Fear and anxiety: divergent effects on human pain thresholds

Does heightened subjective sexual arousal lower pain in women if disgust is minimized?

It has been proposed that acute pain can generally be reduced by sexual activity. Increasing subjective sexual arousal might thus help reduce pain during sex. Yet, in conflict with the view that subjective sexual arousal would generally reduce pain, previous research has failed to find that presenting a sexually arousing film stimulus attenuates pain during a cold pressor test (CPT) in women. This might be due to the sexually arousing film having also elicited disgust. Therefore, this study tested whether subjective sexual arousal could generally reduce pain, provided that concurrently-elicited disgust is minimized. Female undergraduates with no sexual dysfunction were randomly distributed through a digital list randomizer to either watch: a porn film that can elicit similar levels of disgust and sexual arousal, a porn film that elicits greater subjective sexual arousal than disgust, or a neutral train ride film (N = 174). A CPT was utilized for pain induction while simultaneously viewing the assigned films. Pain was indexed by subjective ratings of pain intensity, and CPT duration. The results showed no differences in pain intensity or pain tolerance across conditions. Thus, in this study, disgust appeared no critical moderator of the relationship between sexual arousal and pain. The findings converge to the conclusion that, in women, subjective sexual arousal does not generally reduce the experience of pain. This might also imply that increasing subjective sexual arousal alone might not be sufficient to reduce genital pain, though further research is needed to test this inference given that pain sensitivities may differ across the body.

Women's Pain Management Across the Lifespan-A Narrative Review of Hormonal, Physiological, and Psychosocial Perspectives

Introduction: Pain perception and management differ by sex, with women frequently experiencing more acute and chronic pain and greater disability than men. Yet, anesthesiology and pain control often overlook the physiological, hormonal, and psychological factors shaping women's pain. Methods: This narrative review explores essential considerations from current literature to optimize pain management in women. We examine evidence about the impact of hormonal changes, reproductive transitions, and psychosocial factors on pain perception and responses to analgesics. By highlighting key insights and practical strategies, we aim to support the development of personalized pain management approaches tailored to women's unique needs. Results: Hormonal changes, including variations in estrogen and progesterone levels, significantly influence pain thresholds and the effectiveness of analgesics and anesthetics. The menstrual cycle, menopausal transitions, and pregnancy each alter pain responses, necessitating personalized approaches to pain management. Postmenopausal women are particularly vulnerable to chronic pain conditions, such as those associated with osteoporosis, which require adjustments in long-term treatment strategies. Furthermore, psychosocial factors like anxiety and emotional distress can intensify pain, highlighting the need for holistic, integrative care. Conclusions: The existing gaps in women's pain management across the lifespan highlight the need to revise both anesthesia and pain management protocols to better account for sex-specific biological and psychosocial factors. Addressing the unique biological and psychosocial factors that influence pain in women can enhance both the effectiveness and equity of care. By tailoring treatment strategies in women, clinicians can not only enhance pain management but also greatly improve their overall quality of life.

Best practices for reducing pain associated with intrauterine device placement

Intrauterine devices are highly effective, long-acting, reversible forms of contraception. Despite their benefits, limited uptake persists, particularly among underserved populations, adolescents, and young adults. While most intrauterine device placement procedures are uncomplicated, pain is commonly reported, with more severe pain reported in certain groups. No current standard of care has been established specifically to manage pain with intrauterine device placement, resulting in wide variation in clinical practice. This article aims to provide practical, evidence-based, and expert-informed guidelines for managing pain during intrauterine device placement. The authors (a group of board-certified obstetrician-gynecologists, pediatricians, and a family physician) conducted a virtual expert meeting to develop consensus-based recommendations for pain management. The meeting covered environmental considerations, nonpharmacological, and pharmacological options. Key strategies include using a person-centered care model that focuses on patient values, needs, and preferences to promote shared decision-making around pain relief. Clinicians should assist patients in setting realistic expectations, including a discussion of the placement procedure, anticipated pain, and all options for pain relief, to allow for a comprehensive informed consent process. Nonpharmacological interventions, such as the use of therapeutic language and comforting environmental, complementary and integrative, and mind-body elements, are recommended to reduce patient anxiety and discomfort. In terms of pharmacological options, clinicians may offer pre-procedural-specific nonsteroidal antiinflammatory drugs (eg, naproxen and ketorolac) and anxiolytics to patients with significant anxiety, as well as intraprocedural application of topical anesthesia and paracervical or intracervical blocks. Finally, additional techniques, such as using appropriately sized instruments and ensuring gradual and gentle procedural steps, can also help enhance patient comfort during insertion. These expert guidelines emphasize the importance of personalized, trauma-informed, and evidence-based care, prioritizing patient autonomy and preferences to facilitate a safe and acceptable insertion experience. They are critical to reducing barriers to intrauterine device uptake and improving overall patient outcomes.

Key aspects concerning the role of emotion in the chronic pain experience

Pain and emotions are inherently connected, and this review presents contemporary findings on the pain-emotion connection. We address in what ways pain and emotions are related as well as how the link may be understood and targeted in treatment. Both pain and negative emotions are essential (and ancient) biological and motivational systems which share protective and regulatory functions. There is a marked co-occurrence between chronic pain and mental health conditions. One way to understand the pain-emotion connection, stressed by recent theoretical models, is that pain and emotions share cognitive and behavioral mechanisms that serve to downregulate these unpleasant inner states. Treatments targeting these shared regulatory mechanisms show promising results, but more research is needed on generalization, implementation and dissemination.

Mechanisms of the Native American pain inequity: predicting chronic pain onset prospectively at 5 years in the Oklahoma Study of Native American Pain Risk

ABSTRACT

A pain inequity exists for Native Americans (NAs), but the mechanisms are poorly understood. The Oklahoma Study of Native American Pain Risk (OK-SNAP) addressed this issue and recruited healthy, pain-free NAs and non-Hispanic Whites (NHWs) to attend 2 laboratory visits and assessed mechanisms consistent with the biopsychosocial model of pain: demographics, physical variables, psychosocial factors, and nociceptive/pain phenotypes. Then participants were surveyed every 6 months to assess for chronic pain onset. Results at the 2-year follow-up found that NAs were ∼3x more likely than NHWs to develop chronic pain. Moreover, psychosocial factors (discrimination, stress, pain-related anxiety), cardiometabolic load (higher body mass index and blood pressure, lower heart rate variability), and impaired inhibition of spinal nociception partly mediated the pain inequity. The present study examined mechanisms of chronic pain at the 5-year follow-up for OK-SNAP. Results found that the NA pain inequity worsened-NAs were 4x more likely to develop chronic pain (OR = 4.025; CI = 1.966, 8.239), even after controlling for baseline age, sex assigned at birth, income, and education. Moreover, serial mediation models replicated paths from the 2-year follow-up that linked psychosocial variables, cardiometabolic load, and impaired inhibition of spinal nociception to chronic pain onset. Further, 2 new significant paths were observed. One linked discrimination, stress, sleep problems, and facilitated pain perception to increased pain risk. The other linked discrimination with higher spinal nociceptive threshold and pain risk. These results provide further evidence for a NA pain inequity and identify multiple psychosocial, cardiometabolic, and pronociceptive targets for primary interventions.

