Associations of nocturnal sleep with experimental pain and pain catastrophizing in healthy volunteers

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.

Chronic sleep deficiency and its impact on pain perception in healthy females

Acute sleep deprivation in experimental studies has been shown to induce pain hypersensitivity in females. However, the impact of natural sleep deficiency and fluctuations across the week on pain perception remains unclear. A sleep-monitoring headband and self-reports were utilized to assess objective and subjective sleep in longer (> 6 hr) and short sleepers (< 6 hr). Pain sensitivity measures including heat, cold, pressure pain thresholds, pain inhibition (conditioned pain modulation) and facilitation (tonic pain summation) were assessed on Mondays and Fridays. Forty-one healthy young (23.9 ± 0.74 years) women participated. Short sleepers slept on average 2 hr less than longer sleepers (297.9 ± 8.2 min versus 418.5 ± 10.9 min) and experienced impaired pain inhibitory response (mean = -21.14 ± 7.9°C versus mean = 15.39 ± 9.5°C; p = 0.005). However, no effect was observed in pain thresholds and pain summation (p > 0.05). Furthermore, pain modulatory responses differed between Mondays and Fridays. Chronic sleep deficiency (< 6 hr) compromises pain responses, notably on Mondays. Maintaining a consistent sleep pattern with sufficient sleep (> 6 hr) throughout the week may protect against pain sensitization and the development of chronic pain in females. Further research is needed, especially in patients with chronic pain.

The Impact of Sleep Disturbances on Endogenous Pain Modulation: A Systematic Review and Meta-Analysis

The bidirectional relationship between sleep and pain problems has been extensively demonstrated but despite all the accumulating evidence, their shared mechanisms are currently not fully understood. This review examined the association between sleep disturbances, defined as a broad array of sleep-related outcomes (eg, poor quality, short duration, insomnia), and endogenous pain modulation (EPM) in healthy and clinical populations. Our search yielded 6,151 references, and 37 studies met the eligibility criteria. Qualitative results showed mixed findings regarding the association between sleep disturbances and temporal summation of pain (TSP) and conditioned pain modulation (CPM), with poor sleep more commonly associated with decreased pain inhibition in both populations. Quantitative results indicated that such associations were not statistically significant, neither in healthy populations when EPM outcomes were assessed for changes pre-/post-sleep intervention (TSP: .31 [95%CI: -.30 to .92]; P = .321; CPM: .40 [95%CI: -.06 to .85] P = .088) nor in clinical populations when such association was assessed via correlation (TSP: -.00 [95%CI: -.22 to .21] P = .970; CPM: .12 [95%CI: -.05 to .29]; P = .181). For studies that reported results by sex, meta-analysis showed that experimental sleep disturbances impaired pain inhibition in females (1.43 [95%CI: .98-1.88]; P < .001) but not in males (-.30 [95%CI: -2.69 to 1.60]; P = .760). Only one study investigating the association between sleep disturbances and offset analgesia was identified, while no studies assessing spatial summation of pain were found. Overall, this review provides a comprehensive overview of the association between sleep disturbances and EPM function, emphasizing the need for further investigation to clarify specific mechanisms and phenotypic subtypes. PERSPECTIVE: This review shines a light on the association between sleep disturbances and endogenous pain modulation function. Qualitatively, we found a frequent association between reduced sleep quality and impaired pain inhibition. However, quantitatively such an association was not corroborated. Sex-specific effects were observed, with females presenting sleep-related impaired pain inhibition but not males.

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.

The impact of sleep disturbance on pain perception: A systematic review examining the moderating effect of sex and age

