Psychological Processes in Chronic Pain: Influences of Reward and Fear Learning as Key Mechanisms – Behavioral Evidence, Neural Circuits, and Maladaptive Changes

Beyond the chronic pain stage: default mode network perturbation depends on years lived with back pain

ABSTRACT

Research has indicated that the default mode network (DMN) is perturbated in patients with chronic pain when compared with healthy controls, and this perturbation is correlated with the duration of pain during the chronic pain stage. It remains unclear whether DMN adaptations manifest during the subacute pain stage and progress over time because of the duration of pain experience, rather than being a specific correlate of the chronic pain stage. Furthermore, information regarding whether these adaptations are related to cognitive processes of adaptation is lacking. To this end, we examined the DMN in 31 patients with chronic back pain (CBP), 77 patients with subacute back pain (SBP), as well as 39 healthy pain-free controls (HC) applying a graph-theoretic network approach on functional resting-state magnetic resonance imaging. Beyond the comparison between groups, we used a linear analysis considering the years lived with pain (YLP) across all patients with back pain and additionally performed a mediation analysis of the role of cognitive pain coping. In line with previous studies, we found significant DMN perturbation in CBP compared with HC. However, this did not apply to the comparison of CBP with SBP. Instead, we observed a positive correlation between DMN perturbation and YLP. This was significantly mediated by coping attitudes towards pain. Default mode network perturbation may thus reflect neural adaptation processes to pain experience rather than a single correlate of the chronic pain stage and be modulated by cognitive adaption. This points to potentially underinvestigated significant adaptation processes that could enable more fine-grained patient stratification.

Hydrocortisone Differentially Affects Reinstatement of Pain-related Responses in Patients With Chronic Back Pain and Healthy Volunteers

Despite the crucial role of effective and sustained extinction of conditioned pain-related fear in cognitive-behavioral treatment approaches for chronic pain, experimental research on extinction memory retrieval in chronic pain remains scarce. In healthy populations, extinction efficacy of fear memory is affected by stress. Therefore, we investigated the effects of oral hydrocortisone administration on the reinstatement of pain-related associations in 57 patients with non-specific chronic back pain (CBP) and 59 healthy control (HC) participants in a differential pain-related conditioning paradigm within a placebo-controlled, randomized, and double-blind design. Participants' skin conductance responses indicate hydrocortisone-induced reinstatement effects in HCs but no observable reinstatement in HCs receiving placebo treatment. Interestingly, these effects were reversed in patients with CBP, that is, reinstatement responses were only observed in the placebo and not in the hydrocortisone group. Our findings corroborate previous evidence of stress-induced effects on extinction efficacy and reinstatement of fear memory in HCs, extending them into the pain context, and call for more research to clarify the role of stress in fear extinction and return of fear phenomena possibly contributing to treatment failure in chronic pain treatment. PERSPECTIVE: Opposing effects in HCs and patients with non-specific CBP may be associated with changes in the patients' stress systems. These findings could be of relevance to optimizing psychological, extinction-based treatment approaches.

An amygdala-to-cingulate cortex circuit for conflicting choices in chronic pain

Chronic pain is a complex experience with multifaceted behavioral manifestations, often leading to pain avoidance at the expense of reward approach. How pain facilitates avoidance in situations with mixed outcomes is unknown. The anterior cingulate cortex (ACC) plays a key role in pain processing and in value-based decision-making. Distinct ACC inputs inform about the sensory and emotional quality of pain. However, whether specific ACC circuits underlie pathological conflict assessment in pain remains underexplored. Here, we demonstrate that mice with chronic pain favor cold avoidance rather than reward approach in a conflicting task. This occurs along with selective strengthening of basolateral amygdala inputs onto ACC layer 2/3 pyramidal neurons. The amygdala-cingulate projection is necessary and sufficient for the conflicting cold avoidance. Further, low-frequency stimulation of this pathway restores AMPA receptor function and reduces avoidance in pain mice. Our findings provide insights into the circuits and mechanisms underlying cognitive aspects of pain and offer potential targets for treatment.

