Individual sensitivity to pain expectancy is related to differential activation of the hippocampus and amygdala

The effect of unpredictability on the perception of pain: a systematic review and meta-analysis

ABSTRACT

Despite being widely assumed, the worsening impact of unpredictability on pain perception remains unclear because of conflicting empirical evidence, and a lack of systematic integration of past research findings. To fill this gap, we conducted a systematic review and meta-analysis focusing on the effect of unpredictability on pain perception. We also conducted meta-regression analyses to examine the moderating effect of several moderators associated with pain and unpredictability: stimulus duration, calibrated stimulus pain intensity, pain intensity expectation, controllability, anticipation delay, state and trait negative affectivity, sex/gender and age of the participants, type of unpredictability (intensity, onset, duration, location), and method of pain induction (thermal, electrical, mechanical pressure, mechanical distention). We included 73 experimental studies with adult volunteers manipulating the (un)predictability of painful stimuli and measuring perceived pain intensity and pain unpleasantness in predictable and unpredictable contexts. Because there are insufficient studies with patients, we focused on healthy volunteers. Our results did not reveal any effect of unpredictability on pain perception. However, several significant moderators were found, ie, targeted stimulus pain intensity, expected pain intensity, and state negative affectivity. Trait negative affectivity and uncontrollability showed no significant effect, presumably because of the low number of included studies. Thus, further investigation is necessary to clearly determine their role in unpredictable pain perception.

Exploring the Impact of Affinity and Unpleasantness on Conditioned Pain Modulation among Healthy Individuals

The variability of the Conditioned Pain Modulation (CPM) effect can be attributed to conditioning stimulus (CS) characteristics, such as intensity, duration, unpleasantness, or affinity. This study investigates the impact of affinity and unpleasantness variables on the CPM effect using two protocols (cold water and ischemia) in the same healthy individuals (n = 54). Additional variables were also examined for their potential influence on the CPM effect. The main results are as follows: (1) a higher level of affinity and a lower level of unpleasantness for the stimuli used resulted in a stronger CPM effect; (2) significant differences were observed in the extreme categories (high and low) of both variables, whereas the 'indifferent' group did not show a clear trend; (3) within-subject analysis demonstrated that affinity for the CS had a clear impact on the CPM effect; (4) no correlations were found between the CPM effect and the additional variables, except for the extraversion variable with the CPM effect of the ischemia protocol, and CS duration variable with CPM effect in the cold water protocol; and (5) only the affinity variable explained the CPM effect in both protocols in the multiple linear regression analysis. The affinity variable was found to influence the CPM effects significantly, indicating its important role in our perception and response to pain.

Integration of Prior Expectations and Suppression of Prediction Errors During Expectancy-Induced Pain Modulation: The Influence of Anxiety and Pleasantness

Pain perception arises from the integration of prior expectations with sensory information. Although recent work has demonstrated that treatment expectancy effects (e.g., placebo hypoalgesia) can be explained by a Bayesian integration framework incorporating the precision level of expectations and sensory inputs, the key factor modulating this integration in stimulus expectancy-induced pain modulation remains unclear. In a stimulus expectancy paradigm combining emotion regulation in healthy male and female adults, we found that participants' voluntary reduction in anticipatory anxiety and pleasantness monotonically reduced the magnitude of pain modulation by negative and positive expectations, respectively, indicating a role of emotion. For both types of expectations, Bayesian model comparisons confirmed that an integration model using the respective emotion of expectations and sensory inputs explained stimulus expectancy effects on pain better than using their respective precision. For negative expectations, the role of anxiety is further supported by our fMRI findings that (1) functional coupling within anxiety-processing brain regions (amygdala and anterior cingulate) reflected the integration of expectations with sensory inputs and (2) anxiety appeared to impair the updating of expectations via suppressed prediction error signals in the anterior cingulate, thus perpetuating negative expectancy effects. Regarding positive expectations, their integration with sensory inputs relied on the functional coupling within brain structures processing positive emotion and inhibiting threat responding (medial orbitofrontal cortex and hippocampus). In summary, different from treatment expectancy, pain modulation by stimulus expectancy emanates from emotion-modulated integration of beliefs with sensory evidence and inadequate belief updating.

Systems genetics analysis reveals the common genetic basis for pain sensitivity and cognitive function

BACKGROUND

There is growing evidence of a strong correlation between pain sensitivity and cognitive function under both physiological and pathological conditions. However, the detailed mechanisms remain largely unknown. In the current study, we sought to explore candidate genes and common molecular mechanisms underlying pain sensitivity and cognitive function with a transcriptome-wide association study using recombinant inbred mice from the BXD family.

METHODS

The pain sensitivity determined by Hargreaves' paw withdrawal test and cognition-related phenotypes were systematically analyzed in 60 strains of BXD mice and correlated with hippocampus transcriptomes, followed by quantitative trait locus (QTL) mapping and systems genetics analysis.

RESULTS

The pain sensitivity showed significant variability across the BXD strains and co-varies with cognitive traits. Pain sensitivity correlated hippocampual genes showed a significant involvement in cognition-related pathways, including glutamatergic synapse, and PI3K-Akt signaling pathway. Moreover, QTL mapping identified a genomic region on chromosome 4, potentially regulating the variation of pain sensitivity. Integrative analysis of expression QTL mapping, correlation analysis, and Bayesian network modeling identified Ring finger protein 20 (Rnf20) as the best candidate. Further pathway analysis indicated that Rnf20 may regulate the expression of pain sensitivity and cognitive function through the PI3K-Akt signaling pathway, particularly through interactions with genes Ppp2r2b, Ppp2r5c, Col9a3, Met, Rps6, Tnc, and Kras.

