Pain and emotion: effects of affective picture modulation

Neural dynamics of pain modulation by emotional valence

Definitions of human pain acknowledge at least two dimensions of pain, affective and sensory, described as separable and thus potentially differentially modifiable. Using electroencephalography, we investigated perceptual and neural changes of emotional pain modulation in healthy individuals. Painful electrical stimuli were applied after presentation of priming emotional pictures (negative, neutral, positive) and followed by pain intensity and unpleasantness ratings. We found that perceptual and neural event-related potential responses to painful stimulation were significantly modulated by emotional valence. Specifically, pain unpleasantness but not pain intensity ratings were increased when pain was preceded by negative compared to neutral or positive pictures. Amplitudes of N2 were higher when pain was preceded by neutral compared to negative and positive pictures, and P2 amplitudes were higher for negative compared to neutral and positive pictures. In addition, a hierarchical regression analysis revealed that P2 alone and not N2, predicted pain perception. Finally, source analysis showed the anterior cingulate cortex and the thalamus as main spatial clusters accounting for the neural changes in pain processing. These findings provide evidence for a separation of the sensory and affective dimensions of pain and open new perspectives for mechanisms of pain modulation.

Unconscious Activation of Negative Emotional Memories Increases Pain Unpleasantness

OBJECTIVE

The influence of unconscious emotional processes on pain remains poorly understood. The present study tested whether cues to forgotten unpleasant images might amplify pain (i.e., in the absence of conscious recall).

METHODS

Seventy-two healthy female adults (19 to 34 years) performed an adapted Think/No-think paradigm (T/NT) using 72 combinations of neutral face images (cues) paired with 36 neutral and 36 unpleasant images. After completion of the T/NT task, cues associated with forgotten neutral or unpleasant images were identified. Cues to either neutral or unpleasant images from the NT condition were then presented in randomized order while participants received intermediate-level thermal pain stimulation on the left hand. Ratings of both pain intensity and unpleasantness were acquired after each trial.

RESULTS

Mean pain unpleasantness ratings were greater during presentation of cues to forgotten negative versus neutral images (5.52 [SD = 2.06] versus 5.23 [SD = 2.10]; p = .02). This pattern was also present when comparing cues to remembered negative versus neutral images (5.62 [SD = 1.94] versus 5.04 [SD = 1.90]; p < .001). Mean pain intensity ratings were higher for cues to negative versus neutral images when remembered (5.48 [SD = 1.79] versus 5.00 [SD = 1.69]; p < .001), but not when forgotten (5.27 [SD = 1.96] versus 5.16 [SD = 1.93]; p = .30).

CONCLUSIONS

Using an adapted T/NT-Pain paradigm, this study demonstrated that cues to nonrecallable (but potentially unconsciously activated) negative emotional memories amplify pain unpleasantness, similar to known effects of conscious negative emotions.

Vicarious facilitation of facial responses to pain: Does the others' expression need to be painful?

INTRODUCTION

Prior exposure to others' facial expressions of pain can lead to a facilitation of pain responses, including its corresponding response channel, namely facial responses to pain. It has been questioned, however, whether this vicarious pain facilitation occurs only when observing others' pain or whether the observation of other negative expressions can trigger similar facilitation of facial responses to pain. The study aimed to test this, by comparing the impact of viewing others' facial expressions of pain versus another negative expression (sadness) and two control expressions (neutral, happiness) on facial responses to pain.

METHOD

Participants (N = 56; 31 females), watched short video clips of computer-generated facial expressions (pain, sadness, neutral & happiness) before they received painful and non-painful heat stimuli. Facial responses were analysed using the Facial Action Coding System. In addition, subjective and autonomic responses were assessed.

RESULTS

The prior exposure to others' expressions of pain and sadness versus neutral did not lead to significantly increased facial responses to pain. Likewise, subjective and autonomic pain responses were not facilitated. However, viewing others' expressions of happiness, consistently reduced facial as well as subjective and autonomic responses to pain compared to others' negative or neutral expressions. This dampening effect was not observed for non-painful heat.

DISCUSSION

Facial and other pain responses were most strongly affected by prior exposure to others' facial expressions of happiness, which led to a pain-dampening effect. In contrast, the evidence for vicarious facilitation of pain was rather weak in the present study, with no evidence of pain-specificity.

SIGNIFICANCE STATEMENT

Facial responses to pain - along with subjective and autonomic responses - are reduced when observing others' expressions of happiness, demonstrating pain modulation by positive affective social signals, which may also transfer to clinical contexts.

Unpacking the relationship between Big Five personality traits and experimental pain: A systematic review and meta-analysis

Pain is essential for survival, but individual responses to painful stimuli vary, representing a complex interplay between sensory, cognitive, and affective factors. Individual differences in personality traits and in pain perception covary but it is unclear which traits play the most significant role in understanding the pain experience and whether this depends on pain modality. A systematic search identified 1534 records (CINAHL, MEDLINE, PsycInfo, PubMed and Web of Science), of which 22 were retained and included in a systematic review. Only studies from the pressure pain domain (n=6) could be compared in a formal meta-analysis to evaluate the relationship between Big Five traits and experimental pain. Pressure pain tolerance correlated positively with Extraversion and negatively with Neuroticism with a trivial effect size (<0.1). While these findings suggest personality might be only weakly related to pain in healthy individuals, we emphasize the need to consider standardization, biases, and adequate sample sizes in future research, as well as additional factors that might affect experimental pain sensitivity.

Tactile discrimination as a diagnostic indicator of cognitive decline in patients with mild cognitive impairment: A narrative review

Background

Tactile discrimination, a cognitive task reliant on fingertip touch for stimulus discrimination, encompasses the somatosensory system and working memory, with its acuity diminishing with advancing age. Presently, the evaluation of cognitive capacity to differentiate between individuals with early Alzheimer's disease (AD) and typical older adults predominantly relies on visual or auditory tasks, yet the efficacy of discrimination remains constrained.

Aims

To review the existing tactile cognitive tasks and explore the interaction between tactile perception and the pathological process of Alzheimer's disease. The tactile discrimination task may be used as a reference index of cognitive decline in patients with mild cognitive impairment and provide a new method for clinical evaluation.

Methods

We searched four databases (Embase, PubMed, Web of Science and Google scholar). The reference coverage was from 1936 to 2023. The search terms included "Alzheimer disease" "mild cognitive impairment" "tactile" "tactile discrimination" "tactile test" and so on. Reviews and experimental reports in the field were examined and the effectiveness of different types of tactile tasks was compared.

Main results

Individuals in the initial phases of Alzheimer's spectrum disease, specifically those in the stage of mild cognitive impairment (MCI), exhibit notable impairments in tasks involving tactile discrimination. These tasks possess certain merits, such as their quick and straightforward comparability, independence from educational background, and ability to circumvent the limitations associated with conventional cognitive assessment scales. Furthermore, tactile discrimination tasks offer enhanced accuracy compared to cognitive tasks that employ visual or auditory stimuli.

Conclusions

Tactile discrimination has the potential to serve as an innovative reference indicator for the swift diagnosis of clinical MCI patients, thereby assisting in the screening process on a clinical scale.

From childhood trauma to alcohol use disorder severity - significance of depressive symptoms and expectations towards analgesic effects of alcohol

AIMS

The objective of the current study was to describe and analyse associations between childhood emotional abuse, severity of depressive symptoms, and analgesic expectations of drinking in individuals with alcohol use disorder (AUD).

METHODS

A total of 240 individuals aged 43.85 ± 11.0 with severe AUD entering an inpatient, abstinence-based, and drug-free treatment program were assessed. The data on AUD severity, depressive symptoms, expectations towards the analgesic effects of alcohol and childhood emotional trauma was collected using questionnaire measures. The PROCESS SPSS macro for serial mediation with bootstrapping was used to test whether current severity of depressive symptoms and expectations towards analgesic effects of alcohol use serially mediated the association between childhood emotional abuse on AUD symptom severity.

RESULTS

There was evidence for two simple mediated effects, whereby the severity of depressive symptoms mediated the association between childhood emotional abuse on AUD symptom severity, and expectations towards analgesic effects of alcohol mediated the association between childhood emotional abuse on AUD symptom severity. There was also evidence to support serial mediation whereby both severity of depressive symptoms and expectations towards analgesic effects of alcohol mediated the association between childhood emotional abuse on AUD symptom severity.

