus accumbens

Vulnerability Factors, Adjustment, and Opioid Misuse in Chronic Noncancer Pain Individuals

Several person variables predate injury or pain onset that increase the probability of maladjustment to pain and opioid misuse. The aim of this study was to evaluate the role of 2 diathesis variables (impulsiveness and anxiety sensitivity [AS]) in the adjustment of individuals with chronic noncancer pain and opioid misuse. The sample comprised 187 individuals with chronic noncancer pain. The hypothetical model was tested using correlation and structural equation modeling analyses. The results show a significant association between impulsiveness and AS and all the maladjustment variables, and between impulsiveness and AS and opioid misuse and craving. However, although the correlation analysis showed a significant association between adjustment to pain and opioid misuse, the structural equation modeling analysis showed a nonsignificant association between them (as latent variables). The findings support the hypothesis that both impulsiveness and AS are vulnerability factors for maladaptive adjustment to chronic pain and opioid misuse. PERSPECTIVE: This article adds to the empirical literature by including AS and impulsiveness as antecedent variables in a model of dual vulnerability to chronic pain maladjustment and opioid misuse. The findings suggest the potential utility of assessing both factors in individuals in the first stages of chronic pain.

Enhanced motor network engagement during reward gain anticipation in fibromyalgia

Reward motivation is essential in shaping human behavior and cognition. Both reward motivation and reward brain circuits are altered in chronic pain conditions, including fibromyalgia. In this study of fibromyalgia patients, we used a data-driven independent component analysis (ICA) approach to investigate how brain networks contribute to altered reward processing. From females with fibromyalgia (N = 24) and female healthy controls (N = 24), we acquired fMRI data while participants performed a monetary incentive delay (MID) reward task. After analyzing the task-based fMRI data using ICA to identify networks, we analyzed 3 networks of interest: motor network (left), value-driven attention network, and basal ganglia network. Then, we evaluated correlation coefficients between each network timecourse versus a task-based timecourse which modeled gain anticipation. Compared to controls, the fibromyalgia cohort demonstrated significantly stronger correlation between the left motor network timecourse and the gain anticipation timecourse, indicating the left motor network was more engaged with gain anticipation in fibromyalgia. In an exploratory analysis, we compared motor network engagement during early versus late phases of gain anticipation. Across cohorts, greater motor network engagement (i.e., stronger correlation between network and gain anticipation) occurred during the late timepoint, which reflected enhanced motor preparation immediately prior to response. Consistent with the main results, patients exhibited greater engagement of the motor network during both early and late phases compared with healthy controls. Visual-attention and basal ganglia networks revealed similar engagement in the task across groups. As indicated by post-hoc analyses, motor network engagement was positively related to anxiety and negatively related to reward responsiveness. In summary, we identified enhanced reward-task related engagement of the motor network in fibromyalgia using a novel data-driven ICA approach. Enhanced motor network engagement in fibromyalgia may relate to impaired reward motivation, heightened anxiety, and possibly to altered motor processing, such as restricted movement or dysregulated motor planning.

Functional Stimulation and Imaging to Predict Neuromodulation of Chronic Low Back Pain

Back pain is one of the most common aversive sensations in human experience. Pain is not limited to the sensory transduction of tissue damage; rather, it encompasses a range of nervous system activities including lateral modulation, long-distance transmission, encoding, and decoding. Although spine surgery may address peripheral pain generators directly, aberrant signals along canonical aversive pathways and maladaptive influence of affective and cognitive states can result in persistent subjective pain refractory to classical surgical intervention. The clinical identification of who will benefit from surgery-and who will not-is increasingly grounded in neurophysiology.

Intranasal Oxytocin and Pain Reduction: Testing a Social Cognitive Mediation Model

Oxytocin is well known for its role in relationships and social cognition and has more recently been implicated in pain relief and pain perception. Connections between prosocial feelings and pain relief are also well documented; however, the effects of exogenous oxytocin on social cognition and pain have not been explored. The current study tested whether intranasally delivered oxytocin affects pain perception through prosocial behaviors. Additionally, moderation of the effects of oxytocin by life history or genetic polymorphisms is examined. Young adults (n = 43; 65% female) were administered intranasal oxytocin (24 IU) or placebo in a crossover design on two visits separated by a one-week washout period. Pain was delivered via cold pressor. Baseline measures for decision-making and social cognition were collected, as well as pain sensitivity and medication history. Saliva samples were collected for analysis of genetic markers, and urine samples were collected to assess oxytocin saturation. Following oxytocin administration, participants reported increased prosocial cognition and decision-making. Pain perception appeared to be adaptive, with procedural order and expectation affecting perception. Finally, behavioral trust and cooperation responses were significantly predicted by genetic markers. Oxytocin may increase a patient's trust and cooperation and reduce pain sensitivity while having fewer physiological side effects than current pharmaceutical options.

Pain catastrophizing is associated with reduced neural response to monetary reward

Introduction

Pain catastrophizing, a measure of an individual's negative emotional and cognitive appraisals of pain, has been included as a key treatment target in many psychological interventions for pain. However, the neural correlates of pain catastrophizing have been understudied. Prior neuroimaging evidence suggests that adults with pain show altered reward processing throughout the mesocorticolimbic reward circuitry.