CONCLUSIONS

Our study demonstrated that pain sensitivity is associated with genetic background and Rnf20-mediated PI3K-Akt signaling may involve in the regulation of pain sensitivity and cognitive functions.

Hippocampal volume changes across developmental periods in female migraineurs

Brain-related plasticity can occur at a significant rate varying on the developmental period. Adolescence in particular has been identified as a period of growth and change across the structure and function of the nervous system. Notably, research has identified migraines as common in both pediatric and adult populations, but evidence suggests that the phenotype for migraines may differ in these cohorts due to the unique needs of each developmental period. Accordingly, primary aims of this study were to define hippocampal structure in females (7-27 years of age) with and without migraine, and to determine whether this differs across developmental stages (i.e., childhood, adolescence, and young adulthood). Hippocampal volume was quantified based on high-resolution structural MRI using FMRIB's Integrated Registration and Segmentation Tool. Results indicated that migraine and age may have an interactional relationship with hippocampal volume, such that, while hippocampal volumes were lower in female migraineurs (compared to age-matched controls) during childhood and adolescence, this contrast differed during young adulthood whereby hippocampal volumes were higher in migraineurs (compared to age-matched controls). Subsequent vertex analysis localized this interaction effect in hippocampal volume to displacement of the anterior hippocampus. The transition of hippocampal volume during adolescent development in migraineurs suggests that hippocampal plasticity may dynamically reflect components of migraine that change over the lifespan, exerting possible altered responsivity to stress related to migraine attacks thus having physiological expression and psychosocial impact.

The core of maintaining neuropathic pain: Crosstalk between glial cells and neurons (neural cell crosstalk at spinal cord)

BACKGROUND

Neuropathic pain (NP) caused by the injury or dysfunction of the nervous system is a chronic pain state accompanied by hyperalgesia, and the available clinical treatment is relatively scarce. Hyperalgesia mediated by pro-inflammatory factors and chemokines plays an important role in the occurrence and maintenance of NP.

DATA TREATMENT

Therefore, we conducted a systematic literature review of experimental NP (PubMed Medline), in order to find the mechanism of inducing central sensitization and explore the intervention methods of hyperalgesia caused by real or simulated injury.

RESULT

In this review, we sorted out the activation pathways of microglia, astrocytes and neurons, and the process of crosstalk among them. It was found that in NP, the microglia P2X4 receptor is the key target, which can activate the mitogen-activated protein kinase pathway inward and then activate astrocytes and outwardly activate neuronal tropomyosin receptor kinase B receptor to activate neurons. At the same time, activated neurons continue to maintain the activation of astrocytes and microglia through chemokines on CXCL13/CXCR5 and CX3CL1/CX3CR1. This crosstalk process is the key to maintaining NP.

CONCLUSION

We summarize the further research on crosstalk among neurons, microglia, and astrocytes in the central nervous system, elaborate the ways and connections of relevant crosstalk, and find potential crosstalk targets, which provides a reference for drug development and preclinical research.

Temperament and character dimensions differ in chronic post-surgical neuropathic pain and cold pressure pain

OBJECTIVES

Psychobiological temperament and cognitive-evaluative character link to coping with chronic pain. The aim was to study possible independent role of temperament and character dimensions both in chronic and experimental pain in chronic post-surgical pain patients. This is a substudy of a previously published larger cohort of patients with intercostobrachial nerve injury after breast cancer surgery.

METHODS

We recruited 241 women who had been treated for breast cancer 4-9 years before. They had a surgeon-verified intercostobrachial nerve injury with or without chronic post-surgical neuropathic pain (CPSNP). The patients filled in the Temperament and Character Inventory (TCI), Pain Catastrophizing Scale (PCS), Hospital Anxiety and Depression Scale (HADS), and Brief Pain Inventory (BPI), and underwent the cold pressor test (CPT).

RESULTS

201 (83%) patients reported chronic pain and 135 (56%) met the criteria for CPSNP. Patients with CPSNP showed higher levels of Harm Avoidance (HA) temperament than non-CPSNP patients, which was associated with lower cold pain tolerance and greater increase of pain intensity during CPT. HA subscales Fear of Uncertainty and Fatigability contributed to a stronger pain experience. For character dimensions, CPSNP patients reported higher levels of Self-Transcendence (ST) and lower levels of Self-Directedness (SD) and Cooperativeness (CO) than non-CPSNP patients. Cold pain tolerance, intensity, or unpleasantness did not associate with character dimensions.

CONCLUSIONS

Psychobiological temperament, but not character, is independently from other psychological factors associated with primary pain processing in an experimental pain setting. Patients with and without CPSNP showed different profiles on both temperament and character dimensions suggesting a combination of heightened emotional vulnerability and lowered personality adaptability in CPSNP patients. Character dimensions associated with clinical but not experimental pain.

ETHICAL COMMITTEE NUMBER

The study protocol was approved by the Ethics Committee of the Helsinki and Uusimaa Hospital District (reference number: 149/13/03/00/14).

TRIAL REGISTRY NUMBER

The study is registered in ClinicalTrials.gov (NCT02487524).

