Predicting value of pain and analgesia: nucleus accumbens response to noxious stimuli changes in the presence of chronic pain

Interactive Mechanisms of Supraspinal Sites of Opioid Analgesic Action: A Festschrift to Dr. Gavril W. Pasternak

Almost a half century of research has elaborated the discoveries of the central mechanisms governing the analgesic responses of opiates, including their receptors, endogenous peptides, genes and their putative spinal and supraspinal sites of action. One of the central tenets of "gate-control theories of pain" was the activation of descending supraspinal sites by opiate drugs and opioid peptides thereby controlling further noxious input. This review in the Special Issue dedicated to the research of Dr. Gavril Pasternak indicates his contributions to the understanding of supraspinal mediation of opioid analgesic action within the context of the large body of work over this period. This review will examine (a) the relevant supraspinal sites mediating opioid analgesia, (b) the opioid receptor subtypes and opioid peptides involved, (c) supraspinal site analgesic interactions and their underlying neurophysiology, (d) molecular (particularly AS) tools identifying opioid receptor actions, and (e) relevant physiological variables affecting site-specific opioid analgesia. This review will build on classic initial studies, specify the contributions that Gavril Pasternak and his colleagues did in this specific area, and follow through with studies up to the present.

Cannabidiol in the prelimbic cortex modulates the comorbid condition between the chronic neuropathic pain and depression-like behaviour in rats: The role of medial prefrontal cortex 5-HT1A and CB1 receptors

The prelimbic division (PrL) of the medial prefrontal cortex (mPFC) is a cerebral division that is putatively implicated in the chronic pain and depression. We investigated the activity of PrL cortex neurons in Wistar rats that underwent chronic constriction injury (CCI) of sciatic nerve and were further subjected to the forced swimming (FS) test and mechanical allodynia (by von Frey test). The effect of blockade of synapses with cobalt chloride (CoCl₂), and the treatment of the PrL cortex with cannabidiol (CBD), the CB₁ receptor antagonist AM251 and the 5-HT_1A receptor antagonist WAY-100635 were also investigated. Our results showed that CoCl₂ decreased the time spent immobile during the FS test but did not alter mechanical allodynia. CBD (at 15, 30 and 60 nmol) in the PrL cortex also decreased the frequency and duration of immobility; however, only the dose of 30 nmol of CBD attenuated mechanical allodynia in rats with chronic NP. AM251 and WAY-100635 in the PrL cortex attenuated the antidepressive and analgesic effect caused by CBD but did not alter the immobility and the mechanical allodynia when administered alone. These data show that the PrL cortex is part of the neural substrate underlying the comorbidity between NP and depression. Also, the previous blockade of CB₁ cannabinoid receptors and 5-HT_1A serotonergic receptors in the PrL cortex attenuated the antidepressive and analgesics effect of the CBD. They also suggest that CBD could be a potential medicine for the treatment of depressive and pain symptoms in patients with chronic NP/depression comorbidity.

Corticolimbic Circuitry in Chronic Pain Tracks Pain Intensity Relief Following Exposure In Vivo

Background

A subset of patients with chronic pain who receive exposure in vivo (EXP) treatment experience clinically relevant relief of pain intensity. Although pain relief is not an explicit therapeutic target, it is important to understand how and why this concomitant effect occurs in some patients but not others. This longitudinal study therefore aimed to characterize brain plasticity as well as to explore pretreatment factors related to pain relief.

Methods

Resting-state functional magnetic resonance imaging data were acquired in 30 patients with chronic pain. Twenty-three patients completed EXP, and 6-month follow-up data were available in 20 patients (magnetic resonance imaging data in 17 patients). Pain-free control data were acquired at two time points (n = 29, n = 21). Seed-based resting-state functional connectivity (rsFC) analyses were performed, with seeds in the amygdala, hippocampus, and nucleus accumbens.

Results

Pain relief after EXP was highly variable, with 60% of patients reporting a clinically relevant improvement. Amygdala rsFC with the middle frontal gyrus decreased significantly over time in patients but was not associated with pain relief. In contrast, greater pain relief was associated with greater decreases over time in hippocampus rsFC with the precuneus, which was related to reductions in catastrophizing (EXP therapeutic target) as well. Greater pain relief was also associated with lower pretreatment rsFC between nucleus accumbens and postcentral gyrus.

Conclusions

While changes in hippocampus rsFC were associated with pain relief after EXP, pretreatment nucleus accumbens rsFC showed potential prognostic value. Our findings further support the importance of corticolimbic circuitry in chronic pain, emphasizing its relation to pain relief and identifying potential underlying mechanisms and prognostic factors, warranting further testing in independent samples.

Perception of repeated pain relief with controllable and uncontrollable pain

BACKGROUND

The ultimate goal of pain research is to provide effective routes for pain relief. Nevertheless, the perception pain relief as a change in pain intensity and un-/pleasantness has only been rarely investigated. It has been demonstrated that pain relief has rewarding and reinforcing properties, but it remains unknown whether the perception of pain relief changes when pain reductions occur repeatedly. Further, it remains an open question whether the perception of pain relief depends on the controllability of the preceding pain.

METHODS

In this study, healthy volunteers (N = 38) received five cycles of painful heat stimulation and reduction of this stimulation to a non-painful warm stimulation once in a condition with control of the stimulation and once without control. Participants rated perceived intensity and un-/pleasantness on visual analogue scales during the heat stimulation and immediately after its reduction.

RESULTS

Results showed that perceived pain relief, estimated by the difference in ratings during ongoing heat stimulation and after its reduction, increased with repetitions. However, this increase levelled off after two to four repetitions. Further, perceived pain relief was larger in the condition without control compared to the condition with control.

CONCLUSION

The perception of pain relief can be modulated similar to the perception of pain by stimulus characteristics and psychological factors. Mechanistic knowledge about such modulating factors is important, because they can determine, e.g., the amount of requested pain killers in clinical settings and the efficacy of pain relief as a reinforcing stimulus.

SIGNIFICANCE

When in pain, pain relief can become an all-dominate goal. The perception of such pain relief can vary depending on external and internal characteristics and thus modulate, e.g., requests for pain killers in clinical settings. Here, we show that perceived intensity and pleasantness of pain relief changes with repetitions and whether the preceding pain is perceived as uncontrollable. Such mechanistic knowledge needs to be considered to maximize the effects of pain relief as a rewarding and reinforcing stimulus.

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.

Medication overuse and drug addiction: a narrative review from addiction perspective

Chronic headache is particularly prevalent in migraineurs and it can progress to a condition known as medication overuse headache (MOH). MOH is a secondary headache caused by overuse of analgesics or other medications such as triptans to abort acute migraine attacks. The worsening of headache symptoms associated with medication overuse (MO) generally ameliorates following interruption of regular medication use, although the primary headache symptoms remain unaffected. MO patients may also develop certain behaviors such as ritualized drug administration, psychological drug attachment, and withdrawal symptoms that have been suggested to correlate with drug addiction. Although several reviews have been performed on this topic, to the authors best knowledge none of them have examined this topic from the addiction point of view. Therefore, we aimed to identify features in MO and drug addiction that may correlate. We initiate the review by introducing the classes of analgesics and medications that can cause MOH and those with high risk to produce MO. We further compare differences between sensitization resulting from MO and from drug addiction, the neuronal pathways that may be involved, and the genetic susceptibility that may overlap between the two conditions. Finally, ICHD recommendations to treat MOH will be provided herein.

