Opposite Effects of Stress on Pain Modulation Depend on the Magnitude of Individual Stress Response

Mechanical and thermal thresholds before and after application of a conditioning stimulus in healthy Göttingen Minipigs

Minipigs are widely used in biomedical research for translational studies. However, information about pain elicited by experimental procedures is lacking. Non-invasive methods as quantitative sensory testing and conditioned pain modulation are particularly attractive. Our overarching aim was to explore and refine these methods for assessing post-operative pain in minipigs after myocardial infarction. As first step, we aimed at defining mechanical and thermal thresholds in healthy adults Göttingen Minipigs, evaluating their reliability, and testing their modifications after the application of a conditioning stimulus. Thresholds were assessed at different body sites before and after a painful conditioning stimulus (CS) (cuffed tourniquet) and sham CS (uncuffed tourniquet) in eleven animals. Thresholds' reliability was assessed using interclass correlation coefficient (ICC). The effect of the CS was assessed calculating absolute change, percentage change of the thresholds and standard error of measurement. Baseline mechanical thresholds (Newton) were: left hindlimb 81 [73; 81]; left forearm 81 [72.1; 81]; right forearm 81 [76; 81]; left chest 80.5 [68; 81]; right chest 81 [76.5; 81]; left neck 81 [70.3; 81]; right neck 74.8 [62.3; 80.5]. Reliability of mechanical thresholds was good at right chest (ICC = 0.835) and moderate at left chest (ICC = 0.591), left hindlimb (ICC = 0.606) and left neck (ICC = 0.518). Thermal thresholds showed poor reliability in all the tested sites. A modulatory effect was present at right chest, but it was seen when both a painful CS and a sham CS was applied. Minipigs tendentially showed a pro-nociceptive profile (i.e. conditioning pain facilitation). The measured thresholds are a reference for future trials in this species. Mechanical thresholds showed to be more reliable and, therefore, more useful, than thermal ones. The pain facilitation might be explained by the phenomenon of stress induced hyperalgesia, but this finding needs to be further investigated with a stricter paradigm.

The role of self-reported and physiological stress in nocebo hyperalgesia

Negative expectations can increase pain sensitivity, leading to nocebo hyperalgesia. However, the physiological and psychological factors that predispose individuals to this phenomenon are still not well understood. The present study examined whether stress induced by a social stressor affects nocebo hyperalgesia, and whether this effect is mediated by self-reported and physiological stress responses. We recruited 52 healthy participants (15 men) who were randomly assigned to either the Trier Social Stress Test (TSST) or a control condition (a friendly version of the TSST). Nocebo hyperalgesia was induced using negative suggestions combined with a validated pain conditioning paradigm. We assessed self-reported (anxiety and stress) and physiological (cortisol, alpha-amylase, heart rate, and skin conductance) responses to stress. Both groups exhibited significant nocebo hyperalgesia. The stress group showed higher levels of anxiety, self-reported stress, and cortisol levels compared to the control group while no significant differences were found in other physiological markers. The stress and control groups did not differ in the magnitude of nocebo hyperalgesia, but anxiety levels partially mediated the effects of the stress test on nocebo hyperalgesia. Our findings suggest that an external social stressor does not directly affect nocebo hyperalgesia, but that increased anxiety due to the stressor enhances its magnitude. Thus, it may be worthwhile to investigate whether reducing stress-related anxiety in clinical settings would help alleviate nocebo effects.

Changes in the choice motive and emotional perception of chocolates in response to stress

Although chocolates are often chosen for sensory pleasure, they are also selected to enhance mood and relieve emotional stress, or potentially chosen for its perceived health benefits if stress adversely affects physical well-being. This study aimed to investigate whether emotional stress influenced the motivations behind chocolate selection, subsequent liking, and emotional response. Participants were divided into a control group (n = 76) and a group with induced acute stress (n = 74). Stimuli were presented as dark chocolate packaging, each evoking sensory appeal, health, and emotional stress relief. Participants chose one stimulus from three options that they were most inclined to consume and evaluated the overall liking and emotional attributes of the stimuli. They also rated the overall liking and emotional attributes of three types of chocolates, each identical but paired with distinct stimuli. Their food attitudes were also assessed. Stress did not change the choice of stimuli, indicating that stress did not influence the motivation for chocolate selection. Instead, the choice of stimuli aligned with participants' food attitudes; those favoring sensory appeal and emotional stress relief prioritized pleasure in their usual food choices. Stress tended to increase liking and chocolate-associated positive emotions with sensory appeal, as opposed to others, to immediately alleviate negative emotions. The most robust motivation to consume chocolates was sensory pleasure, irrespective of stress, because of a preestablished association between sensory pleasure and mood enhancement.