Hippocampus mediates nocebo impairment of opioid analgesia through changes in functional connectivity

The neural mechanisms underlying placebo analgesia have attracted considerable attention over the recent years. In contrast, little is known about the neural underpinnings of a nocebo-induced increase in pain. We previously showed that nocebo-induced hyperalgesia is accompanied by increased activity in the hippocampus that scaled with the perceived level of anxiety. As a key node of the neural circuitry of perceived threat and fear, the hippocampus has recently been proposed to coordinate defensive behaviour in a context-dependent manner. Such a role requires close interactions with other regions involved in the detection of and responses to threat. Here, we investigated the functional connectivity of the hippocampus during nocebo-induced hyperalgesia. Our results show an increase in functional connectivity between hippocampus and brain regions implicated in the processing of sensory-discriminative aspects of pain (posterior insula and primary somatosensory/motor cortex) as well as the periaqueductal gray (PAG). This nocebo-induced increase in connectivity scaled with an individual's increase in anxiety. Moreover, hippocampus connectivity with the amygdala was negatively correlated with the pain intensity reported during nocebo hyperalgesia relative to the placebo condition. Our findings suggest that the hippocampus links nocebo-induced anxiety to a heightened responsiveness to nociceptive input through changes in its crosstalk with pain-modulatory brain areas.

The Brain Structural-Functional Vulnerability in Drug-Naive Children With Juvenile Idiopathic Arthritis: Insights From the Hippocampus

Objective

Leveraging an integrative multimodal MRI paradigm to elaborate on the hippocampus-derived structural and functional changes in children and adolescents with juvenile idiopathic arthritis (JIA) and to explore potential correlations within the “joint-inflammation-brain” axis during the period of central neural system (CNS) development.

Methods

Twenty-one patients with JIA all completed the multimodal MRI scanning, laboratory tests, and neuropsychological assessments; meanwhile, 23 matched controls were recruited. We then harnessed the spherical harmonics with a point distribution model (SPHARM-PDM) and the ROI-to-voxel functional connectivity (FC) to measure the hippocampal shape and hippocampo-cortical FC patterns. Correlation analysis was performed to explore the potential links in neuroimaging features with disease-related indices.

Results

Compared to controls, JIA patients only presented an atrophic tendency in the posterior part of the bilateral hippocampus. The hippocampo-cortical FC revealed the between-group divergences mainly located at the pain matrix, striatum, and temporal lobe. Remarkably, the enhanced FC between the right hippocampus and postcentral cortex is positively correlated with the disability index, while the weakened FC of right anterior hippocampus with right insula and that of left posterior hippocampus with left superior temporal gyrus was inversely related to the erythrocyte sedimentation rate and anxiety status, separately.

Conclusion

As with macroscopic damages, the altered functional-connectome patterns of the hippocampus in JIA patients might be more sensitive to detect the early neuropathological changes. Moreover, the functional disturbances were demonstrated associated with the physical disability, inflammation, and emotional status. These findings may enlighten us on the underlying neuropathological mechanism of CNS comorbidities in JIA.

Regional cerebral blood flow as predictor of response to occipital nerve block in cluster headache

Background

Cluster headache is an excruciating disorder with no cure. Greater occipital nerve blockades can transiently suppress attacks in approximately 50% of patients, however, its mechanism of action remains uncertain, and there are no reliable predictors of treatment response. To address this, we investigated the effect of occipital nerve blockade on regional cerebral blood flow (rCBF), an index of brain activity, and differences between treatment responders and non-responders. Finally, we compared baseline perfusion maps from patients to a matched group of healthy controls.

Methods

21 male, treatment-naive patients were recruited while in a cluster headache bout. During a pain-free phase between headaches, patients underwent pseudo-continuous arterial spin labelled MRI assessments to provide quantitative indices of rCBF. MRIs were performed prior to and 7-to-21 days following treatment. Patients also recorded the frequency of their headache attacks in a daily paper diary. Neuropsychological assessment including anxiety, depression and quality of life measures was performed in a first, scanning free session for each patient.

Results

Following treatment, patients demonstrated relative rCBF reductions in posterior temporal gyrus, cerebellum and caudate, and rCBF increases in occipital cortex. Responders demonstrated relative rCBF increases, compared to non-responders, in medial prefrontal cortex and lateral occipital cortex at baseline, but relative reductions in cingulate and middle temporal cortices. rCBF was increased in patients compared to healthy controls in cerebellum and hippocampus, but reduced in orbitofrontal cortex, insula and middle temporal gyrus.

Conclusions

We provide new mechanistic insights regarding the aetiology of cluster headache, the mechanisms of action of occipital nerve blockades and potential predictors of treatment response. Future investigation should determine whether observed effects are reproducible and extend to other headache disorders.

Brain Structures Associated With Individual Differences in Somatic Symptoms and Emotional Distress in a Healthy Sample

Stress-related psychosomatic responses are viewed as important risks to our physical health. Growing evidence from structural imaging studies has implicated that stress and trauma exposures have negative effects on brain structural alterations. However, whether stress-related emotional distress and somatic symptoms are related to the structure of brain systems remains unclear. Also, stress-related somatic symptoms have adverse effects on emotional distress. In turn, emotional distress may influence somatic symptom reports via negative cognitive bias. However, whether this relationship is mediated by specific brain morphology remains poorly understood. First, we used voxel-based morphometric approaches to investigate the neuroanatomical basis underlying somatic symptoms and emotional distress in a large sample of healthy subjects (ages 18–27 years). We found that relatively high stress-related somatic symptoms were associated with reduced gray matter volumes (GMVs) in the ventral medial prefrontal cortex (vmPFC), anterior insula, somatosensory cortex, hippocampus, and amygdala. Furthermore, a moderator analysis was performed to investigate the impact of recent stressful life events (moderators) on the association between specific GMVs (independent variables) and emotional distress (dependent variables). Interestingly, high levels of emotional distress were associated with small volumes of the vmPFC, anterior insula, hippocampus, and amygdala in participants with experience with more recent stressful life events. Finally, we performed mediation analyses to investigate the specific brain areas that mediate the association between emotional distress and somatic symptoms. The results showed that the effect of emotional distress on somatic symptoms is mediated by reductions in the volume of the hippocampus, the impact of somatic symptoms on emotional distress is mediated by the volume of the vmPFC. These results provided evidence that higher stress-related somatic symptoms are associated with smaller volume in prefrontal, insula, and limbic regions involved in emotion, interoception, and memory processing. The vmPFC and hippocampus play different roles in the relationship between emotional distress and somatic symptoms.