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.

Training endogenous pain modulation: a preliminary investigation of neural adaptation following repeated exposure to clinically-relevant pain

Analgesic treatments that aim to eliminate pain display marginal success in relieving chronic pain and may increase pain vulnerability. Repeated exposure to pain may result in increased pain modulation via engagement of anti-nociceptive brain regions. It was hypothesized that repeated exposure to delayed onset muscle soreness (DOMS) would result in increased pain modulatory capacity (PMC) via functional neural adaptation. 23 healthy participants completed Baseline and Follow Up resting-state fMRI and quantitative sensory testing (QST) visits 40 days apart. Participants were randomized to two groups: A Repeated DOMS Group (RD Group) that received four, weekly DOMS inductions and a Control Group that received one baseline induction. Daily pain ratings were collected for seven days post-induction, as were quantitative sensory testing (QST) metrics at baseline and Follow Up. Regional functional connectivity (FC) was estimated among areas involved in pain modulation. Seed and network FC was estimated among areas involved in pain modulation and sensory processing. Changes in FC were compared between groups. The RD Group displayed significant reductions in post-DOMS pain ratings and significant changes in thermal QST measures. RD Group participants displayed greater adaptation in nucleus accumbens-medial prefrontal cortex (NAc-mPFC) FC and in sensorimotor network (SMN) connectivity with the dorsomedial, ventromedial, and rostromedial prefrontal cortices. Changes in SMN-PFC connectivity correlated with reductions in post-DOMS affective distress. Results suggest that repeated exposure to clinically-relevant pain results in adaptations among brain regions involved in pain modulation. Repeated exposure to clinically-relevant pain may serve as a mechanism to increase PMC via inhibition of emotional valuation of painful stimuli.

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.

An orbitofrontal cortex to midbrain projection modulates hypersensitivity after peripheral nerve injury

Neuropathic pain is a debilitating condition that is often refractory to treatment. The network of neural substrates for pain transmission and control within the brain is complex and remains poorly understood. Through a combination of neuronal tracing, optogenetics, chemogenetics, electrophysiological recordings, and behavioral assessment, we demonstrate that activation of layer 5 pyramidal neurons in the ventrolateral orbitofrontal cortex (vlOFC) attenuates mechanical and thermal hypersensitivity and cold allodynia in mice with neuropathic pain induced by spared nerve injury (SNI). These vlOFC output neurons project to the posterior ventrolateral periaqueductal gray (vlPAG) region and receive inputs from the ventromedial thalamus (VM). Specific optogenetic and chemogenetic activation of the vlOFC-vlPAG and the VM-vlOFC circuits inhibits hypersensitivity associated with neuropathy. Thus, we reveal a modulatory role of the vlOFC and its projections to the vlPAG circuit in the processing of hypersensitive nociception.

Naloxone-induced analgesia mediated by central kappa opioid system in chronic inflammatory pain

Opioids, which are widely used for the treatment of chronic pain, have an analgesic effect by mainly activating mu-opioid receptor (MOR). Paradoxically, a high dose of naloxone, non-selective opioid receptor antagonist, is also known to induce analgesia, but the underlying mechanism remains unclear. Since kappa-opioid receptor (KOR) and dynorphin (KOR ligand) have been implicated in the naloxone-induced analgesia, we aimed to elucidate its mechanism by focusing on the kappa-opioid system in the brain under inflammatory pain condition. Systemic administration of naloxone (10 mg/kg, i.p.) decreased spontaneous pain behaviors only in complete Freund's adjuvant (CFA)-induced chronic inflammatory pain model but not in the formalin-induced acute pain model. Immunohistochemistry analysis in the CFA model revealed both a significant decrease in MOR expression and an increase in prodynorphin density in the central nucleus of theamygdala (CeA) and nucleus accumbens (NAc) but not in other brain areas. Systemic administration of KOR antagonist (norbinaltorphimine, nor-BNI 10 mg/kg) also decreased spontaneous pain behaviors in the CFA model. Furthermore, microinjection of both naloxone and nor-BNI into NAc and CeA significantly reduced spontaneous chronic pain behavior. Taken together, our results suggest that naloxone-induced analgesia may be mediated by blocking facilitated kappa-opioid systems in the NAc and CeA.

A pain-induced tonic hypodopaminergic state augments phasic dopamine release in the nucleus accumbens

Diseases and disorders such as Parkinson disease, schizophrenia, and chronic pain are characterized by altered mesolimbic dopaminergic neurotransmission. Dopamine release in the nucleus accumbens influences behavior through both tonic and phasic signaling. Tonic dopamine levels are hypothesized to inversely regulate phasic signals through dopamine D2 receptor feedback inhibition. We tested this hypothesis directly in the context of ongoing pain. Tonic and phasic dopamine signals were measured using fast-scan controlled-adsorption voltammetry and fast-scan cyclic voltammetry, respectively, in the nucleus accumbens shell of male rats with standardized levels of anesthesia. Application of capsaicin to the cornea produced a transient decrease in tonic dopamine levels. During the pain-induced hypodopaminergic state, electrically evoked phasic dopamine release was significantly increased when compared to baseline, evoked phasic release. A second application of capsaicin to the same eye had a lessened effect on tonic dopamine suggesting desensitization of TRPV1 channels in that eye. Capsaicin treatment in the alternate cornea, however, again produced coincident decreased dopaminergic tone and increased phasic dopamine release. These findings occurred independently of stimulus lateralization relative to the hemisphere of dopamine measurement. Our data show that (1) the mesolimbic dopamine circuit reliably encodes acute noxious stimuli; (2) ongoing pain produces decreases in dopaminergic tone; and (3) pain-induced decreases in tonic dopamine correspond to augmented evoked phasic dopamine release. Enhanced phasic dopamine neurotransmission resulting from salient stimuli may contribute to increased impulsivity and cognitive deficits often observed in conditions associated with decreased dopaminergic tone, including Parkinson disease and chronic pain.

AMPAkines potentiate the corticostriatal pathway to reduce acute and chronic pain

The corticostriatal circuit plays an important role in the regulation of reward- and aversion-types of behaviors. Specifically, the projection from the prelimbic cortex (PL) to the nucleus accumbens (NAc) has been shown to regulate sensory and affective aspects of pain in a number of rodent models. Previous studies have shown that enhancement of glutamate signaling through the NAc by AMPAkines, a class of agents that specifically potentiate the function of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, reduces acute and persistent pain. However, it is not known whether postsynaptic potentiation of the NAc with these agents can achieve the full anti-nociceptive effects of PL activation. Here we compared the impact of AMPAkine treatment in the NAc with optogenetic activation of the PL on pain behaviors in rats. We found that not only does AMPAkine treatment partially reconstitute the PL inhibition of sensory withdrawals, it fully occludes the effect of the PL on reducing the aversive component of pain. These results indicate that the NAc is likely one of the key targets for the PL, especially in the regulation of pain aversion. Furthermore, our results lend support for neuromodulation or pharmacological activation of the corticostriatal circuit as an important analgesic approach.