Methods

In this study, we tested the association between Pain Catastrophizing Scale (PCS) scores and neural activation to the Monetary Incentive Delay (MID) reward neuroimaging task in 94 adults reporting a range of pain, insomnia, and mood symptoms.

Results

Results indicated that PCS score but not pain intensity was significantly associated with blunted activation in the caudate and putamen in response to feedback of successful vs. unsuccessful trials on the MID task. Mediation analyses indicated that PCS score fully mediated the relationship between depression symptoms and reward activation.

Discussion

These findings provide evidence that pain catastrophizing is independently associated with altered striatal function apart from depression symptoms and pain intensity. Thus, in individuals experiencing pain and/or co- morbid conditions, reward dysfunction is directly related to pain catastrophizing.

Pain Management in the Most Vulnerable Intellectual Disability: A Review

This review is made up of two parts; the first part discussing intellectual disability (ID) in general, while the second part covers the pain associated with intellectual disability and the challenges and practical tips for the management of pain associated with (ID). Intellectual disability is characterized by deficits in general mental abilities, such as reasoning, problem solving, planning, abstract thinking, judgment, academic learning, and learning from experience. ID is a disorder with no definite cause but has multiple risk factors, including genetic, medical, and acquired. Vulnerable populations such as individuals with intellectual disability may experience more pain than the general population due to additional comorbidities and secondary conditions, or at least the same frequency of pain as in the general population. Pain in patients with ID remains largely unrecognized and untreated due to barriers to verbal and non-verbal communication. It is important to identify patients at risk to promptly prevent or minimize those risk factors. As pain is multifactorial, thus, a multimodal approach using both pharmacotherapy and non-pharmacological management is often the most beneficial. Parents and caregivers should be oriented to this disorder, given adequate training and education, and be actively involved with the treatment program. Significant work to create new pain assessment tools to improve pain practices for individuals with ID has taken place, including neuroimaging and electrophysiological studies. Recent advances in technology-based interventions such as virtual reality and artificial intelligence are rapidly growing to help give patients with ID promising results to develop pain coping skills with effective reduction of pain and anxiety. Therefore, this narrative review highlights the different aspects regarding the current status of the pain associated with intellectual disability, with more emphasis on the recent pieces of evidence for the assessment and management of pain among populations with intellectual disability.

The Biology of Placebo and Nocebo Effects on Experimental and Chronic Pain: State of the Art

(1) Background: In recent years, placebo and nocebo effects have been extensively documented in different medical conditions, including pain. The scientific literature has provided strong evidence of how the psychosocial context accompanying the treatment administration can influence the therapeutic outcome positively (placebo effects) or negatively (nocebo effects). (2) Methods: This state-of-the-art paper aims to provide an updated overview of placebo and nocebo effects on pain. (3) Results: The most common study designs, the psychological mechanisms, and neurobiological/genetic determinants of these phenomena are discussed, focusing on the differences between positive and negative context effects on pain in experimental settings on healthy volunteers and in clinical settings on chronic pain patients. Finally, the last section describes the implications for clinical and research practice to maximize the medical and scientific routine and correctly interpret the results of research studies on placebo and nocebo effects. (4) Conclusions: While studies on healthy participants seem consistent and provide a clear picture of how the brain reacts to the context, there are no unique results of the occurrence and magnitude of placebo and nocebo effects in chronic pain patients, mainly due to the heterogeneity of pain. This opens up the need for future studies on the topic.

Altered Functional Networks during Gain Anticipation in Fibromyalgia

Reward motivation is essential in shaping human behavior and cognition. Previous studies have shown altered reward motivation and reward brain circuitry in chronic pain conditions, including fibromyalgia. Fibromyalgia is a chronic disorder characterized by widespread musculoskeletal pain, fatigue, cognitive problems, and mood-related symptoms. In this study, we analyzed brain reward networks in patients with fibromyalgia by using a data-driven approach with task-based fMRI data. fMRI data from 24 patients with fibromyalgia and 24 healthy controls were acquired while subjects performed a monetary incentive delay (MID) reward task. Functional networks were derived using independent component analysis (ICA) focused on the gain anticipation phase of the reward task. Functional activity in the motor, value-driven attention, and basal ganglia networks was evaluated during gain anticipation in both patient and healthy control groups. Compared to controls, the motor network was more engaged during gain anticipation in patients with fibromyalgia. Our findings suggest that reward motivation may lead to hyperactivity in the motor network, possibly related to altered motor processing, such as restricted movement or dysregulated motor planning in fibromyalgia. As an exploratory analysis, we compared levels of motor network engagement during early and late timepoints of the gain anticipation phase. Both groups showed greater motor network engagement during the late timepoint (i.e., closer to response), which reflected motor preparation prior to target response. Importantly, compared to controls and consistent with the initial findings described above, patients exhibited greater engagement of the motor network during both early and late timepoints. In summary, by using a novel data-driven ICA approach to analyze task-based fMRI data, we identified elevated motor network engagement during gain anticipation in fibromyalgia.

Meditation Practice, Mindfulness, and Pain-Related Outcomes in Mindfulness-Based Treatment for Episodic Migraine

Objectives

Mindfulness-based interventions (MBIs) have emerged as promising prophylactic episodic migraine treatments. The present study investigated biopsychosocial predictors and outcomes associated with formal, daily-life meditation practice in migraine patients undergoing MBI, and whether augmented mindfulness mechanistically underlies change.