CONCLUSIONS

It might be clinically relevant to address experiences of childhood emotional trauma, as well as individual expectations of analgesic effects of alcohol, in AUD treatment programs.

The Influence of Subjective Sexual Arousal and Disgust on Pain

Current models propose that inhibited sexual arousal is a key component in maintaining sexual pain in women with Genito-Pelvic Pain/Penetration Disorder. It thus follows that enhancing sexual arousal may be an effective strategy to modulate pain, but this effect has not been successfully demonstrated with women, although it has been successful with men. This study built on previous works and examined if the pain-killing effect of sexual arousal might have been undermined by concurrently-elicited disgust. We tested whether women experience disgust as well as sexual arousal when viewing sex stimuli, and whether disgust has an exacerbating effect on pain. Female participants (N = 164) were randomly distributed to watch a porn, disgust, or neutral train-ride film. A cold pressor test (CPT) was utilized to induce pain at the same time that participants viewed their respective film. Pain was indexed by the duration that participants kept their hand in the cold water, and by self-reported pain intensity at the time they quit the CPT. The results showed no differences in pain across conditions. The sex stimulus elicited substantial disgust as well as sexual arousal, and there was a negative correlation between the two emotions. Disgust was not found to increase pain compared to both the neutral and sex conditions. Thus, the findings provide no support for a pain-modulatory effect of subjective sexual arousal on pain in women. This might, however, be due to the sex stimulus having elicited an ambivalent state between an appetitive and aversive emotion concurrently.

Is conditioned pain modulation (CPM) affected by negative emotional state?

BACKGROUND

Conditioned pain modulation (CPM) is an experimental paradigm, which describes the inhibition of responses to a noxious or strong-innocuous stimulus, the test stimulus (TS), by the additional application of a second noxious or strong-innocuous stimulus, the conditioning stimulus (CS). As inadequate CPM efficiency has been assumed to be predisposing for clinical pain, the search for moderating factors explaining inter-individual variations in CPM is ongoing. Psychological factors have received credits in this context. However, research concerning associations between CPM and trait factors relating to negative emotions has yielded disappointing results. Yet, the influence of anxious or fearful states on CPM has not attracted much interest despite ample evidence that negative affective states enhance pain. Our study aimed at investigating the effect of fear induction by symbolic threat on CPM.

METHODS

Thirty-seven healthy participants completed two experimental blocks: one presenting aversive pictures showing burn wounds (high-threat block) and one presenting neutral pictures (low-threat block). Both blocks contained a CPM paradigm with contact heat as TS and hot water as CS; subjective numerical ratings as well as contact-heat evoked potentials (CHEPs) were assessed.

RESULTS

We detected an overall inhibitory CPM effect for CHEPs amplitudes but not for pain ratings. However, we found no evidence for a modulation of CPM by threat despite threat ratings indicating that our manipulation was successful.

DISCUSSION

These results suggest that heat/thermal CPM is resistant to this specific type of symbolic threat induction and further research is necessary to examine whether it is resistant to fearful states in general.

SIGNIFICANCE

The attempt of modulating heat conditioned pain modulation (CPM) by emotional threat (fear/anxiety state) failed. Thus, heat CPM inhibition again appeared resistant to emotional influences. Pain-related brain potentials proved to be more sensitive for CPM effects than subjective ratings.

Pain, Fear, Anxiety, and Stress: Relations to the Endogenous Opioid System

Pain, fear, stress, and anxiety are separate yet interrelated phenomena. Each of these concepts has an extensive individual body of research, with some more recent work focusing on points of conceptual overlap. The role of the endogenous opioid system in each of these phenomena is only beginning to be examined and understood. Research examining the ways in which endogenous opioids (e.g., beta-endorphin; βE) may mediate the relations among pain, fear, stress, and anxiety is even more nascent. This chapter explores the extant evidence for endogenous opioid activity as an underpinning mechanism of these related constructs, with an emphasis on research examining βE.

Vicarious facilitation of facial responses to pain

INTRODUCTION

Observing facial expressions of pain has been shown to lead to increased subjective, neural and autonomic pain responses. Surprisingly, these vicarious facilitation effects on its corresponding response channel, namely facial responses to pain have mostly been neglected. We aim to examine whether the prior exposure to facial expressions of pain leads to a facilitation of facial responses to experimental pain; and whether this facilitation is linked to the valence (pain vs. neutral expression) or also linked to specific motor-features of the facial pain expressions (different facial muscle movements).

METHOD

Subjective (intensity and unpleasantness ratings) and facial responses (Facial Action Coding System) of 64 participants (34 female) to painful and non-painful heat stimuli were assessed. Before each heat stimulus, video clips of computer-generated facial expressions (three different pain expressions and a neutral expression) were presented.

RESULTS

The prior exposure to facial expressions of pain led to increased subjective and facial responses to pain. Further, vicarious pain facilitation of facial responses was significantly correlated with facilitation of unpleasantness ratings. We also found evidence that this vicarious facilitation of facial responses was not only linked to the presentation of pain versus neutral expressions but also to specific motor-features of the pain cue (increase in congruent facial muscle movements).

DISCUSSION

Vicarious pain facilitation was found for subjective and facial responses to pain. The results are discussed with reference to the motivational priming hypothesis as well as with reference to motor priming.

SIGNIFICANCE

Our study uncovers evidence that facial pain responses are not only influenced by motivational priming (similar to other types of pain responses), but also by motor-priming. These findings shed light on the complexity - ranging from social, affective and motor mechanisms - underling vicarious facilitation of pain.

Examining the role of mood in pain-limited treadmill walking duration in young healthy individuals

PURPOSE

The purpose of the study was to examine the effects of acute mood modulation on treadmill walking duration during experimental pain application.

METHODS

This was a repeated measure, within-subject study design. 30 healthy individuals (Males: Females 16:14; age 22.9 ± 2.5 years; height 170.9 ± 9.5 cm; body mass 68.4 ± 14.6 kg) attended a familiarization session and three experimental sessions, whereby they simultaneously viewed emotionally evoking stimulus from the International Affective Picture System (IAPS) and performed two treadmill walking tests (maximum 10 min duration) with a fixed nociceptive input applied to the thigh (pressure cuff). The primary outcome was treadmill walking duration during pain application to achieve a fixed pain score. During walking, mood (Self-Assessment Manikin: SAM 0-9) and pain (numerical rating scale: NRS 0-10) were measured.

RESULTS

Mood valence scores were significantly different in all conditions (p < 0.001), negative (2.4 ± 0.3), neutral (4.9 ± 0.6) and positive (6.6 ± 0.3). There was a significant difference (p = 0.04) in the treadmill walking duration for different mood states. For the primary outcome, post hoc analysis found differences between the negative and positive mood conditions for the treadmill walking durations to reach pain scores of 3 (negative: 224 ± 49 s; positive: 259 ± 60s, effect size [ES]: 0.80), 4 (negative: 262 ± 59 s; positive: 326 ± 90s, ES: 0.92), 5 (negative: 313 ± 86 s; positive: 385 ± 113 s, ES: 0.90), 6 (negative: 367 ± 106 s; positive: 447 ± 113 s, ES: 1.04) and 7 (negative: 423 ± 114 s; positive: 521 ± 110 s, ES: 1.02). There was no significant difference in the treadmill walking duration between the neutral vs negative mood and neutral vs positive mood conditions.

CONCLUSION

These results highlight the potential psychophysiological impacts on the pain experience in healthy individuals and encourages pursuit in strategies to minimize pain-limited exercise, a highly prevalent issue in the chronic pain population.

SIGNIFICANCE

Walking-based rehabilitation, designed to improve physical activity, has been shown to improve pain and disability. However active participation and adherence in walking-based rehabilitation has shown to be jeopardized by pain and pain-related cognitive and behavioural adaptations. This study examined the effect of a shift in mood on pain perception and treadmill walking tolerance. We found that with a worse mood, individuals were less tolerant of pain and walked on the treadmill for a shorter duration. These results suggest that factors which improve mood should be combined with walking-based training to improve tolerance.