Animal models for the study of depressive disorder

Depressive disorder is one of the most widespread forms of psychiatric pathology, worldwide. According to a report by the World Health Organization, the number of people with depression, globally, is increasing dramatically with each year. Previous studies have demonstrated that various factors, including genetics and environmental stress, contribute to the risk of depression. As such, it is crucial to develop a detailed understanding of the pathogenesis of depressive disorder and animal studies are essential for identifying the mechanisms and genetic disorders underlying depression. Recently, many researchers have reported on the pathology of depression via various models of depressive disorder. Given that different animal models of depression show differences in terms of patterns of depressive behavior and pathology, the comparison between depressive animal models is necessary for progress in the field of the depression study. However, the various animal models of depression have not been fully compared or evaluated until now. In this paper, we reviewed the pathophysiology of the depressive disorder and its current animal models with the analysis of their transcriptomic profiles. We provide insights for selecting different animal models for the study of depression.

Adaptive alterations in the mesoaccumbal network after peripheral nerve injury

ABSTRACT

The nucleus accumbens (NAc) and the ventral tegmental area (VTA) are critical hubs in the brain circuitry controlling chronic pain. Yet, how these 2 regions interact to shape the chronic pain state is poorly understood. Our studies show that in mice, spared nerve injury (SNI) induced alterations in the functional connectome of D2-receptor expressing spiny projection neurons in the core region of the NAc-enhancing connections with prelimbic cortex and weakening them with basolateral amygdala. These changes, which were attributable in part to SNI-induced suppression of VTA dopaminergic signaling, were adaptive because mimicking them chemogenetically alleviated the anxiety and social withdrawal accompanying injury. By contrast, chemogenetic enhancement of activity in VTA dopaminergic neurons projecting to the medial shell of the NAc selectively suppressed tactile allodynia in SNI mice. These results suggest that SNI induces regionally specific alterations in VTA dopaminergic signaling in the NAc to promote environmental reengagement after injury. However, countervailing, homeostatic mechanisms limit these adaptive changes, potentially leading to the chronic pain state.

Air Hunger: A Primal Sensation and a Primary Element of Dyspnea

The sensation that develops as a long breath hold continues is what this article is about. We term this sensation of an urge to breathe "air hunger." Air hunger, a primal sensation, alerts us to a failure to meet an urgent homeostatic need maintaining gas exchange. Anxiety, frustration, and fear evoked by air hunger motivate behavioral actions to address the failure. The unpleasantness and emotional consequences of air hunger make it the most debilitating component of clinical dyspnea, a symptom associated with respiratory, cardiovascular, and metabolic diseases. In most clinical populations studied, air hunger is the predominant form of dyspnea (colloquially, shortness of breath). Most experimental subjects can reliably quantify air hunger using rating scales, that is, there is a consistent relationship between stimulus and rating. Stimuli that increase air hunger include hypercapnia, hypoxia, exercise, and acidosis; tidal expansion of the lungs reduces air hunger. Thus, the defining experimental paradigm to evoke air hunger is to elevate the drive to breathe while mechanically restricting ventilation. Functional brain imaging studies have shown that air hunger activates the insular cortex (an integration center for perceptions related to homeostasis, including pain, food hunger, and thirst), as well as limbic structures involved with anxiety and fear. Although much has been learned about air hunger in the past few decades, much remains to be discovered, such as an accepted method to quantify air hunger in nonhuman animals, fundamental questions about neural mechanisms, and adequate and safe methods to mitigate air hunger in clinical situations. © 2021 American Physiological Society. Compr Physiol 11:1449-1483, 2021.

Brain Structure and Function of Chronic Low Back Pain Patients on Long-Term Opioid Analgesic Treatment: A Preliminary Study

Chronic low back pain (CLBP) is often treated with opioid analgesics (OA), a class of medications associated with a significant risk of misuse. However, little is known about how treatment with OA affect the brain in chronic pain patients. Gaining this knowledge is a necessary first step towards understanding OA associated analgesia and elucidating long-term risk of OA misuse. Here we study CLBP patients chronically medicated with opioids without any evidence of misuse and compare them to CLBP patients not on opioids and to healthy controls using structural and functional brain imaging. CLBP patients medicated with OA showed loss of volume in the nucleus accumbens and thalamus, and an overall significant decrease in signal to noise ratio in their sub-cortical areas. Power spectral density analysis (PSD) of frequency content in the accumbens’ resting state activity revealed that both medicated and unmedicated patients showed loss of PSD within the slow-5 frequency band (0.01–0.027 Hz) while only CLBP patients on OA showed additional density loss within the slow-4 frequency band (0.027–0.073 Hz). We conclude that chronic treatment with OA is associated with altered brain structure and function within sensory limbic areas.

Foot shock facilitates reward seeking in an experience-dependent manner

Animals organize reward seeking around aversive events. An abundance of research shows that foot shock, as well as a shock-associated cue, can elicit freezing and suppress reward seeking. Yet, there is evidence that experience can flip the effect of foot shock to facilitate reward seeking. Here we examined cue suppression, foot shock suppression and foot shock facilitation of reward seeking in a single behavioural setting. Male Long Evans rats received fear discrimination consisting of danger, uncertainty, and safety cues. Discrimination took place over a baseline of rewarded nose poking. With limited experience (1-2 sessions), all cues and foot shock suppressed reward seeking. With continued experience (10-16 sessions), suppression became specific to shock-associated cues, foot shock briefly suppressed, then facilitated reward seeking. Our results provide a means of assessing positive properties of foot shock, and may provide insight into maladaptive behaviour around aversive events.

Brain Responses to Noxious Stimuli in Patients With Chronic Pain: A Systematic Review and Meta-analysis

IMPORTANCE

Functional neuroimaging is a valuable tool for understanding how patients with chronic pain respond to painful stimuli. However, past studies have reported heterogenous results, highlighting opportunities for a quantitative meta-analysis to integrate existing data and delineate consistent associations across studies.

OBJECTIVE

To identify differential brain responses to noxious stimuli in patients with chronic pain using functional magnetic resonance imaging (fMRI) while adhering to current best practices for neuroimaging meta-analyses.

DATA SOURCES

All fMRI experiments published from January 1, 1990, to May 28, 2019, were identified in a literature search of PubMed/MEDLINE, EMBASE, Web of Science, Cochrane Library, PsycINFO, and SCOPUS.

STUDY SELECTION

Experiments comparing brain responses to noxious stimuli in fMRI between patients and controls were selected if they reported whole-brain results, included at least 10 patients and 10 healthy control participants, and used adequate statistical thresholding (voxel-height P < .001 or cluster-corrected P < .05). Two independent reviewers evaluated titles and abstracts returned by the search. In total, 3682 abstracts were screened, and 1129 full-text articles were evaluated.