Effects of Geometric Sound on Brainwave Activity Patterns, Autonomic Nervous System Markers, Emotional Response, and Faraday Wave Pattern Morphology

This study introduces Geometric Sound as a subfield of spatial sound featuring audio stimuli which are sonic holograms of mathematically defined 3D shapes. The effects of Geometric Sound on human physiology were investigated through EEG, heart rate, blood pressure, and a combination of questionnaires monitoring 50 healthy participants in two separate experiments. The impact of Geometric Sound on Faraday wave pattern morphology was further studied. The shapes examined, pyramid, cube, and sphere, exhibited varying significant effects on autonomic nervous system markers, brainwave power amplitude, topology, and connectivity patterns, in comparison to both the control (traditional stereo), and recorded baseline where no sound was presented. Brain activity in the Alpha band exhibited the most significant results, additional noteworthy results were observed across analysis paradigms in all frequency bands. Geometric Sound was found to significantly reduce heart rate and blood pressure and enhance relaxation and general well-being. Changes in EEG, heart rate, and blood pressure were primarily shape-dependent, and to a lesser extent sex-dependent. Pyramid Geometric Sound yielded the most significant results in most analysis paradigms. Faraday Waves patterns morphology analysis indicated that identical frequencies result in patterns that correlate with the excitation Geometric Sound shape. We suggest that Geometric Sound shows promise as a noninvasive therapeutic approach for physical and psychological conditions, stress-related disorders, depression, anxiety, and neurotrauma. Further research is warranted to elucidate underlying mechanisms and expand its applications.

Interindividual variability in cold-pressor pain sensitivity is not explained by peripheral vascular responding and generalizes to a C-nociceptor-specific pain phenotype

ABSTRACT

Pain sensitivity of healthy subjects in the cold-pressor (CP) test was proposed to be dichotomously distributed and to represent a pain sensitivity trait. Still, it has not been systematically explored which factors influence this pain sensitivity readout. The aim of this study was to distinguish potential contributions of local tissue-related factors such as perfusion and thermoregulation or gain settings in nociceptive systems. Cold-pressor-sensitive and CP-insensitive students screened from a medical student laboratory course were recruited for a CP retest with additional cardiovascular and bilateral local vascular monitoring. In addition, comprehensive quantitative sensory testing according to Deutscher Forschungsverbund Neuropathischer Schmerz standards and a sustained pinch test were performed. Cold pressor was reproducible across sessions (Cohen kappa 0.61 ± 0.14, P < 0.005). At 30 seconds in ice water, CP-sensitive subjects exhibited not only more pain (78.6 ± 26.3 vs 29.5 ± 17.5, P < 0.0001) but also significantly stronger increases in mean arterial blood pressure (12.6 ± 9.3 vs 5.6 ± 8.1 mm Hg, P < 0.05) and heart rate (15.0 ± 8.2 vs 7.1 ± 6.2 bpm, P < 0.005), and lower baroreflex sensitivity, but not local or vasoconstrictor reflex-mediated microcirculatory responses. Cold-pressor-sensitive subjects exhibited significantly lower pain thresholds also for cold, heat, and blunt pressure, and enhanced pain summation, but no significant differences in Aδ-nociceptor-mediated punctate mechanical pain. In conclusion, differences in nociceptive signal processing drove systemic cardiovascular responses. Baroreceptor activation suppressed pain and cardiovascular responses more efficiently in CP-insensitive subjects. Cold-pressor sensitivity generalized to a pain trait of C-fiber-mediated nociceptive channels, which was independent of local thermal and vascular changes in the ice-water-exposed hand. Thus, the C-fiber pain trait reflects gain setting of the nociceptive system.

Environmental factors and their impact on chronic pain development and maintenance

It is more than recognized and accepted that the environment affects the physiological responses of all living things, from bacteria to superior vertebrates, constituting an important factor in the evolution of all species. Environmental influences range from natural processes such as sunlight, seasons of the year, and rest to complex processes like stress and other mood disorders, infections, and air pollution, being all of them influenced by how each creature deals with them. In this chapter, it will be discussed how some of the environmental elements affect directly or indirectly neuropathic pain, a type of chronic pain caused by a lesion or disease of the somatosensory nervous system. For that, it was considered the edge of knowledge in translational research, thus including data from human and experimental animals as well as the applicability of such findings.

Nociception related biomolecules in the adult human saliva: A scoping review with additional quantitative focus on cortisol

Nociception related salivary biomolecules can be useful patients who are not able to self-report pain. We present the existing evidence on this topic using the PRISMA-ScR guidelines and a more focused analysis of cortisol change after cold pain induction using the direction of effect analysis combined with risk of bias analysis using ROBINS-I. Five data bases were searched systematically for articles on adults with acute pain secondary to disease, injury, or experimentally induced pain. Forty three articles met the inclusion criteria for the general review and 11 of these were included in the cortisol-cold pain analysis. Salivary melatonin, kallikreins, pro-inflammatory cytokines, soluable TNF-α receptor II, secretory IgA, testosterone, salivary α-amylase (sAA) and, most commonly, cortisol have been studied in relation to acute pain. There is greatest information about cortisol and sAA which both rise after cold pain when compared with other modalities. Where participants have been subjected to both pain and stress, stress is consistently a more reliable predictor of salivary biomarker change than pain. There remain considerable challenges in identifying biomarkers that can be used in clinical practice to guide the measurement of nociception and treatment of pain. Standardization of methodology and researchers' greater awareness of the factors that affect salivary biomolecule concentrations are needed to improve our understanding of this field towards creating a clinically relevant body of evidence.