Resilience is associated with cortical gray matter of the antinociceptive pathway in people with chronic pain

Resilience is an important personal characteristic that influences health and recovery. Previous studies of chronic pain suggest that highly resilient people may be more effective at modulating their pain. Since brain gray matter in the antinociceptive pathway has also been shown to be abnormal in people with chronic pain, we examined whether resilience is related to gray matter in regions of interest (ROIs) of the antinociceptive pathway (rostral and subgenual anterior cingulate cortex (rACC, sgACC), anterior insula (aINS), dorsolateral prefrontal cortex (dlPFC)) normally and in people who are experiencing chronic pain. We extracted gray matter volume (GMV) and cortical thickness (CT) from 3T MRIs of 88 people with chronic pain (half males/females) and 86 healthy controls (HCs), who completed The Resilience Scale and Brief Pain Inventory. We found that resilience scores were significantly lower in people with chronic pain compared to HCs, whereas ROI GMV and CT were not different between groups. Resilience negatively correlated with average pain scores and positively correlated with GMV in the bilateral rACC, sgACC, and left dlPFC of people with chronic pain. Mediation analyses revealed that GMV in the right rACC and left sgACC partially co-mediated the relationship between resilience and average pain in people with chronic pain. The resilience-pain and some resilience-GMV relationships were sex-dependent. These findings suggest that the antinociceptive pathway may play a role in the impact of resilience on one's ability to modulate chronic pain. A better understanding of the brain-resilience relationship may help advance evidence-based approaches to pain management.

Pain in Huntington's disease and its potential mechanisms

Pain is common and frequent in many neurodegenerative diseases, although it has not received much attention. In Huntington's disease (HD), pain is often ignored and under-researched because attention is more focused on motor and cognitive decline than psychiatric symptoms. In HD progression, pain symptoms are complex and involved in multiple etiologies, particularly mental issues such as apathy, anxiety and irritability. Because of psychiatric issues, HD patients rarely complain of pain, although their bodies show severe pain symptoms, ultimately resulting in insufficient awareness and lack of research. In HD, few studies have focused on pain and pain-related features. A detailed and systemic pain history is crucial to assess and explore pain pathophysiology in HD. This review provides an overview concentrating on pain-related factors in HD, including neuropathology, frequency, features, affecting factors and mechanisms. More attention and studies are still needed in this interesting field in the future.

Dog assisted education in children with rheumatic diseases and adolescents with chronic pain in Germany

Objectives

Animal assisted intervention is an increasingly accepted tool to improve human well-being. The present study was performed to assess whether dog assisted education has a positive effect on children suffering from rheumatic disorders with pain and adolescents with chronic pain syndrome.

Design

Two groups of juvenile patients were recruited: 7-17-year-old children in children with rheumatic diseases and adolescents with chronic pain syndromes. Overall, n=26 participated in the intervention, and n=29 in the control group.

Setting

The intervention group met once a month, 12 times overall, for working with man trailing dogs in various locations.

Main outcome measures

The influence of dog assisted education on quality of life (PedsQLTM Scoring Algorithm), pain intensity, perception, coping (Paediatric Pain Coping Inventory-Revised), and state anxiety (State Trait Anxiety Inventory) was assessed.

Results

The quality of life increased significantly in the investigated period, but for both, the intervention and the control group. The state anxiety of children was lower after the dog assisted education than before. After the dog training sessions, state anxiety was 18% to 30% lower than before the intervention. Some participants noted subjectively improved pain coping and changes in pain perception, which were not found in the data.

Conclusion

Our results indicate that for children with rheumatic diseases and adolescents with chronic pain syndromes dog assisted education (1) might lead to an increase of the quality of life, (2) leads to decreased state anxiety from pre to post intervention and (3) does not influence pain perception, frequency and intensity.

Post-injury pain and behaviour: a control theory perspective

Injuries of various types occur commonly in the lives of humans and other animals and lead to a pattern of persistent pain and recuperative behaviour that allows safe and effective recovery. In this Perspective, we propose a control-theoretic framework to explain the adaptive processes in the brain that drive physiological post-injury behaviour. We set out an evolutionary and ethological view on how animals respond to injury, illustrating how the behavioural state associated with persistent pain and recuperation may be just as important as phasic pain in ensuring survival. Adopting a normative approach, we suggest that the brain implements a continuous optimal inference of the current state of injury from diverse sensory and physiological signals. This drives the various effector control mechanisms of behavioural homeostasis, which span the modulation of ongoing motivation and perception to drive rest and hyper-protective behaviours. However, an inherent problem with this is that these protective behaviours may partially obscure information about whether injury has resolved. Such information restriction may seed a tendency to aberrantly or persistently infer injury, and may thus promote the transition to pathological chronic pain states.

Prefrontal engrams of long-term fear memory perpetuate pain perception

A painful episode can lead to a life-long increase in an individual's experience of pain. Fearful anticipation of imminent pain could play a role in this phenomenon, but the neurobiological underpinnings are unclear because fear can both suppress and enhance pain. Here, we show in mice that long-term associative fear memory stored in neuronal engrams in the prefrontal cortex determines whether a painful episode shapes pain experience later in life. Furthermore, under conditions of inflammatory and neuropathic pain, prefrontal fear engrams expand to encompass neurons representing nociception and tactile sensation, leading to pronounced changes in prefrontal connectivity to fear-relevant brain areas. Conversely, silencing prefrontal fear engrams reverses chronically established hyperalgesia and allodynia. These results reveal that a discrete subset of prefrontal cortex neurons can account for the debilitating comorbidity of fear and chronic pain and show that attenuating the fear memory of pain can alleviate chronic pain itself.