DATA EXTRACTION AND SYNTHESIS

Thirty-seven experiments from 29 articles met inclusion criteria for meta-analysis. Coordinates reporting significant activation differences between patients with chronic pain and healthy controls were extracted. These data were meta-analyzed using activation likelihood estimation. Data were analyzed from December 2019 to February 2020.

MAIN OUTCOMES AND MEASURES

A whole-brain meta-analysis evaluated whether reported differences in brain activation in response to noxious stimuli between patients and healthy controls were spatially convergent. Follow-up analyses examined the directionality of any differences. Finally, an exploratory (nonpreregistered) region-of-interest analysis examined differences within the pain network.

RESULTS

The 37 experiments from 29 unique articles included a total of 511 patients and 433 controls (944 participants). Whole-brain meta-analyses did not reveal significant differences between patients and controls in brain responses to noxious stimuli at the preregistered statistical threshold. However, exploratory analyses restricted to the pain network revealed aberrant activity in patients.

CONCLUSIONS AND RELEVANCE

In this systematic review and meta-analysis, preregistered, whole-brain analyses did not reveal aberrant fMRI activity in patients with chronic pain. Exploratory analyses suggested that subtle, spatially diffuse differences may exist within the pain network. Future work on chronic pain biomarkers may benefit from focus on this core set of pain-responsive areas.

Neurogenesis of medium spiny neurons in the nucleus accumbens continues into adulthood and is enhanced by pathological pain

In mammals, most adult neural stem cells (NSCs) are located in the ventricular-subventricular zone (V-SVZ) along the wall of the lateral ventricles and they are the source of olfactory bulb interneurons. Adult NSCs exhibit an apico-basal polarity; they harbor a short apical process and a long basal process, reminiscent of radial glia morphology. In the adult mouse brain, we detected extremely long radial glia-like fibers that originate from the anterior-ventral V-SVZ and that are directed to the ventral striatum. Interestingly, a fraction of adult V-SVZ-derived neuroblasts dispersed in close association with the radial glia-like fibers in the nucleus accumbens (NAc). Using several in vivo mouse models, we show that newborn neurons integrate into preexisting circuits in the NAc where they mature as medium spiny neurons (MSNs), i.e., a type of projection neurons formerly believed to be generated only during embryonic development. Moreover, we found that the number of newborn neurons in the NAc is dynamically regulated by persistent pain, suggesting that adult neurogenesis of MSNs is an experience-modulated process.

A neuroimaging marker for predicting longitudinal changes in pain intensity of subacute back pain based on large-scale brain network interactions

Identification of predictive neuroimaging markers of pain intensity changes is a crucial issue to better understand macroscopic neural mechanisms of pain. Although a single connection between the medial prefrontal cortex and nucleus accumbens has been suggested as a powerful marker, how the complex interactions on a large-scale brain network can serve as the markers is underexplored. Here, we aimed to identify a set of functional connections predictive of longitudinal changes in pain intensity using large-scale brain networks. We re-analyzed previously published resting-state functional magnetic resonance imaging data of 49 subacute back pain (SBP) patients. We built a network-level model that predicts changes in pain intensity over one year by combining independent component analysis and a penalized regression framework. Connections involving top-down pain modulation, multisensory integration, and mesocorticolimbic circuits were identified as predictive markers for pain intensity changes. Pearson’s correlations between actual and predicted pain scores were r = 0.33–0.72, and group classification results between SBP patients with persisting pain and recovering patients, in terms of area under the curve (AUC), were 0.89/0.75/0.75 for visits four/three/two, thus outperforming the previous work (AUC 0.83/0.73/0.67). This study identified functional connections important for longitudinal changes in pain intensity in SBP patients, providing provisional markers to predict future pain using large-scale brain networks.

Back Pain Related with Age, Anthropometric Variables, Sagittal Spinal Curvatures, Hamstring Extensibility, Physical Activity and Health Related Quality of Life in Male and Female High School Students

Spinal pain (SP) is widely extended among adolescents. The origin of SP can be multifactorial; thus, the present study aimed to estimate the prevalence and risk of SP in high school students and to determine the differences in sagittal spinal curvatures and pelvic tilt, hamstring extensibility, age, anthropometric variables and healthy lifestyle habits dependent on SP between sexes. Two hundred seventy-three teenagers took part in this cross-sectional study. Age, sagittal spinal curvatures, hamstring extensibility, physical activity, sedentary lifestyle, anthropometric variables and health related quality of life (HRQL) were recorded. SP was reported by 16.12% of adolescents. Differences were observed in the HRQL according to SP (p < 0.05). Participants without SP were less sedentary (22.12%) and younger (13.10 years old) than participants with SP (40.91% and 13.66, respectively) (p < 0.05). A logistic regression model showed that both variables were significantly collinear (VIF = 1.01; Durbin-Watson = 2.10). Subjects with low back pain (LBP) had a higher weight, body max index, and hip girth than subjects without pain (p < 0.05). A misalignment in the lumbar spine was associated with LBP for males (Cramer’s V = 0.204, p = 0.022). In conclusion, adolescents with SP were older and had a lower HRQL in all dimensions. SP could be predicted according to age and sedentary habits.

Resilience to Stress and Resilience to Pain: Lessons from Molecular Neurobiology and Genetics

What biological factors account for resilience to pain or to behavioral stress? Here, we discuss examples of cellular and molecular mechanisms within disparate parts of the nervous system as contributors to such resilience. In some especially well-studied humans, it is possible to identify particular neuronal cell types in the peripheral nervous system (PNS) and pinpoint specific genes that are major contributors to pain resilience. We also discuss more complex factors that operate within the central nervous system (CNS) to confer resilience to behavioral stress. We propose that genetic and neurobiological substrates for resilience are discoverable and suggest more generally that neurology and psychiatry hold lessons for each other as investigators search for actionable, biological underpinnings of disease.

Pain Pathways and Nervous System Plasticity: Learning and Memory in Pain

Objective This article reviews the structural and functional changes in pain chronification and explores the association between memory and the development of chronic pain. Methods PubMed was searched using the terms "chronic pain," "central sensitization," "learning," "memory," "long-term potentiation," "long-term depression," and "pain memory." Relevant findings were synthesized into a narrative of the processes affecting pain chronification. Results Pain pathways represent a complex sensory system with cognitive, emotional, and behavioral influences. Anatomically, the hippocampus, amygdala, and anterior cortex-central to the encoding and consolidation of memory-are also implicated in experiential aspects of pain. Common neurotransmitters and similar mechanisms of neural plasticity (eg, central sensitization, long-term potentiation) suggest a mechanistic overlap between chronic pain and memory. These anatomic and mechanistic correlates indicate that chronic pain and memory intimately interact on several levels. Longitudinal imaging studies suggest that spatiotemporal reorganization of brain activity accompanies the transition to chronic pain, during which the representation of pain gradually shifts from sensory to emotional and limbic structures. Conclusions The chronification of pain can be conceptualized as activity-induced plasticity of the limbic-cortical circuitry resulting in reorganization of the neocortex. The state of the limbic-cortical network determines whether nociceptive signals are transient or chronic by extinguishing pathways or amplifying signals that intensify the emotional component of nociceptive inputs. Thus, chronic pain can be seen as the persistence of the memory of pain and/or the inability to extinguish painful memories. Ideally, pharmacologic, physical, and/or psychological approaches should reverse the reorganization accompanying chronic pain.