Hippocampal circuits underlie improvements in self-reported anxiety following mindfulness training

INTRODUCTION

Mindfulness meditation has successfully been applied to cultivate skills in self-regulation of emotion, as it employs the unbiased present moment awareness of experience. This heightened attention to and awareness of sensory experience has been postulated to create an optimal therapeutic exposure condition and thereby improve extinction learning. We recently demonstrated increased connectivity in hippocampal circuits during the contextual retrieval of extinction memory following mindfulness training.

METHODS

Here, we examine the role of structural changes in hippocampal subfields following mindfulness training in a randomized controlled longitudinal study using a two-day fear-conditioning and extinction protocol.

RESULTS

We demonstrate an association between mindfulness training-related increases in subiculum and decreased hippocampal connectivity to lateral occipital regions during contextual retrieval of extinguished fear. Further, we demonstrate an association between decreased connectivity and decreases in self-reported anxiety following mindfulness training.

CONCLUSIONS

The results highlight the role of the subiculum in gating interactions with contextual stimuli during memory retrieval and, also, the mechanisms through which mindfulness training may foster resilience.

A Regions of Interest Voxel-Based Morphometry Study of the Human Brain During High-Frequency Spinal Cord Stimulation in Patients With Failed Back Surgery Syndrome

INTRODUCTION

The effectiveness of spinal cord stimulation (SCS) as pain-relieving treatment for failed back surgery syndrome (FBSS) has already been demonstrated. However, potential structural and functional brain alterations resulting from subsensory SCS are less clear. The aim of this study was to test structural volumetric changes in a priori chosen regions of interest related to chronic pain after 1 month and 3 months of high-frequency SCS in patients with FBSS.

METHODS

Eleven patients with FBSS who were scheduled for SCS device implantation were included in this study. All patients underwent a magnetic resonance imaging protocol before SCS device implantation 1 and 3 months after high-frequency SCS. Pain intensity, pain catastrophizing, and sleep quality were also measured. Regions-of-interest voxel-based morphometry was used to explore grey matter volumetric changes over time. Additionally, volumetric changes were correlated with changes in pain intensity, catastrophizing, and sleep quality.

RESULTS

Significant decreases were found in volume in the left and right hippocampus over time. More specifically, a significant difference was revealed between volumes before SCS implantation and after 3 months of SCS. Repeated-measures correlations revealed a significant positive correlation between volumetric changes in the left hippocampus and changes in back pain score over time and between volumetric changes in the right hippocampus and changes in back pain score over time.

CONCLUSION

In patients with FBSS, high-frequency SCS influences structural brain regions over time. The volume of the hippocampus was decreased bilaterally after 3 months of high-frequency SCS with a positive correlation with back pain intensity.

The medial temporal lobe in nociception: a meta-analytic and functional connectivity study

Recent neuroimaging studies implicate the medial temporal lobe (MTL) in nociception and pain modulation. Here, we aim to identify which subregions of the MTL are involved in human pain and to test its connectivity in a cohort of chronic low-back pain patients (CBP). We conducted 2 coordinate-based meta-analyses to determine which regions within the MTL showed consistent spatial patterns of functional activation (1) in response to experimental pain in healthy participants and (2) in chronic pain compared with healthy participants. We followed PRISMA guidelines and performed activation likelihood estimate (ALE) meta-analyses. The first meta-analysis revealed consistent activation in the right anterior hippocampus (right antHC), parahippocampal gyrus, and amygdala. The second meta-analysis revealed consistently less activation in patients' right antHC, compared with healthy participants. We then conducted a seed-to-voxel resting state functional connectivity of the right antHC seed with the rest of the brain in 77 CBP and 79 age-matched healthy participants. We found that CBP had significantly weaker antHC functional connectivity to the medial prefrontal cortex compared with healthy participants. Taken together, these data indicate that the antHC has abnormally lower activity in chronic pain and reduced connectivity to the medial prefrontal cortex in CBP. Future studies should investigate the specific role of the antHC in the development and management of chronic pain.

Stressful experiences in youth: "Set-up" for diminished resilience to chronic pain

Chronic pain in youth is common, with prevalence rates in some reports exceeding 50%. Given the plasticity of brain systems in youth and their general level of activity, the underlying processes relating to the evolution of chronic pain may be different from that observed in adults. One aspect that affects brain development is childhood stress. Preliminary research indicates that maladaptive responses to stressful events that induce biological and psychological inability to adapt may be related to pain chronicity in youth. This relationship is particularly notable given the high rates of exposure to stressful events in pediatric pain populations. A review of the literature was performed in the areas of biological, cognitive, psychological and social processes associated with chronic pain and psychological stress and trauma in youth and adult populations. The current review presents a theoretical framework, adapted from McEwen's model (1998) on stress and allostatic load, which aims to outline the potential connection between exposure to stressful events and pediatric chronic pain. Avenues for future investigation are also identified.