Fibromyalgia is associated with hypersensitivity but not with abnormal pain modulation: evidence from QST trials and spinal fMRI

Widespread pain and hyperalgesia are characteristics of chronic musculoskeletal pain conditions, including fibromyalgia syndrome (FM). Despite mixed evidence, there is increasing consensus that these characteristics depend on abnormal pain augmentation and dysfunctional pain inhibition. Our recent investigations of pain modulation with individually adjusted nociceptive stimuli have confirmed the mechanical and thermal hyperalgesia of FM patients but failed to detect abnormalities of pain summation or descending pain inhibition. Furthermore, our functional magnetic resonance imaging evaluations of spinal and brainstem pain processing during application of sensitivity-adjusted heat stimuli demonstrated similar temporal patterns of spinal cord activation in FM and HC participants. However, detailed modeling of brainstem activation showed that BOLD activity during "pain summation" was increased in FM subjects, suggesting differences in brain stem modulation of nociceptive stimuli compared to HC. Whereas these differences in brain stem activation are likely related to the hypersensitivity of FM patients, the overall central pain modulation of FM showed no significant abnormalities. These findings suggest that FM patients are hyperalgesic but modulate nociceptive input as effectively as HC.

Electrophysiological correlates of semantic pain processing in the affective priming

Introduction

Pain plays a fundamental role in the well-being of the individual, and its semantic content may have specific properties compared to other negative domains (i.e., fear and anger) which allows the cognitive system to detect it with priority. Considering the influence of the affective context in which stimuli (targets) are evaluated, it is possible that their valence could be differentially processed if preceded by negative stimuli (primes) associated with pain than negative stimuli not associated with pain. Thus, the present study aims to investigate the electrophysiological correlates of the implicit processing of words with pain content by using an affective priming paradigm.

Methods

Event-related potentials (ERPs) were recorded while participants were presented with positive and negative word targets (not associated with pain) that were preceded by positive, negative (not associated with pain), and pain word primes. Participants were asked to judge the valence of the target word.

Results

Results showed faster reaction times (RTs) in congruent conditions, especially when the negative target was preceded by a pain prime rather than a positive one. ERPs analyses showed no effect of pain at an early-stage processing (N400), but a larger waveform when the pain prime preceded the positive prime on the LPP.

Discussion

These results reaffirm the importance that valence has in establishing the priority with which stimuli are encoded in the environment and highlight the role that pain has in the processing of stimuli, supporting the hypothesis according to which the valence and the semantics of a stimulus interact with each other generating a specific response for each type of emotion.

Physical strength and mental health mediate the association between pain and falls (recurrent and/or injurious) among community-dwelling older adults in Singapore

OBJECTIVE

This study aims to understand if poor physical strength and depression mediate the association between pain and recurrent and/or injurious falls in a community of older adults.

METHODS

Data was obtained from a nationally representative longitudinal cohort study conducted in Singapore, PHASE (Wave I and II), which collected information from community-dwelling older adults above 60 years old. A hurdle negative binomial regression and binomial logistic regression were used to assess the association between pain and recurrent falls, and pain and injurious falls respectively. A subsequent mediation analysis was conducted.

RESULTS

Almost half of the participants (N = 1144, 39.7%) reported having either mild, moderate, or severe pain at baseline, 166 (5.4%) participants experienced injurious falls and 144 (4.7%) participants experienced recurrent falls at Wave II. After adjusting for covariates, the presence of pain significantly influenced recurrent (OR 2.8; 95% CI: 1.8, 4.4) and injurious falls (OR: 1.8; 95% CI: 1.3, 2.5). Mediation analyses demonstrated that poor physical strength and depression had a significant mediation effect between all pain characteristics on recurrent falls. Poor physical strength partially mediates the effects of pain and injurious falls as well. However, the mediating effect of poor physical strength and depression was not observed between other pain characteristics and injurious falls.

CONCLUSIONS

The findings highlighted differences in the underlying mechanisms between pain characteristics affecting recurrent and injurious falls. These insights will be useful for identifying patients most at risk for recurrent or injurious falls, and for tailoring future community-based fall intervention programmes.

A randomized, placebo-controlled, double-blinded mechanistic clinical trial using endotoxin to evaluate the relationship between insomnia, inflammation, and affective disturbance on pain in older adults: A protocol for the sleep and Healthy Aging Research for pain (SHARE-P) study

Chronic pain is prevalent in older adults. Treatment, especially with opioids, is often ineffective and poses considerable negative consequences in this population. To improve treatment, it is important to understand why older adults are at a heightened risk for developing chronic pain. Insomnia is a major modifiable risk factor for chronic pain that is ubiquitous among older adults. Insomnia can also lead to heightened systemic inflammation and affective disturbance, both of which may further exacerbate pain conditions in older adults. Endotoxin exposure can be used as an experimental model of systemic inflammation and affective disturbance. The current study aims to understand how insomnia status and endotoxin-induced changes in inflammation and affect (increased negative affect and decreased positive affect) may interact to impact pain facilitatory and inhibitory processes in older adults. Longitudinal data will also assess how pain processing, affective, and inflammatory responses to endotoxin may predict the development of pain and/or depressive symptoms. The current study is a randomized, double-blinded, placebo-controlled, mechanistic clinical trial in men and women, with and without insomnia, aged 50 years and older. Participants were randomized to either 0.8ng/kg endotoxin injection or saline placebo injection. Daily diaries were used to collect variables related to sleep, mood, and pain at two-week intervals during baseline and 3-, 6-, 9-, and 12-months post-injection. Primary outcomes during the experimental phase include conditioned pain modulation, temporal summation, and affective pain modulation ∼5.5 hours after injection. Primary outcomes for longitudinal assessments are self-reported pain intensity and depressive symptoms. The current study uses endotoxin as an experimental model for pain. In doing so, it aims to extend the current literature by: (1) including older adults, (2) investigating insomnia as a potential risk factor for chronic pain, (3) evaluating the role of endotoxin-induced affective disturbances on pain sensitivity, and (4) assessing sex differences in endotoxin-induced hyperalgesia.

Clinicaltrialsgov

NCT03256760.

Trial sponsor

NIH R01AG057750-01.

The effect of preferred music versus disliked music on pain thresholds in healthy volunteers. An observational study

Pain is a prevalent and debilitating healthcare problem. Since pharmacological treatments have numerous side-effects, additional treatment could be beneficial. Music has been shown to affect the pain perception and the pain threshold. The objective of this observational study was to evaluate the effect of preferred music as opposed to disliked music on pain (tolerance) thresholds and perceived pain intensity in healthy volunteers. Pain thresholds were measured via quantitative sensory testing. The volunteers were randomly assigned to either handheld pressure algometry to assess the pressure pain threshold to or electrical measurements to assess the electrical pain tolerance threshold while listening to preferred and disliked music. The pain thresholds were administered on the dorsal side of the forearm. The perceived pain intensity was assessed via a numerical rating scale, ranging from 0 (no pain) to 10 (worst pain imaginable). In total 415 volunteers were included in this study. The pressure pain threshold was assessed in 277 volunteers and in the electrical pain tolerance threshold test 138 volunteers were entered. In both groups, preferred music yielded higher pain thresholds than disliked music (P<0.001) and lower perceived pain intensity during the stimulus (P = 0.003). Moreover, the highest pain thresholds of both pressure pain and electrical pain tolerance thresholds were obtained when the preferred music was preceded by disliked music. Listening to preferred music when receiving noxious stimuli leads to higher pain thresholds and lower perceived pain scores in comparison with disliked music. Preferred music could be beneficial for patients with pain or undergoing painful procedures.

Are acupuncture and dry needling effective in the management of masticatory muscle pain: A network meta‐analysis of randomised clinical trials

BACKGROUND

Several studies have shown that both acupuncture and dry needling are effective in the treatment of musculoskeletal pains. Therefore, the aim of this network meta-analysis (NMA) was to investigate the treatment outcome of acupuncture and dry-needling for masticatory muscle pain (TMD-M) and to compare with active and inactive placebo.

MATERIAL AND METHOD

An electronic search was performed to identify randomised controlled trials (RCTs) published until September 2019, comparing dry-needling, acupuncture, and inactive as well as active placebo in patients with TMD-M. Outcome variables were post-treatment pain intensity, pressure pain threshold (PPT), and maximum mouth opening (MMO). The quality of evidence was rated according to Cochrane's tool for assessing the risk of bias. Mean difference was used to analyse via frequentist NMA using STATA-software.

RESULTS

Both NMA and direct pairwise meta-analysis have shown that there was no difference between active treatment with either acupuncture or dry-needling when compared to active and inactive placebo in patients with TMD-M with respect to pain intensity, and PPT (p > .05). However, there was a significant increase in MMO following dry-needling when compared to the placebo (very low-quality evidence).