Effects of conditioned pain modulation on Capsaicin-induced spreading muscle hyperalgesia in humans

OBJECTIVES

Muscle pain can be associated with hyperalgesia that may spread outside the area of primary injury due to both peripheral and central sensitization. However, the influence of endogenous pain inhibition is yet unknown. This study investigated how endogenous pain inhibition might influence spreading hyperalgesia in experimental muscle pain.

METHODS

Conditioned pain modulation (CPM) was assessed in 30 male volunteers by cold pressor test at the non-dominant hand as conditioning and pressure pain thresholds (PPT) at the dominant 2nd toe as test stimuli. Subjects were classified as having inhibitory or facilitating CPM based on published reference values. Subsequently, muscle pain and hyperalgesia were induced by capsaicin injection into the non-dominant supraspinatus muscle. Before and 5, 10, 15, 20, 30, 40, 50 and 60 min later, PPTs were recorded at the supraspinatus, infraspinatus and deltoid muscle, ring finger and toe.

RESULTS

Compared to baseline, PPTs decreased at the supraspinatus, infraspinatus and deltoid muscle (p≤0.03), and increased at the finger and toe (p<0.001). In facilitating CPM (n=10), hyperalgesia occurred at 5, 10, 15, 20 and 40 min (p≤0.026). In inhibitory CPM (n=20), hyperalgesia only occurred after 10 and 15 min (p≤0.03). At the infraspinatus muscle, groups differed after 5 and 40 min (p≤0.008).

CONCLUSIONS

The results suggest that facilitating CPM is associated with more spreading hyperalgesia than inhibitory CPM. This implies that poor endogenous pain modulation may predispose to muscle pain and spreading hyperalgesia after injury, and suggest that strategies to enhance endogenous pain modulation may provide clinical benefits.

The effects of high-definition transcranial direct current stimulation on pain modulation and stress-induced hyperalgesia

Background

The dorsolateral prefrontal cortex (DLPFC) has been implicated in the modulation of pain-related signals. Given this involvement, manipulation of the DLPFC through transcranial direct current stimulation (tDCS) may influence internal pain modulation and decrease pain sensitivity. Acute stress is also thought to affect pain, with increased pain sensitivity observed following the presentation of an acute stressor.

Methods

A total of 40 healthy adults (50% male), ranging in age from 19 to 28 years (M = 22.13, SD = 1.92), were randomly allocated to one of two stimulation conditions (active and sham). High-definition tDCS (HD-tDCS) was applied for 10 min at 2 mA, with the anode placed over the left DLPFC. Stress was induced after HD-tDCS administration using a modified version of the Trier Social Stress Test. Pain modulation and sensitivity were assessed through the conditioned pain modulation paradigm and pressure pain threshold measurements, respectively.

Results

Compared to sham stimulation, active stimulation produced a significant increase in pain modulation capacity. No significant change in pain sensitivity and stress-induced hyperalgesia was observed following active tDCS.

Conclusion

This research shows novel evidence that anodal HD-tDCS over the DLPFC significantly enhances pain modulation. However, HD-tDCS had no effect on pain sensitivity or stress-induced hyperalgesia. The observed effect on pain modulation after a single dose of HD-tDCS over the DLPFC is a novel finding that informs further research into the utility of HD-tDCS in the treatment of chronic pain by presenting the DLPFC as an alternative target site for tDCS-induced analgesia.

Higher self-perceived stress reactivity is associated with increased chronic pain risk

Self-perceived stress reactivity—how a person cognitively and emotionally responds to a stressor—is longitudinally associated with increased odds for the development of chronic pain.

Introduction:

Experiencing stress can contribute to unfavorable pain experiences, but outcomes vary across individuals. Evidence suggests that a person's specific reactivity to stressful events may influence pain responses. Previous studies measuring physiological stress reactivity have found associations with pain both clinically and in the laboratory. However, the time and cost required for testing physiological stress reactivity may limit clinical application.

Objective:

Self-reported perception of one's own stress reactivity has been shown to correlate with physiological stress reactivity in relation to health outcomes and may represent a valuable tool in clinical pain assessment.

Methods:

Using data from the Midlife in the US survey, we selected participants who did not have chronic pain at baseline (n = 1512) and who had data at follow-up 9 years later. Stress reactivity was assessed using a subscale of the Multidimensional Personality Questionnaire. We conducted a binary logistic regression to determine the odds of developing chronic pain, controlling for demographics and other health-related variables.

Results:

Results indicate that higher reported stress reactivity at baseline increased the odds of developing chronic pain at follow-up (odds ratio (OR) = 1.085, 95% confidence interval (CI) (1.021, 1.153), P = 0.008), with the only other significant predictor being the number of chronic conditions (OR = 1.118, 95% CI (1.045, 1.197), P = 0.001).