An intra-brainstem circuitry for pain-induced inhibition of itch

Pain and itch are unpleasant and distinct sensations that give rise to behaviors such as reflexive withdrawal and scratching in humans and mice. Interestingly, it has been observed that pain modulates itch through the neural circuits housed in the brain and spinal cord. However, we have yet to fully understand the identities and mechanisms by which specific neural circuits mediate pain-induced modulation of itch. Independent studies indicate that brainstem nuclei such as the lateral parabrachial nucleus (LPBN), and rostral ventromedial medulla (RVM) are important for suppressing itch by noxious somatosensory stimuli. Here, using mouse and viral genetics, rabies tracing, chemogenetics, and calcium imaging, we show that the synaptic connections between LPBN and RVM play an instrumental role in the interactions between pain and itch. Notably, we found that the LPBN neurons that express the gene encoding the substance P receptor, Tacr1 (LPBNTacr1), synapse onto Tacr1-expressing RVM neurons (RVMTacr1). The RVMTacr1 neurons were found to be nociceptive, sufficient for inhibiting itch, and necessary for pain-induced itch suppression. Moreover, through brain-wide anterograde and retrograde viral tracing studies, we found that the RVMTacr1 neurons are bidirectionally connected with LPBN, periaqueductal gray (PAG), and lateral hypothalamic area (LHA). Thus, together, our data indicate that the RVMTacr1 neurons integrate nociceptive information to mediate itch-induced scratching and can mediate the physiological effects of itch through their downstream targets.

Hypercapnia Reduces Perceived Heat Pain in Healthy Subjects

BACKGROUND

Danger signals modulate pain perception. Both amplification and attenuation of perceived pain are observed in healthy subjects exposed to danger signals, such as transient threats of an imminent electrical shock. However, exposure to danger signals in real life typically is not transient but constant over minutes to hours. Here, this was experimentally achieved by administering hypercapnic air (7.5% CO2). The primary objective was to investigate whether perceived heat pain would be differentially modulated during this intervention compared to regular air administration. The secondary objective assessed the potential differences of such a modulation with respect to heat intensity level.

METHODS

Thirty-eight participants (19 women) received two air mixtures (hypercapnic and regular air) for 13 min each, during which 18 (6 × 3) noxious heat stimuli of three different intensities were applied to the calf and rated on two scales (intensity and pleasantness/unpleasantness). Psychological and physiological states were compared between conditions using the body sensations questionnaire, self-assessment manikins, heart rate, and galvanic skin response. Statistical analyses were performed using Bayesian estimation testing.

RESULTS

Between-condition differences were statistically meaningful for all heat intensity levels, always showing reduced pain perception during hypercapnia compared to normocapnia. The magnitude of the observed hypoalgesia did not depend on heat intensity levels.

CONCLUSIONS

The presence of a continuous physiological danger signal results in hypoalgesia. Future studies need to determine whether the present results only hold for hypercapnia in healthy subjects or are generalisable to interactions between pain perception and continuous physiological danger signals in clinical pain populations.

SIGNIFICANCE STATEMENT

It was shown that hypercapnia leads to reduced perception of noxious heat stimuli. If confirmed by neural data in future studies this could help to better understand the interaction of pain perception and continuous physiological danger signals in clinical pain conditions, potentially allowing for improved treatment of affected individuals.

Counterirritation by pain inhibits the responsiveness to aversive loud tones: the role of state anxiety and state fear triggered in the NPU paradigm

AIM OF THE STUDY

The application of a noxious stimulus reduces the perception and responsiveness to other pain stimuli. This inhibition can be experimentally assessed with a method called 'counterirritation'. The question arises if counterirritation acts also on the perception and responsiveness to aversive but non-nociceptive stimuli (e.g., loud tones). Since aversive stimulation is often associated with state anxiety or state fear, we investigated in addition the modulatory effects of these emotions on counterirritation.

MATERIAL AND METHODS

51 subjects participated in our study. We presented tones with aversive loudness (105 dB), first alone then during counterirritation (immersion of the hand in a hot water bath of 46 °C) to assess inhibition of loudness perception and responsiveness. Influences of state anxiety and state fear on counterirritation were investigated by using the Neutral-Predictable(fear)- Unpredictable(anxiety) Paradigm (NPU), which is based on classical conditioning. Loudness ratings (perception of the aversive tones) and startle reflex (defensive reaction to aversive tones) were assessed.

RESULTS

Counterirritation reduced startle reflex amplitudes, but not the loudness ratings. Although state anxiety and state fear were successfully induced, counterirritation remained unaffected.

CONCLUSIONS

Our study showed that pain inhibits the responsiveness to aversive stimuli (loud tones). Thus, the postulate that 'pain inhibits pain' might be better changed to 'pain inhibits aversiveness'. Consequently, our findings may also question the assumption of a clear pain specificity in inhibitory action as assumed by theoretical approaches like 'conditioned pain modulation' (CPM). Furthermore, counterirritation appeared one more time resistant to the influence of negative emotions.

Qualitative and quantitative assessments of pain in anxious and depressed patients : Are there differences?

BACKGROUND

Pain is a multidimensional and subjective experience, and its perception is influenced by sensory, emotional, and behavioral factors. This work aims to evaluate the influence of depression and anxiety in the quantitative and qualitative assessment of chronic pain.

METHODS

This is a cross-sectional study carried out at the Multidisciplinary Pain Center of the Clinical Hospital of the Federal University of Minas Gerais. A total of 103 patients were interviewed and evaluated using the following instruments: McGill Questionnaire, visual numerical scale, Hospital Anxiety and Depression Scale and the Medical Outcomes Study SF-36.

RESULTS

The affective, sensory and miscellaneous categories of anxious patients were higher than the nonanxious population (p < 0.05). In the depressed population, the "affective" category was higher than the nondepressed population (p < 0.05). Regarding the anxious and depressed population, the affective, sensory and miscellaneous categories were superior to the nonanxious and nondepressed population (p < 0.05).

DISCUSSION

Depression and anxiety are the most common psychiatric disorders in the population with chronic pain, with a prevalence of 30-40%. In the presence of anxiety and depression, a worse qualitative evaluation was observed. The higher the scores obtained in the assessment of these two mental disorders, the higher the pain index found, and the higher pain index correlates with a lower quality of life.

CONCLUSION

The presence of anxiety and depression altered the qualitative assessment of pain, making it more unpleasant. The pain index correlated with quality of life without, however, being related to pain intensity.

Is Cystoscopic Intravesical Injection of OnabotulinumtoxinA Acceptable in an Outpatient Clinic?

PURPOSE

Cystoscopic intravesical onabotulinumtoxinA injection is a safe and effective minimally invasive treatment for refractory overactive bladder. While the procedure can be performed in outpatient clinics under local anesthetic, some clinicians still use sedation or general anesthesia in an operating theatre. Our study aimed to assess acceptability of intravesical onabotulinumtoxinA injection versus widely accepted diagnostic cystoscopy in the outpatient setting via the medium of patient experience.