CONCLUSION

Despite the short-term positive effect of MMO by dry-needling, this NMA could not show any pain-reducing effect in patients with TMD-M by acupuncture or dry-needling when compared to an active or inactive placebo. Taken together, this NMA indicates that it is the placebo effect that accounts for the majority of the treatment effect of TMD-M, rather than a real therapeutic effect of acupuncture/dry-needling.

The influence of sexual arousal on subjective pain intensity during a cold pressor test in women

BACKGROUND & OBJECTIVES

Pain can be significantly lessened by sex/orgasm, likely due to the release of endorphins during sex, considered potent analgesics. The evidence suggests that endorphins are also present during sexual arousal (that is, prior to sex/orgasm). It follows then that pain can be modulated during sexual arousal, independent of sex/orgasm, too. Accordingly, sexual arousal induced by erotic slides has been demonstrated to lessen pain in men, but not in women. One explanation could be that for women, the erotic slides were not potent enough to elicit a lasting primed state of sexual arousal by the time pain was induced. Thus, the current study aims to optimize the means of inducing a potent state of sexual arousal and subsequently examine the potentially analgesic influence of sexual arousal on pain in women. As a subsidiary aim, the study also assesses whether the anticipated analgesic effect of sexual arousal would be stronger than that of distraction or generalized (non-sexual) arousal.

METHODS

Female participants (N = 151) were randomly distributed across four conditions: sexual arousal, generalized arousal, distraction, neutral. Mild pain was induced using a cold pressor while participants were concurrently exposed to film stimuli (pornographic, exciting, distracting, neutral) to induce the targeted emotional states. A visual analogue scale was utilized to measure the subjective level of pain perceived by the participants.

RESULTS

Sexual arousal did not reduce subjective pain. Generalized arousal and distraction did not result in stronger analgesic effects than the neutral condition.

CONCLUSION

The present findings do not support the hypothesis that sexual arousal alone modulates subjective pain in women. This might be due to the possibility that genital stimulation and/or orgasm are key in pain reduction, or, that feelings of disgust may inadvertently have been induced by the pornographic stimulus and interfered with sexual arousal in influencing pain.

Exploration of the trait-activation model of pain catastrophizing in Native Americans: results from the Oklahoma Study of Native American pain risk (OK-SNAP)

OBJECTIVES

Native Americans (NAs) have the highest prevalence of chronic pain of any racial/ethnic group. This issue has received little attention from the scientific community. One factor that may contribute to racial pain disparities is pain catastrophizing. Pain catastrophizing is a construct related to negative pain outcomes in persons with/without chronic pain. It has been suggested that the relationship between trait catastrophizing and pain is mediated by situation-specific (state) catastrophizing. The present study has 2 aims: (1) to investigate whether state pain catastrophizing mediates the relationship between trait catastrophizing and experimental pain (e.g., cold, ischemic, heat and electric tolerance), and (2) to investigate whether this relationship is stronger for NAs.

METHODS

145 non-Hispanic Whites (NHWs) and 137 NAs completed the study. Bootstrapped indirect effects were calculated for 4 unmoderated and 8 moderated mediation models (4 models with path a moderated and 4 with path b).

RESULTS

Consistent with trait-activation theory, significant indirect effects indicated a tendency for trait catastrophizing to be associated with greater state catastrophizing which in turn is associated with reduced pain tolerance during tonic cold (a × b=-0.158) and ischemia stimuli (a × b=-0.126), but not during phasic electric and heat stimuli. Moderation was only noted for the prediction of cold tolerance (path a). Contrary to expectations, the indirect path was stronger for NHWs (a × b for NHW=-.142).

CONCLUSIONS

Together, these findings suggest that state catastrophizing mediates the relationship between trait catastrophizing and some measures of pain tolerance but this indirect effect was non-significant for NAs.

Comparison between the Impacts of Memory and Arithmetic-Based Dual Tasks on Physical Performance in Women with Fibromyalgia

Background: Fibromyalgia symptoms have a significant impact on the ability to perform activities of daily living. These activities require the ability to perform two or more tasks at the same time, which is known as a dual task. Purpose: To analyze physical and cognitive performance differences between memory and arithmetic dual tasks. Methods: Twenty-five women with fibromyalgia participated in this study. Participants performed three physical tests (back scratch, arm curl, and 10-step stair) as a single task and under two types of dual task (memory and arithmetic). Results: Differences between the single and dual tasks were observed in the back scratch and the 10-step stair tests using the arithmetic dual-task. Significant differences were only observed for the memory dual-task in the 10-step stair test. In addition, the performance in the back scratch and in the 10-step stair was significantly lower under the arithmetic compared to the memory-based dual task. Furthermore, a significant difference between these two types of dual task was obtained in the dual-task cost of 10-step stair. Regarding cognitive performance, a significantly lower percentage of correct responses was found in the AbDT compared to the MbDT in the 10-step stair test. Conclusions: the AbDT could have a higher impact on physical performance than the MbDT during the back scratch and the 10-step stair tests. The characteristics of the sample, environment, complexity of the motor task, and difficulty of the simultaneous cognitive task may also be relevant for understanding the differences in dual-task interference.

Psychosocial and cardiometabolic predictors of chronic pain onset in Native Americans: serial mediation analyses of 2-year prospective data from the Oklahoma Study of Native American Pain Risk

ABSTRACT

Chronic pain results in considerable suffering, as well as significant economic and societal costs. Previous evidence suggests that Native Americans (NAs) have higher rates of chronic pain than other U.S. racial or ethnic groups, but the mechanisms contributing to this pain disparity are poorly understood. The Oklahoma Study of Native American Pain Risk was developed to address this issue and recruited healthy, pain-free NAs and non-Hispanic Whites. Cross-sectional analyses identified several measures of adversity (eg, trauma and discrimination), cognitive-affective factors (perceived stress and pain-related anxiety/catastrophizing), and cardiometabolic factors (eg, body mass index, blood pressure, and heart rate variability) that were associated with pronociceptive processes (eg, central sensitization, descending inhibition, and hyperalgesia). Every 6-months after enrollment, eligible participants (N = 277) were recontacted and assessed for the onset of chronic pain. This study examines predictors of chronic pain onset in the 222 participants (80%) who responded over the first 2 years. The results show that NAs developed chronic pain at a higher rate than non-Hispanic Whites (OR = 2.902, P < 0.05), even after controlling for age, sex, income, and education. Moreover, serial mediation models identified several potential pathways to chronic pain onset within the NA group. These paths included perceived discrimination, psychological stress, pain-related anxiety, a composite measure of cardiometabolic risk, and impaired descending inhibition of spinal nociception (assessed from conditioned pain modulation of the nociceptive flexion reflex). These results provide the first prospective evidence for a pain disparity in NAs that seems to be promoted by psychosocial, cardiometabolic, and pronociceptive mechanisms.

Are Cardiometabolic Markers of Allostatic Load Associated With Pronociceptive Processes in Native Americans?: A Structural Equation Modeling Analysis From the Oklahoma Study of Native American Pain Risk

Native Americans (NAs) experience higher rates of chronic pain than the general U.S. population, but the risk factors for this pain disparity are unknown. NAs also experience high rates of stressors and cardiovascular and metabolic health disparities (eg, diabetes, cardiovascular disease) consistent with allostatic load (stress-related wear-and-tear on homeostatic systems). Given that allostatic load is associated with chronic pain, then allostatic load may contribute to their pain disparity. Data from 302 healthy, pain-free men and women (153 NAs, 149 non-Hispanic Whites [NHW]) were analyzed using structural equation modeling to determine whether cardiometabolic allostatic load (body mass index, blood pressure, heart rate variability) mediated the relationship between NA ethnicity and experimental measures of pronociceptive processes: temporal summation of pain (TS-pain) and the nociceptive flexion reflex (TS-NFR), conditioned pain modulation of pain (CPM-pain) and NFR (CPM-NFR), and pain tolerance. Results indicated that NAs experienced greater cardiometabolic allostatic load that was related to enhanced TS-NFR and impaired CPM-NFR. Cardiometabolic allostatic load was unrelated to measures of pain perception (CPM-pain, TS-pain, pain sensitivity). This suggests cardiometabolic allostatic load may promote spinal sensitization in healthy NAs, that is not concomitant with pain sensitization, perhaps representing a unique pain risk phenotype in NAs. PERSPECTIVE: Healthy, pain-free Native Americans experienced greater cardiometabolic allostatic load that was associated with a pronociceptive pain phenotype indicative of latent spinal sensitization (ie, spinal sensitization not associated with hyperalgesia). This latent spinal sensitization could represent a pain risk phenotype for this population.