Fear-Avoidance Beliefs for Physical Activity Among Chronic Low Back Pain: A Multicenter Cross-Sectional Study

Background

Among different psychological predictors of outcome in low back pain (LBP) adults, the negative influence of fear-avoidance beliefs in physical activity is an area of research attention. However, there is a lack of evidence on the burden of fear avoidance about physical activity among chronic LBP adults in Ethiopia.

Objective

To describe fear-avoidance beliefs about physical activity and explore its association with socio-demographic and clinical factors among low back pain patients attending physiotherapy treatment in 3 Amhara regional comprehensive hospitals.

Methods

A multi-center cross-sectional study was conducted and adults with chronic LBP (n = 263) participated. Data were collected by face-to-face interview using the modified Fear-Avoidance Belief Questionnaire about Physical Activity (mFABQ-PA) tool. Multivariable logistic regression at a p-value <0.05 significance level was used to identify predictors of fear-avoidance beliefs about physical activity.

Results

Among the 263 participants, 113 subjects (43%, 95% CI (36.9-49.0)) reported a higher cut-off (>15) mFABQ-PA. The logistic regression model demonstrated that LBP adults with a higher mFABQ-PA score were more likely to be urban residents (AOR 2.75, 95% CI (1.32, 5.88)), and ADL-related LBP (AOR 1.97 95% CI (1.18, 3.29)). The clinical-specific factor indicative of a higher cut-off score of mFABQ-PA was using analgesic medications (AOR 2.00, 95% CI (1.19, 3.37)). The model fit was 0.21 and 0.11 (R² = Nagelkerke's, Cox & snell respectively).

Conclusion

High fear avoidance beliefs about physical activity in adults with low back pain were found and associated with residence, work, and medication intake. These findings might urge the researchers to explore further associations and assist clinicians in choosing subgroups to use behavioral therapy and graded exposure to physical activity.

A psychometric evaluation of the Italian short version of the Fear of Pain Questionnaire-III: Psychometric properties, measurement invariance across gender, convergent, and discriminant validity

Introduction

The Fear of Pain Questionnaire-III (FPQ-III) is a self-assessment instrument developed specifically to measure fear based on various pain stimuli converging on three factors: severe pain, medical pain, and minor pain. It actually remains the most studied and internationally used tool even in its short versions. The aim of this work was to propose a new validation study oriented to confirm the good psychometric properties of a short model of the FPQ-III for the Italian context.

Methods

A large sample of participants was recruited (n  = 1,064) and Exploratory Factor Analysis (EFA) as well as Confirmatory Factor Analysis (CFA) were performed. Measurement invariance of the FPQ-III across gender was also evaluated. In order to examine convergent validity, a further convenient sample (n  = 292) was used and variables related to the individual's pain experience, locus of control and coping orientations were assessed. A final discriminant assessment using experimental manipulation through fear eliciting videos was performed.

Results

The three factors structure of the 13-item version of the questionnaire was confirmed (χ² = 148.092, CFI = 0.971, TLI = 0.962, RMSEA = 0.046, RMSEA 90% CI = 0.037-0.056) as well as the measurement invariance across gender. Item internal reliability was satisfactory. The results provided evidence of the good predictive validity of the FPQ-III and the discriminant assessment demonstrated that the instrument is suitable in detecting changes in fear of pain induced by specific situational conditions.

Discussion

The scale in this short version is suitable for quickly and efficiently gathering information about the perceived intensity of such anticipatory fears that might affect even the healthy person dysfunctionally.

Impaired pain-related threat and safety learning in patients with chronic back pain

ABSTRACT

Pain-related learning mechanisms likely play a key role in the development and maintenance of chronic pain. Previous smaller-scale studies have suggested impaired pain-related learning in patients with chronic pain, but results are mixed, and chronic back pain (CBP) particularly has been poorly studied. In a differential conditioning paradigm with painful heat as unconditioned stimuli, we examined pain-related acquisition and extinction learning in 62 patients with CBP and 61 pain-free healthy male and female volunteers using valence and contingency ratings and skin conductance responses. Valence ratings indicate significantly reduced threat and safety learning in patients with CBP, whereas no significant differences were observed in contingency awareness and physiological responding. Moreover, threat learning in this group was more impaired the longer patients had been in pain. State anxiety was linked to increased safety learning in healthy volunteers but enhanced threat learning in the patient group. Our findings corroborate previous evidence of altered pain-related threat and safety learning in patients with chronic pain. Longitudinal studies exploring pain-related learning in (sub)acute and chronic pain are needed to further unravel the role of aberrant pain-related learning in the development and maintenance of chronic pain.