METHODS

A 16-item patient experience survey was administered following diagnostic cystoscopy or intravesical onabotulinumtoxinA injection in an outpatient clinic. Both procedures were performed using a flexible cystoscope with local anesthetic gel. A visual analogue scale (VAS) assessed intraprocedure pain. Dichotomous questions assessed whether significant pain or postprocedure symptoms were experienced and if these required medical attention. A free-text question assessed which symptoms had occurred.

RESULTS

One hundred responses from 188 patients were received (53.2% response rate). Sixty-eight patients underwent cystoscopic intravesical onabotulinumtoxinA injection and 32 diagnostic cystoscopy. Mean VAS scores were higher for onabotulinumtoxinA injection (24 of 100) than diagnostic cystoscopy (11 of 100) (P=0.002). VAS scores were higher among patients reporting preprocedure anxiety (31 of 100 vs. 14 of 100, P=0.0013). Twenty-four percent of onabotulinumtoxinA injection patients experienced symptoms postprocedure versus 41% for cystoscopy. Medical attention was sought more frequently in the diagnostic cystoscopy group (9.4% vs. 1.5%). Common symptoms following both procedures were dysuria, urinary frequency, urgency, abdominal pain and urine discoloration.

CONCLUSION

Cystoscopic intravesical injection of onabotulinumtoxinA appears more painful than diagnostic cystoscopy. However, as VAS scores were relatively low, this is unlikely to represent clinically significant discomfort burdensome to the patient. There were no significant complications postprocedure. Cystoscopic intravesical onabotulinumtoxinA injection is acceptable in an outpatient setting.

Feelings of Patients Admitted to the Emergency Department

Background/Objectives: Very few studies describe the various feelings experienced in the emergency department (ED). Our study describes the pain, stress, and negative and positive emotions experienced by patients admitted to the ED in relation to age, gender, and reason for ED admission. Methods: Patients admitted to the ED of seven French hospitals were surveyed as part of the randomised multicentre study SOFTER IV (n = 2846). They reported the intensity of their pain on a numerical rating scale of 0 to 10, the intensity of their stress on an equivalent scale, and their emotions on a five-point rating scale using an adapted version of the Geneva Emotion Wheel proposed by Scherer, based on eight core emotions: fear, anger, regret, sadness, relief, interest, joy, and satisfaction. Results: Patients reported an average pain rating of 4.5 (SD = 3.0) and an average stress rating of 3.4 (SD = 3.1). Forty-six percent reported at least one strong negative emotion, and the two most frequently reported were fear and sadness. Forty-seven percent of patients described feeling at least one strong positive emotion, and the two most frequently reported were interest and relief. Pain was significantly higher among female patients under 60 admitted for injury. Stress was significantly higher among female patients under 60 admitted for illness. Emotions of negative valency were significantly higher among women admitted for injury. Emotions of positive valency were significantly higher among men over 60 admitted for illness. Conclusions: Experiences of pain, stress, and emotions have a strong presence in the ED. The reporting of these feelings varies depending on age, gender, and reason for ED admission.

More and Less Fear in Serotonin Transporter Knockout Mice

Recent theories suggest that reduced serotonin transporter (5-HTT) function, which increases serotonin (5-HT) levels at the synapse, enhances neural plasticity and affects sensitivity to environmental cues. This may promote learning about emotionally relevant events. However, the boundaries that define such emotional learning remain to be established. This was investigated using 5-HTT knockout (5-HTTKO) mice which provide a model of long-term elevated 5-HT transmission and are associated with increased anxiety. Compared to wild-type controls, 5-HTTKO mice were faster to discriminate between an auditory cue that predicted footshock (CS+) and a cue predicting no footshock (CS-). Notably, this enhanced discrimination performance was driven not by faster learning that the CS+ predicted footshock, but rather by faster learning that the CS- cue signals the absence of footshock and thus provides temporary relief from fear/anxiety. Similarly, 5-HTTKO mice were also faster to reduce their fear of the CS+ cue during subsequent extinction. These findings are consistent with facilitated inhibitory learning that predicts the absence of potential threats in 5-HTTKO mice. However, 5-HTTKO mice also exhibited increased generalisation of fear learning about ambiguous aversive cues in a novel context, different from the training context. Thus, 5-HTTKO mice can exhibit both more and less fear compared to wild-type controls. Taken together, our results support the idea that loss of 5-HTT function, and corresponding increases in synaptic 5-HT availability, may facilitate learning by priming of aversive memories. This both facilitates inhibitory learning for fear memories but also enhances generalisation of fear.

Attention and nocebo hyperalgesia: Testing a novel virtual reality attention bias modification paradigm

Nocebo effects in pain (nocebo hyperalgesia) have received significant attention recently, with negative expectancies and anxiety proposed to be explanatory factors. While both expectancy and anxiety can bias attention, attention has been rarely explored as a potential mechanism involved in nocebo hyperalgesia. The present study aimed to explore whether attention bias modification (ABM) using an immersive, ecologically valid VR paradigm successfully induced attention biases (AB) and subsequently influenced nocebo hyperalgesia. One-hundred and two healthy participants were randomised in a 2 (AB training: towards vs. away from pain) x 2 (nocebo condition: nocebo vs. control) design. Pain-related AB was successfully changed by the VR paradigm as measured by reaction time and gaze, with moderate to large effects. Participants then completed either a nocebo instruction and conditioning procedure (nocebo paradigm) or a matched control procedure. The primary outcome was self-reported pain intensity. Secondary outcomes were attention bias and self-reports of expectancy, anticipatory anxiety, and state anxiety. The nocebo paradigm induced significantly greater pain expectancy, anticipatory anxiety and pain intensity during the test phase for the nocebo group compared to control. Pain expectancy also fully mediated the effect of the nocebo group on nocebo hyperalgesia and anticipatory anxiety in separate models. ABM did not, however, affect nocebo hyperalgesia or pain expectancy, casting doubt on the potential for ABM to inoculate against nocebo hyperalgesia. Unexpected effects of ABM were observed for state anxiety and anticipatory anxiety, whereby training away from pain exacerbated each, which necessitates further exploration. PERSPECTIVE: This article tests the efficacy of a novel attention bias modification paradigm, designed in virtual reality, for inducing pain-related biases, and whether these biases exacerbate or inoculate against nocebo hyperalgesia. While pain-related biases were successfully induced, there was no relationship with the strength of induced nocebo hyperalgesia.

Bilateral tDCS over the DLPFC enhances baroreceptor reflex sensitivity and inhibits blood pressure-related hypoalgesia

OBJECTIVE

This study investigated the impact of transcranial direct stimulation (tDCS) on pain perception, baroreflex sensitivity (BRS), and blood pressure (BP)-related hypoalgesia.