The role of self-evaluated pain sensitivity as a mediator of objectively measured pain tolerance in Native Americans: findings from the Oklahoma Study of Native American Pain Risk (OK-SNAP)

Native Americans (NAs) are at increased risk for chronic pain. One mechanism contributing to this pain disparity could be personal pain beliefs, which may influence actual pain sensitivity. Thus, we examined whether self-evaluated pain sensitivity (SEPS) mediates the relationship between ethnicity [NAs vs. non-Hispanic Whites (NHWs)] and objectively-measured pain tolerance, and whether catastrophic thinking and pain-related anxiety influence these pain beliefs. 232 healthy, pain-free NAs and NHWs completed questionnaires measuring SEPS, catastrophizing, and anxiety. Objective pain tolerance was also assessed. Results suggested: (1) NAs reported higher levels of SEPS, catastrophizing, and anxiety, (2) catastrophizing may have enhanced anxiety and both catastrophizing and anxiety were associated with higher SEPS, and (3) anxiety and SEPS were associated with lower pain tolerance. A significant bootstrapped mediation analysis suggested NAs experienced higher pain-related anxiety, which may have promoted higher SEPS, that in turn reduced pain tolerance. Longitudinal research is needed to confirm this.

Positive affect and distraction enhance while negative affect impairs pain modulation in recurrent low back pain patients and matched controls

ABSTRACT

Pathophysiological causes of low back pain (LBP) remain generally unclear, so focus has shifted to psychosocial features and central pain processing. Effects of attentional and affective manipulation on conditioned pain modulation (CPM) and tonic pain perception were examined in thirty recurrent LBP patients in two sessions, one with and one without clinical pain, and compared to healthy participants. Phasic cuff pressure on one leg, scored on a numerical rating scale (NRS), was used for test-stimuli (TS) and contralateral tonic cuff pain rated on an electronic visual analogue scale (eVAS) was the conditioning-stimulus (CS). TS were assessed before and during: 1) control with no manipulation/CS, 2) three attentional manipulations (Flanker with/without CS or CS-Only), and 3) three affective manipulations (positive, neutral, negative pictures) with CS. Greater inhibition of TS-NRS scores was observed in CS-only (P=0.028), combined CS&attention (P=0.026), and CS&Positive (P=0.006) than Control paradigms, and greater in CS&Positive (P=0.019) than CS&Negative paradigms. eVAS scores of CS pain increased throughout all paradigms with CS (P<0.05), except the CS&Positive paradigm, and greater facilitation was observed in the CS-Only paradigm than all others (P<0.02) and lower facilitation was additionally observed in the CS&Positive paradigm compared to CS&Attention and CS&Negative paradigms (P<0.01). Flanker effects and interruptive effects of CS pain on attention were observed consistent with prior findings, and affective manipulation produced less shift in valence among people with RLBP than controls (P<0.05). Attention and positive affect with CS pain evoked CPM, and all attentional/affective tasks, especially positive affect, reduced facilitation of CS pain.

Brain Asymmetry in Pain Affective Modulation

OBJECTIVE

The aim of this study was to characterize the dynamic brain networks underlying the affective modulation of pleasant, unpleasant, and neutral image perception due to painful stimulations in healthy subjects.

METHODS

Forty volunteers, 20 men and 20 women, participated in this study. Brain activity was recorded by 64-channel electroencephalography. After data cleaning, functional brain networks were built using the motif synchronization method.

RESULTS

We found that increased cerebral connectivity in the left hemisphere under the pain condition broke the connection symmetry. Both women and men showed homophilic connections (intra-hemispheric), but women were more homophilic than men. The pain condition increased homophily in the left hemisphere and emotions could modulate pain. Frontal, central, and left temporal regions showed homophilic variation, depending on the emotional stimulus.

CONCLUSIONS

Pain and emotions altered brain activity. There was increased connectivity and homophily in the left brain hemisphere for the painful experience. The emotions modulated the brain activity in pain condition. Overall, the brain presented homophilic characteristics; homophily changed, depending on emotion or pain. The left brain hemisphere seems to be related to pain processing.

Impaired pain empathic abilities among patients with functional dyspepsia

INTRODUCTION

Brain structure or functioning abnormality in regions such as insula and anterior cingulate cortex (ACC) is associated with functional dyspepsia (FD) and pain empathy, but the relationship between FD and pain empathy remains unclear. The aim of this study was to compare the pain empathic abilities of FD patients and healthy controls (HCs) and investigate the association of pain empathy with clinical characteristics and quality of life of FD patients.

METHODS

Pain empathic abilities was measured in 30 FD patients and 30 HCs using a validated pain empathy paradigm. Demographic characteristics, Helicobacter pylori status, duration, dyspeptic symptom score and Nepean Dyspepsia Life Quality Index (NDLQI) were obtained from all patients.

RESULTS

FD patients scored higher than HCs when rating painful pictures, but the accuracy for painful pictures was significantly lower than HCs. Pearson correlation analysis showed significant negative correlation between NDLQI and pain rating scores for painful pictures. When sex, age, educational level, the number of complaints, duration, H. pylori infection and NDLQI were included in multiple linear regression analysis, NDLQI was independently associated with pain ratings.

CONCLUSIONS

FD patients showed abnormally enhanced pain empathic abilities, which may be associated with the severity of symptoms and quality of life.

Pain Sensitivity, Negative Affect, and Alcohol Use Disorder Status: A Moderated Mediation Study of Emotion Dysregulation

Previous work suggests that the association between pain and emotional processes among individuals with alcohol use disorder (AUD) may differ from healthy controls. This study investigates whether pain sensitivity mediates the association between negative affect and emotional dysregulation and whether this association differs across AUD status using moderated mediation. The sample included 165 individuals diagnosed with AUD and 110 healthy controls. Of interest was pain sensitivity, as assessed with the Pain Sensitivity Questionnaire, negative affect, as assessed with the Beck Depression Inventory, and emotional dysregulation, as assessed with the Difficulties in Emotional regulation Scale. Age, biological sex, and current pain severity were included as covariates. The results support a moderated partial mediation model that explained 44% of the variance in emotional dysregulation. The findings indicate that negative affect is related to higher pain sensitivity across groups. Moreover, pain sensitivity partially mediated the association between negative affect and emotional dysregulation, but in opposite directions depending on AUD status. Among healthy controls, greater pain sensitivity was related to better emotional regulation, while greater pain sensitivity led to greater emotional dysregulation among individuals with AUD. The potential parallels in the underlying neurobiological mechanisms of emotionality, pain, and AUD suggest that interventions targeting pain may improve adaptive affect regulation skills, which in turn could reduce negative affect and its effect on pain sensitivity among individuals with AUD.

Medial Prefrontal Transcranial Direct Current Stimulation Aimed to Improve Affective and Attentional Modulation of Pain in Chronic Low Back Pain Patients

Chronic low back pain (CLBP) is often without clear underlying pathology. Affective disturbance and dysfunctional pain mechanisms, commonly observed in populations with CLBP, have, therefore, been suggested as potential contributors to CLBP development and maintenance. However, little consensus exists on how these features interact and if they can be targeted using non-invasive brain stimulation. In this pilot trial, 12 participants completed two phases (Active or Sham) of high-definition transcranial direct current stimulation (HD-tDCS) to the medial prefrontal cortex, applied for 20 min on three consecutive days. Clinical pain ratings, questionnaires, and sensitivity to painful cuff pressure were completed at baseline, then 4 trials of conditioned pain modulation (CPM; alone, with distraction using a Flanker task, with positive affect induction, and with negative affect induction using an image slideshow) were performed prior to HD-tDCS on Day 1 and Day 4 (24 h post-HD-tDCS). At baseline, attentional and affective manipulations were effective in inducing the desired state (p < 0.001) but did not significantly change the magnitude of CPM-effect. Active HD-tDCS was unable to significantly alter the magnitude of the shift in valence and arousal due to affective manipulations, nor did it alter the magnitude of CPM under any basal, attentional, or affective manipulation trial significantly on Day 4 compared to sham. The CPM-effect was greater across all manipulations on Day 1 than Day 4 (p < 0.02) but also showed poor reliability across days. Future work is needed to expand upon these findings and better understand how and if HD-tDCS can be used to enhance attentional and affective effects on pain modulation.