Gingerol-Enriched Ginger Supplementation Mitigates Neuropathic Pain via Mitigating Intestinal Permeability and Neuroinflammation: Gut-Brain Connection

Objectives: Emerging evidence suggests an important role of the gut-brain axis in the development of neuropathic pain (NP). We investigated the effects of gingerol-enriched ginger (GEG) on pain behaviors, as well as mRNA expressions of inflammation via tight junction proteins in GI tissues (colon) and brain tissues (amygdala, both left and right) in animals with NP.

Methods: Seventeen male rats were randomly divided into three groups: Sham, spinal nerve ligation (SNL, pain model), and SNL+0.375% GEG (wt/wt in diet) for 4 weeks. Mechanosensitivity was assessed by von Frey filament tests and hindpaw compression tests. Emotional responsiveness was measured from evoked audible and ultrasonic vocalizations. Ongoing spontaneous pain was measured in rodent grimace tests. Intestinal permeability was assessed by the lactulose/D-mannitol ratio in urine. The mRNA expression levels of neuroinflammation (NF-κB, TNF-α) in the colon and amygdala (right and left) were determined by qRT-PCR. Data was analyzed statistically.

Results: Compared to the sham group, the SNL group had significantly greater mechanosensitivity (von Frey and compression tests), emotional responsiveness (audible and ultrasonic vocalizations to innocuous and noxious mechanical stimuli), and spontaneous pain (rodent grimace tests). GEG supplementation significantly reduced mechanosensitivity, emotional responses, and spontaneous pain measures in SNL rats. GEG supplementation also tended to decrease SNL-induced intestinal permeability markers. The SNL group had increased mRNA expression of NF-κB and TNF-α in the right amygdala and colon; GEG supplementation mitigated these changes in SNL-treated rats.

Conclusion: This study suggests GEG supplementation palliated a variety of pain spectrum behaviors in a preclinical NP animal model. GEG also decreased SNL-induced intestinal permeability and neuroinflammation, which may explain the behavioral effects of GEG.

Acquisition learning is stronger for aversive than appetitive events

Appetitive and aversive learning are both key building blocks of adaptive behavior, yet knowledge regarding their differences is sparse. Using a capsaicin heat pain model in 36 healthy participants, this study directly compared the acquisition and extinction of conditioned stimuli (CS) predicting pain exacerbation and relief. Valence ratings show stronger acquisition during aversive compared to appetitive learning, but no differences in extinction. Skin conductance responses and contingency ratings confirmed these results. Findings were unrelated to individual differences in pain sensitivity or psychological factors. Our results support the notion of an evolutionarily hardwired preponderance to acquire aversive rather than appetitive cues as is protective for acute aversive states such as pain but may contribute to the development and maintenance of clinical conditions such as chronic pain, depression or anxiety disorders.

In this study, acquisition and extinction of conditioned stimuli are compared in a capsaicin heat pain paradigm in healthy human participants. The results demonstrate a preponderance to acquire aversive rather than appetitive cues, which could initially have a protective function but eventually contribute to the maintenance of chronic pain.

Advances in targeting central sensitization and brain plasticity in chronic pain

Maladaptation in sensory neural plasticity of nociceptive pathways is associated with various types of chronic pain through central sensitization and remodeling of brain connectivity. Within this context, extensive research has been conducted to evaluate the mechanisms and efficacy of certain non-pharmacological pain treatment modalities. These include neurostimulation, virtual reality, cognitive therapy and rehabilitation. Here, we summarize the involved mechanisms and review novel findings in relation to nociceptive desensitization and modulation of plasticity for the management of intractable chronic pain and prevention of acute-to-chronic pain transition.

Fear Extinction-Based Inter-Individual and Sex Differences in Pain-Related Vocalizations and Anxiety-like Behaviors but Not Nocifensive Reflexes

Inter-individual and sex differences in pain responses are recognized but their mechanisms are not well understood. This study was intended to provide the behavioral framework for analyses of pain mechanisms using fear extinction learning as a predictor of phenotypic and sex differences in sensory (mechanical withdrawal thresholds) and emotional-affective aspects (open field tests for anxiety-like behaviors and audible and ultrasonic components of vocalizations) of acute and chronic pain. In acute arthritis and chronic neuropathic pain models, greater increases in vocalizations were found in females than males and in females with poor fear extinction abilities than females with strong fear extinction, particularly in the neuropathic pain model. Female rats showed higher anxiety-like behavior than males under baseline conditions but no inter-individual or sex differences were seen in the pain models. No inter-individual and sex differences in mechanosensitivity were observed. The data suggest that vocalizations are uniquely suited to detect inter-individual and sex differences in pain models, particularly in chronic neuropathic pain, whereas no such differences were found for mechanosensitivity, and baseline differences in anxiety-like behaviors disappeared in the pain models.