Females have increased pain sensitivity and are more vulnerable to chronic pain conditions. Sleep disturbances are comorbid with chronic pain and exacerbate pain symptoms. Different types of sleep disturbance affect pain perception distinctly, but it is not clear if these effects are equal in men and women. This systematic review investigated potential differences in how sleep disturbance affects pain in males and females. We searched EBSCO, MEDLINE, Psych INFO, Science Direct, and Web of Science from January 2001 to November 2022 and found 38 studies with 978 participants. Separate random-effects models were used to estimate the pooled effect sizes based on standardized mean differences (SMDs) of experimental sleep disturbance paradigms on various pain outcomes. Sex moderated the effect of sleep disturbance on pain facilitation (SMD = 0.13; 95%CI: 0.004 to 0.022; p=.009) and pain inhibition (SMD = 0.033; 95%CI: 0.011 to 0.054; p=.005), with increased facilitation and decreased inhibition in females, but the opposite effect in males. Further, age moderated the effects of total sleep deprivation (SMD = -0.194; 95%CI -0.328 to -0.060; p=.008) on pain sensitivity and fragmented sleep (SMD = -0.110; 95%CI: 0.148 to -0.072; p<.001) on pain threshold. While the moderating effect of sex and age on the sleep-pain relationship was small, these factors need to be considered in future sleep-pain research.

The Effects of Recovery Sleep on Experimental Pain

Recent research suggests that recovery sleep (RS) has the potential to restore pain sensitivity and modulation after hyperalgesia due to preceding sleep deprivation. However, it has not yet been systematically examined whether the restoration of these pain parameters is driven by sleep characteristics of RS. Thus, the present study assessed changes in experimental pain during RS after total sleep deprivation (TSD) to test whether RS parameters predicted the restoration of the pain system. Thirty healthy participants completed one night of habitual sleep, one night of TSD and a subsequent recovery night. At-home sleep during baseline and recovery was assessed using portable polysomnography and a questionnaire. Before and after each night pressure pain thresholds (PPTs), temporal pain summation (TSP) and conditioned pain modulation (CPM) were assessed. PPTs decreased after TSD and increased following RS, indicating a restoration of pain sensitivity after hyperalgesia. RS characteristics did not predict this restoration, suggesting other mechanisms (eg, changes in serotonergic activity) underlying the observed pain changes. TSP indicated a lack of effect of experimental sleep manipulations on excitatory processes whereas CPM lacked sufficient reliability to investigate inhibitory processes. Thus, results indicate moderate effects of sleep manipulations on pain sensitivity, but not on pain modulation. PERSPECTIVE: This article highlights the potential of recovery sleep to let pain thresholds return to normal following their decrease after a night of total sleep deprivation. In contrast, endogenous pain modulation (temporal pain summation, conditioned pain modulation) was not affected by sleep deprivation and recovery sleep.

The complexities of the sleep-pain relationship in adolescents: A critical review

Chronic pain is a common and disabling condition in adolescents. Disturbed sleep is associated with many detrimental effects in adolescents with acute and chronic pain. While sleep and pain are known to share a reciprocal relationship, the sleep-pain relationship in adolescence warrants further contextualization within normally occurring maturation of several biopsychological processes. Since sleep and pain disorders begin to emerge in early adolescence and are often comorbid, there is a need for a comprehensive picture of their interrelation especially related to temporal relationships and mechanistic drivers. While existing reviews provide a solid foundation for the interaction between disturbed sleep and pain in youth, we will extend this review by highlighting current methodological challenges for both sleep and pain assessments, exploring the recent evidence for directionality in the sleep-pain relationship, reviewing potential mechanisms and factors underlying the relationship, and providing direction for future investigations. We will also highlight the potential role of digital technologies in advancing the understanding of the sleep and pain relationship. Ultimately, we anticipate this information will facilitate further research and inform the management of pain and poor sleep, which will ultimately improve the quality of life in adolescents and reduce the risk of pain persisting into adulthood.

Perioperative Sleep Disturbance Following Mastectomy: A Longitudinal Investigation of the Relationship to Pain, Opioid Use, Treatment, and Psychosocial Symptoms

OBJECTIVES

Sleep disturbance negatively impacts the quality of life and recovery. Our objective was to evaluate the relationship between the individual patient and surgical factors with greater sleep disturbance following breast surgery.

METHODS

In this prospective longitudinal study, patients completed validated measures regarding sleep disturbance, pain, opioid use, and psychological symptoms preoperatively and then 2 weeks, 6 and 12 months postoperatively. Univariable and multivariable generalized estimating equations evaluated demographic, surgical, pain, and psychological predictors of sleep disturbance during the first year after breast surgery.