Anhedonia in chronic pain and prescription opioid misuse

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The migraineur’s brain networks: Continuous resting state fMRI over 30 days

Objective

The aim of the current study was to identify typical alterations in resting state connectivity within different stages of the migraine cycle and to thus explore task-free mechanisms of headache attack generation in migraineurs.

Background

Recent evidence in migraine pathophysiology suggests that hours and even days before headache certain changes in brain activity take place, ultimately leading to an attack. Here, we investigate changes before headache onset using resting state functional magnetic resonance imaging (fMRI).

Methods

Nine episodic migraineurs underwent daily resting state functional magnetic resonance imaging for a minimum period of 30 consecutive days, leading to a cumulative number of 282 total days scanned. Thus, data from 15 spontaneous headache attacks were acquired. This allows analysing not only the ictal and the interictal phase of migraine but also the preictal phase. ROI-to-ROI (region of interest) and ROI-to-voxel connectivity was calculated over the migraine cycle.

Results

Within the ROI-to-ROI analysis, the right nucleus accumbens showed enhanced functional connectivity to the left amygdala, hippocampus and gyrus parahippocampalis in the preictal phase compared to the interictal phase. ROI-to-voxel connectivity of the right accumbens with the dorsal rostral pons was enhanced during the preictal phase compared to interictally. Regarding custom defined ROIs, the dorsal pons was ictally functionally more strongly coupled to the hypothalamic area than interictally.

Conclusions

This unique data set suggests that particularly connectivity changes in dopaminergic centres and between the dorsal pons and the hypothalamus are important within migraine attack generation and sustainment.

SIRT1 Mediates Neuropathic Pain Induced by Sciatic Nerve Chronic Constrictive Injury in the VTA-NAc Pathway

Background

Mounting evidence has shown that sirtuin 1 (SIRT1), a class III histone deacetylase, alleviated several types of neuropathic pain in the spinal cord and dorsal root ganglion and regulated some aberrant behaviors in the ventral tegmental area (VTA) and the nucleus accumbens (NAc).

Methods

In this context, the effect of SIRT1 on neuropathic pain in the VTA-NAc pathway was investigated in the model of chronic constrictive injury (CCI).

Results

SIRT1 was localized in the VTA neurons in naive mice. The expression of SIRT1 was decreased in the contralateral VTA of CCI mice. After microinjection of SRT1720 (an activator of SIRT1) in the contralateral VTA of CCI mice, the established thermal hyperalgesia was attenuated. However, it was further exacerbated by EX-527 (an inhibitor of SIRT1). The elevated level of acetyl-histone 3 was reduced by SRT1720 but further elevated by EX-527 in the contralateral VTA of CCI mice. The increased expression of Fos in both VTA and NAc was downregulated by SRT1720 but further upregulated by EX-527 in CCI mice.

Conclusions

The discovery of the effect of SIRT1 on neuropathic pain in the VTA represents an important step forward in understanding the analgesic mechanisms of the VTA-NAc pathway.

Brain-behaviour correlates of habitual motivation in chronic back pain

Chronic pain may sap the motivation for positive events and stimuli. This may lead to a negative behavioural cycle reducing the establishment of appetitive habitual engagement. One potential mechanism for this might be biased learning. In our experiment, chronic back pain patients and healthy controls completed an appetitive Pavlovian-instrumental transfer procedure. We examined participants` behaviour and brain activity and reported pain, depression and anxiety. Patients showed reduced habitual behaviour and increased responses in the hippocampus than controls. This behavioural bias was related to motivational value and reflected in the updating of brain activity in prefrontal–striatal–limbic circuits. Moreover, this was influenced by pain symptom duration, depression and anxiety (explained variance: up to 50.7%). Together, findings identify brain-behaviour pathways for maladaptive habitual learning and motivation in chronic back pain, which helps explaining why chronic pain can be resistant to change, and where clinical characteristics are significant modulators.

Pain memory in patients with chronic pain versus asymptomatic individuals: A prospective cohort study

BACKGROUND

The main objective of this study was to assess pain memory as well as long-term episodic memory, both in patients with chronic pain (CP) and in asymptomatic participants (AP).

METHODS

A prospective cohort study design was used. Sixty-eight participants were divided into two groups: CP (n = 34) and AP (n = 34). The protocol consisted of taking eight tests, four painful provocation tests and four distracting tests, and completing a memory test on the order of the tests at the end of the experiment and at 1-month post-experiment.

RESULTS

Patients with CP showed acceptable concordance in the classification, in ascending order from lower to higher pain perception, both post-experiment and 1-month post-experiment (κ = 0.41-0.60, p < .001). No differences were found regarding recall of the order of the tests, but differences were found in painful tests isolated only post-experiment in the CP group with a moderate effect size (p < .05, d = 0.77).

CONCLUSIONS

Patients with CP had a more reliable memory than AP in relation to the memory of the pain caused experimentally until at least 1 month after the experiment. Interspersing distraction tests appeared to result in increased complexity and difficulty in coding and decoding information in patients with CP, leading to similar reliable long-term memory consolidation in comparison with AP.

SIGNIFICANCE

Treatments directed towards chronic pain should consider the influence of painful memories and their establishment towards long-term explicit episodic memories in patients with chronic pain, as well as the influence of cognitive-evaluative and affective-motivational variables on memory. Not causing pain while implementing a treatment whose objective is to reduce pain could reduce the probability of developing new painful memories in patients with chronic pain.

The Cerebral Localization of Pain: Anatomical and Functional Considerations for Targeted Electrical Therapies

Millions of people in the United States are affected by chronic pain, and the financial cost of pain treatment is weighing on the healthcare system. In some cases, current pharmacological treatments may do more harm than good, as with the United States opioid crisis. Direct electrical stimulation of the brain is one potential non-pharmacological treatment with a long history of investigation. Yet brain stimulation has been far less successful than peripheral or spinal cord stimulation, perhaps because of our limited understanding of the neural circuits involved in pain perception. In this paper, we review the history of using electrical stimulation of the brain to treat pain, as well as contemporary studies identifying the structures involved in pain networks, such as the thalamus, insula, and anterior cingulate. We propose that the thermal grill illusion, an experimental pain model, can facilitate further investigation of these structures. Pairing this model with intracranial recording will provide insight toward disentangling the neural correlates from the described anatomic areas. Finally, the possibility of altering pain perception with brain stimulation in these regions could be highly informative for the development of novel brain stimulation therapies for chronic pain.

Clinical and biobehavioral perspectives: Is medication overuse headache a behavior of dependence?