Interaction Between Sex and Cardiac Interoceptive Accuracy in Measures of Induced Pain

Pain perception is influenced by several factors, and among them, affect, sex, and perception of bodily signals are assumed to play a prominent role. The aim of the present study is to explore how sex, cardiac interoceptive accuracy, and the interaction of the latter two influence the perception of experimentally induced pain. We investigated a large sample of young adults (n = 159, 50.9% female, age: 23.45, SD = 3.767), assessing current positive and negative affective state with the Positive and Negative Affect Schedule (both involved as control variables), cardiac interoceptive accuracy with the mental heartbeat tracking task, and pain sensitivity with electrical stimulation on the back of the dominant hand, applying a repeated-measures staircase protocol. Males showed a significantly higher pain threshold and tolerance level than females, whereas cardiac interoceptive accuracy was not associated with pain sensitivity. The impact of sex × cardiac interoceptive accuracy interaction was significant for pain threshold only, while pain tolerance was predicted only by sex. According to these findings, the associations between pain sensitivity, cardiac IAc, and sex might be more complicated than it was supposed in previous studies. Interactions between factors impacting pain perception appear worthy of further investigation.

Salivary Alpha-Amylase in Experimentally-Induced Muscle Pain

Salivary alpha-amylase (sAA) is a marker of psychological stress and might also be a potential marker for pain-associated stress due its non-invasive, cost-effective, and stress-free collection. The current study aimed to investigate whether the levels of sAA are influenced by experimentally induced muscle pain. In this study, 26 healthy, pain-free and age-matched participants (23.8 ± 2.6 years) were included, 13 women and 13 men. Prior to the experiment, questionnaires assessing health and anxiety were completed. Muscle pain was then induced through intramuscular injection of 0.4 mL hypertonic saline (56.5 mg/mL) into the masseter muscle and unstimulated whole saliva samples were collected at baseline before injection, 2 min, and 15 min after injection. A commercially available colorimetric assay was used to analyze the sAA. Perceived pain and stress were assessed using a 0–100 Numeric Rating Scale for each sample. There were no significant differences in sAA levels prior and after injection of hypertonic saline (p > 0.05) although sAA levels showed a slight decrease during experimentally-induced muscle pain. However, a strong correlation was observed between self-reported pain and perceived level of stress during experimentally-induced muscle pain (r₂ = 0.744; p < 0.0001). Furthermore, there was a moderate correlation between the levels of sAA at baseline and during experimental pain (r₂ = 0.687; p < 0.0001). In conclusion, this study could not show any association between the levels of sAA and perceived pain and or/stress. However, since a significant strong correlation could be observed between perceived stress and pain intensity, this study indicates that experimentally-induced muscle pain could be used as a stress model.

Dispositional empathy is associated with experimental pain reduction during provision of social support by romantic partners

Background and aims While social interactions like verbal support and physical touch have repeatedly been shown to reduce experimental pain, analgesic effects of passive social support, i.e. the sole physical presence of a supportive other, remain unclear. Moreover, little is known about individual factors influencing the extent of pain attenuation during social support. This study investigated analgesic effects of passive support by a romantic partner and the role of partner empathy therein. Methods In 48 heterosexual couples, sensitivity to pressure pain was assessed; each participant was tested alone and in the passive presence of his/her partner. Dispositional empathy was quantified by a questionnaire. Results In the presence, as compared to absence, of their partners men and women exhibited higher pain threshold and tolerance, as well as lower sensory and affective pain ratings on constant pressure stimuli. Partner empathy was positively associated with pain tolerance and inversely associated with sensory pain experience. Conclusions The results confirm the analgesic effects of social support, which may even occur without verbal or physical contact. Partner empathy may buffer affective distress during pain exposure, thereby reducing pain sensitivity and promoting pain coping. These processes may occur solely due to a partner's physical presence and do not necessarily require direct empathetic feedback.

Images depicting human pain increase exercise-induced pain and impair endurance cycling performance

The current study investigated whether viewing images of others in pain influences exercise-induced pain (EIP) and cycling performance. Twenty-one recreational cyclists attended five laboratory visits. The first two visits involved measuring participants' maximal aerobic capacity and familiarized participants to the fixed power (FP) and 16.1 km cycling time trial (TT) tasks. The FP task required participants to cycle at 70% of their maximal aerobic power for 10-minutes. In the subsequent three visits, participants performed the FP and TT tasks after viewing pleasant, ‎painful or neutral images. Participants rated the subset of painful images as more painful than the pleasant and neutral images; with no difference in the pain ratings of the pleasant and neutral images. In the FP task, EIP ratings were higher following painful compared to pleasant images, while no differences in EIP were observed between any other condition . In the TT, performance did not differ between the pleasant and neutral conditions. However, TT performance was reduced after viewing painful images compared to neutral or pleasant images. HR, B[La], perceived exertion and EIP did not differ between the three conditions. These results suggest that viewing painful images decreases TT performance and increases pain during fixed intensity cycling.‎ Abbreviations: EIP: Exercise Induced Pain; FP: Fixed Power; TT: Time Trial; HR:Heart Rate; B[La]: Blood Lactate; RPE: Rating of Perceived Exertion; IAPS: International Affective Picture System; PO: Power Output.

Brain moderators supporting the relationship between depressive mood and pain

Pain and depressive mood commonly exhibit a comorbid relationship. Yet, the brain mechanisms that moderate the relationship between dysphoric mood and pain remain unknown. An exploratory analysis of functional magnetic resonance imaging, behavioral, and psychophysical data was collected from a previous study in 76 healthy, nondepressed, and pain-free individuals. Participants completed the Beck Depression Inventory-II (BDI), a measure of negative mood/depressive symptomology, and provided pain intensity and pain unpleasantness ratings in response to noxious heat (49°C) during perfusion-based, arterial spin-labeled functional magnetic resonance imaging. Moderation analyses were conducted to determine neural mechanisms involved in facilitating the hypothesized relationship between depressive mood and pain sensitivity. Higher BDI-II scores were positively associated with pain intensity (R = 0.10; P = 0.006) and pain unpleasantness (R = 0.12; P = 0.003) ratings. There was a high correlation between pain intensity and unpleasantness ratings (r = 0.94; P < 0.001); thus, brain moderation analyses were focused on pain intensity ratings. Individuals with higher levels of depressive mood exhibited heightened sensitivity to experimental pain. Greater activation in regions supporting the evaluation of pain (ventrolateral prefrontal cortex; anterior insula) and sensory-discrimination (secondary somatosensory cortex; posterior insula) moderated the relationship between higher BDI-II scores and pain intensity ratings. This study demonstrates that executive-level and sensory-discriminative brain mechanisms play a multimodal role in facilitating the bidirectional relationship between negative mood and pain.

Emerging Clinical Technology: Application of Machine Learning to Chronic Pain Assessments Based on Emotional Body Maps

Depression and anxiety co-occur with chronic pain, and all three are thought to be caused by dysregulation of shared brain systems related to emotional processing associated with body sensations. Understanding the connection between emotional states, pain, and bodily sensations may help understand chronic pain conditions. We developed a mobile platform for measuring pain, emotions, and associated bodily feelings in chronic pain patients in their daily life conditions. Sixty-five chronic back pain patients reported the intensity of their pain, 11 emotional states, and the corresponding body locations. These variables were used to predict pain 2 weeks later. Applying machine learning, we developed two predictive models of future pain, emphasizing interpretability. One model excluded pain-related features as predictors of future pain, and the other included pain-related predictors. The best predictors of future pain were interactive effects of (a) body maps of fatigue with negative affect and (b) positive affect with past pain. Our findings emphasize the contribution of emotions, especially emotional experience felt in the body, to understanding chronic pain above and beyond the mere tracking of pain levels. The results may contribute to the generation of a novel artificial intelligence framework to help in the development of better diagnostic and therapeutic approaches to chronic pain.