Altered neural activity to monetary reward/loss processing in episodic migraine

The dysfunctions of the mesolimbic cortical reward circuit have been proposed to contribute to migraine pain. Although supporting empirical evidence was mainly found in connection with primary rewards or in chronic migraine where the pain experience is (almost) constant. Our goal however was to investigate the neural correlates of secondary reward/loss anticipation and consumption using the monetary incentive delay task in 29 episodic migraine patients and 41 headache-free controls. Migraine patients showed decreased activation in one cluster covering the right inferior frontal gyrus during reward consumption compared to controls. We also found significant negative correlation between the time of the last migraine attack before the scan and activation of the parahippocampal gyrus and the right hippocampus yielded to loss anticipation. During reward/loss consumption, a relative increase in the activity of the visual areas was observed the more time passed between the last attack and the scan session. Our results suggest intact reward/loss anticipation but altered reward consumption in migraine, indicating a decreased reactivity to monetary rewards. The findings also raise the possibility that neural responses to loss anticipation and reward/loss consumption could be altered by the proximity of the last migraine attack not just during pre-ictal periods, but interictally as well.

Brain activations associated with fearful experience show common and distinct patterns between younger and older adults in the hippocampus and the amygdala

Revisiting threat-related scenes elicits fear and activates a brain network related to cognitive-affective processing. Prior experience may contribute to the present fearful experience. We aimed to investigate (a) patterns of brain activation associated with individual differences in past fearful experiences (pFear) and the present fear elicited by watching videos (eFear) and (b) age-related differences in the activation patterns. Forty healthy adults, including 20 younger adults (YA) and 20 older adults (OA), underwent functional magnetic resonance imaging while watching videos containing high- and low-threat scenes of medical treatment. Both age subgroups showed positive correlations between pFear and bilateral hippocampal activation. Only YA showed threat-related activation in the bilateral anterior insula and activation positively correlated with pFear in the bilateral S1 and the amygdala. The evidence suggests that the hippocampus, amygdala and S1 may play key roles in bridging past fearful experiences and the present fear elicited by revisiting visual scenes and that the interaction between memory and emotional processing may be age dependent.

New evidence for a pain personality? A critical review of the last 120 years of pain and personality

BACKGROUND

Personality traits may influence development and adjustment to ongoing pain. Over the past 120 years, there has been considerable research into the relationship between pain and personality. This paper presents new evidence for common personality traits found amongst chronic pain sufferers. In particular, it evaluates evidence for Cloninger's biopsychosocial model of personality in distinguishing typical personality features of chronic pain sufferers. It evaluates this evidence in the context of the past 120 years of research including psychodynamic formulations, MMPI studies, personality disorder investigations, and the influence of neuroticism on chronic pain.

METHODS

A literature search was conducted using PubMed, Medline, PsycINFO, SCOPUS and Cochrane library. Search terms included chronic pain, pain, personality, neuroticism, harm avoidance, self-directedness, attachment, Temperament and Character Inventory (TCI-R), MMPI, MMPI-2, NEO-PI, EPI, Millon Clinical Multiaxial Inventory, Millon Behavioral Health Inventory, Millon Behavioral Medicine Diagnostic, the Personality Assessment Inventory, the Locus of Control Construct and different combinations of these terms.

CONCLUSIONS

Recent descriptive studies using Cloninger's Temperament and Character Inventory (TCI-R) suggest that higher harm avoidance and lower self-directedness may be the most distinguishing personality features of chronic pain sufferers. High harm avoidance refers to a tendency to be fearful, pessimistic, sensitive to criticism, and requiring high levels of re-assurance. Low self-directedness often manifests as difficulty with defining and setting meaningful goals, low motivation, and problems with adaptive coping. Evidence for this personality profile is found across a wide variety of chronic pain conditions including fibromyalgia, headache and migraine, temporomandibular disorder, trigeminal neuropathy, musculo-skeletal disorders and heterogeneous pain groups. Limitations are also discussed. For example, high harm avoidance is also found in those suffering anxiety and depression. While many studies control for such factors, some do not and thus future research should address such confounds carefully. The evidence is also evaluated within the context of past research into the existence of 'a pain personality'. Psychodynamic formulations are found to be deficient in objective scientific methods. MMPI studies lack sufficient evidence to support 'a pain personality' and may be confounded by somatic items in the instrument. More recent neuroticism studies suggest a relationship between neuroticism and pain, particularly for adjustment to chronic pain. Personality disorders are more prevalent in chronic pain populations than non-pain samples.

CLINICAL IMPLICATIONS

Because harm avoidance reflects a tendency to developed conditioned fear responses, we suggest that higher harm avoidance may create more vulnerability to developing a fear-avoidance response to chronic pain. Furthermore, lower self-directedness may contribute to keeping a sufferer within this vicious cycle of fear, avoidance and suffering. Moreover, we suggest that harm avoidance and self-directedness are broader and more complex constructs than current clinical targets of CBT such as fear-avoidance and self-efficacy. Thus, assessing such personality traits may help to address the complexity of chronic pain presentations. For example, it may help to identify and treat sufferers more resistant to treatment, more prone to comorbidity and more vulnerable to entering the vicious cycle of chronic pain, suffering and disability.

The Role of Stress Regulation on Neural Plasticity in Pain Chronification

Pain, especially chronic pain, is one of the most common clinical symptoms and has been considered as a worldwide healthcare problem. The transition from acute to chronic pain is accompanied by a chain of alterations in physiology, pathology, and psychology. Increasing clinical studies and complementary animal models have elucidated effects of stress regulation on the pain chronification via investigating activations of the hypothalamic-pituitary-adrenal (HPA) axis and changes in some crucial brain regions, including the amygdala, prefrontal cortex, and hippocampus. Although individuals suffer from acute pain benefit from such physiological alterations, chronic pain is commonly associated with maladaptive responses, like the HPA dysfunction and abnormal brain plasticity. However, the causal relationship among pain chronification, stress regulation, and brain alterations is rarely discussed. To call for more attention on this issue, we review recent findings obtained from clinical populations and animal models, propose an integrated stress model of pain chronification based on the existing models in perspectives of environmental influences and genetic predispositions, and discuss the significance of investigating the role of stress regulation on brain alteration in pain chronification for various clinical applications.