RESULTS

Female patients (n=259) reported varying degrees of sleep disturbance, which were longitudinally associated with pain and psychosocial factors (eg, anxiety, depression, and affect). Independent preoperative predictors of worse sleep disturbance included younger age (B=-0.09, P =0.006), opioid use (B=3.09, P =0.02), and higher pain (B=0.19, P =<0.001) and anxiety (B=0.45, P =<0.001) at baseline. In addition, higher baseline positive affect (B=-0.14, P =<0.012) and the surgical category total mastectomy without reconstruction (B=-2.81, P =<0.006) were independently associated with lower sleep disturbance. Those with worse baseline sleep required more opioid analgesics during surgical recovery, and continued use of opioids at 2 weeks postsurgery was associated with disturbed sleep.

DISCUSSION

Certain patient characteristics, including younger age and baseline anxiety, positive affect, pain, and opioid use, were associated with greater sleep disturbance in the first year after breast surgery. Sleep disturbance was also associated with the greater perioperative and postoperative opioid requirements. Preoperative interventions (eg, anxiety management, cultivating positive affect, and multimodal pain management) in high-risk individuals may enhance sleep and recovery postoperatively, and allow more moderate and less prolonged opioid use.

The Effect of Induced Optimism on Situational Pain Catastrophizing

Background

There is broad evidence that optimism is associated with less pain, while pain catastrophizing leads to increased pain. The aim of this study was to examine whether experimentally induced optimism can reduce situational pain catastrophizing and whether this relation is moderated by dispositional optimism and/or dispositional pain catastrophizing.

Methods

Situational pain catastrophizing during two thermal stimulations was measured in 40 healthy participants with the Situational Catastrophizing Questionnaire (SCQ). Between the two stimulations, the Best Possible Self (BPS) imagery and writing task was performed to induce situational optimism in the experimental group while the control group wrote about their typical day. Questionnaires were administered to assess dispositional optimism [Life Orientation Test-Revised (LOT-R)] and dispositional pain catastrophizing [Pain Catastrophizing Scale (PCS)].

Results

There was a significant interaction between the optimism induction and trait pain catastrophizing: the association of trait pain catastrophizing with state pain catastrophizing was weakened after the optimism induction. No overall effect of induced optimism on situational pain catastrophizing and no significant moderating influence of trait optimism were found.

Conclusion

The state optimism induction apparently counteracted the manifestation of dispositional pain catastrophizing as situational pain catastrophizing. This implies that high trait pain catastrophizers may have especially benefitted from the optimism induction, which is in line with resilience models stressing the buffering role of optimism.

Personal influencing factors for pressure pain threshold in healthy people: A systematic review and meta-analysis

All studies that investigated personal factors influencing pressure pain threshold (PPT) in healthy people were synthesized. Data was summarized, and risk of bias (RoB) and level of evidence were determined. Results were pooled per influencing factor, grouped by body region and included in meta-analyses. Fifty-four studies were eligible. Five had low, nine moderate, and 40 high RoB. Following meta-analyses, a strong conclusion was found for the influence of scapular position, a moderate for the influence of gender, and a weak for the influence of age (shoulder/arm region) and blood pressure on PPT. In addition, body mass index, gender (leg region), alcohol consumption and pain vigilance may not influence PPT. Based on qualitative summary, depression and menopause may not influence PPT. For other variables there was only preliminary or conflicting evidence. However, caution is advised, since the majority of included studies showed a high RoB and several were not eligible to include in meta-analyses. Heterogeneity was high in the performed meta-analyses, and most conclusions were weak. More standardized research is necessary.

Assessment of effects of total sleep deprivation and subsequent recovery sleep: a methodological strategy feasible without sleep laboratory

Background

Sleep is critical for maintaining homeostasis in bodily and neurobehavioral functions. This homeostasis can be disturbed by sleep interruption and restored to normal by subsequent recovery sleep. Most research regarding recovery sleep (RS) effects has been conducted in specialized sleep laboratories, whereas small, less-well equipped research units may lack the possibilities to run studies in this area. Hence, the aims of the present study were to develop and validate an experimental protocol, which allows a thorough assessment of at-home recovery sleep after sleep deprivation.