Conclusion:

Findings provide evidence for the predictive criterion validity of self-reported stress reactivity in the context of chronic pain risk. More generally, with increased need for virtual assessment and care, self-reported stress reactivity may be a useful, time-efficient, and cost-efficient tool for predicting pain outcomes in research and clinical contexts.

The Biology of Stress Intolerance in Patients with Chronic Pain—State of the Art and Future Directions

Stress has been consistently linked to negative impacts on physical and mental health. More specifically, patients with chronic pain experience stress intolerance, which is an exacerbation or occurrence of symptoms in response to any type of stress. The pathophysiological mechanisms underlying this phenomenon remain unsolved. In this state-of-the-art paper, we summarised the role of the autonomic nervous system (ANS) and hypothalamus-pituitary-adrenal (HPA) axis, the two major stress response systems in stress intolerance. We provided insights into such mechanisms based on evidence from clinical studies in both patients with chronic pain, showing dysregulated stress systems, and healthy controls supported by preclinical studies, highlighting the link between these systems and symptoms of stress intolerance. Furthermore, we explored the possible regulating role for (epi)genetic mechanisms influencing the ANS and HPA axis. The link between stress and chronic pain has become an important area of research as it has the potential to inform the development of interventions to improve the quality of life for individuals living with chronic pain. As stress has become a prevalent concern in modern society, understanding the connection between stress, HPA axis, ANS, and chronic health conditions such as chronic pain is crucial to improve public health and well-being.

Sex effects in the interaction of acute stress and pain perception

ABSTRACT

A reciprocity between the stress and the pain system is recognized; however, the manner by which sex affects this reciprocity is unclear. Understanding the interactions of stress, pain, and sex may shed light on the apparent women's vulnerability to chronic pain, which often coexists with increased distress, and to affective disorders, which often coexist with chronic pain. The study's aim was to examine the effect of acute, validated, psychosocial stress on pain perception and modulation of women and men in a controlled manner. Participants were 82 women and 66 men. Heat-pain threshold, heat-pain tolerance, and pain modulation by temporal summation of pain (TSP), and pain adaptation were measured before and after exposure to the Montreal Imaging Stress Task (MIST) or to a sham task. The stress response was verified by perceived ratings of stress and anxiety, autonomic variables, and salivary cortisol. A significant stress response was obtained by the MIST among both sexes; however, women displayed a greater increase in perceived distress, and men displayed a greater increase in cortisol. Among women, TSP decreased and pain adaptation increased following the MIST, responses that were predicted by perceived distress levels. Among men, TSP increased following the MIST but was not predicted by the stress variables. In conclusion, acute stress manipulation seems to differentially affect both stress and pain responses of women and men: women exhibited stress-induced antinociception and men exhibited stress-induced pronociception. Higher perceived stress levels among women may trigger a temporary increase in pain inhibition mechanisms to serve evolutionary purposes.

COVID-Related Distress Is Associated with Increased Menstrual Pain and Symptoms in Adult Women

The COVID-19 pandemic resulted in heightened stress for many individuals, with women reporting more stress than men. Although a large body of evidence has demonstrated that stress, in general, can impact the menstrual cycle, it is not yet clear if COVID-specific stress would impact women's menstrual health. The current study explored the relationship between COVID-related stress and distress and menstrual variables (menstrual pain, number and severity of menstrual symptoms, and menstrual pain interference) in a sample of reproductive-age adult women. Seven-hundred fifteen women completed the initial survey and were re-contacted to complete the same survey three months later. Of those recontacted, 223 completed the follow-up survey. Results indicated that COVID-related stress and distress was associated with higher levels of menstrual pain, more frequent and more severe menstrual symptoms, and greater menstrual pain interference, even after accounting for age, hormonal use, bodily pain, and pain catastrophizing. Our findings suggest that women experience unique vulnerabilities that directly impact their health and functioning, and both research and clinical care should address these symptoms through careful assessment and treatment of menstrual pain and symptoms, particularly during and after periods of high stress and distress.

Correlation among Routinary Physical Activity, Salivary Cortisol, and Chronic Neck Pain Severity in Office Workers: A Cross-Sectional Study

This study aimed to assess the correlation between different aspects of routinary physical activity with chronic neck pain severity indicators and salivary cortisol. This cross-sectional observational study included ninety-four office workers with non-specific chronic neck pain in the analyses. Pain related outcomes (pain intensity, pressure pain thresholds and disability), physical activity outcomes using the International Physical Activity Questionnaire, and salivary cortisol levels were evaluated. Pearson’s correlation analysis was used to investigate internal associations and regression models to explain and calculate which factors contribute to the variance of salivary cortisol and neck pain severity. Female sex (p < 0.01), sedentary behaviors (p < 0.05), and pain sensitivity (p < 0.05) were associated with greater cortisol levels (p < 0.05), but disability and pain intensity were not associated (p > 0.05). Worse disability, pain intensity, and pain pressure thresholds were also associated with lower routinary physical activity (p < 0.05). Regression models explained 20.6% of pain intensity (based on walking time to their workplace, age and pain sensitivity); 27.3% of disability (based on moderate physical activity at home, vigorous physical activity during leisure time and pain sensitivity); 54.2% of pain sensitivity (based on cycling time from home to their workplace, gender and vigorous activity during leisure time) and 38.2% of salivary cortisol concentration (based on systolic pressure, vigorous activity at work and both moderate and vigorous activity at home). Our results demonstrated the association between salivary cortisol concentration with moderate and vigorous physical activity, sitting time at work, and PPTs. However, salivary cortisol was not associated with disability or pain intensity.