Inverted Perceptual Judgment of Nociceptive Stimuli at Threshold Level following Inconsistent Cues

Objective

The perception of pain is susceptible to modulation by psychological and contextual factors. It has been shown that subjects judge noxious stimuli as more painful in a respective suggestive context, which disappears when the modifying context is resolved. However, a context in which subjects judge the painfulness of a nociceptive stimulus in exactly the opposite direction to that of the cues has never been shown so far.

Methods

Nociceptive stimuli (300 ms intranasal gaseous CO₂) at the individual pain threshold level were applied after a visual cue announcing the stimulus as either “no pain”, merely a “stimulus”, or “pain”. Among the stimuli at threshold level, other CO₂ stimuli that were clearly below or above pain threshold were randomly interspersed. These were announced beforehand in 12 subjects randomly with correct or incorrect cues, i.e., clearly painful or clearly non-painful stimuli were announced equally often as not painful or painful. By contrast, in a subsequent group of another 12 subjects, the stimuli were always announced correctly with respect to the evoked pain.

Results

The random and often incorrect announcement of stimuli clearly below or above pain threshold caused the subjects to rate the stimuli at pain-threshold level in the opposite direction of the cue, i.e., when the stimuli were announced as “pain” significantly more often than as non-painful and vice versa (p < 10^-4). By contrast, in the absence of incongruence between announcement and perception of the far-from-threshold stimuli, stimuli at pain threshold were rated in the cued direction.

Conclusions

The present study revealed the induction of associations incongruent with a given message in the perception of pain. We created a context of unreliable cues whereby subjects perceived the stimulus opposite to that suggested by a prior cue, i.e., potentially nociceptive stimuli at pain threshold level that were announced as painful were judged as non-painful and vice versa. These findings are consistent with reported data on the effects of distrust on non-painful cognitive responses.

The effects of prediction on the perception for own-race and other-race faces

Human beings do not passively perceive important social features about others such as race and age in social interactions. Instead, it is proposed that humans might continuously generate predictions about these social features based on prior similar experiences. Pre-awareness of racial information conveyed by others' faces enables individuals to act in “culturally appropriate” ways, which is useful for interpersonal relations in different ethnicity groups. However, little is known about the effects of prediction on the perception for own-race and other-race faces. Here, we addressed this issue using high temporal resolution event-related potential techniques. In total, data from 24 participants (13 women and 11 men) were analyzed. It was found that the N170 amplitudes elicited by other-race faces, but not own-race faces, were significantly smaller in the predictable condition compared to the unpredictable condition, reflecting a switch to holistic processing of other-race faces when those faces were predictable. In this respect, top-down prediction about face race might contribute to the elimination of the other-race effect (one face recognition impairment). Furthermore, smaller P300 amplitudes were observed for the predictable than for unpredictable conditions, which suggested that the prediction of race reduced the neural responses of human brains.

The association of depression and anxiety with pain: a study from NESDA

Chronic pain is commonly co-morbid with a depressive or anxiety disorder. Objective of this study is to examine the influence of depression, along with anxiety, on pain-related disability, pain intensity, and pain location in a large sample of adults with and without a depressive and/or anxiety disorder. The study population consisted of 2981 participants with a depressive, anxiety, co-morbid depressive and anxiety disorder, remitted disorder or no current disorder (controls). Severity of depressive and anxiety symptoms was also assessed. In separate multinomial regression analyses, the association of presence of depressive or anxiety disorders and symptom severity with the Chronic Pain Grade and location of pain was explored. Presence of a depressive (OR = 6.67; P<.001), anxiety (OR = 4.84; P<.001), or co-morbid depressive and anxiety disorder (OR = 30.26; P<.001) was associated with the Chronic Pain Grade. Moreover, symptom severity was associated with more disabling and severely limiting pain. Also, a remitted depressive or anxiety disorder showed more disabling and severely limiting pain (OR = 3.53; P<.001) as compared to controls. A current anxiety disorder (OR = 2.96; p<.001) and a co-morbid depressive and anxiety disorder (OR = 5.15; P<.001) were more strongly associated with cardio-respiratory pain, than gastro-intestinal or musculoskeletal pain. These findings remain after adjustment for chronic cardio respiratory illness. Patients with a current and remitted depressive and/or anxiety disorder and those with more severe symptoms have more disabling pain and pain of cardio-respiratory nature, than persons without a depressive or anxiety disorder. This warrants further research.

Moderate-vigorous physical activity across body mass index in females: moderating effect of endocannabinoids and temperament

BACKGROUND

Endocannabinoids and temperament traits have been linked to both physical activity and body mass index (BMI) however no study has explored how these factors interact in females. The aims of this cross-sectional study were to 1) examine differences among distinct BMI groups on daytime physical activity and time spent in moderate-vigorous physical activity (MVPA), temperament traits and plasma endocannabinoid concentrations; and 2) explore the association and interaction between MVPA, temperament, endocannabinoids and BMI.