METHOD

Fifty-eight healthy participants were randomized to receive 1) bi-hemispheric tDCS over the dorsolateral prefrontal cortex (DLPFC) at 2 mA for 20 min, or 2) non-stimulation (Sham). Pain measures (threshold, tolerance, intensity and unpleasantness), emotional state (anxiety and mood), continuous BP, and electrocardiogram (ECG) data were recorded before, during, and after stimulation.

RESULTS

tDCS stimulation was followed by increases in BRS, pain intensity and unpleasantness. Anxiety decreased in the Sham group, but not in the tDCS group. Positive correlations between BP and pain threshold and tolerance before stimulation were observed. These remained during stimulation in the Sham group, but not in the tDCS group. Moreover, negative associations between BRS and BP only persisted in the Sham group.

DISCUSSION

The results suggest that bilateral tDCS over the DLPFC enhances BRS and modulates pain perception and BP-related mechanisms. tDCS increases pain perception by inhibiting BP-related hypoalgesia and preventing habituation of anxiety.

SIGNIFICANCE

Low BRS is a powerful prognostic factor of cardiovascular disease, such that its increase via tDCS may be a new therapeutic strategy for cardiovascular health promotion.

Neuroanatomical and neurochemical substrates mediating fear-induced antinociception: A systematic review of rodent preclinical studies

Fear-induced antinociception (FIA), an instinctive defensive response producing pain suppression in stressful and/or dangerous situations, has been the subject of extensive research to elucidate the mechanisms involved in triggering and controlling pain during emotional disorders. In this systematic review, we synthesized pre-clinical studies that demonstrated the neural hodology and the neurochemical bases of FIA in laboratory animals. The literature search in PubMed, Web of Science, Science Direct, and Scopus, from inception up to July 2022, retrieved 797 articles from which 50 studies were included in this review. This review highlights key encephalic regions implicated in the modulation of FIA, such as the prefrontal cortex, the amygdaloid complex, the hippocampus, the hypothalamus, the corpora quadrigemina, the periaqueductal gray matter, and some reticular formation nuclei. FIA-related neural pathways, neurotransmitters and neuromodulators such as glutamatergic, serotonergic, norepinephrine, GABAergic, nitrergic, opioidergic and endocannabinoid connections across these encephalic regions were also addressed. Understanding these neural circuits and molecular neural mediation sheds light on the complex interplay between fear, anxiety, and pain modulation, offering potential avenues for therapeutic interventions targeting pain management in the context of heightened emotional states.

Affective and social pain modulation in children-Experimental evidence using picture viewing

BACKGROUND

Children frequently encounter pain. Their pain like adults' pain is probably modulated by social-affective factors. Despite its clinical relevance, such pain modulation has not been explored experimentally in children, and little is known about specific factors accounting for it such as catastrophizing. We examined pain modulating effects of pictures varying in social-affective content and personal meaning (e.g., mothers' vs. strangers' faces) using subjective and psychophysiological measures (skin conductance, heart rate, corrugator electromyography) as outcomes.

METHODS

Forty-two children (8-13 years) underwent tonic heat pain stimulation while viewing pictures (social-affective: their mothers' faces with neutral expression, strangers' neutral and happy faces; affective: positive and negative scenes). Furthermore, the contribution of children's characteristics (e.g., anxiety, catastrophizing) and facets of the parent-child relationship to pain modulation was determined.

RESULTS

Viewing mothers' faces or positive scenes reduced subjective pain intensity and corrugator activity in response to pain. Viewing happy strangers' faces lowered corrugator activity. Enhanced pain experience due to negative affective stimuli was primarily observed psychophysiologically. The correlation between children's tendency to catastrophize and pain relief by mothers' faces was mediated by induced arousal, likely reflecting the degree of motivational activation of seeking social support.

CONCLUSIONS

Pain relief by positive affective and social-affective stimuli extends previous findings in adults, especially regarding reduced pain-related facial muscle activity. Moreover, the results shed light on the interplay between catastrophizing and social context on children's pain experience. Clinically, our results imply that just looking at pictures of their mothers (or positive scenes) might help to alleviate pain in children.

Virtual reality-enhanced interventions on preoperative anxiety symptoms in adults undergoing elective surgery: A meta-analysis and meta-regression

BACKGROUND

Virtual reality exposure and distraction are recent novel technologies for reducing preoperative anxiety symptoms. However, the effectiveness of virtual reality-enhanced interventions in adults is still controversial and has yet to be evaluated in a systematic review.

OBJECTIVES

The study aimed to (1) evaluate the effectiveness of virtual reality-enhanced interventions on preoperative anxiety symptoms in adults compared to comparators; and (2) identify the factors affecting the effectiveness of interventions.

DESIGN

Systematic review, meta-analysis, and meta-regression analysis of randomised controlled trials.

METHODS

We conducted a three-step systematic search from inception until May 1, 2024, using (1) eleven databases, (2) two clinical registries, and (3) citation and grey literature searches in either English or Chinese. The package meta of R software version 4.3.1 was used to perform the meta-analysis, subgroup analysis, and meta-regression analyses. We adopted the restricted maximum likelihood estimator for random-effects meta-analysis and univariate random-effects meta-regression analyses. The Cochrane risk-of-bias tool version 2 and the Grading of Recommendations, Assessment, Development, and Evaluation criteria were used to examine quality assessment and the certainty of evidence.

RESULTS

We selected 26 randomised controlled trials with 2357 participants from 12 different countries. Random-effects meta-analyses showed that virtual reality-enhanced interventions had a statistically significant reduction in preoperative anxiety symptoms (t = -5.58, p < 0.001) with a moderate to large effect size (Hedges' g = -0.76, 95 % confidence interval: -1.03 to -0.48) compared to usual care. Statistically significant subgroup differences were found for the nature of the intervention, geographical region, country, and type of surgery. The improvement in preoperative anxiety symptom outcomes was greater when the virtual reality-enhanced interventions were chosen by patients (g = -2.55, 95 % CI: -3.08 to -2.02) when compared to virtual reality exposure interventions with educational content (g = -0.72, 95%CI: -1.07 to -0.38) or virtual reality distraction interventions (g = -0.64, 95 % CI: -1.04 to -0.23). Trials conducted in Asia had a greater effect on preoperative anxiety symptom outcomes (g = -0.98, 95 % CI: -1.33 to -0. 62) in comparison with those conducted in non-Asia (g = -0.23, 95 % CI: -0.54 to 0.07). The random-effects meta-regression identified sample size (β = -0.008, p = 0.031) as a statistically significant covariate of preoperative anxiety symptoms. The overall certainty of the evidence was very low.

CONCLUSIONS

Virtual reality-enhanced interventions can be considered supplementary interventions for adults undergoing elective surgery. Future trials on a large scale with follow-up assessments are needed.

REGISTRATION

PROSPERO registration ID: CRD42024486343.

Patient-related predictors of post-operative pain following root canal treatment: A structural model analysis

AIM

The pathways to post-operative pain are complex and encompass factors that extend beyond the treatment protocol employed. This study aimed to identify patient-related predictors of post-operative pain following root canal treatment.