Effects of psychosocial stress and performance feedback on pain processing and its correlation with subjective and neuroendocrine parameters

OBJECTIVES

Previous research on stress-induced pain modulation suggests that moderate psychological stress usually leads to hyperalgesia while more severe threat results in hypoalgesia. However, existing studies often lack suitable control conditions imperative to identify mere stress effects. Similarly, research mainly focused on pure anticipation of a social threat, not taking into consideration actual experiences of social evaluation. Therefore, we set out to investigate actual social up- and downgrading combined with a standardized stress paradigm to evaluate short-term and prolonged changes in pain perception and their potential association with neuroendocrine and subjective stress parameters.

METHODS

We allocated 177 healthy women to four experimental conditions, either the standard version of the Trier Social Stress Test (TSST) followed by positive, negative or no performance feedback, or a well-matched but less demanding placebo version of the TSST. Stress responses were assessed with ratings, salivary alpha-amylase, and salivary cortisol. To capture putative effects of stress on pain, heat pain threshold, ratings of phasic heat pain stimuli, and conditioned pain modulation were measured.

RESULTS

Despite a largely successful stress induction, results do not support a reliable influence of experimentally induced social stress-with or without subsequent performance feedback-on pain in women. Further, we found no clear association of pain modulation and changes in neuroendocrine or subjective stress responses.

CONCLUSIONS

Our results contrast previous studies, which repeatedly demonstrated stress-induced hypo- or hyperalgesia. This might be due to methodological reasons as former research was often characterized by high heterogeneity regarding the applied stressors, low sample sizes, and lacking or inconclusive control conditions. Thus, our results raise the question whether pain modulation in women by experimental psychosocial stress might have been overestimated in the past. Future research is necessary, which should employ parametric stress induction methods including well-matched control tasks, taking into consideration the participants' gender/sex and the time course of the stress response relative to pain assessment. The study is registered as DRKS00026946 at 'Deutsches Register Klinischer Studien' (DRKS) and can be also found at the World Health Organization's search portal.

Interaction Matters: The Effect of Touching the Social Robot PARO on Pain and Stress is Stronger When Turned ON vs. OFF

Social touch between humans, as well as between humans and animals, was previously found to reduce pain and stress. We previously reported that touching a social robot can also induce a reduction in pain ratings. However, it is unclear if the effect that touching a robot has on pain perception is due to its appearance and its pleasant touch, or due to its ability to socially interact with humans. In the current experiment, we aimed to assess the contribution of the interactive quality to pain perception. We assessed the effect of touching the social robot PARO on mild and strong pain ratings and on stress perception, on a total of 60 healthy young participants. The robot either interacted with participants (ON group, n = 30) or was turned off (OFF group, n = 30). Touching the robot induced a decrease in mild pain ratings (compared to baseline) only in the ON group while strong pain ratings decreased similarly in both the ON and the OFF groups. The decrease in mild pain ratings in the ON group was significantly greater in participants with a higher positive perception of the interaction with PARO. We conclude that part of the effect that touching the robot has on pain stems from its interactive features.

Exploring the relationship between meaningful conditioned pain modulation and stress system reactivity in healthy adults following exposure to the cold pressor task

BACKGROUND

The sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal (HPA) axis have been implicated in conditioned pain modulation (CPM). As there has recently been a push to identify meaningful CPM responses based on ± 2 SEM of the test stimulus, we sought to evaluate if meaningful CPM had relationships with both SNS and HPA axis reactivity.

METHODS

50 university-aged healthy participants (25 males, 25 females) underwent evaluation of pressure pain detection threshold (PPDT), conditioned pain modulation (CPM), galvanic skin response (GSR) and salivary cortisol before and after a cold pressor test (CPT). Meaningful CPM was evaluated based on change ±2 SEM of baseline PPDT to classify participants as experiencing inhibition of pain, facilitation, or non-response.

RESULTS

As a group, there were no significant changes in PPDT or salivary cortisol after exposure to noxious cold. GSR was significantly elevated from baseline values during the CPT, and 10 min after (p < 0.001). When meaningful CPM was assessed, only 30% of participants experienced inhibitory CPM. Within this group, there was a large positive correlation ranging from r = 0.63 to 0.69 (p < 0.01) between CPM and the absolute change in GSR from baseline to immersion, and the immediate 5 min after immersion.