Brain Circuits Involved in the Development of Chronic Musculoskeletal Pain: Evidence From Non-invasive Brain Stimulation

It has been well-documented that the brain changes in states of chronic pain. Less is known about changes in the brain that predict the transition from acute to chronic pain. Evidence from neuroimaging studies suggests a shift from brain regions involved in nociceptive processing to corticostriatal brain regions that are instrumental in the processing of reward and emotional learning in the transition to the chronic state. In addition, dysfunction in descending pain modulatory circuits encompassing the periaqueductal gray and the rostral anterior cingulate cortex may also be a key risk factor for pain chronicity. Although longitudinal imaging studies have revealed potential predictors of pain chronicity, their causal role has not yet been determined. Here we review evidence from studies that involve non-invasive brain stimulation to elucidate to what extent they may help to elucidate the brain circuits involved in pain chronicity. Especially, we focus on studies using non-invasive brain stimulation techniques [e.g., transcranial magnetic stimulation (TMS), particularly its repetitive form (rTMS), transcranial alternating current stimulation (tACS), and transcranial direct current stimulation (tDCS)] in the context of musculoskeletal pain chronicity. We focus on the role of the motor cortex because of its known contribution to sensory components of pain via thalamic inhibition, and the role of the dorsolateral prefrontal cortex because of its role on cognitive and affective processing of pain. We will also discuss findings from studies using experimentally induced prolonged pain and studies implicating the DLPFC, which may shed light on the earliest transition phase to chronicity. We propose that combined brain stimulation and imaging studies might further advance mechanistic models of the chronicity process and involved brain circuits. Implications and challenges for translating the research on mechanistic models of the development of chronic pain to clinical practice will also be addressed.

Neocortical circuits in pain and pain relief

The sensory, associative and limbic neocortical structures play a critical role in shaping incoming noxious inputs to generate variable pain perceptions. Technological advances in tracing circuitry and interrogation of pathways and complex behaviours are now yielding critical knowledge of neocortical circuits, cellular contributions and causal relationships between pain perception and its abnormalities in chronic pain. Emerging insights into neocortical pain processing suggest the existence of neocortical causality and specificity for pain at the level of subdomains, circuits and cellular entities and the activity patterns they encode. These mechanisms provide opportunities for therapeutic intervention for improved pain management.

Optimizing Long-term Outcomes of Exposure for Chronic Primary Pain from the Lens of Learning Theory

Exposure in vivo is a theory-driven and widely used treatment to tackle functional disability in people with chronic primary pain. Exposure is quite effective; yet, in line with exposure outcomes for anxiety disorders, a number of patients may not profit from it, or relapse. In this focus article, we critically reflect on the current exposure protocols in chronic primary pain, and provide recommendations on how to optimize them. We propose several adaptations that are expected to strengthen inhibitory learning and/or retrieval of the extinction memory, thus likely decreasing relapse. We summarize the limited, but emerging experimental data in the pain domain, and draw parallels with experimental evidence in the anxiety literature. Our reflections and suggestions pertain to the use of the fear hierarchy, reassurance, positive psychology interventions, exposure with a range of stimuli and within different contexts, and the use of safety behaviors during treatment, as well as associating the fear-inducing stimuli with novel outcomes. In addition, we reflect on the importance of specifically tackling (the return of) pain-related avoidance behavior with techniques such as disentangling fear from avoidance and reinforcing approach behaviors. Finally, we discuss challenges in the clinical application of exposure to improve functioning in chronic primary pain and possible avenues for future research. Perspectives: Inspired by recent advances in learning theory and its applications on the treatment of anxiety disorders, we reflect on the delivery of exposure treatment for chronic primary pain and propose strategies to improve its long-term outcomes.

Neural correlates of conditioned pain responses in fibromyalgia subjects indicate preferential formation of new pain associations rather than extinction of irrelevant ones

Supplemental Digital Content is Available in the Text.

Functional magnetic resonance imaging pain conditioning data suggest that fibromyalgia prioritizes updating their cerebral representation to forming new potential pain-related associations while simultaneously maintaining no longer relevant ones.