METHODOLOGY

A total of 154 patients received a single-visit root canal treatment for asymptomatic necrotic mandibular molars. Before treatment, dental anxiety, dental fear and sense of coherence (SOC) were measured as predictors for each patient using validated questionnaires. Other measured predictors included gender, age, previous negative experiences at the dental offices and prior root canal treatment. Post-operative pain was assessed using the Numeric Rating Scale at multiple time-points over 30 days. Structural equation analysis was employed to evaluate the direct and indirect effects of patient-related predictors on a theoretical model of post-operative pain. The irrigant solution was also included in the model, as it was the only aspect that varied in the treatment protocol (sodium hypochlorite 2.5% and 8.25%).

RESULTS

Dental anxiety (coefficient 0.028; p < .01), dental fear (coefficient 0.007; p = .02) and irrigant solution (coefficient 0.004; p = .03) exerted a direct effect on post-operative pain. SOC exerted an indirect effect on post-operative (coefficient 0.006; p = .01) through dental anxiety and dental fear. Moreover, previous negative experiences (coefficient 0.048; p = .04) exerted an indirect effect on post-operative pain through dental anxiety.

CONCLUSIONS

Dental anxiety, dental fear, previous negative experiences and SOC are patient-related predictors of post-operative pain following root canal treatment. These factors should be taken into consideration in clinical practice, as patients with these characteristics may be at an increased risk of experiencing post-operative pain.

COVID-19 Pandemic-Related Stressors, Distress, and Bodily Pain in Native Americans: Results from the Oklahoma Study of Native American Pain Risk

The COVID-19 pandemic disproportionately impacted minoritized individuals. This study examined the relationships between pandemic-related stressors/distress and bodily pain in 79 Native American (NA) and 101 non-Hispanic White (NHW) participants from the Oklahoma Study of Native American Pain Risk. Online surveys were administered in May/June 2020 (wave 1), March/April 2021 (wave 2), and Sept/Oct 2021 (wave 3). Pandemic-related stressors (e.g., resource loss and added responsibilities) and distress were assessed from a custom-built questionnaire. Bodily pain was assessed from pain items on the Patient Health Questionnaire-15 (PHQ-15). The results indicate NAs and NHWs reported similar pandemic-related stressors and distress at wave 1, which remained at similar levels across all waves in NHWs. By contrast, stressors and distress increased in NAs at waves 2 and 3. Moreover, bodily pain was higher in NAs than NHWs across all waves. Regression-based multilevel analyses predicting bodily pain found that NHWs with more pandemic-related stressors/distress experienced more bodily pain, but stress/distress did not predict bodily pain in NAs. Findings demonstrated that NAs experienced more bodily pain and pandemic-related stressors/distress than NHWs. However, pandemic-related stressors/distress did not further exacerbate NA pain as observed in NHWs. This implies NAs may have demonstrated resiliency that buffered the pronociceptive effects of pandemic-related stress.

Does Body Postural Configuration Affect Upper Limb Performance During Point-to-Point Hand Movements?

Adopting a postural configuration may be regarded as preparation for the performance of an upcoming movement. However, it is unclear how different postural configurations affect motor performance. The aim of the current study was to examine how body posture - sitting versus standing - influences fast and accurate planar point-to-point hand movements. Twenty-three healthy adults performed a "Go/No-go" paradigm while doing repetitive point-to-point movements. Arousal levels, which may change due to the change in posture, were independently manipulated by using a sham threat of electrical stimulation. Upper limb kinematics, center of pressure displacement, and galvanic skin responses were recorded in four test conditions: sitting and standing with and without arousal manipulation. Descriptive performance measures were computed and analyzed using multiple analyses of variance. A difference in arousal level was observed in the two conditions with the arousal manipulation, but no difference in arousal level was found between sitting and standing. Center of pressure displacement onset was found to be earlier in the two standing conditions compared to those in sitting. No difference was found in upper limb performance between the two postures, nor due to the arousal manipulation. We concluded that under the tested conditions, body posture does not appear to affect upper limb performance.

Psychological Factors Modulate Quantitative Sensory Testing Measures in Fibromyalgia Patients: A Systematic Review and Meta-Regression Analysis

OBJECTIVE

Considering the growing evidence that psychological variables might contribute to fibromyalgia syndrome (FMS), our study aims to understand the impact of psychological factors in quantitative sensory testing (QST) in FMS patients by performing a systematic review with meta-analysis.

METHODS

A systematic search was carried out in PubMed/MEDLINE, EMBASE, Web of Science, and PsycINFO databases for records up until January 2024. We included 20 studies ( n = 1623, 16 randomized controlled trials, and 4 nonrandomized controlled trials) with low or moderate risk of bias included.

RESULTS

From nonrandomized evidence, our meta-analysis found a baseline relationship between anxiety, depression, and pain catastrophizing and QST measures in FMS patients. Higher pain catastrophizing levels were associated with less efficient conditioned pain modulation. Higher anxiety and depression were associated with lower pain threshold (PT). Randomized evidence showed a statistically significant increase in PT after fibromyalgia treatments (effect size = 0.29, 95% confidence interval = 0.03-0.56). The effect was not influenced by treatment type. Moreover, we found that only anxiety levels before treatment negatively influenced the PT improvements after treatment.

CONCLUSION

FMS patients with higher anxiety levels at baseline showed a smaller increase in PT after the intervention. Depression factor was not significant in either changes in anxiety or depression. Baseline anxiety levels should be monitored as possible confounders of QST measurements. Understanding how psychological factors and QST are related in FMS patients is critical for improving the syndrome's management and treatment.Protocol Registration: CRD42023429397.

Impact of preoperative anxiety on postoperative outcomes in patients undergoing minimally invasive thoracoscopic surgery: A prospective cohort study

BACKGROUND

Preoperative anxiety is a common preoperative psychological state in patients with cancer and associated with worsening perioperative outcomes. However, high-quality prospective studies on preoperative anxiety in patients undergoing lung surgery are scarce.

METHODS

We conducted a prospective cohort study, enrolling a total of 540 patients. Preoperative anxiety in patients undergoing thoracic surgery was measured using the Hospitalization Anxiety Scale. Patients were grouped according to the Hospitalization Anxiety Scale scores as follows: no anxiety (score <8) and anxiety (score ≥8). The association of preoperative anxiety with postoperative complications and non-complicated adverse events was determined by univariate regression and polynomial regression analyses.

RESULTS

A total of 121 patients (22.4 %) experienced preoperative anxiety. The anxiety group had a longer average hospital stay (4.33 vs. 3.85 days). Postoperative complications were similar between groups, but the anxiety group reported worse sleep quality (measured by the Athens Insomnia Scale). Regarding postoperative pain, both groups had comparable rates of mild and severe pain on postoperative day 1. However, the anxiety group experienced significantly higher rates of severe pain on postoperative day 2 and mild pain on postoperative day 3. Additionally, the incidence of postoperative nausea and vomiting was significantly higher in the anxiety group on postoperative day 1.

CONCLUSIONS

Preoperative anxiety may not increase the rates of postoperative complications in patients undergoing lung surgery. However, it may be associated with postoperative sleep disturbances, pain, nausea, and vomiting, as well as prolong the length of postoperative hospitalization.