CONCLUSIONS

This work continues to support the growing body of literature suggesting that CPM is not universally experienced. Inhibitory CPM may be associated with an increase in SNS activity for healthy participants in reaction to noxious cold. Future work is required to ascertain individual characteristics (e.g., age, sex) that relate to CPM responses.

When Less Is More: Investigating Factors Influencing the Distraction Effect of Virtual Reality From Pain

Virtual reality (VR) is a powerful method of redirecting attention away from pain. Yet, little is known about which factors modulate the size of this distraction effect. The aim of this study was to investigate the role of cognitive load and inter-individual differences in the cognitive and affective domain on heat pain thresholds during a VR game. Ninety healthy participants (mean age ± SD: 23.46 ± 3.28; 50% identified as male and 50% as female) played a low and high load version of a VR game while heat pain thresholds and heart rate were recorded. The effects of cognitive load were assessed by computing the difference in pain thresholds between the high and low load condition for each participant. In addition, we computed the difference in heart rate variability (HRV) measures between both conditions to explore whether these would be correlated with the difference in heat pain thresholds. Prior to the VR session, participants completed questionnaires about their emotional distress, pain-related cognitions, and different executive functioning tasks. Contrary to our expectations, not all participants benefitted from a higher load in terms of distraction from pain. Logistic regression analysis revealed that participants who reported more emotional distress were more likely to exhibit higher pain thresholds in the low relative to the high load condition. Accordingly, these participants tended to show marginally higher HRV in the low compared to the high load condition. Our study demonstrates that the potential benefits of an increased cognitive load in VR on pain sensitivity depends on individual differences in affective state.

Effects of acute mental stress on conditioned pain modulation in temporomandibular disorders patients and healthy individuals

Stress is a contributing factor to painful temporomandibular disorders (TMD). Nevertheless, the underpinnings of this relationship are not fully understood.

The Effect of Stress on Repeated Painful Stimuli with and Without Painful Conditioning

OBJECTIVES

Stress and pain have been interrelated in clinical widespread pain conditions. Studies indicate that acute experimental stress in healthy volunteers has a negative effect on the descending inhibitory pain control system and thus the ability to inhibit one painful stimulus with another (conditioned pain modulation [CPM]) although without effect on general pain sensitivity. CPM effects can be assessed immediately after the stress induction, whereas some physiological stress responses (e.g., cortisol release) are delayed and longer lasting. It is unclear whether CPM may relate to stress-induced increases in cortisol.

DESIGN

Twenty-five healthy men had CPM effects measured over a period of 10 minutes. Pain detection thresholds (PDTs) were assessed by repeated test stimuli with cuff algometry on one leg, with and without painful cuff pressure conditioning on the contralateral leg. CPM effects, assessed as the increase in PDT during conditioning stimulation compared with without, were measured before and after experimental stress and a control condition (Montreal Imaging Stress Task [MIST]). Saliva cortisol levels and self-perceived stress were collected.

RESULTS

Participants reported the MIST to be more stressful compared with the MIST control, but cortisol levels did not change significantly from baseline. In all sessions, PDT increased during conditioning (P = 0.001), although the MIST compared with the MIST control had no significant effect on PDT or CPM effects. A negative correlation between changes in cortisol and conditioned PDT was found when applying the MIST (P < 0.03).

CONCLUSIONS

No significant effect of stress was found on CPM compared with a matched control condition. Individual changes in experimental stress and in conditioned pain sensitivity may be linked with cortisol.

The effect of mindful attention training for pain modulation capacity: Exploring the mindfulness-pain link

OBJECTIVE

Mindfulness has been shown to be beneficial for chronic pain. The underlying mechanisms of the mindfulness-pain link, however, are yet to be established. Particularly, the effects of mindfulness on pain modulation, which is shown to be dysfunctional among chronic pain patients, barely has been tested. This study investigated whether a short mindful attention training based on Langerian mindfulness mitigates reductions in pain modulation.

METHOD

Systemic quantitative-somatosensory testing of conditioned pain modulation (CPM) was conducted in 60 undergraduates, who were randomly assigned to one of three groups: (1) Pain-specific mindful attention training; (2) nonspecific mindful attention training; and (3) no mindful attention training. CPM was tested before and after the intervention.

RESULTS

As hypothesized, a reduction in CPM magnitude was observed only in the control group, whereas this reduction was abolished in the two mindfulness groups.

CONCLUSIONS

Langerian mindfulness may mitigate pain modulation reduction as observed in chronic pain, thus shedding light on its potential advantages.