Medication overuse headache (MOH), previously known as analgesic abuse headache or medication misuse headaches, is a common form of chronic headache disorder that has a detrimental impact on health and society. Although it has been widely accepted that overusing abortive medications is paradoxically the cause of MOH and drug discontinuation is the treatment of choice, ongoing debates exist as to whether drug consumption per se is the cause or consequence of headache chronification. Certain features in MOH such as their compulsive drug-seeking behavior, withdrawal headaches and high relapse rates share similarities with drug dependence, suggesting that there might be common underlying biological and psychobehavioral mechanisms. In this regard, this article will discuss the updated evidence and current debates on the possible biobehavioral overlap between MOH and drug dependence. To begin with, we will discuss whether MOH has characteristics of substance dependence based on standard psychiatry diagnostic criteria and other widely used dependence scales. Recent epidemiological studies underscoring common psychiatric comorbidities between the two disorders will also be presented. Although both demonstrate seemingly distinct personality traits, recent studies revealed similar decision-making impairment from a cognitive perspective, indicating the presence of a maladaptive reward system in both disorders. In addition, emerging imaging studies also support this notion by showing reversible morphological and functional brain changes related to the mesocorticolimbic reward circuitry in MOH, with a strong resemblance to those in addiction. Finally, an increased familial risk for drug dependence and genetic association with dopaminergic and drug dependence molecular pathways in MOH also support a possible link between MOH and addiction. Understanding the role of dependence in MOH will have a great impact on disease management as this will provide the missing piece of the puzzle in current therapeutic strategies.

Medial Orbitofrontal De-Activation During Tonic Cold Pain Stimulation: A fMRI Study Examining the Opponent-Process Theory

BACKGROUND

While the concomitant administration of painful and rewarding stimuli tends to reduce the perception of one another, recent evidence shows that pleasant pain relief is experience after the interruption of noxious stimuli. On neurobiological grounds, these opponent processes should translate into decreased activity in brain reward regions during nociceptive stimulation and increased activity in these regions after its interruption. While growing evidence supports the latter assumption, evidence is lacking in humans in support of the former.

METHODS

Twenty-six healthy individuals underwent a functional magnetic resonance imaging (fMRI) session during which they were administered a cold pain stimulation, using a novel paradigm which consisted in a cold gel applied on the right foot of participants.

RESULTS

After the interruption of noxious stimulation, participants experienced significant levels of pleasant pain relief. During cold pain stimulation, brain activations were observed in key regions of the pain matrix (eg, thalamus, primary somatosensory cortex and insula). Conversely, the medial orbitofrontal cortex was found to be de-activated. Medial orbitofrontal de-activations were negatively correlated with subclinical pain symptoms.

DISCUSSION

Our results show that a key brain reward region (eg, medial orbitofrontal cortex) is de-activated during cold pain stimulation, a result which is consistent with one of the central assumptions of the opponent-process theory. On methodological grounds, our results show that the cold gel applied to the foot can be used to trigger activations in the pain matrix, and that the interruption of the cold pressor test elicits significant levels of pleasant pain relief. fMRI studies on pain-reward interactions in chronic pain patients are warranted.

Brain functional connectivity changes by low back extension pain model in low back pain patients

PURPOSE

Low back pain (LBP) is a common ailment in most developed countries. Because most cases of LBP are known as 'non-specific', it has been challenging to develop experimental pain models of LBP which reproduce patients' clinical pain. In addition, previous models have limited applicability in a steady-pain-state neuroimaging environment. Thus, this study aims to devise a low back pain model with a simple methodology to induce experimental LBP, which has similar pain properties to patients' clinical pain, and to apply the model in a steady-pain-state neuroimaging study.

METHODS

Our low back extension (LBE) pain model was tested on 217 LBP patients outside the magnetic resonance imaging (MRI) scanner to determine the reproducibility of endogenous pain and the similarity to their own clinical pain (STUDY1), and applied in a steady-pain-state functional MRI study (47 LBP patients and 23 healthy controls) to determine its applicability (induced head motions and brain functional connectivity changes; STUDY2).

RESULTS

By the LBE pain model, 68.2% of the LBP patients reported increased LBP with high similarity of sensations to their own clinical pain (STUDY1), and the head motions were statistically similar to and correlated with those in resting state (STUDY2). Furthermore, the LBE model altered brain functional connectivity by decreasing the default-mode and the sensorimotor networks, and increasing the salience network, which was significantly associated with the intensity of the induced pain. Conversely, the healthy controls showed increased somatosensory network (but not of the cognitive pain processing).

CONCLUSION

Our investigations suggest that our LBE pain model, which increased LBP with high similarity to the LBP patients' own pain sensation and induced patient-specific brain responses with acceptable head motion, could be applied to neuroimaging studies investigating brain responses to different levels of endogenous LBP.

Impaired mesocorticolimbic connectivity underlies increased pain sensitivity in chronic low back pain

Chronic low back pain (cLBP) is a prevalent disorder. A growing body of evidence linking the pathology of the reward network to chronic pain suggests that pain sensitization may contribute to cLBP chronification via disruptions of mesocortical and mesolimbic circuits in the reward system. Resting-state (RS) functional magnetic resonance imaging (fMRI) data was acquired from 90 patients with cLBP and 74 matched pain-free controls (HCs) at baseline and after a manipulation for back pain intensification. The ventral tegmental area (VTA) was chosen as a seed region to perform RS functional connectivity (FC) analysis. Baseline rsFC of both the mesocortical (between the VTA and bilateral rostral anterior cingulate cortex (rACC)/and medial prefrontal cortex (mPFC)) and mesolimbic (between the VTA and bilateral hippocampus/parahippocampus) pathways was reduced in patients with cLBP (vs. HCs). In addition, patients exhibiting higher back pain intensity (compared to the relatively lower back pain intensity condition) also showed increases in both mesocortical and mesolimbic connectivity, implicating these pathways in pain downregulation in cLBP. Mediation analysis further isolated the mesolimbic (VTA-hippocampus/parahippocampus) dysconnectivity as a neural mechanism mediating the association between mechanical pain sensitivity (indexed by P40 pressure) and cLBP severity. In sum, the current study demonstrates deficient mesocorticolimbic connectivity in cLBP, with mesolimbic dysconnectivity potentially mediating the contribution of pain sensitization to pain chronification. These reward network dysfunctions and purportedly, dopaminergic dysregulations, may help us to identify key brain targets of neuromodulation in the treatment of cLBP.

The Medial Prefrontal Cortex as a Central Hub for Mental Comorbidities Associated with Chronic Pain

Chronic pain patients frequently develop and suffer from mental comorbidities such as depressive mood, impaired cognition, and other significant constraints of daily life, which can only insufficiently be overcome by medication. The emotional and cognitive components of pain are processed by the medial prefrontal cortex, which comprises the anterior cingulate cortex, the prelimbic, and the infralimbic cortex. All three subregions are significantly affected by chronic pain: magnetic resonance imaging has revealed gray matter loss in all these areas in chronic pain conditions. While the anterior cingulate cortex appears hyperactive, prelimbic, and infralimbic regions show reduced activity. The medial prefrontal cortex receives ascending, nociceptive input, but also exerts important top-down control of pain sensation: its projections are the main cortical input of the periaqueductal gray, which is part of the descending inhibitory pain control system at the spinal level. A multitude of neurotransmitter systems contributes to the fine-tuning of the local circuitry, of which cholinergic and GABAergic signaling are particularly emerging as relevant components of affective pain processing within the prefrontal cortex. Accordingly, factors such as distraction, positive mood, and anticipation of pain relief such as placebo can ameliorate pain by affecting mPFC function, making this cortical area a promising target region for medical as well as psychosocial interventions for pain therapy.