Pain reflects the informational value of nociceptive inputs

ABSTRACT

Pain perception and its modulation are fundamental to human learning and adaptive behavior. This study investigated the hypothesis that pain perception is tied to pain's learning function. Thirty-one participants performed a threat conditioning task where certain cues were associated with a possibility of receiving a painful electric shock. The cues that signaled potential pain or safety were regularly changed, requiring participants to continually establish new associations. Using computational models, we quantified participants' pain expectations and prediction errors throughout the task and assessed their relationship with pain perception and electrophysiological responses. Our findings suggest that subjective pain perception increases with prediction error, that is, when pain was unexpected. Prediction errors were also related to physiological nociceptive responses, including the amplitude of nociceptive flexion reflex and electroencephalography markers of cortical nociceptive processing (N1-P2-evoked potential and gamma-band power). In addition, higher pain expectations were related to increased late event-related potential responses and alpha/beta decreases in amplitude during cue presentation. These results further strengthen the idea of a crucial link between pain and learning and suggest that understanding the influence of learning mechanisms in pain modulation could help us understand when and why pain perception is modulated in health and disease.

Examining the risk factors of chronic pelvic pain and its effect on the quality of life in refugee and non-refugee women

BACKGROUND

This study aimed to determine the prevalence of chronic pelvic pain(CPP) in refugee and non-refugee women, determine the factors associated with CPP, and evaluate the effect of CPP on life quality.

METHODS

This was a cross-sectional study conducted among 283 non-refugee and 278 refugee women in Turkey. A questionnaire including questions assessing chronic pelvic pain and related factors, World Health Organization Quality of Life Scale Short Form(WHOQOL-BREF), Depression Anxiety Stress Scale-21, were administered to the participants. Chi-square test, Mann-Whitney U test and multiple logistic regression analysis were used for statistical analysis.

RESULTS

The prevalence of chronic pelvic pain was 41.0% in refugee women and 19.1% in non-refugee women (p< 0.001). The prevalence of CPP was 1.68 times higher in refugee women than in non-refugee women (OR;95%CI:1.68;1.01-2.81). In the multivariate analysis performed in the study group, refugee status, low family income status(OR;95%CI:2.09;1.26-3.46), low back pain(OR;95%CI:2.02;1.21-3.35), dyspareunia (OR; 95%CI:2.96;1.75-4.99), number of three or more miscarriages (OR;95%CI:3.07;1.18-8.01), history of gynaecological surgery (OR;95%CI:2.44;1.33-4.50), diarrhea (OR;95%CI:2.01;1.07-3.76), urinary tract infections(OR; 95%CI:1.66;1.02-2.71) and anxiety(OR; 95%CI:1.17;1.10-1.24) were found to be risk factors for CPP. In the refugee and non-refugee groups, those with CPP had lower scores in all subdomains of the WHOQOL-BREF scale than those without CPP (p < 0.05).

CONCLUSIONS

Refugee status independently contributes to the risk of developing CPP. Targeted interventions to address CPP and its associated risk factors are needed, particularly in vulnerable refugee populations, to improve their quality of life.

Weighted Blankets for Pain and Anxiety Relief in Acutely Injured Trauma Patients

To determine the impact of a weighted blanket on acute pain and anxiety in trauma patients, a preliminary prospective/retrospective study at a level-one trauma center (n = 24 patients) was conducted. In this study, 12 patients using weighted blankets for five consecutive days were compared to a matched retrospective cohort of 12 patients not using a blanket. The change in morphine milligram equivalents (MME) and alprazolam milligram equivalents (AME) over five days were compared. There was a significant difference of MME per day between the intervention group (mean MME change = -22.9) and matched controls (mean MME change = 6.2; p = 0.0072) by blanket use. Total MMEs in the intervention group decreased by 275.5 and in the control group increased by 75 between day 1 and day 5. There was no significant difference in AME change between groups (p = 0.3227). The majority of patients who took a post-intervention questionnaire reported less pain and less anxiety with blanket use compared to those without blanket use (78% and 56% of patients, respectively). To summarize, trauma patients in acute pain had less opioid use and reported less pain and anxiety when using a weighted blanket for five consecutive days compared to a control group who did not use a blanket.

Effects of chronic daily headache with subclinical depression on brain volume: A systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

The relationship between chronic daily headache (CDH), depression symptoms, and brain volume remains unclear.

METHODS

To investigate the effects of CDH on brain volume and the impact of depressive symptoms (DSs) as well as the effects of demography and medication overuse, PubMed, Embase, and Web of Science databases were systematically searched using appropriate keyword strings to retrieve observational studies from inception to May 2023.

RESULTS

Two distinct comparisons were made in CDH patients: (1) those with DSs versus their pain-free counterparts and (2) those without DSs versus pain-free controls. The first comprised nine studies enrolling 225 CDH patients with DSs and 234 controls. Beck depression inventory, Hamilton depression scale, and Hospital anxiety/depression scale were used to assess DSs, revealing significantly more DSs in CDH patients with DSs compared to their controls (all p < 0.05). Besides, the second analysed four studies involving 117 CDH patients without DSs and 155 comparators. Compared to CDH patients without DSs, those with DSs had a smaller brain volume than controls (p = 0.03). Furthermore, CDH patients with DSs who did not overuse medications showed a smaller right cerebral cortical volume than overusers (p = 0.003). A significant inverse correlation between female prevalence and brain volume (p = 0.02) was revealed using regression analysis.

CONCLUSIONS

Pain-induced persistent depressive symptoms not only incur structural alterations but also encompass affective-motivational changes, involving medication use and gender-specific health concerns.

SIGNIFICANCE

This study highlighted the importance of an integrated CDH treatment, emphasizing psychological interventions for the affective-motivational component alongside pain management.

Electroacupuncture Alleviates Hyperalgesia and Anxiety-Like Behaviors in Pain Memory Model Rats Through Activation of GABAergic Neurons and GABA Receptor in the Rostral Anterior Cingulate Cortex

Recent studies have confirmed that pain memory is often accompanied by negative emotions. Electroacupuncture (EA) can block the retrieval of painful memories, thereby alleviating the associated negative behaviors. However, the underlying mechanism is poorly understood. This study revealed that the effect of EA on pain memory-induced negative behaviors is related to the mediation of GABAergic neuron activity and GABA receptor expression in the rostral anterior cingulate cortex (rACC). Previous studies have shown that the rACC is a crucial area for regulating nociceptive behaviors and negative emotions in pain memory models. The GABAergic neurons and receptors in the rACC are largely involved in pain sensation and related effects. However, the relationships among pain memory, GABAergic neurons and receptors in the rACC have not been investigated. In this study, we established a pain memory model via secondary plantar cross-injection of carrageenan and EA treatment. Using chemogenetic methods and behavioral assessments of pain and negative emotion, we found that early excitation of GABAergic neurons in the rACC blocked the recall of pain memories and reduced anxiety-like behaviors in pain memory model rats. Furthermore, pharmacological methods revealed that excitation of GABAA and GABAB receptors in the rACC blocks hyperpathia associated with pain memory and pain-induced anxiety-like behaviors, while inhibition of GABAA and GABAB receptors reverses these effects. These results suggest that EA may alleviate pain and associated anxiety-like behaviors related to pain memories through the activation of GABAergic neurons and excitation of GABAA and GABAB receptors in the rACC.