Individual variability and sex differences in conditioned pain modulation and the impact of resilience, and conditioning stimulus pain unpleasantness and salience

Distinct pain experiences are shaped both by personal attributes and characteristics of noxious stimuli. An Individual's capacity for endogenous pain inhibition (reflected by conditioned pain modulation [CPM]), their resilience, and the pain unpleasantness and salience of painful stimuli can impact their pain perception. Here, we aimed to determine how individual variability in CPM relates to sex and resilience as personal attributes, and pain unpleasantness and salience of the CPM conditioning stimulus (CS). We evaluated CPM in 106 healthy participants (51 female and 55 male) based on the change in test stimulus pain applied concurrently with a painful CS, both delivered by painful heat. The CS reduced test stimulus pain in only half of the participants (CPM subgroup), but did not do so for the other half (no-CPM subgroup), many who exhibited pain facilitation. A regression model explained CPM effects after accounting for sex, resilience, CS pain unpleasantness and salience. In the CPM subgroup regression model, the CPM effect was positively related to CS pain unpleasantness, while the CPM effect was not related to any variable in the no-CPM subgroup model. Correlation analyses revealed that the CPM effect was anticorrelated with resilience in males with no-CPM. The CPM effect was correlated with CS pain unpleasantness in males with CPM and in females with no-CPM. The CPM effect and CS salience were correlated in the whole group more strongly than in the subgroups. These data reveal that the complexity of contributors to CPM variability include both personal attributes and attributes of the CS.

Neuropeptide and cytokine regulation of pain in the context of substance use disorders

Substance use disorders (SUDs) are frequently accompanied by affective symptoms that promote negative reinforcement mechanisms contributing to SUD maintenance or progression. Despite their widespread use as analgesics, chronic or excessive exposure to alcohol, opioids, and nicotine produces heightened nociceptive sensitivity, termed hyperalgesia. This review focuses on the contributions of neuropeptide (CRF, melanocortin, opioid peptide) and cytokine (IL-1β, TNF-α, chemokine) systems in the development and maintenance of substance-induced hyperalgesia. Few effective therapies exist for either chronic pain or SUD, and the common interaction of these disease states likely complicates their effective treatment. Here we highlight promising new discoveries as well as identify gaps in research that could lead to more effective and even simultaneous treatment of SUDs and co-morbid hyperalgesia symptoms.

A Systematic Review of Biological Mechanisms and Chronic Pain Outcomes During Stress Reduction Interventions

BACKGROUND

Nonpharmacologic stress reduction interventions provide an opportunity to modify chronic pain trajectories; however, the biological mechanisms underlying these interventions are poorly understood.

OBJECTIVES

To examine clinical literature published in 2012-2018 with the goals of (1) identifying which biological mechanisms or biomarkers are currently being measured in nonpharmacologic stress reduction intervention studies for individuals with chronic pain and (2) evaluating the evidence to determine whether these stress reduction interventions lead to changes in (a) pain outcomes and/or (b) measured biomarkers.

DATA SOURCES

Scientific articles in the electronic databases PubMed/Medline, Cumulative Index of Nursing and Allied Health Literature, PsychINFO, and SCOPUS following the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines.

STUDY SELECTION

Randomized controlled trials and quasi-experimental studies that recruited subjects with a chronic pain condition, examined a relationship between a nonpharmacologic stress reduction intervention and pain-related outcome(s), and included measurement of a biomarker.

RESULTS

The 13 articles that met inclusion criteria spanned four nonpharmacologic stress reduction categories: mindfulness-based stress reduction, physical exercise, manual therapies, and biofeedback. Methods for studying biomarkers included measuring biological samples, neurological function, and autonomic control. Although all studies investigated both biological measures and pain outcomes, only three demonstrated an association between the biomarker(s) and pain-related outcomes.

CONCLUSIONS

The results of this review highlight the complex nature of stress-pain relationships and the lack of rigorous clinical research identifying specific stress-related biological factors that modulate pain outcomes. Stress reduction interventions remain a favorable method for symptom management in patients living with chronic pain, but consistency in study measures and design is needed for robust evaluation.

Widespread Hypersensitivity to Pressure Pain in Men With Cluster Headache During Prolonged Remission Is Not Related to the Levels of Depression and Anxiety

BACKGROUND

Diminished pressure pain thresholds (PPTs) have been found in patients with cluster headache (CH), suggesting the presence of central sensitization. However, it is not known whether sensitization persists over time during the asymptomatic periods.

OBJECTIVE

To investigate if men with episodic CH in a long-lasting remission phase exhibit widespread pressure pain hypersensitivity.

METHODS

Forty men with episodic CH and 40 matched controls were enrolled. PPTs were assessed bilaterally over 1 trigeminal (temporalis muscle) and 3 extra-trigeminal points (C5/C6 zygapophyseal joint, second metacarpal, tibialis anterior muscle) by a blinded assessor. Patients were assessed in a prolonged remission phase, at least 6 months after their last CH attack and without taking any medication. Depression and anxiety levels were assessed with the Hospital Anxiety and Depression Scale (HADS). For each point, differences in PPTs were evaluated with a multivariate mixed-model analysis of covariance test, with side and group as main factors and depression and anxiety levels as covariates.

RESULTS

PPTs were significantly decreased bilaterally over the temporalis muscle (mean difference: 85 to 100 kPa), C5/C6 zygapophyseal joint (mean difference: 65 to 80 kPa), second metacarpal (mean difference: 65 to 90 kPa), and tibialis anterior muscle (mean difference: 135 to 155 kPa) in patients with CH when compared to headache-free subjects (all, P < 0.001). No effect of anxiety or depression levels was found.