Behavioral studies have demonstrated aberrant safety processing in fibromyalgia subjects (FMSs) and suggested that patients accumulate new potential pain-related threats more effectively than extinguishing no longer relevant ones. The aim of the current study was to investigate the neural correlates of conditioned pain responses and their relationship with emotional distress in FMS (n = 67) and healthy controls (HCs, n = 34). Using functional magnetic resonance imaging, we traced conditioned pain responses to an identical moderately painful pressure (P30) depending on whether it was following a green (P30green) or a red (P30red) cue. The cues were previously associated with individually calibrated painful pressure stimuli of low and high intensity, corresponding to visual analogue scale 10 and 50 mm, respectively. Fibromyalgia subjects displayed increased P30green ratings over time, while P30red ratings remained elevated. Healthy controls adapted all pain ratings to resemble moderate pain. Fibromyalgia subjects exhibited increased activation for [P30green>P30red] in M1/anterior insula, whereas HC showed increased S2/mid-insula response to [P30red>P30green]. High pain catastrophizing scale (PCS) ratings in fibromyalgia (FM) covaried with heightened brain activation for [P30green] × PCS in left dorsolateral prefrontal cortex and medial prefrontal cortex/orbitofrontal cortex; and [P30green>P30red] × PCS in dorsal anterior cingulate cortex/mid-cingulate cortex; superior temporal pole, extending to anterior insula; bilateral thalamus; and posterior insula. Psychophysiological interaction analysis for FM [P30green>P30red] × PCS revealed a dissociation in functional connectivity between thalamus and bilateral inferior parietal lobe. In alignment with behavioral data, FMS displayed a cerebral response suggesting preferential formation of new pain-related associations while simultaneously maintaining no longer relevant ones. The opposite was observed in HC. Increased responses to pain-related threats in FM may contribute to dysfunctional pain-protective behaviors and disability.

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.

Altered mesocorticolimbic functional connectivity in chronic low back pain patients at rest and following sad mood induction

Depressive symptoms are common among individuals with chronic pain. Previous work suggests that chronic pain patients have difficulty regulating emotional responses, which is a risk factor for the development of major depressive disorder (MDD). Function of the mesocorticolimbic system, a neural network associated with reward processing, contributes to emotion regulation. This network's dysfunction has been described in chronic pain and MDD research and potentially underlies the relationship among emotion dysregulation, chronic pain, and MDD development. Given that mood induction paradigms have been used to measure emotion regulation, the present study examined intrinsic mesocorticolimbic functional connectivity (FC) after induced sad mood in individuals with and without chronic low back pain (cLBP). Thirty-three MDD-free individuals (17 cLBP) underwent resting-state scanning before and after sad memory-evoked mood induction. A Group [cLBP, healthy control (HC)] x Mood (Neutral, Sadness) repeated measures ANCOVA was conducted on seed-based FC data using a mesolimbic a priori region of interest. Interaction effects were identified in the orbital frontal cortex and inferior frontal gyrus [F_(2,29) = 21.07, p_FDR < .05. h_p² = .5]. Whereas cLBP showed significantly greater FC between these two regions and the mesolimbic seed under neutral mood, FC among these regions increased in HC and decreased in cLBP under sad mood. Exploratory graph theory analyses further describe between-group differences in mesocorticolimbic network properties. Findings support previous literature describing mesocorticolimbic dysfunction in cLBP and demonstrate aberrant function in emotion regulation. Mesocorticolimbic dysfunction during emotion regulation might contribute to the development of certain depressive phenotypes in chronic pain patients.

Will that hurt? A contingency learning task to assess pain-expectancy judgments for low back postures

BACKGROUND AND OBJECTIVES

Contingency learning, i.e. learning that a cue predicts the presence (or absence) of an event, is central to the formation of beliefs regarding painfulness of body postures. Such beliefs may spread to safe cues due to compromised learning (e.g., excessive generalization, impaired safety learning), prompting avoidance and leading to disability. Despite its importance, compromised learning about low back pain is underinvestigated. We propose a low back pain scenario contingency learning task for the investigation of back pain-related learning.

METHODS

Sixty healthy participants viewed pictures of an avatar in various back postures, and for each posture gave pain-expectancy judgments and viewed the verbal outcome (pain/no pain) for a fictive back pain patient. During acquisition, one posture was followed by pain (conditioned stimulus; CS+), whereas another was not (CS-). During generalization, unreinforced novel intermediate back postures (generalization stimuli; GSs) were tested. During extinction, only the CSs were presented, not followed by pain. During generalization of extinction, only the GSs were presented, not followed by pain.

RESULTS

Participants expected pain more for the CS + than the CS- (differential acquisition) and generalized their pain-expectancy to the GS most similar to the CS+ (generalization). During extinction, pain-expectancy for the CS + decreased and generalized to the GS most similar to the CS+ (generalization of extinction).

LIMITATIONS

Future research should investigate generalizability of findings to clinical samples and consider the role of pre-existing pain threat beliefs.