Assessing peripheral fibers, pain sensitivity, central sensitization, and descending inhibition in Native Americans: main findings from the Oklahoma Study of Native American Pain Risk

Native Americans (NAs) have a higher prevalence of chronic pain than other U.S. racial/ethnic groups, but there have been few attempts to understand the mechanisms of this pain disparity. This study used a comprehensive battery of laboratory tasks to assess peripheral fiber function (cool/warm detection thresholds), pain sensitivity (eg, thresholds/tolerances), central sensitization (eg, temporal summation), and pain inhibition (conditioned pain modulation) in healthy, pain-free adults (N = 155 NAs, N = 150 non-Hispanic Whites [NHWs]). Multiple pain stimulus modalities were used (eg, cold, heat, pressure, ischemic, and electric), and subjective (eg, pain ratings and pain tolerance) and physiological (eg, nociceptive flexion reflex) outcomes were measured. There were no group differences on any measure, except that NAs had lower cold-pressor pain thresholds and tolerances, indicating greater pain sensitivity than NHWs. These findings suggest that there are no group differences between healthy NAs and NHWs on peripheral fiber function, central sensitization, or central pain inhibition, but NAs may have greater sensitivity to cold pain. Future studies are needed to examine potential within-group factors that might contribute to NA pain risk.

Pain-related anxiety promotes pronociceptive processes in Native Americans: bootstrapped mediation analyses from the Oklahoma Study of Native American Pain Risk

INTRODUCTION

Evidence suggests Native Americans (NAs) experience higher rates of chronic pain than the general US population, but the mechanisms contributing to this disparity are poorly understood. Recently, we conducted a study of healthy, pain-free NAs (n = 155), and non-Hispanic whites (NHWs, n = 150) to address this issue and found little evidence that NAs and NHWs differ in pain processing (assessed from multiple quantitative sensory tests). However, NAs reported higher levels of pain-related anxiety during many of the tasks.

OBJECTIVE

The current study is a secondary analysis of those data to examine whether pain-related anxiety could promote pronociceptive processes in NAs to put them at chronic pain risk.

METHODS

Bootstrapped indirect effect tests were conducted to examine whether pain-related anxiety mediated the relationships between race (NHW vs NA) and measures of pain tolerance (electric, heat, ischemia, and cold pressor), temporal summation of pain and the nociceptive flexion reflex (NFR), and conditioned pain modulation of pain/NFR.

RESULTS

Pain-related anxiety mediated the relationships between NA race and pain tolerance and conditioned pain modulation of NFR. Exploratory analyses failed to show that race moderated relationships between pain-related anxiety and pain outcomes.

CONCLUSION

These findings imply that pain-related anxiety is not a unique mechanism of pain risk for NAs, but that the greater tendency to experience pain-related anxiety by NAs impairs their ability to engage descending inhibition of spinal nociception and decreases their pain tolerance (more so than NHWs). Thus, pain-related anxiety may promote pronociceptive processes in NAs to place them at risk for future chronic pain.

A Pleasant Sensation Evoked by Knee or Hand Icing Influences the Effect on Pain Intensity in Patients After Total knee Arthroplasty: A Prospective, Randomized, Cross-Over Study

Purpose

Cold therapy on the operated area after surgery is often used as an analgesic and to reduce pain, swelling, and increase range of motion. However, evidence to support the results of cold therapy is still scarce and the mechanism underlying its effectiveness remains unclear. The present study aimed to investigate whether a pleasant sensation evoked by icing the treated knee or a site distant from the treated site (the hand) influenced the acute effect on pain intensity in patients who have undergone total knee arthroplasty (TKA).

Patients and methods

A total of 37 patients with knee OA who underwent TKA were enrolled in this study. This prospective, randomized, cross-over study was performed for 2 days consecutively between days 8 and 15 postoperatively. Cold pack was placed on the anterior surface of the treated knee and palm for 10 mins, respectively. The main primary outcomes were the intensity of knee pain during maximal passive knee flexion.

Results

The two-way ANOVA showed significance only in the main effect of a pleasant sensation (F = 11.3, p = 0.001), but not in the icing site (F = 0.005, p = 0.94) and interaction (F = 0.65, p = 0.42).

Conclusion

This study shows that a pleasant sensation evoked by knee or hand icing influenced the effect on pain intensity during maximal knee flexion in patients after TKA. Even if knee icing has no effect on pain and evokes no pleasant sensation, it may be worthwhile to conduct hand icing to reduce pain.

Hyperalgesia when observing pain-related images is a genuine bias in perception and enhances autonomic responses

Observing pain in others can enhance our own pain. Two aspects of this effect remain unknown or controversial: first, whether it depends on the 'painfulness' of the visual stimulus; second, whether it reflects a genuine bias in perception or rather a bias in the memory encoding of the percept. Pain ratings and vegetative skin responses were recorded while 21 healthy volunteers received electric nociceptive shocks under three experimental conditions: (i) observing a painful contact between the body and a harmful object; (ii) observing a non-painful body contact, (iii) observing a control scene where the body and the object are not in contact. Pain reports and vegetative responses were enhanced exclusively when the subjects observed a painful body contact. The effect on perception was immediate, abated 3 sec after the shock, and positively correlated with the magnitude of vegetative arousal. This suggests that (a) hyperalgesia during observation of painful scenes was induced by their pain-related nature, and not by the simple body contact, and (b) hyperalgesia emerged from a very rapid bias in the perceptual encoding of the stimulus, and was not the result of a retrospective bias in memory recollection. Observing pain-depicting scenes can modify the processing of concomitant somatic stimuli, increasing their arousal value and shifting perception toward more painful levels.

Sensory, Affective, and Catastrophizing Reactions to Multiple Stimulus Modalities: Results from the Oklahoma Study of Native American Pain Risk

Native Americans (NAs) have a higher prevalence of chronic pain than any other U.S. racial/ethnic group; however, little is known about the mechanisms for this pain disparity. This study used quantitative sensory testing to assess pain experience in healthy, pain-free adults (n = 137 NAs (87 female), n = 145 non-Hispanic whites (NHW; 68 female)) after painful electric, heat, cold, ischemic, and pressure stimuli. After each stimulus, ratings of pain intensity, sensory pain, affective pain, pain-related anxiety, and situation-specific pain catastrophizing were assessed. The results suggested that NAs reported greater sensory pain in response to suprathreshold electric and heat stimuli, greater pain-related anxiety to heat and ischemic stimuli, and more catastrophic thoughts in response to electric and heat stimuli. Sex differences were also noted; however, with the exception of catastrophic thoughts to cold, these finding were not moderated by race/ethnicity. Together, findings suggest NAs experience heightened sensory, anxiety, and catastrophizing reactions to painful stimuli. This could place NAs at risk for future chronic pain and could ultimately lead to a vicious cycle that maintains pain (eg, pain → anxiety/catastrophizing → pain). PERSPECTIVE: NAs experienced heightened sensory, anxiety, and catastrophizing reactions in response to multiple pain stimuli. Given the potential for anxiety and catastrophic thoughts to amplify pain, this characteristic may place them at risk for pain disorders and could lead to a vicious cycle that maintains pain.

Differential effects of experimentally induced anxiety and fear on pain: the role of anxiety sensitivity

Background: Anxiety has been associated with both increased and decreased pain perception. Rhudy and Meagher (2000) showed that pain sensitivity is enhanced by anxiety (anticipation of shocks), but diminished by fear (confrontation with shocks). A problem of this approach is the confounding of emotional and attentional effects: Administered shocks (fear induction) divert attention away from pain, which might account for lower pain in this condition. Moreover, heterogeneous findings in the past might be due to inter-individual differences in the proneness to react to anxiety and fear such as ones anxiety sensitivity (AS) level.

Objectives: Our aim was to clarify the association between anxiety, fear and pain. We used the NPU paradigm for inducing these emotions and recording pain sensitivity at once with one stimulus to prevent interference by distraction. We assumed that anxiety and fear affect pain differently. Moreover, we hypothesized that subjects with clinically relevant (high) AS (H-AS group) show enhanced pain perception in contrast to low AS subjects (L-AS group).

Method: Forty healthy subjects (female: N=20; age M=23.53 years) participated and H-AS or L-AS status was determined by clinically discriminating cut-off scores of the Anxiety Sensitivity Index-3 (ASI-III). Emotions were induced by the application of unpredictable (anxiety) and predictable (fear) electric stimuli. Pain ratings of electric stimuli were compared between the conditions. Startle reflex and anxiety ratings were recorded.

Results: Results showed no general effects of anxiety and fear on pain perception. However, anxiety enhanced pain sensitivity in H-AS subjects, whereas fear did not affect pain sensitivity. In L-AS subjects no effects on pain perception were found.

Conclusion: Results revealed that anxiety, not fear, enhanced pain perception but only in subjects with clinically relevant AS levels. This indicates that subclinical AS levels are sufficient to increase pain sensitivity, in uncertain situations.