Methods

Secondary analyses of clinical trial data comparing a 12-week enhanced mindfulness-based stress reduction course (MBSR + ; n = 50) to stress management for headache (SMH; n = 48) were conducted.

Results

Pre-treatment mesocorticolimbic system functioning (i.e., greater resting state ventromedial prefrontal cortex-right nucleus accumbens [vmPFC-rNAC] functional connectivity) predicted greater meditation practice duration over MBSR + (r = 0.58, p = 0.001), as well as the change in headache frequency from pre- to post-treatment (B = -12.60, p = 0.02) such that MBSR + participants with greater vmPFC-rNAC connectivity showed greater reductions in headache frequency. MBSR + participants who meditated more showed greater increases in mindfulness (B = 0.52, p = 0.02) and reductions in the helplessness facet of pain catastrophizing (B = -0.13, p = 0.01), but not headache frequency, severity, or impact. Augmented mindfulness mediated reductions in headache impact resulting from MBSR + , but not headache frequency.

Conclusions

Mesocorticolimbic system function is implicated in motivated behavior, and thus, motivation-enhancing interventions might be delivered alongside mindfulness-based training to enhance meditation practice engagement. Formal, daily-life meditation practice duration appears to benefit pain-related cognitions, but not clinical pain, while mindfulness emerges as a mechanism of MBIs on headache impact, but not frequency. Further research is needed to investigate the day-to-day effects of formal, daily-life meditation practice on pain, and continue to characterize the specific mechanisms of MBIs on headache outcomes.

Preregistration

This study is not preregistered.

Replication of neural responses to monetary incentives and exploration of reward-influenced network connectivity in fibromyalgia

Neuroimaging research has begun to implicate alterations of brain reward systems in chronic pain. Previously, using functional magnetic resonance imaging (fMRI) and a monetary incentive delay (MID) task, Martucci et al. (2018) showed that neural responses to reward anticipation and outcome are altered in fibromyalgia. In the present study, we aimed to test the replicability of these altered neural responses to reward in a separate fibromyalgia cohort. In addition, the present study was conducted at a distinct U.S. location but involved a similar study design. For the present study, 20 patients with fibromyalgia and 20 healthy controls participated in MID task fMRI scan procedures and completed clinical/psychological questionnaires. fMRI analyses comparing patient and control groups revealed a consistent trend of main results which were largely similar to the prior reported results. Specifically, in the replication fibromyalgia cohort, medial prefrontal cortex (MPFC) response was reduced during gain anticipation and was increased during no-loss (non-punishment) outcome compared to controls. Also consistent with previous findings, the nucleus accumbens response to gain anticipation did not differ in patients vs. controls. Further, results from similarly-designed behavioral, correlational, and exploratory analyses were complementary to previous findings. Finally, a novel network-based functional connectivity analysis of the MID task fMRI data across patients vs. controls implied enhanced connectivity within the default mode network in participants with fibromyalgia. Together, based on replicating prior univariate results and new network-based functional connectivity analyses of MID task fMRI data, we provide further evidence of altered brain reward responses, particularly in the MPFC response to reward outcomes, in patients with fibromyalgia.

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.

Decision Making and Fibromyalgia: A Systematic Review

Decision making (DM) is the ability to choose among multiple options, considering external and internal variables and identifying potential paths of action that need to be assessed. Some brain areas involved in decision making are also implicated in pain processing, such as in fibromyalgia (FM). FM is a syndrome characterized by chronic widespread musculoskeletal pain and cognitive difficulties. We conducted a systematic review with the aim of identifying articles that evaluated DM in people with fibromyalgia, highlighting the main assessment tools. This work was conducted according to the PRISMA statement by consulting six online databases and providing a quality assessment of each search that met the inclusion criteria. In line with the limited interest in this in the scientific landscape to date, we found nine studies that evaluated the performance of DM in patients with FM; furthermore, we discovered that only certain types of DM were tested. The importance of our work lies in shedding light on a cognitive ability that is often undervalued in the scientific landscape but essential in everyday life. This review can serve as a starting point for further studies to clarify the relationship between DM and FM, improving understanding of the topic.

Endogenous opioid systems alterations in pain and opioid use disorder

Decades of research advances have established a central role for endogenous opioid systems in regulating reward processing, mood, motivation, learning and memory, gastrointestinal function, and pain relief. Endogenous opioid systems are present ubiquitously throughout the central and peripheral nervous system. They are composed of four families, namely the μ (MOPR), κ (KOPR), δ (DOPR), and nociceptin/orphanin FQ (NOPR) opioid receptors systems. These receptors signal through the action of their endogenous opioid peptides β-endorphins, dynorphins, enkephalins, and nociceptins, respectfully, to maintain homeostasis under normal physiological states. Due to their prominent role in pain regulation, exogenous opioids-primarily targeting the MOPR, have been historically used in medicine as analgesics, but their ability to produce euphoric effects also present high risks for abuse. The ability of pain and opioid use to perturb endogenous opioid system function, particularly within the central nervous system, may increase the likelihood of developing opioid use disorder (OUD). Today, the opioid crisis represents a major social, economic, and public health concern. In this review, we summarize the current state of the literature on the function, expression, pharmacology, and regulation of endogenous opioid systems in pain. Additionally, we discuss the adaptations in the endogenous opioid systems upon use of exogenous opioids which contribute to the development of OUD. Finally, we describe the intricate relationship between pain, endogenous opioid systems, and the proclivity for opioid misuse, as well as potential advances in generating safer and more efficient pain therapies.