CONCLUSIONS

This task is an easily applicable, non-invasive way to investigate the formation of back pain-related threat beliefs.

Subjective hearing ability, physical and mental comorbidities in individuals with bothersome tinnitus in a Swedish population sample

OBJECTIVE

This study investigates associations of subjective hearing ability, physical comorbidities, and mental comorbidities with bothersome (vs. non-bothersome) tinnitus and mediating effects between these influences.

METHODS

The Swedish LifeGene cohort was used to sample cross-sectional survey data (collected 2009-2016) of 7615 participants with tinnitus, 697 (9.2%) of whom rated their tinnitus as bothersome. Associations between bothersome tinnitus and subjective hearing ability, physical and mental comorbidities were investigated by separate age- and gender-adjusted multiple logistic regression models. Interrelationships between these associations were investigated by logistic mediation models.

RESULTS

Compared to non-bothersome tinnitus, bothersome tinnitus was associated with higher age, reduced subjective hearing ability, hearing-related difficulties in social situations, cardiovascular disease, chronic shoulder pain, thyroid disease, Ménière's disease, depression, anxiety syndrome, and social anxiety. Subjective hearing impairment or hearing-related difficulties mediated 13-36% of the effects of mental comorbidities on bothersome tinnitus. Depression or anxiety syndrome mediated 5-8% of most relationships between physical comorbidities and bothersome tinnitus. Depression, anxiety syndrome, or social anxiety mediated 2-4% of the effects of subjective hearing impairment or hearing-related difficulties on bothersome tinnitus.

CONCLUSION

Psychological factors, subjective hearing impairment, and hearing-related difficulties in social situations play key roles in predicting bothersome (vs. non-bothersome) tinnitus in a large population sample. Psychological factors contribute to explaining the impact of physical comorbidities and hearing-related effects on bothersome tinnitus. This highlights their transdiagnostic importance for aggravating varied physical symptom clusters. Interventions to improve or prevent high tinnitus burden should be interdisciplinary/multimodal and target auditory, physical, and psychological factors.

Translation and Validation of Fear of Pain-9 Items into Simplified Chinese Version for Mainland China

Purpose

This study aimed to obtain a translation and validation of the Fear of Pain Questionnaire 9 Items (FOP-9) into simplified Chinese.

Methods

The questionnaire was translated following the forward-backward method. The final version was filled out by (n = 300) patients. Cronbach’s coefficient was calculated to test the internal consistency of simplified Chinese version of FOP-9 (sc-FOP-9), and 50 painless patients completed the sc-FOP-9 questionnaire within a 2-weeks interval to evaluate test–retest reliability. To verify the construct validity, exploratory factor analysis was used to explore the factor structure, and confirmatory factor analysis was conducted to evaluate the goodness fit of models.

Results

Satisfactory psychometric qualities were obtained (Cronbach’s α of the total score was 0.873 and intraclass correlation coefficient was 0.975). Three first-order models were tested and all show a good model fit and the 3-factor structure may be better due to its higher factor loading.

Conclusion

The sc-FOP-9 is a reliable and valid instrument to evaluate the fear of pain among Chinese patients with or without pain. Fear of pain may have an important effect on perioperative pain and chronic pain, and this tool is a good complement to the measurement in mainland China.

Enhanced pain-related conditioning for face compared to hand pain

Pain is evolutionarily hardwired to signal potential danger and threat. It has been proposed that altered pain-related associative learning processes, i.e., emotional or fear conditioning, might contribute to the development and maintenance of chronic pain. Pain in or near the face plays a special role in pain perception and processing, especially with regard to increased pain-related fear and unpleasantness. However, differences in pain-related learning mechanisms between the face and other body parts have not yet been investigated. Here, we examined body-site specific differences in associative emotional conditioning using electrical stimuli applied to the face and the hand. Acquisition, extinction, and reinstatement of cue-pain associations were assessed in a 2-day emotional conditioning paradigm using a within-subject design. Data of 34 healthy subjects revealed higher fear of face pain as compared to hand pain. During acquisition, face pain (as compared to hand pain) led to a steeper increase in pain-related negative emotions in response to conditioned stimuli (CS) as assessed using valence ratings. While no significant differences between both conditions were observed during the extinction phase, a reinstatement effect for face but not for hand pain was revealed on the descriptive level and contingency awareness was higher for face pain compared to hand pain. Our results indicate a stronger propensity to acquire cue-pain-associations for face compared to hand pain, which might also be reinstated more easily. These differences in learning and resultant pain-related emotions might play an important role in the chronification and high prevalence of chronic facial pain and stress the evolutionary significance of pain in the head and face.