CONCLUSIONS

Patients with CH exhibited bilateral widespread hypersensitivity to pressure pain during long-lasting remission periods, which was not associated with depression or anxiety. These results support the persistence of central sensitization in episodic CH, even in remote asymptomatic phases.

Punishing the Self: Post-Traumatic Guilt Mediates the Link Between Trauma and Deficient Pain Modulation

Trauma survivors may suffer from post-traumatic stress disorder (PTSD), elevated post-traumatic guilt (PG), and alterations in the pain system. However, the association between PG and alterations in pain perception and modulation among trauma survivors has not been established, nor has the possible underlying role of PG. This longitudinal study investigated: 1) the unique contribution of PG in predicting pain perception and modulation, while controlling for PTSD symptoms; and 2) the mediating role of PG in explaining pain perception and modulation among torture survivors, above and beyond PTSD symptoms. Participants were 59 torture survivors and 44 age-matched controls. PG and PTSD symptoms were assessed in 2003 (T1). Heat-pain threshold, heat-pain tolerance, temporal summation of pain (TSP), and conditioned pain modulation (CPM) were measured 5 years later (T2). Torture survivors had elevated PG and PTSD symptoms, enhanced TSP, and reduced CPM, compared to controls. While PTSD predicted reduced pain tolerance and CPM, PG predicted increased pain tolerance. Moreover, PG mediated the associations between torture and (increased) pain threshold, pain tolerance, and TSP. It appears that PTSD and PG induce opposite effects on the pain modulation capacity of torture survivors, a dichotomy that may explain paradoxical pain responses among trauma survivors, as discussed. PERSPECTIVE: This longitudinal study sheds light on the possible mechanisms underlying variations in pain perception and modulation among trauma survivors. PTSD and PG each mediated opposing pain modulation profiles, suggesting that individual responses to trauma, rather than the trauma itself, influence pain responses.

Hypothalamic-pituitary-adrenal axis feedback sensitivity in different states of back pain

Pain normally signals a threat to bodily integrity and causes emotional distress. Acute pain serves a protective function, yet, when pain turns chronic, the protective function is lost. A chain of psychophysiological alterations including changes in the stress regulation system, apparent in dysfunctional activity and responsivity of the hypothalamic-pituitary-adrenal (HPA) axis, might be an important factor in this context. Moreover, maladaptive responses may be complicated by affective comorbid symptoms such as anxiety and depression, and alter nociceptive processing. However, the relationship among pain chronicity, stress regulation, and contributing components of comorbid symptomatology as well as somatosensory profiles has rarely been examined. In the present study, we obtained diurnal cortisol profiles at baseline and feedback regulation (following a dexamethasone suppression test (DST)) in subacute (SABP) and chronic (CBP) back pain patients and healthy control individuals (HC). We also assessed anxiety, depression and chronic stress levels and used quantitative sensory testing (QST) to detect sensory abnormalities. We found a hyper-suppression of cortisol following DST and thus enhanced negative stress feedback sensitivity in SABP compared to both CBP and HC. In SABP, DST-related cortisol levels were negatively associated with pain intensity, mediated by cold pain thresholds and anxiety. These data support a stress model of pain chronicity and suggest that stress responses might be indicators of individual vulnerability in the transition period of subacute pain.

Can disbudding of calves (one versus four weeks of age) induce chronic pain?

BACKGROUND

Calf disbudding is a welfare-relevant invasive husbandry procedure. While it is widely recognized that disbudding elicits acute pain, its chronic consequences are currently unknown.

OBJECTIVES

Primary aim of this study was to investigate whether disbudding leads to chronic pain in calves; secondary aim was to evaluate the influence of age at disbudding (1 week versus 4 weeks).

METHODS

Thirty-four Holstein bull calves, enrolled in a prospective, controlled, randomized trial, underwent either early disbudding (ED) or late disbudding (LD) or sham treatment (control) at 1 and 4 weeks of age. Pain scoring and quantitative sensory tests (von Frey filaments and algometry) were performed at regular intervals up to 105 days of life; neurophysiological determination of nociceptive reflex thresholds and conditioned pain modulation (CPM) up to 90 days. Data was analyzed with the Brunner and Langer model followed by post-hoc test, with level of significance set at 0.05.

RESULTS

Thirty-one calves completed the data collection. Signs of chronic sensitization were observed in 38% of disbudded calves (4 in ED and 4 in LD). Pain scores (until 105 days) and allodynia scores (until 60 days) were significantly higher while pressure thresholds (until 105 days) were significantly lower in both groups ED and LD compared to control. Late disbudded calves showed impairment of trigeminal CPM. Lower laser-evoked trigeminal reflex thresholds were found in clinically painful calves compared to control.

CONCLUSIONS

The sequelae of disbudding can extend beyond the acute post-procedural phase. Chronic trigeminal sensitization, independently from the age at disbudding can affect individual calves.