Altered resting-state functional connectivity within corticostriatal and subcortical-striatal circuits in chronic pain

Brain corticostriatal circuits are important for understanding chronic pain and highly relevant to motivation and cognitive processes. It has been demonstrated that in patients with chronic back pain, altered nucleus accumbens (NAcc)-medial prefrontal cortex (MPFC) circuit fMRI-based activity is predictive of patient outcome. We evaluated the NAcc-MPFC circuit in patients with another chronic pain condition, fibromyalgia, to extend these important findings. First, we compared fMRI-based NAcc-MPFC resting-state functional connectivity in patients with fibromyalgia (N = 32) vs. healthy controls (N = 37). Compared to controls, the NAcc-MPFC circuit's connectivity was significantly reduced in fibromyalgia. In addition, within the fibromyalgia group, NAcc-MPFC connectivity was significantly correlated with trait anxiety. Our expanded connectivity analysis of the NAcc to subcortical brain regions showed reduced connectivity of the right NAcc with mesolimbic circuit regions (putamen, thalamus, and ventral pallidum) in fibromyalgia. Lastly, in an exploratory analysis comparing our fibromyalgia and healthy control cohorts to a separate publicly available dataset from patients with chronic back pain, we identified reduced NAcc-MPFC connectivity across both the patient groups with unique alterations in NAcc-mesolimbic connectivity. Together, expanding upon prior observed alterations in brain corticostriatal circuits, our results provide novel evidence of altered corticostriatal and mesolimbic circuits in chronic pain.

Assessing Pain Research: A Narrative Review of Emerging Pain Methods, Their Technosocial Implications, and Opportunities for Multidisciplinary Approaches

Pain research traverses many disciplines and methodologies. Yet, despite our understanding and field-wide acceptance of the multifactorial essence of pain as a sensory perception, emotional experience, and biopsychosocial condition, pain scientists and practitioners often remain siloed within their domain expertise and associated techniques. The context in which the field finds itself today-with increasing reliance on digital technologies, an on-going pandemic, and continued disparities in pain care-requires new collaborations and different approaches to measuring pain. Here, we review the state-of-the-art in human pain research, summarizing emerging practices and cutting-edge techniques across multiple methods and technologies. For each, we outline foreseeable technosocial considerations, reflecting on implications for standards of care, pain management, research, and societal impact. Through overviewing alternative data sources and varied ways of measuring pain and by reflecting on the concerns, limitations, and challenges facing the field, we hope to create critical dialogues, inspire more collaborations, and foster new ideas for future pain research methods.

Delay and Effort-Based Discounting, and the Role of Bodily Awareness, In People Experiencing Long-Term Pain: A Cross-Sectional Study

Pain interventions typically include effortful exercise and long-term treatment - ie, short-term costs (effort) with delayed benefit (improved pain and/or function). Thus, understanding if long-term pain influences decision-making in context of delays and effort is essential given clear relevance to treatment uptake and/or adherence. We evaluated delay and effort attitudes in those experiencing chronic pain (n = 391) and in pain-free controls (n = 263). Additionally, we investigated the role of bodily sensation awareness and/or interpretation as potential contributing factors to altered decision-making. Volunteers completed three discounting questionnaires, assessing the influence of temporal delays (gains, losses) and effort on devaluation of monetary outcomes. Individuals with chronic pain had more short-sighted decisions for monetary gains, but not losses, and decreased willingness to undertake effort for monetary gains than the No Pain group. The Pain group had higher bodily sensation awareness and while this related to higher impulsivity, delay and effort discounting, neither awareness nor interpretation of bodily sensations interacted with pain levels or explained group differences in discounting behavior. These findings suggest that impaired delay and effort-based discounting is present in people with chronic pain, and that this may be driven by pain-induced changes, but not pain-induced enhancements in bodily sensation awareness and/or interpretation. Exploring the utility of interventions targeting discounting behavior is warranted. Data availability: Study materials are available here: https://osf.io/zexm7/?view_only=c9848597361c41808c612874da6f33b7. PERSPECTIVE: People with chronic pain make more short-sighted decisions (prefer less reward sooner) and decreased willingness to undertake effort (prefer less reward with little effort) for monetary gains than people without pain. Interventions targeting discounting behavior may help improve both uptake and adherence for evidence-based, effortful treatments, such as exercise.