Parasympathetic tone activity, heart rate, and grimace scale in conscious horses of 3 breeds before, during, and after nociceptive mechanical stimulation

BACKGROUND

Parasympathetic tone activity (PTA) in response to nociceptive stimulus in conscious non-sedated horses is unknown.

OBJECTIVES

Study PTA, heart rate (HR), and horse grimace scale (HGS) at rest and during mechanical nociceptive stimulation.

ANIMALS

Ninety healthy young adult horses (females, males): 30 each of Friesians, Quarter Horses, and Warmbloods.

METHODS

Prospective control study. The study consisted of habituation to equipment (Day 1), baseline recordings (Days 2 and 3), and nociceptive testing applying mild pressure to the metacarpus (Day 4). Parasympathetic tone, HR, and HGS were recorded simultaneously on Days 2 to 4. Each study lasted 30 minutes and was done in triplicate at 3 different time points per day.

RESULTS

Baseline PTA was not different among breeds. It decreased in Warmbloods and Quarter Horses during placement of the stimulus device without stimulation (P < .01). A significant decrease in PTA (P < .001) occurred during nociceptive stimulus (marked in Quarter Horses, intermediate in Warmbloods, and mild in Friesians). Heart rate and HGS increased significantly (P < .001) during the stimulus in all breeds but returned to baseline poststimulation. Friesians required higher pressure (P < .05) to elicit an aversive response to the stimulus.

CONCLUSIONS

Horses' PTA, HR, and HGS change in response to a mild mechanical nociceptive stimulus with Friesians showing less variation. Stress induced a decrease in PTA in Quarter Horses and Warmbloods but not in Friesians. Friesians appeared to be more tolerant to pain based on PTA, HR, and HGS findings compared with other breeds.

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

ABSTRACT

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

Anticipating noxious stimulation rather than afferent nociceptive input may evoke pupil asymmetry

Unilateral nociceptive stimulation is associated with subtle signs of pupil asymmetry that may reflect lateralized activity in the locus coeruleus. To explore drivers of this pupil asymmetry, electrical stimuli, delivered alone or 200 ms before or after an acoustic startle stimulus, were administered to one ankle under four experimental conditions: with or without a 1.6 s anticipatory period, or while the forearm ipsilateral or contralateral to the electrical stimulus was heated tonically to induce moderate pain (15 healthy participants in each condition). Pupil diameter was measured at the start of each trial, at stimulus delivery, and each second for 5 s after stimulus delivery. At the start of the first trial, the pupil ipsilateral to the side on which electric shocks were later delivered was larger than the contralateral pupil. Both pupils dilated robustly during the anticipatory period and dilated further during single- and dual-stimulus trials. However, pupil asymmetry persisted throughout the experiment. Tonically-applied forearm heat-pain modulated the pupillary response to phasic electrical stimuli, with a slight trend for dilatation to be greater contralateral to the forearm being heated. Together, these findings suggest that focusing anxiously on the expected site of noxious stimulation was associated with dilatation of the ipsilateral pupil whereas phasic nociceptive stimuli and psychological arousal triggered bilateral pupillary dilatation. It was concluded that preparatory cognitive activity rather than phasic afferent nociceptive input is associated with pupillary signs of lateralized activity in the locus coeruleus.

Neuropathic pain, mood, and stress-related disorders: A literature review of comorbidity and co-pathogenesis

Neuropathic pain can be caused by multiple factors, and its prevalence can reach 10% of the global population. It is becoming increasingly evident that limited or short-lasting response to treatments for neuropathic pain is associated with psychological factors, which include psychiatric comorbidities known to affect quality of life. It is estimated that 60% of patients with neuropathic pain also experience depression, anxiety, and stress symptoms. Altered mood, including stress, can be a consequence of several painful conditions but can also favor pain chronicization when preexisting. Despite the apparent tight connection between clinical pain and mood/stress disorders, the exact physiological mechanisms remain unclear. This review aims to provide an overview of state-of-the-art research on the mechanisms of pain related to the pathophysiology of depression, anxiety, and stress disorders.

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.

Relationship between intraoperative requirement for anesthetics and postoperative analgesic consumption in laparoscopic colectomy: a randomized controlled double-blinded study

BACKGROUND

This study investigated the relationship between intraoperative requirement for an inhalational anesthetic (sevoflurane) or an opioid (remifentanil) and postoperative analgesic consumption.

METHODS

The study included 200 adult patients undergoing elective laparoscopic colectomy. In the sevoflurane group, the effect-site concentration of remifentanil was fixed at 1.0 ng/ml, while the inspiratory sevoflurane concentration was adjusted to maintain an appropriate anesthetic depth. In the remifentanil group, the end-expiratory sevoflurane concentration was fixed at 1.0 vol.%, and the remifentanil concentration was adjusted. Pain scores and cumulative postoperative analgesic consumptions were evaluated at 2, 6, 24, and 48 h after surgery.

RESULTS

Average end-tidal concentration of sevoflurane and effect-site concentration of remifentanil were 2.0 ± 0.4 vol.% and 3.9 ± 1.4 ng/ml in the sevoflurane and remifentanil groups, respectively. Cumulative postoperative analgesic consumption at 48 h postoperatively was 55 ± 26 ml in the sevoflurane group and 57 ± 33 ml in the remifentanil group. In the remifentanil group, the postoperative cumulative analgesic consumptions at 2 and 6 h were positively correlated with intraoperative remifentanil requirements (2 h: r = 0.36, P < 0.001; 6 h: r = 0.38, P < 0.001). However, there was no significant correlation in the sevoflurane group (r = 0.04, P = 0.691).

CONCLUSIONS

The amount of intraoperative requirement of short acting opioid, remifentanil, is correlated with postoperative analgesic consumption within postoperative 6 h. It may be contributed by the development of acute opioid tolerance. However, intraoperative sevoflurane requirement had no effect on postoperative analgesic consumption.