Pain in neuropsychiatry: Insights from animal models

Pain is the most common symptom reported in clinical practice, meaning that it is associated with many pathologies as either the origin or a consequence of other illnesses. Furthermore, pain is a complex emotional and sensorial experience, as the correspondence between pain and body damage varies considerably. While these issues are widely acknowledged in clinical pain research, until recently they have not been extensively considered when exploring animal models, important tools for understanding pain pathophysiology. Interestingly, chronic pain is currently considered a risk factor to suffer psychiatric disorders, mainly stress-related disorders like anxiety and depression. Conversely, pain appears to be altered in many psychiatric disorders, such as depression, anxiety and schizophrenia. Thus, pain and psychiatric disorders have been linked in epidemiological and clinical terms, although the neurobiological mechanisms involved in this pathological bidirectional relationship remain unclear. Here we review the evidence obtained from animal models about the co-morbidity of pain and psychiatric disorders, placing special emphasis on the different dimensions of pain.

Neural and sociocultural mediators of ethnic differences in pain

Understanding ethnic differences in pain is important for addressing disparities in pain care. A common belief is that African Americans are hyposensitive to pain compared to Whites, but African Americans show increased pain sensitivity in clinical and laboratory settings. The neurobiological mechanisms underlying these differences are unknown. We studied an ethnicity- and gender-balanced sample of African Americans, Hispanics and non-Hispanic Whites using functional magnetic resonance imaging during thermal pain. Higher pain report in African Americans was mediated by discrimination and increased frontostriatal circuit activations associated with pain rating, discrimination, experimenter trust and extranociceptive aspects of pain elsewhere. In contrast, the neurologic pain signature, a neuromarker sensitive and specific to nociceptive pain, mediated painful heat effects on pain report largely similarly in African American and other groups. Findings identify a brain basis for higher pain in African Americans related to interpersonal context and extranociceptive central pain mechanisms and suggest that nociceptive pain processing may be similar across ethnicities.

Cerebral regional and network characteristics in asthma patients: a resting-state fMRI study

Asthma is a serious health problem that involves not only the respiratory system but also the central nervous system. Previous studies identified either regional or network alterations in patients with asthma, but inconsistent results were obtained. A key question remains unclear: are the regional and neural network deficits related or are they two independent characteristics in asthma? Answering this question is the aim of this study. By collecting resting-state functional magnetic resonance imaging from 39 patients with asthma and 40 matched health controls, brain functional measures including regional activity (amplitude of low-frequency fluctuations) and neural network function (degree centrality (DC) and functional connectivity) were calculated to systematically characterize the functional alterations. Patients exhibited regional abnormities in the left angular gyrus, right precuneus, and inferior temporal gyrus within the default mode network. Network abnormalities involved both the sensorimotor network and visual network with key regions including the superior frontal gyrus and occipital lobes. Altered DC in the lingual gyrus was correlated with the degree of airway obstruction. This study elucidated different patterns of regional and network changes, thereby suggesting that the two parameters reflect different brain characteristics of asthma. These findings provide evidence for further understanding the potential cerebral alterations in the pathophysiology of asthma.

The projections from the anterior cingulate cortex to the nucleus accumbens and ventral tegmental area contribute to neuropathic pain-evoked aversion in rats

Although the anterior cingulate cortex (ACC) plays a vital role in neuropathic pain-related aversion, the underlying mechanisms haven't been fully studied. The mesolimbic dopamine system encodes reward and aversion, and participates in the exacerbation of chronic pain. Therefore, we investigated whether the ACC modulates aversion to neuropathic pain via control of the mesolimbic dopamine system, in a rat model of chronic constriction injury (CCI) to the sciatic nerve. Using anterograde and retrograde tracings, we confirmed that a subgroup of ACC neurons projected to the nucleus accumbens (NAc) and ventral tegmental area (VTA), which are two crucial nodes of the mesolimbic dopamine system. Combining electrophysiology in juvenile rats 7 days post-CCI, we found that the NAc/VTA-projecting neurons were hyperexcitable after CCI. Chemogenetic inhibition of these projections induced conditioned place preference in young adult rats 10-14 days post-CCI, without modulating the evoked pain threshold, whereas activation of these projections in sham rats mimicked aversive behavior. Furthermore, the function of the ACC projections was probably mediated by NAc D2-type medium spiny neurons and VTA GABAergic neurons. Taken together, our findings suggest that projections from the ACC to the NAc and VTA mediate neuropathic pain-related aversive behavior.

Role of Descending Dopaminergic Pathways in Pain Modulation

Pain, especially when chronic, is a common reason patients seek medical care and it affects the quality of life and well-being of the patients. Unfortunately, currently available therapies for chronic pain are often inadequate because the neurobiological basis of such pain is still not fully understood. Although dopamine has been known as a neurotransmitter to mediate reward and motivation, accumulating evidence has shown that dopamine systems in the brain are also involved in the central regulation of chronic pain. Most importantly, descending dopaminergic pathways play an important role in pain modulation. In this review, we discuss dopamine receptors, dopaminergic systems in the brain, and the role of descending dopaminergic pathways in the modulation of different types of pain.

Multiple Brain Networks Mediating Stimulus-Pain Relationships in Humans

The brain transforms nociceptive input into a complex pain experience comprised of sensory, affective, motivational, and cognitive components. However, it is still unclear how pain arises from nociceptive input and which brain networks coordinate to generate pain experiences. We introduce a new high-dimensional mediation analysis technique to estimate distributed, network-level patterns that formally mediate the relationship between stimulus intensity and pain. We applied the model to a large-scale analysis of functional magnetic resonance imaging data (N = 284), focusing on brain mediators of the relationship between noxious stimulus intensity and trial-to-trial variation in pain reports. We identify mediators in both traditional nociceptive pathways and in prefrontal, midbrain, striatal, and default-mode regions unrelated to nociception in standard analyses. The whole-brain mediators are specific for pain versus aversive sounds and are organized into five functional networks. Brain mediators predicted pain ratings better than previous brain measures, including the neurologic pain signature (Wager et al. 2013). Our results provide a broader view of the networks underlying pain experience, as well as novel brain targets for interventions.

Should musicians play in pain?