Supraspinal nociceptive networks in neuropathic pain after spinal cord injury

Neuropathic pain following spinal cord injury involves plastic changes along the whole neuroaxis. Current neuroimaging studies have identified grey matter volume (GMV) and resting-state functional connectivity changes of pain processing regions related to neuropathic pain intensity in spinal cord injury subjects. However, the relationship between the underlying neural processes and pain extent, a complementary characteristic of neuropathic pain, is unknown. We therefore aimed to reveal the neural markers of widespread neuropathic pain in spinal cord injury subjects and hypothesized that those with greater pain extent will show higher GMV and stronger connectivity within pain related regions. Thus, 29 chronic paraplegic subjects and 25 healthy controls underwent clinical and electrophysiological examinations combined with neuroimaging. Paraplegics were demarcated based on neuropathic pain and were thoroughly matched demographically. Our findings indicate that (a) spinal cord injury subjects with neuropathic pain display stronger connectivity between prefrontal cortices and regions involved with sensory integration and multimodal processing, (b) greater neuropathic pain extent, is associated with stronger connectivity between the posterior insular cortex and thalamic sub-regions which partake in the lateral pain system and (c) greater intensity of neuropathic pain is related to stronger connectivity of regions involved with multimodal integration and the affective-motivational component of pain. Overall, this study provides neuroimaging evidence that the pain phenotype of spinal cord injury subjects is related to the underlying function of their resting brain.

Reward processing as a common diathesis for chronic pain and depression

Pain disorders and psychiatric illness are strongly comorbid, particularly in the context of Major Depressive Disorder (MDD). While these disorders account for a significant amount of global disability, the mechanisms of their overlap remain unclear. Understanding these mechanisms is of vital importance to developing prevention strategies and interventions that target both disorders. Of note, brain reward processing may be relevant to explaining how the comorbidity arises, given pain disorders and MDD can result in maladaptive reward responsivity that limits reward learning, appetitive approach behaviours and consummatory response. In this review, we discuss this research and explore the possibility of reward processing deficits as a common diathesis to explain the manifestation of pain disorders and MDD. Specifically, we hypothesize that contextual physical or psychological events (e.g. surgery, divorce) in the presence of a reward impairment diathesis worsens symptoms and results in a negative feedback loop that increases the chronicity and probability of developing the other disorder. We also highlight the implications for treatment and provide a framework for future research.

Deep Brain Stimulation of the Subgenual Cingulate Cortex for the Treatment of Chronic Low Back Pain

OBJECTIVES

Despite converging basic scientific and clinical evidence of the link between chronic pain and depression, existing therapies do not often take advantage of this overlap. Here, we provide a critical review of the literature that highlights the intersection in brain networks between chronic low back pain (CLBP) and depression and discuss findings from previous deep brain stimulation (DBS) studies for pain. Based on a multidimensional model of pain processing and the connectivity of the subgenual cingulate cortex (SCC) with areas that are implicated in both CLBP and depression, we propose a novel approach to the treatment of CLBP using DBS of the SCC.

MATERIALS AND METHODS

A narrative review with literature assessment.

RESULTS

CLBP is associated with a shift away from somatosensory representation toward brain regions that mediate emotional processes. There is a high degree of overlap between these regions and those involved in depression, including the anterior cingulate cortex, medial prefrontal cortex, nucleus accumbens, and amygdala. Whereas targets sites from previous DBS trials for pain were not anatomically positioned to engage these areas and their associated networks, the SCC is structurally connected to all of these regions and as well as others involved in mediating sensory, cognitive, and affective processing in CLBP.

CONCLUSIONS

CLBP and depression share a common underlying brain network interconnected by the SCC. Current data and novel technology provide an optimal opportunity to develop clinically effective trials of SCC DBS for CLBP.

Striatal hypofunction as a neural correlate of mood alterations in chronic pain patients

BACKGROUND

Chronic pain and mood disorders share common neuroanatomical substrates involving disruption of the reward system. Although increase in negative affect (NA) and decrease in positive affect (PA) are well-known factors complicating the clinical presentation of chronic pain patients, our understanding of the mechanisms underlying the interaction between pain and PA/NA remains limited. Here, we used a validated task probing behavioral and neural responses to monetary rewards and losses in conjunction with functional magnetic resonance imaging (fMRI) to test the hypothesis that dysfunction of the striatum, a key mesolimbic structure involved in the encoding of motivational salience, relates to mood alterations comorbid with chronic pain.

METHODS

Twenty-eight chronic musculoskeletal pain patients (chronic low back pain, n=15; fibromyalgia, n=13) and 18 healthy controls underwent fMRI while performing the Monetary Incentive Delay (MID) task. Behavioral and neural responses were compared across groups and correlated against measures of depression (Beck Depression Inventory) and hedonic capacity (Snaith-Hamilton Pleasure Scale).

RESULTS

Compared to controls, patients demonstrated higher anhedonia and depression scores, and a dampening of striatal activation and incentive-related behavioral facilitation (reduction in reaction times) during reward and loss trials of the MID task (ps ​< ​0.05). In all participants, lower activation of the right striatum during reward trials was correlated with lower incentive-related behavioral facilitation and higher anhedonia scores (ps ​< ​0.05). Finally, among patients, lower bilateral striatal activation during loss trials was correlated with higher depression scores (ps ​< ​0.05).

CONCLUSIONS

In chronic pain, PA reduction and NA increase are accompanied by striatal hypofunction as measured by the MID task.

High trait impulsivity potentiates the effects of chronic pain on impulsive behavior

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We explored a potential relation between trait and chronic pain-induced impulsivity.

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Low trait impulsivity rats with neuropathic pain perform similarly to controls.

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High trait impulsivity rats are delay intolerant in chronic pain conditions.

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Trait characteristics influence chronic pain comorbid manifestations.