Measuring pain-Physiological and self-rated measurements in relation to pain stimulation and anxiety

INTRODUCTION

The aim of the present study was to investigate how emotions influence pain, measured by one subjective self-rated measure, the numeric rating scale (NRS), and one objective physiological measure, the number of skin conductance responses (NSCR).

METHOD

Eighteen volunteers were exposed to conditions with pictorial emotional stimuli (neutral, positive, negative), authentic ICU-sound (noise, no-noise) and electrical stimulation (pain, no-pain) individually titrated to induce moderate pain. When using all combinations of picture inducing emotions, sound, and pain, each of these conditions (12 conditions lasting for 60 seconds each) were followed by pain ratings. Ratings of arousal (low to high) and valence (pleasant to unpleasant) were used as indicators of affective state for each condition. Mean NSCR was also measured throughout the experiment for each condition.

RESULTS

Even though NRS and NSCR increased during painful stimuli, they did not correlate during the trial. However, NSCR was positively correlated with the strength of the electrical stimulation, r = 0.48, P = 0.046, whereas NRS showed positive correlations with the anxiety level, assessed by affective ratings (arousal, r = 0.61, P < 0.001, and valence, r = 0.37, P < 0.001).

CONCLUSIONS

The NRS was strongly influenced by affective state, with higher pain ratings during more anxiety-like states, whereas NSCR correlated to the strength of electrical pain stimulation. That reported pain is moderated by anxiety, puts forward a discussion whether reduction of the anxiety level should be considered during analgesia treatment.

Unique brain regions involved in positive versus negative emotional modulation of pain

Background and aims

Research has shown that negative emotions increase perceived pain whereas positive emotions reduce pain. Here we aim to investigate the neural mechanisms underlying this phenomenon.

Methods

While undergoing functional magnetic resonance imaging of the brain, 20 healthy adult females were presented with negative, neutral, and positive emotion-evoking visual stimuli in combination with the presentation of a noxious thermal stimulus to the hand. Participants rated the intensity and unpleasantness of the noxious thermal stimulus during each of the valence conditions. General linear model analyses were performed on the imaging data for each valence condition and specific contrasts were run.

Results

Significant differences were detected for the emotional modulation of pain (EMP) between the positive and negative conditions. Unique to the positive condition, there was increased activity in the inferior parietal, parahippocampal/perirhinal, precuneus/superior parietal, and the prefrontal cortices. Unique to the negative condition, there was increased activity in anterior and posterior cingulate and angular gyrus.

Conclusions

Positive and negative EMP appear to involve different brain regions.

Implications

Although there is some overlap in the brain regions involved in the positive and negative EMP, brain regions unique to each condition are identified and, moreover, the regions identified are involved in internal and external focus, respectively, pointing to a potential mechanism underlying this phenomenon.

Race/Ethnicity Does Not Moderate the Relationship Between Adverse Life Experiences and Temporal Summation of the Nociceptive Flexion Reflex and Pain: Results From the Oklahoma Study of Native American Pain Risk

Adverse life experiences (ALEs) are associated with hyperalgesia and chronic pain, but the underlying mechanisms are poorly understood. One potential mechanism is hyperexcitability of spinal neurons (ie, central sensitization). Given that Native Americans (NAs) are more likely to have ALEs and to have a higher prevalence of chronic pain, the relationship between ALEs and spinal hyperexcitability might contribute to their pain risk. The present study assessed temporal summation of the nociceptive flexion reflex (TS-NFR; a correlate of spinal hyperexcitability) and pain (TS-Pain) in 246 healthy, pain-free non-Hispanic whites and NAs. The Life Events Checklist was used to assess the number of ALEs. Multilevel growth models were used to predict TS-NFR and TS-Pain, after controlling for age, perceived stress, psychological problems, negative and positive affect, and painful stimulus intensity. ALEs and negative affect were significantly associated with greater pain, but not enhanced TS-Pain. By contrast, ALEs were associated with enhanced TS-NFR. Race did not moderate these relationships. This finding implies that ALEs promote hyperalgesia as a result of increased spinal neuron excitability. Although relationships between ALEs and the nociceptive flexion reflex/pain were not stronger in NAs, given prior evidence that NAs experience more ALEs, this factor might contribute to the higher prevalence of chronic pain in NAs. PERSPECTIVE: This study found a dose-dependent relationship between ALEs and spinal neuron excitability. Although the relationship was not stronger in NAs than non-Hispanic whites, given prior evidence that NAs experience more ALEs, this could contribute to the higher prevalence of chronic pain in NAs.

An incremental dual-task paradigm to investigate pain attenuation by task difficulty, affective content and threat value

There is accumulating evidence that task demands and psychological states can affect perceived pain intensity. Different accounts have been proposed to explain this attenuation based either on how limited attentional resources are allocated to the pain stimulus or on how the threat value of the pain stimulus biases attention. However, the evidence for both proposals remains mixed. Here we introduce an incremental dual-task paradigm in which participants were asked to detect pain on their fingertip without any additional tasks during baseline phases or while concurrently detecting visual targets during task phases. The force applied to participants' fingertip in all phases increased incrementally until they detected moderate pain. In Experiment 1, we used coloured shapes and in Experiment 2 we used affective images as visual targets. We also manipulated the threat value of the pain stimulus in Experiment 2. For both experiments, we found that a concurrent task attenuated perceived pain intensity: mean force was significantly greater for the same moderate pain during task compared to baseline phases. Furthermore although task difficulty and affective content did not affect pain perception, the threat value of the pain stimulus moderated the magnitude of pain attenuation.

Do multiple body modifications alter pain threshold?

In recent years, epidemiological data has shown an increasing number of young people who deliberately self-injure. There have also been parallel increases in the number of people with tattoos and those who voluntarily undergo painful procedures associated with piercing, scarification, and tattooing. People with self-injury behaviors often say that they do not feel the pain. However, there is no information regarding pain perception in those that visit tattoo parlors and piercing studios compared to those who don't. The aim of this study was to compare nociceptive sensitivity in four groups of subjects (n=105, mean age 26 years, 48 women and 57 men) with different motivations to experience pain (i.e., with and without multiple body modifications) in two different situations; (1) in controlled, emotionally neutral conditions, and (2) at a "Hell Party" (HP), an event organized by a piercing and tattoo parlor, with a main event featuring a public demonstration of painful techniques (burn scars, hanging on hooks, etc.). Pain thresholds of the fingers of the hand were measured using a thermal stimulator and mechanical algometer. In HP participants, information about alcohol intake, self-harming behavior, and psychiatric history were used in the analysis as intervening variables. Individuals with body modifications as well as without body modifications had higher thermal pain thresholds at Hell Party, compared to thresholds measured at control neutral conditions. No such differences were found relative to mechanical pain thresholds. Increased pain threshold in all HP participants, irrespectively of body modification, cannot be simply explained by a decrease in the sensory component of pain; instead, we found that the environment significantly influenced the cognitive and affective component of pain.

Effects of Cognitive-Behavioral Therapy on Empathy in Patients with Chronic Pain

OBJECTIVE

Cognitive-behavioral therapy (CBT) is effective in patients with chronic pain. However, the efficacy of CBT for impaired empathy has not been studied in this population. We investigated the effect of CBT on empathy in patients with chronic pain.

METHODS

Patients with severe chronic pain were recruited. Empathy was assessed before and after CBT using the Interpersonal Reactivity Index (IRI). The patients underwent eight sessions over the course of 1 month conducted. Additional symptoms were assessed using the Short-Form McGill Pain Questionnaire (SF-MPQ), Beck Depression Inventory, Beck Anxiety Inventory, World Health Organization Quality of Life Scale Abbreviated Version, and the Scale for Suicide Ideation.

RESULTS

A total of 26 participants were included. Pre-CBT pain severity assessed using the SF-MPQ was significantly correlated with the IRI-empathic concern subscale score (p=0.021), and the relationship remained significant after adjusting for sex, age, education level, and marital status. After CBT, the IRI-perspective-taking subscale scores (p=0.004) increased significantly and the IRI-personal distress subscale scores (p=0.013) decreased significantly in all participants. The SF-MPQ scores increased significantly (p=0.021).

CONCLUSION

CBT improved empathy in patients with chronic pain independent of its effect on pain, suggesting that CBT is useful for improving interpersonal relationships in patients with chronic pain.