Musculoskeletal symptoms, including pain, are often experienced by musicians at all levels. These symptoms may have a detrimental impact on musicians' personal and work lives, and may also impact upon the ensembles they work within. Providing musicians with appropriate, evidence-based advice regarding pain management is therefore paramount. In this review, we aim to improve the advice given to musicians regarding playing when in pain, by answering the question 'should musicians play in pain?'. This multidisciplinary narrative review draws upon contemporary pain science, including factors associated with poorer prognoses for those in pain, as well as the reported experiences of musicians with pain (including those who have taken time off from playing). Our current understanding of pain science provides further support for the potential for consequences related to avoiding activities due to pain. Pain is modulated by a number of neuro-immunological processes and is influenced by a range of psychosocial factors. Taking time off from playing might therefore not have any benefit. Importantly, one of the leading causes of a transition from acute to chronic pain is fear-avoidance behaviour (e.g. not playing when in pain); hence, encouraging such behaviour cannot be supported. Musicians who have taken time off from playing due to pain have experienced a range of consequences, including emotional and financial consequences. These experiences indicate that there are potential negative consequences related to taking time off from playing which need to be weighed against any benefits. We conclude that musicians should not necessarily be advised to take time off from playing to manage their pain, in keeping with current best practice for pain management. Instead, we recommend that musicians be educated on contemporary pain science and when to seek treatment from a health professional for individualised advice to reduce the burden of musicians' pain.

Oxytocin modulates intrinsic neural activity in patients with chronic low back pain

BACKGROUND

Modulation of pain perception by oxytocin (OXT) has attracted increased scientific and clinical interest. Neural mechanisms underlying these effects are poorly understood. In this study, we aimed to investigate the effects of intranasally applied OXT on intrinsic neural activity in patients with chronic low back pain (cLBP).

METHODS

Twenty-four male patients with cLBP and 23 healthy males were examined using resting-state functional magnetic resonance imaging. Participants were scanned twice and received either intranasally applied OXT (24 international units) or placebo 40 min before scanning. The fractional amplitude of low-frequency fluctuations (fALFF) was computed to investigate regionally specific effects of OXT on intrinsic neural activity. In addition a multivariate statistical data analysis strategy was employed to explore OXT-effects on functional network strength.

RESULTS

Differential effects of OXT were observed in cLBP and healthy controls. FALFF decreased in left nucleus accumbens and right thalamus in cLBP and increased in right thalamus in healthy controls after OXT application compared to placebo. OXT also induced activity changes in bilateral thalamus, left caudate nucleus and right amygdala in cLBP. OXT was associated with increased medial frontal, parietal and occipital functional network strength, though this effect was not group-specific. Regression analyses revealed significant associations between left nucleus accumbens, left caudate nucleus and right amygdala with pain-specific psychometric scores in cLBP.

CONCLUSIONS

These data suggest OXT-related modulation of regional activity and neural network strength in patients with cLBP and healthy controls. In patients, distinct regions of the pain matrix may be responsive to modulation by OXT.

SIGNIFICANCE

Our data suggest significant oxytocin-related modulation of intrinsic regional activity and neural network strength in patients with chronic low back pain and healthy controls. In patients, distinct regions of the pain matrix may be responsive to modulation by oxytocin. Therapeutic effects of oxytocin for improved pain treatment need to be further investigated.

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.

Exploring the neural correlates of touch and pain in women with provoked vestibulodynia

Group differences in touch and pain thresholds-and their neural correlates-were studied in women with provoked vestibulodynia (PVD; N = 15), a common subtype of vulvodynia (chronic vulvar pain), and pain-free control women (N = 15). Results from quantitative sensory testing and self-report measures indicated that, as compared with control participants, women with PVD exhibited allodynia (ie, pain in response to a normally nonpainful stimulus) and hyperalgesia (ie, an increased response to a normally painful stimulus) at vulvar and nonvulvar sites. In addition, brain imaging analyses demonstrated reduced difference scores between touch and pain in the S2 area in women with PVD compared with control participants, supporting previous findings of allodynia in women with PVD. There were no significant reductions in difference scores between touch and pain for regions related to cognitive and affective processing of painful stimuli. The results of this study contribute important information to the general pain and vulvodynia literatures in elucidating the specific sensorimotor neural mechanisms that underlie hyperalgesia in a chronic pain population. These results have implications for differentiating neural processing of touch and pain for women with and without PVD. Future research should attempt to examine alterations related to hyperalgesia in commonly comorbid conditions of PVD.

Neuropathic Pain Dysregulates Gene Expression of the Forebrain Opioid and Dopamine Systems

Disturbances in the function of the mesostriatal dopamine system may contribute to the development and maintenance of chronic pain, including its sensory and emotional/cognitive aspects. In the present study, we assessed the influence of chronic constriction injury (CCI) of the sciatic nerve on the expression of genes coding for dopamine and opioid receptors as well as opioid propeptides in the mouse mesostriatal system, particularly in the nucleus accumbens. We demonstrated bilateral increases in mRNA levels of the dopamine D1 and D2 receptors (the latter accompanied by elevated protein level), opioid propeptides proenkephalin and prodynorphin, as well as delta and kappa (but not mu) opioid receptors in the nucleus accumbens at 7 to 14 days after CCI. These results show that CCI-induced neuropathic pain is accompanied by a major transcriptional dysregulation of molecules involved in dopaminergic and opioidergic signaling in the striatum/nucleus accumbens. Possible functional consequences of these changes include opposite effects of upregulated enkephalin/delta opioid receptor signaling vs. dynorphin/kappa opioid receptor signaling, with the former most likely having an analgesic effect and the latter exacerbating pain and contributing to pain-related negative emotional states.

Neural responses during extinction learning predict exposure therapy outcome in phobia: results from a randomized-controlled trial

Extinction learning is assumed to represent a core mechanism underlying exposure therapy. Empirical evaluations of this assumption, however, are largely lacking. The current study investigated whether neural activations and self-report outcomes during extinction learning and extinction recall could specifically predict exposure therapy response in specific phobia. In this double-blind randomized controlled trial, individuals with spider phobia (N = 45; female/male = 41/4) were on group basis randomly allocated to exposure therapy (n = 25; female/male = 24/1) or progressive muscle relaxation (PMR; n = 20; female/male = 17/3). Intervention effects were measured with the Fears of Spiders questionnaire. Participants also underwent a three-day fear conditioning, extinction learning, and extinction recall paradigm during functional magnetic resonance imaging at baseline. Extinction outcomes were self-reported fear and threat expectancy, and neural responses during conditioned stimulus processing and during extinction-related prediction errors (US omissions) in regions of interest (ventromedial prefrontal cortex (vmPFC) and nucleus accumbens). Results showed that exposure therapy resulted in stronger symptom reductions than PMR (Cohen's d = 0.90). Exposure therapy response was specifically predicted by prediction-error related vmPFC activation during early extinction. There were also indications vmPFC activations during conditioned safety stimulus processing at early extinction predicted therapy outcome. Neural activations during extinction recall and self-report data did however not predict therapy outcome. These findings indicate that exposure therapy may rely on neural extinction learning processes. Prediction errors are thought to drive the extinction learning process, and prediction error-related vmPFC activation specifically predicted therapy outcome. The extent to which vmPFC processes safety signals may additionally be predictive of exposure therapy response, but the specificity is less clear.