Preclinical studies on impulsive decision-making in chronic pain conditions are sparse and often contradictory. Outbred rat populations are heterogeneous regarding trait impulsivity manifestations and therefore we hypothesized that chronic pain-related alterations depend on individual traits. To test this hypothesis, we used male Wistar-Han rats in two independent experiments. Firstly, we tested the impact of spared nerve injury (SNI) in impulsive behavior evaluated by the variable delay-to-signal test (VDS). In the second experiment, SNI impact on impulsivity was again tested, but in groups previously categorized as high (HI) and low (LI) trait impulsivity in the VDS.

Results showed that in an heterogenous population SNI-related impact on motor impulsivity and delay intolerance cannot be detected. However, when baseline impulsivity was considered, HI showed a significantly higher delay intolerance than the respective controls more prevalent in left-lesioned animals and appearing to result from a response correction on prematurity from VDS I to VDS II, which was present in Sham and right-lesioned animals.

In conclusion, baseline differences should be more often considered when analyzing chronic pain impact. While this study pertained to impulsive behavior, other reports indicate that this can be generalized to other behavioral dimensions and that trait differences can influence not only the manifestation of comorbid behaviors but also pain itself in a complex and not totally understood manner.

Evaluating Cortical Alterations in Patients With Chronic Back Pain Using Neuroimaging Techniques: Recent Advances and Perspectives

Chronic back pain (CBP) is a leading cause of disability and results in considerable socio-economic burdens worldwide. Although CBP patients are commonly diagnosed and treated with a focus on the “end organ dysfunction” (i.e., peripheral nerve injuries or diseases), the evaluation of CBP remains flawed and problematic with great challenges. Given that the peripheral nerve injuries or diseases are insufficient to define the etiology of CBP in some cases, the evaluation of alterations in the central nervous system becomes particularly necessary and important. With the development of advanced neuroimaging techniques, extensive studies have been carried out to identify the cortical abnormalities in CBP patients. Here, we provide a comprehensive overview on a series of novel findings from these neuroimaging studies to improve our understanding of the cortical abnormalities originated in the disease. First, CBP patients normally exhibit central sensitization to external painful stimuli, which is indexed by increased pain sensitivity and brain activations in pain-related brain regions. Second, long-term suffering from chronic pain leads to emotional disorders, cognitive impairments, and the abnormalities of the relevant brain networks among CBP patients. Third, CBP is associated with massive cortical reorganization, including structural, functional, and metabolic brain changes. Overall, a deep insight into the neural mechanisms underlying the development and outcome of CBP through more sophisticated neuroimaging investigations could not only improve our current understanding of the etiology of CBP but also facilitate the diagnosis and treatment of CBP based on precision medicine.

Neuroimaging of Pain: Human Evidence and Clinical Relevance of Central Nervous System Processes and Modulation

Neuroimaging research has demonstrated definitive involvement of the central nervous system in the development, maintenance, and experience of chronic pain. Structural and functional neuroimaging has helped elucidate central nervous system contributors to chronic pain in humans. Neuroimaging of pain has provided a tool for increasing our understanding of how pharmacologic and psychologic therapies improve chronic pain. To date, findings from neuroimaging pain research have benefitted clinical practice by providing clinicians with an educational framework to discuss the biopsychosocial nature of pain with patients. Future advances in neuroimaging-based therapeutics (e.g., transcranial magnetic stimulation, real-time functional magnetic resonance imaging neurofeedback) may provide additional benefits for clinical practice. In the future, with standardization and validation, brain imaging could provide objective biomarkers of chronic pain, and guide treatment for personalized pain management. Similarly, brain-based biomarkers may provide an additional predictor of perioperative prognoses.

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.

Effects of stress on the corticolimbic system: implications for chronic pain

Stress has multifaceted effects on pain. On the one hand, it is a powerful inhibitor of nociception and inflammation; on the other hand, it contributes to enhanced pathological states including the establishment and continuation of chronic pain. These seemingly paradoxical effects can be better understood by investigating how stress-induced plasticity in particular brain circuitry contributes to the chronic pain state. This review presents the rationale and evidence for the interactions between stress and pain, emphasizing underlying mechanisms and putting forth the hypothesis that stress partly mediates the deleterious effects of pain on the corticolimbic system. First, a general description of the corticolimbic circuitry predisposing and amplifying chronic pain will be discussed, followed by an overview of the neurotoxic effects of stress hormones on this circuitry. Recent studies show that the resulting perturbations to these brain circuits have significant consequences both for chronic pain and for general regulation of the stress response, primarily through feedback mechanisms controlling the hypothalamic-pituitary-adrenal axis. This overlap in effected circuitry provides a key point of comparison between stress and pain, and the similarities between the plasticity induced by chronic pain and chronic stress will be examined here. Chronic pain patients have been shown to exhibit maladaptive stress responses in general and in response to pain; the cause of this response and its consequence on pain severity will then be reviewed. Finally, factors that have been shown to lead to resilience or vulnerability for chronic pain and maladaptive stress responses will be summarized.