METHODS

Physical activity was measured with the wrist-worn accelerometer Actiwatch AW7, in a sample of 189 female participants (43 morbid obese, 30 obese, and 116 healthy-weight controls). The Temperament and Character Inventory-Revised questionnaire was used to assess personality traits. BMI was calculated by bioelectrical impedance analysis via the TANITA digital scale. Blood analyses were conducted to measure levels of endocannabinoids and endocannabinoid-related compounds. Path-analysis was performed to examine the association between predictive variables and MVPA.

RESULTS

Obese groups showed lower MVPA and dysfunctional temperament traits compared to healthy-weight controls. Plasma concentrations of 2-arachidonoylglyceryl (2-AG) were greater in obese groups. Path-analysis identified a direct effect between greater MVPA and low BMI (b = -0.13, p = .039) and high MVPA levels were associated with elevated anandamide (AEA) levels (b = 0.16, p = .049) and N-oleylethanolamide (OEA) levels (b = 0.22, p = .004), as well as high Novelty seeking (b = 0.18, p<.001) and low Harm avoidance (b = -0.16, p<.001).

CONCLUSIONS

Obese individuals showed a distinct temperament profile and circulating endocannabinoids compared to controls. Temperament and endocannabinoids may act as moderators of the low MVPA in obesity.

Harm avoiders suppress motor resonance to observed immoral actions

Motor resonance (MR) contingent upon action observation is thought to occur largely automatically. Although recent studies suggest that this process is not completely impervious to top-down modulations, much less is known on the possible role of the moral connotation of observed action goal in modulating MR. Here, we explored whether observing actions with different moral connotations modulates MR and whether any modulation depends on the onlookers' personality. To this aim, we recorded motor potentials evoked by single-pulse transcranial magnetic stimulation from hand muscles of participants who were watching images of a model performing hand actions with the same postures and low-level goals (i.e. grasping an object) but with different moral connotations ('stealing a wallet' vs 'picking up a notepaper'). Participants' personality traits were measured using the temperament and character inventory. Results show a selective suppression of corticospinal excitability during observation of immoral actions in individuals with high scores in harm avoidance, a personality trait characterized by excessive worrying and fearfulness. Thus, a combination of dispositional (personality traits) and situational (morality of an action) variables appears to influence MR with the observed actions.

Behaviourally inhibited temperament and female sex, two vulnerability factors for anxiety disorders, facilitate conditioned avoidance (also) in humans

Acquisition and maintenance of avoidance behaviour is a key feature of all human anxiety disorders. Animal models have been useful in understanding how anxiety vulnerability could translate into avoidance learning. For example, behaviourally inhibited temperament and female sex, two vulnerability factors for clinical anxiety, are associated with faster acquisition of avoidance responses in rodents. However, to date, the translation of such empirical data to human populations has been limited since many features of animal avoidance paradigms are not typically captured in human research. Here, using a computer-based task that captures many features of rodent escape-avoidance learning paradigms, we investigated whether avoidance learning would be faster in humans with inhibited temperament and/or female sex and, if so, whether this facilitation would take the same form. Results showed that, as in rats, both vulnerability factors were associated with facilitated acquisition of avoidance behaviour in humans. Specifically, inhibited temperament was associated with higher rate of avoidance responding, while female sex was associated with longer avoidance duration. These findings strengthen the direct link between animal avoidance work and human anxiety vulnerability, further motivating the study of animal models while also providing a simple testbed for a direct human testing.

Complex regional pain syndrome is associated with structural abnormalities in pain-related regions of the human brain

Complex regional pain syndrome (CRPS) is a chronic condition that involves significant hyperalgesia of the affected limb, typically accompanied by localized autonomic abnormalities and frequently by motor dysfunction. Although central brain systems are thought to play a role in the development and maintenance of CRPS, these systems have not been well characterized. In this study, we used structural magnetic resonance imaging to characterize differences in gray matter volume between patients with right upper extremity CRPS and matched controls. Analyses were carried out using a whole brain voxel-based morphometry approach. The CRPS group showed decreased gray matter volume in several pain-affect regions, including the dorsal insula, left orbitofrontal cortex, and several aspects of the cingulate cortex. Greater gray matter volume in CRPS patients was seen in the bilateral dorsal putamen and right hypothalamus. Correlation analyses with self-reported pain were then performed on the CRPS group. Pain duration was associated with decreased gray matter in the left dorsolateral prefrontal cortex. Pain intensity was positively correlated with volume in the left posterior hippocampus and left amygdala, and negatively correlated with the bilateral dorsolateral prefrontal cortex. Our findings demonstrate that CRPS is associated with abnormal brain system morphology, particularly pain-related sensory, affect, motor, and autonomic systems.

PERSPECTIVE

This paper presents structural changes in the brains of patients with CRPS, helping us differentiate CRPS from other chronic pain syndromes and furthering our understanding of this challenging disease.

Dimensions of disinhibited personality and their relation with alcohol use and problems

Although alcohol use disorders (AUDs) have been associated with different aspects of disinhibited personality and antisociality, less is known about the specific relationships among different domains of disinhibited personality, antisociality, alcohol use, and alcohol problems. The current study was designed to address three goals, (i) to provide evidence of a three-factor model of disinhibited personality (comprised of impulsivity [IMP], risk taking/low harm avoidance [RTHA], excitement seeking [ES]), (ii) to test hypotheses regarding the association between each dimension and alcohol use and problems, and (iii) to test the hypothesis that antisociality (social deviance proneness [SDP]) accounts for the direct association between IMP and alcohol problems, while ES is directly related to alcohol use. Measures of disinhibited personality IMP, RTHA, ES and SDP and alcohol use and problems were assessed in a sample of young adults (N=474), which included a high proportion of individuals with AUDs. Confirmatory factor analyses supported a three-factor model of disinhibited personality reflecting IMP, RTHA, and ES. A structural equation model (SEM) showed that IMP was specifically associated with alcohol problems, while ES was specifically associated with alcohol use. In a second SEM, SDP accounted for the majority of the variance in alcohol problems associated with IMP. The results suggest that aspects of IMP associated with SDP represent a direct vulnerability to alcohol problems. In addition, the results suggest that ES reflects a specific vulnerability to excessive alcohol use, which is then associated with alcohol problems, while RTHA is not specifically associated with alcohol use or problems when controlling for IMP and ES.