The Operant Plantar Thermal Assay: A Novel Device for Assessing Thermal Pain Tolerance in Mice

Pain is a multidimensional experience of sensory-discriminative, cognitive, and affective processes; however, current basic research methods rely heavily on response to threshold stimuli, bypassing the supraspinal processing that ultimately gives rise to the pain experience. We developed the operant plantar thermal assay (OPTA), which utilizes a novel, conflict-based operant task requiring evaluation and active decision-making to obtain reward under thermally aversive conditions to quantify thermal pain tolerance. In baseline measures, male and female mice exhibited similar temperature preferences, however in the OPTA, female mice exhibited greater temperature-dependent tolerance, as defined by choice time spent in an adverse thermal condition to obtain reward. Increasing reward salience (4% vs 10% sucrose solution) led to increased thermal tolerance for males but not females. To determine whether neuropathic and inflammatory pain models alter thermal tolerance, animals with chronic constriction injury (CCI) or complete Freund's adjuvant (CFA), respectively, were tested in the OPTA. Surprisingly, neuropathic animals exhibited increased thermal tolerance, as shown by greater time spent in the reward zone in an adverse thermal condition, compared with sham animals. There was no effect of inflammation on thermal tolerance. Administration of clonidine in the CCI model led to increased thermal tolerance in both injured and sham animals. In contrast, the non-steroidal anti-inflammatory meloxicam was anti-hyperalgesic in the CFA model, but reduced thermal pain tolerance. These data support the feasibility of using the OPTA to assess thermal pain tolerance to gain new insights into complex pain behaviors and to investigate novel aspects of analgesic efficacy.

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.

The Fear of Pain Questionnaire: Factor structure, validity and reliability of the Italian translation

Background

The Fear of Pain Questionnaire-III (FPQ-III) is a self-report instrument developed to assess fear of different stimuli usually causing pain. The present study aimed to construct an Italian version of the FPQ-III and examine its psychometric properties in a heterogeneous sample of Italian healthy individuals.

Methods

The questionnaire was translated following the forward-backward method and completed by 511 Italian adults who met the inclusion criteria. Within 2 months of the first assessment, a subgroup of participants (n = 164) was re-tested. The factorial structure of the FPQ-III was assessed by confirmatory factor analysis (CFA). To better comprehend the FPQ-III’s factorial structure, a CFA was also performed for each of the two reduced versions of the FPQ-III, namely the FPQ-Short Form and the FPQ-9. Divergent validity, test-retest reliability, and gender/age measurement invariance were also evaluated.

Results

The results of the CFA revealed that the original three-factor model poorly fitted the data, but it became satisfactory after allowing correlated error terms. Concerning divergent validity, correlations between FPQ-III scores and pain intensity, depression, and anxiety were found to be positive but weak in magnitude (< .20). FPQ-III subscales and total scores showed good internal consistency and time reliability. Finally, scalar invariance was only partially obtained, whereas all the other types of invariance were fully respected both for gender and age.

Conclusions

The current findings indicate that the Italian version of the FPQ-III provides valid and reliable scores for the assessment of fear of pain in the Italian population.

Understanding osteoporotic pain and its pharmacological treatment

Osteoporosis, a disorder that affects millions of people worldwide, is characterized by decreased bone mass and microstructural alterations giving rise to an increased risk of fractures. Osteoporotic fractures can cause acute and chronic pain that mainly affects elderly patients with multiple comorbidities and commonly on different drug regimens. The aim of this paper is to summarize the pathogenesis and systemic treatment of osteoporotic pain. This narrative review summarizes the main pathogenetic aspects of osteoporotic pain and the cornerstones of its treatment. Osteoporotic fractures induce both acute and chronic nociceptive and neuropathic pain. Central sensitization seems to play a pivotal role in developing and maintaining chronicity of post-fracture pain in osteoporosis. Antiosteoporosis drugs are able to partially control pain, but additional analgesics are always necessary for pain due to bone fractures. Nonsteroidal anti-inflammatory drugs (NSAIDs) and selective COX-2 inhibitors reduce acute pain but with a poor effect on the chronic neuropathic component of pain and with relevant side effects. Opioid drugs can control the whole spectrum of acute and chronic bone pain, but they differ with respect to their efficacy on neuropathic components, their tolerability and safety. Chronic pain after osteoporotic fractures requires a multifaceted approach, which includes a large spectrum of drugs (antiosteoporosis treatment, acetaminophen, NSAIDs, selective COX-2 inhibitors, weak and strong opioids) and non-pharmacological treatment. Based on a better understanding of the pathogenesis of osteoporotic and post-fracture pain, a guided stepwise approach to post-fracture osteoporotic pain will also better meet the needs of these patients.