Corticolimbic circuitry in the modulation of chronic pain and substance abuse

The transition from acute to chronic pain is accompanied by increased engagement of emotional and motivational circuits. Adaptations within this corticolimbic circuitry contribute to the cellular and behavioral maladaptations associated with chronic pain. Central regions within the corticolimbic brain include the mesolimbic dopamine system, the amygdala, and the medial prefrontal cortex. The evidence reviewed herein supports the notion that chronic pain induces significant changes within these corticolimbic regions that contribute to the chronicity and intractability of pain. In addition, pain-induced changes in corticolimbic circuitry are poised to impact motivated behavior and reward responsiveness to environmental stimuli, and may modulate the addiction liability of drugs of abuse, such as opioids.

Does Pain Affect Preference? The Effect of Tonic Laboratory Pain on Discounting of Delayed Rewards

Chronic pain patients show elevated risk behavior on decision-making tasks, as well as increased health risk behaviors (eg, smoking, prescription opioid abuse). Determining pain's effect on underlying cognitive processes that are associated with risk behavior is confounded by comorbidities linked with chronic pain, including depression, anxiety, and substance abuse. Therefore, to understand pain's effect on delay discounting, a behavioral process assessing the extent to which outcomes are devalued as a function of their delay, the present study evaluated the effect of laboratory pain on delay discounting in healthy young adults (N = 85). Using a mixed factorial design, pain (topical capsaicin and warmth) as well as active control (warmth) groups completed a delay discounting task before and during exposure to their respective manipulations. Whereas the pain condition had no effect on delay discounting, participants' pain intensity, unpleasantness, and pain-induced negative valence were associated with less discounting of delayed rewards. However, the effects were very small.

PERSPECTIVE

The results suggest that experimental pain may not increase delay discounting, rather sensitivity to pain predicts a very small decrease in discounting of delayed rewards. Although the results are limited to healthy volunteers, this experimental approach allows us to examine the relationship between pain and delay discounting in a controlled manner. Better understanding of pain-related decision-making may lead to improved treatment of health risk behaviors for individuals experiencing pain.

Hippocampal morphology mediates biased memories of chronic pain

Experiences and memories are often mismatched. While multiple studies have investigated psychological underpinnings of recall error with respect to emotional events, the neurobiological mechanisms underlying the divergence between experiences and memories remain relatively unexplored in the domain of chronic pain. Here we examined the discrepancy between experienced chronic low back pain (CBP) intensity (twice daily ratings) and remembered pain intensity (n = 48 subjects) relative to psychometric properties, hippocampus morphology, memory capabilities, and personality traits related to reward. 77% of CBP patients exaggerated remembered pain, which depended on their strongest experienced pain and their most recent mood rating. This bias persisted over nearly 1 year and was related to reward memory bias and loss aversion. Shape displacement of a specific region in the left posterior hippocampus mediated personality effects on pain memory bias, predicted pain memory bias in a validation CBP group (n = 21), and accounted for 55% of the variance of pain memory bias. In two independent groups (n = 20/group), morphology of this region was stable over time and unperturbed by the development of chronic pain. These results imply that a localized hippocampal circuit, and personality traits associated with reward processing, largely determine exaggeration of daily pain experiences in chronic pain patients.

Chronic Pain and Chronic Stress: Two Sides of the Same Coin?

Pain and stress share significant conceptual and physiological overlaps. Both phenomena challenge the body's homeostasis and necessitate decision-making to help animals adapt to their environment. In addition, chronic stress and chronic pain share a common behavioral model of failure to extinguish negative memories. Yet, they also have discrepancies such that the final brain endophenotype of posttraumatic stress disorder, depression, and chronic pain appears to be different among the three conditions, and the role of the hypothalamic-pituitary-adrenal axis remains unclear in the physiology of pain. Persistence of either stress or pain is maladaptive and could lead to compromised well-being. In this brief review, we highlight the commonalities and differences between chronic stress and chronic pain, while focusing particularly on the central role of the limbic brain. We assess the current attempts in the field to conceptualize and understand chronic pain, within the context of knowledge gained from the stress literature. The limbic brain-including hippocampus, amygdala, and ventromedial pre-frontal cortex-plays a critical role in learning. These brain areas integrate incoming nociceptive or stress signals with internal state, and generate learning signals necessary for decision-making. Therefore, the physiological and structural remodeling of this learning circuitry is observed in conditions such as chronic pain, depression, and posttraumatic stress disorder, and is also linked to the risk of onset of these conditions.

The effect of acute pain on risky and intertemporal choice

Pain is a highly salient and attention-demanding experience that motivates people to act. We investigated the effect of pain on decision making by delivering acute thermal pain to participants' forearm while they made risky and intertemporal choices involving money. Participants (n = 107) were more risk seeking under pain than in a no-pain control condition when decisions involved gains but not when they involved equivalent losses. Pain also resulted in greater preference for immediate (smaller) over future (larger) monetary rewards. We interpret these results as a motivation to offset the aversive, pain-induced state, where monetary rewards become more appealing under pain than under no pain and when delivered sooner rather than later. Our findings add to the long-standing debate regarding the role of intuition and reflection in decision making.