Methods

The experimental protocol, comprising one night of baseline sleep (BL) at home, one night of monitored total sleep deprivation and a subsequent recovery night at home, was tested in a sample of 30 healthy participants. Subjects’ fatigue and alertness were assessed prior to and after each night. Sleep at home (BL, RS) was objectively assessed using portable polysomnography. To check whether our at-home sleep assessments yielded results that are comparable to those conducted in sleep laboratories, we compared the sleep data assessed in our study with sleep data assessed in laboratory studies.

Results

Sleep parameters assessed during RS exhibited changes as expected (prolonged total sleep time, better sleep efficiency, slow wave sleep rebound). Sleep parameters of BL and RS were in line with parameters assessed in previous studies examining sleep in a laboratory setting. Fatigue normalized after one night of RS; alertness partly recovered.

Conclusions

Our results suggest a successful implementation of our new experimental protocol, emphasizing it as a useful tool for future studies on RS outside of well-equipped sleep laboratories.

Conditioned Pain Modulation (CPM) Effects Captured in Facial Expressions

Purpose

Conditioned pain modulation (CPM) is most often assessed using self-report of pain. However, self-report of pain is not always available (eg in individuals with cognitive impairment) and is susceptible to report bias. In comparison, the facial expression of pain is more reflex-like and represents one of the most sensitive and specific non-verbal signals of pain. The aim of the present study was to investigate whether the facial expression of pain is sensitive enough to capture endogenous pain inhibition as elicited during CPM paradigms.

Patients and Methods

In total, 26 female participants took part in this study. Facial and verbal responses to phasic heat pain were assessed once while participants immersed their hand in a hot water bath and once without additional stimulation. Facial responses were analyzed using the Facial Action Coding System (FACS). Verbal responses were assessed using a Numerical Rating Scale (NRS).

Results

Pain-relevant facial responses as well as pain ratings to phasic heat pain were significantly reduced when participants simultaneously immersed their hand in a hot water bath compared to baseline. Thus, CPM effects could be demonstrated both on subjective as well as on facial responses. Moreover, CPM-induced changes in pain-relevant facial responses and in NRS ratings were significantly correlated.

Conclusion

The present study shows that facial expressions of pain are sensitive enough to capture CPM effects. Given the proven clinical usefulness of assessing CPM, the parallel assessment of verbal and facial CPM effects might be a promising approach with wider scope of applications. Further research in other demographic healthy participant and clinical cohorts is warranted.

Sleep, Experimental Pain and Clinical Pain in Patients with Chronic Musculoskeletal Pain and Healthy Controls

Purpose

Everyday variations in night sleep in healthy pain-free subjects are at most weakly associated with pain, whereas strong alterations (eg, sleep deprivation, insomnia) lead to hyperalgesic pain changes. Since it remains unclear how substantial sleep alterations need to be in order to affect the pain system and lead to a coupling of both functions, the present study aimed at providing sufficient variance for co-variance analyses by examining a sample consisting of both healthy subjects and chronic pain patients.

Methods

A sample of 20 chronic musculoskeletal pain patients and 20 healthy controls was examined. This sample was assumed to show high inter-individual variability in sleep and pain, as pain patients frequently report sleep disturbances, whereas healthy subjects were required to be pain-free and normal sleepers. Sleep of two non-consecutive nights was measured using portable polysomnography and questionnaires. Experimental pain parameters (pressure pain thresholds (PPT), temporal summation of pain (TSP), conditioned pain modulation (CPM)) and situational pain catastrophizing (SCQ) were assessed in laboratory sessions before and after sleep. Pain patients’ clinical pain was assessed via questionnaire.

Results

As expected, both groups differed in several sleep parameters (reduced total sleep time and sleep efficiency, more time awake after sleep onset, lower subjective sleep quality in the patients) and in a few pain parameters (lower PPTs in the patients). In contrast, no differences were found in TSP, CPM, and SCQ. Contrary to our expectations, regression analyses indicated no prediction of overnight pain changes by sleep parameters.

Conclusion

Since sleep parameters were hardly apt to predict overnight pain changes, this leaves the association of both systems mainly unproven when using between-subject variance for verification.