Structural basis of empathy and the domain general region in the anterior insular cortex

Empathy is key for healthy social functioning and individual differences in empathy have strong implications for manifold domains of social behavior. Empathy comprises of emotional and cognitive components and may also be closely linked to sensorimotor processes, which go along with the motivation and behavior to respond compassionately to another person's feelings. There is growing evidence for local plastic change in the structure of the healthy adult human brain in response to environmental demands or intrinsic factors. Here we have investigated changes in brain structure resulting from or predisposing to empathy. Structural MRI data of 101 healthy adult females was analyzed. Empathy in fictitious as well as real-life situations was assessed using a validated self-evaluation measure. Furthermore, empathy-related structural effects were also put into the context of a functional map of the anterior insular cortex (AIC) determined by activation likelihood estimate (ALE) meta-analysis of previous functional imaging studies. We found that gray matter (GM) density in the left dorsal AIC correlates with empathy and that this area overlaps with the domain general region (DGR) of the anterior insula that is situated in-between functional systems involved in emotion-cognition, pain, and motor tasks as determined by our meta-analysis. Thus, we propose that this insular region where we find structural differences depending on individual empathy may play a crucial role in modulating the efficiency of neural integration underlying emotional, cognitive, and sensorimotor information which is essential for global empathy.

Pain, decisions, and actions: a motivational perspective

Because pain signals potential harm to the organism, it immediately attracts attention and motivates decisions and action. However, pain is also subject to motivations—an aspect that has led to considerable changes in our understanding of (chronic) pain over the recent years. The relationship between pain and motivational states is therefore clearly bidirectional. This review provides an overview on behavioral and neuroimaging studies investigating motivational aspects of pain. We highlight recent insights into the modulation of pain through fear and social factors, summarize findings on the role of pain in fear conditioning, avoidance learning and goal conflicts and discuss evidence on pain-related cognitive interference and motivational aspects of pain relief.

Common brain activations for painful and non-painful aversive stimuli

BACKGROUND

Identification of potentially harmful stimuli is necessary for the well-being and self-preservation of all organisms. However, the neural substrates involved in the processing of aversive stimuli are not well understood. For instance, painful and non-painful aversive stimuli are largely thought to activate different neural networks. However, it is presently unclear whether there is a common aversion-related network of brain regions responsible for the basic processing of aversive stimuli. To help clarify this issue, this report used a cross-species translational approach in humans (i.e. meta-analysis) and rodents (i.e. systematic review of functional neuroanatomy).

RESULTS

Animal and human data combined to show a core aversion-related network, consisting of similar cortical (i.e. MCC, PCC, AI, DMPFC, RTG, SMA, VLOFC; see results section or abbreviation section for full names) and subcortical (i.e. Amyg, BNST, DS, Hab, Hipp/Parahipp, Hyp, NAc, NTS, PAG, PBN, raphe, septal nuclei, Thal, LC, midbrain) regions. In addition, a number of regions appeared to be more involved in pain-related (e.g. sensory cortex) or non-pain-related (e.g. amygdala) aversive processing.

CONCLUSIONS

This investigation suggests that aversive processing, at the most basic level, relies on similar neural substrates, and that differential responses may be due, in part, to the recruitment of additional structures as well as the spatio-temporal dynamic activity of the network. This network perspective may provide a clearer understanding of why components of this circuit appear dysfunctional in some psychiatric and pain-related disorders.

Influence of body position on cortical pain-related somatosensory processing: an ERP study

BACKGROUND

Despite the consistent information available on the physiological changes induced by head down bed rest, a condition which simulates space microgravity, our knowledge on the possible perceptual-cortical alterations is still poor. The present study investigated the effects of 2-h head-down bed rest on subjective and cortical responses elicited by electrical, pain-related somatosensory stimulation.

METHODOLOGY/PRINCIPAL FINDINGS

Twenty male subjects were randomly assigned to two groups, head-down bed rest (BR) or sitting control condition. Starting from individual electrical thresholds, Somatosensory Evoked Potentials were elicited by electrical stimuli administered randomly to the left wrist and divided into four conditions: control painless condition, electrical pain threshold, 30% above pain threshold, 30% below pain threshold. Subjective pain ratings collected during the EEG session showed significantly reduced pain perception in BR compared to Control group. Statistical analysis on four electrode clusters and sLORETA source analysis revealed, in sitting controls, a P1 component (40-50 ms) in the right somatosensory cortex, whereas it was bilateral and differently located in BR group. Controls' N1 (80-90 ms) had widespread right hemisphere activation, involving also anterior cingulate, whereas BR group showed primary somatosensory cortex activation. The P2 (190-220 ms) was larger in left-central locations of Controls compared with BR group.

CONCLUSIONS/SIGNIFICANCE

Head-down bed rest was associated to an overall decrease of pain sensitivity and an altered pain network also outside the primary somatosensory cortex. Results have implications not only for astronauts' health and spaceflight risks, but also for the clinical aspects of pain detection in bedridden patients at risk of fatal undetected complications.