Functional and Structural Signatures of the Anterior Insula are associated with Risk-taking Tendency of Analgesic Decision-making

In a medical context, decision-making is associated with complicated assessment of gains, losses and uncertainty of outcomes. We here provide novel evidence about the brain mechanisms underlying decision-making of analgesic treatment. Thirty-six healthy participants were recruited and completed the Analgesic Decision-making Task (ADT), which quantified individual tendency of risk-taking (RPI), as the frequency of choosing a riskier option to relieve pain. All the participants received resting-state (rs) functional magnetic resonance imaging (MRI) and structural MRI. On rs-functional connectome, degree centrality (DC) of the bilateral anterior insula (aINS) was positively correlated with the RPI. The functional connectivity between the aINS, the nucleus accumbens and multiple brain regions, predominantly the medial frontal cortex, was positively correlated with the RPI. On structural signatures, the RPI was positively correlated with grey matter volume at the right aINS, and such an association was mediated by DC of the left aINS. Regression analyses revealed that both DC of the left aINS and participants’ imagined pain relief, as the utility of pain reduction, could predict the individual RPI. The findings suggest that the functional and structural brain signature of the aINS is associated with the individual differences of risk-taking tendency in the context of analgesic decision-making.

[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.

Modulation of pain, nociception, and analgesia by the brain reward center

The midbrain dopamine center comprises a key network for reward, salience, motivation, and mood. Evidence from various clinical and preclinical settings points to the midbrain dopamine circuit as an important modulator of pain perception and pain-induced anxiety and depression. This review summarizes recent findings that shed light to the neuroanatomical, electrophysiological and molecular adaptations that chronic pain conditions promote in the mesolimbic dopamine system. Chronic pain states induce changes in neuronal plasticity and functional connectivity in several parts of the brain reward center, including nucleus accumbens, the ventral tegmental area and the prefrontal cortex. Here, we discuss recent findings on the mechanisms involved in the perception of chronic pain, in pain-induced anxiety and depression, as well as in pain-killer addiction vulnerability. Several new studies also show that the mesolimbic dopamine circuit potently modulates responsiveness to opioids and antidepressants used for the treatment of chronic pain. We discuss recent data supporting a role of the brain reward pathway in treatment efficacy and we summarize novel findings on intracellular adaptations in the brain reward circuit under chronic pain states.

Psychological Considerations in the Assessment and Treatment of Pain in Neurorehabilitation and Psychological Factors Predictive of Therapeutic Response: Evidence and Recommendations from the Italian Consensus Conference on Pain in Neurorehabilitation

Background: In order to provide effective care to patients suffering from chronic pain secondary to neurological diseases, health professionals must appraise the role of the psychosocial factors in the genesis and maintenance of this condition whilst considering how emotions and cognitions influence the course of treatment. Furthermore, it is important not only to recognize the psychological reactions to pain that are common to the various conditions, but also to evaluate how these syndromes differ with regards to the psychological factors that may be involved. As an extensive evaluation of these factors is still lacking, the Italian Consensus Conference on Pain in Neurorehabilitation (ICCPN) aimed to collate the evidence available across these topics.

Objectives: To determine the psychological factors which are associated with or predictive of pain secondary to neurological conditions and to assess the influence of these aspects on the outcome of neurorehabilitation.

Methods: Two reviews were performed. In the first, a PUBMED search of the studies assessing the association between psychological factors and pain or the predictive value of these aspects with respect to chronic pain was conducted. The included papers were then rated with regards to their methodological quality and recommendations were made accordingly. In the second study, the same methodology was used to collect the available evidence on the predictive role of psychological factors on the therapeutic response to pain treatments in the setting of neurorehabilitation.

Results: The first literature search identified 1170 results and the final database included 189 articles. Factors such as depression, anxiety, pain catastrophizing, coping strategies, and cognitive functions were found to be associated with pain across the various conditions. However, there are differences between chronic musculoskeletal pain, migraine, neuropathy, and conditions associated with complex disability with regards to the psychological aspects that are involved. The second PUBMED search yielded 252 studies, which were all evaluated. Anxiety, depression, pain catastrophizing, coping strategies, and pain beliefs were found to be associated to different degrees with the outcomes of multidisciplinary programs, surgery, physical therapies, and psychological interventions. Finally, sense of presence was found to be related to the effectiveness of virtual reality as a distraction tool.

Conclusions: Several psychological factors are associated with pain secondary to neurological conditions and should be acknowledged and addressed in order to effectively treat this condition. These factors also predict the therapeutic response to the neurorehabilitative interventions.

An epigenetic hypothesis for the genomic memory of pain

Chronic pain is accompanied with long-term sensory, affective and cognitive disturbances. What are the mechanisms that mediate the long-term consequences of painful experiences and embed them in the genome? We hypothesize that alterations in DNA methylation, an enzymatic covalent modification of cytosine bases in DNA, serve as a "genomic" memory of pain in the adult cortex. DNA methylation is an epigenetic mechanism for long-term regulation of gene expression. Neuronal plasticity at the neuroanatomical, functional, morphological, physiological and molecular levels has been demonstrated throughout the neuroaxis in response to persistent pain, including in the adult prefrontal cortex (PFC). We have previously reported widespread changes in gene expression and DNA methylation in the PFC many months following peripheral nerve injury. In support of this hypothesis, we show here that up-regulation of a gene involved with synaptic function, Synaptotagmin II (syt2), in the PFC in a chronic pain model is associated with long-term changes in DNA methylation. The challenges of understanding the contributions of epigenetic mechanisms such as DNA methylation within the PFC to pain chronicity and their therapeutic implications are discussed.