Correlation between psychosocial stresses, stress coping ability, pain intensity and degree of disability in patients with non-specific neck pain

This study was conducted to find out which factor among stress inducing factors and stress coping factors that can affect patients with non-specific neck pain has more correlation with the intensity of neck pain and the degree of disability. This study is a cross-sectional correlational study. 100 patients diagnosed with non-specific neck pain participated in this study. The characteristics of the participants in this study are as follows. There were 56 men and 44 women, with an average age of 34.11 years, height of 169.91, and weight of 66.97 kg. The participant`s pain intensity was 5.18 and disability index was 21.44. In order to evaluate the pain intensity and disability level of patients with non-specific neck pain, Numeric Pain Rating SCALE (NPRS), and Neck Disability Index (NDI) were investigated, respectively. Depression, Anxiety, Stress Scale-21 (DASS-21), and Tampa Scale of Kinesiophobia (TSK) were used to evaluate stress inducing factors. Brief Resolution Scale (BRS), Latack Coping Scale (LCS), and Pain Self-Efficacy Questionnaire (PSEQ) were used to evaluate stress coping factors. Spearman correlation coefficients were used to determine the correlation between NPRS, NDI, and DASS-21, TSK, BRS, LCS, and PSEQ in patients with non-specific neck pain. As a results of this study, the NPRS was correlated with NDI and TSK. The NPRS and NDI were found to have a moderate correlation, but they were correlated with TSK, but showed a weak correlation. The NDI was found to be correlated with TSK, DASS, BRS, and PSEQ. In addition, NDI showed a weak correlation with TSK, BRS, and PSEQ, but the DASS showed a moderate correlation, showing the strongest correlation among the factors. These outcomes suggest that psychosocial factors, particularly stress-related factors such as depression, anxiety, and fear of movement, exert a more pronounced influence on pain intensity and disability in individuals with non-specific neck pain.

Neuroimaging-based evidence for sympathetic correlation between brain activity and peripheral vasomotion during pain anticipation

Anticipation of pain engenders anxiety and fear, potentially shaping pain perception and governing bodily responses such as peripheral vasomotion through the sympathetic nervous system (SNS). Sympathetic innervation of vascular tone during pain perception has been quantified using a peripheral arterial stiffness index; however, its innervation role during pain anticipation remains unclear. This paper reports on a neuroimaging-based study designed to investigate the responsivity and attribution of the index at different levels of anticipatory anxiety and pain perception. The index was measured in a functional magnetic resonance imaging experiment that randomly combined three visual anticipation cues and painful stimuli of two intensities. The peripheral and cerebral responses to pain anticipation and perception were quantified to corroborate bodily responsivity, and their temporal correlation was also assessed to identify the response attribution of the index. Contrasting with the high responsivity across levels of pain sensation, a low responsivity of the index across levels of anticipatory anxiety revealed its specificity across pain experiences. Discrepancies between the effects of perception and anticipation were validated across regions and levels of brain activity, providing a brain basis for peripheral response specificity. The index was also characterized by a 1-s lag in both anticipation and perception of pain, implying top-down innervation of the periphery. Our findings suggest that the SNS responds to pain in an emotion-specific and sensation-unbiased manner, thus enabling an early assessment of individual pain perception using this index. This study integrates peripheral and cerebral hemodynamic responses toward a comprehensive understanding of bodily responses to pain.

Potential Benefits of a 'Trauma-Informed Care' Approach to Improve the Assessment and Management of Dogs Presented with Anxiety Disorders

Dog caregiver reporting on the spectrum of fearful-aggressive behaviours often describes 'unpredictable' or 'exaggerated' responses to a situation/animal/person. A possible explanation for these behavioural responses considers that the dog is reacting to triggered memories for which the dog has a negative association. For many dogs undergoing veterinary behavioural treatment or rehabilitation through a canine rescue organisation, the assessing clinician relies on "proxy" reporting of the history/background by a caregiver (dog owner, foster carer, or shelter personnel). Detailed information on the event or circumstances resulting in this negative association may be limited or absent altogether. Consideration of a trauma-informed care (TIC) approach, currently applied in a wide range of human psychology and social care fields, may be helpful in guiding the clinical approach taken. The literature relating to adverse early experience (AEE) and trauma-informed care (TIC) in puppies/dogs compared to children/adults was evaluated to identify common themes and conclusions identified across both species. In the absence of known/identifiable trauma, behavioural assessment and management should consider that a 'problem' dog may behave as it does, as the result of previous trauma. The dog can then be viewed through a lens of empathy and understanding, often lacking for dogs presenting with impulsive, reactive, or aggressive behaviours. Assessment must avoid re-traumatising the animal through exposure to triggering stimuli and, treatment options should include counselling of caregivers on the impact of adverse early experiences, consideration of the window of tolerance, and TIC behavioural modification techniques.

Sex differences in stress-induced hyperalgesia and its mechanisms

Chronic stress induces a variety of physiological and/or psychological abnormalities, including hyperalgesia. Researchers have discovered sex differences in the prevalence of stress-induced hyperalgesia (SIH) in recent years. Sex differences may be one of the reasons for the heterogeneity of susceptibility to stress-related diseases. In this review, the potential mechanisms of sex differences in SIH are discussed, such as hypothalamus-pituitary-adrenal axis responses, regulation of sex hormones, and immune system responses.

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.

The temporal effect of uncertain context on the perceptual processing of painful and non-painful stimulation

Uncertainty has been demonstrated to influence the perception of noxious stimuli, but little is known about the effects of prolonged uncertain contexts on the perception of painful and non-painful stimuli. To address this knowledge gap, the present study utilized a cue-based NPU-threat task, where uncertain and certain trials were separated into distinct blocks. The objective was to investigate the impact of uncertain contexts on the temporal dynamics of electroencephalogram (EEG) activity during the processing of painful and non-painful stimuli. The results revealed that the influence of uncertain contexts on neural responses extends beyond painful trials and is also evident in non-painful trials. In uncertain contexts, it has been observed that painful stimuli elicit larger P2 amplitudes and late beta band (13-30 Hz) event-related desynchronization (ERD) around 500-700 ms. However, in certain contexts, painful stimuli evoke stronger late gamma band (50-70 Hz) event-related synchronization (ERS) around 600-700 ms. For non-painful trials, in uncertain contexts, significantly higher amplitudes of the late positive potential (LPP) component and delta-theta band (2-7 Hz) ERS were observed compared to certain non-painful stimuli. These findings demonstrate that uncertain contexts exert a significant impact on the processing of both painful and non-painful stimuli, and this influence is mediated by distinct neural mechanisms.

Better safe than sorry?-On the influence of learned safety on pain perception

The experience of threat was found to result-mostly-in increased pain, however it is still unclear whether the exact opposite, namely the feeling of safety may lead to a reduction of pain. To test this hypothesis, we conducted two between-subject experiments (N = 94; N = 87), investigating whether learned safety relative to a neutral control condition can reduce pain, while threat should lead to increased pain compared to a neutral condition. Therefore, participants first underwent either threat or safety conditioning, before entering an identical test phase, where the previously conditioned threat or safety cue and a newly introduced visual cue were presented simultaneously with heat pain stimuli. Methodological changes were performed in experiment 2 to prevent safety extinction and to facilitate conditioning in the first place: We included additional verbal instructions, increased the maximum length of the ISI and raised CS-US contingency in the threat group from 50% to 75%. In addition to pain ratings and ratings of the visual cues (threat, safety, arousal, valence, and contingency), in both experiments, we collected heart rate and skin conductance. Analysis of the cue ratings during acquisition indicate successful threat and safety induction, however results of the test phase, when also heat pain was administered, demonstrate rapid safety extinction in both experiments. Results suggest rather small modulation of subjective and physiological pain responses following threat or safety cues relative to the neutral condition. However, exploratory analysis revealed reduced pain ratings in later trials of the experiment in the safety group compared to the threat group in both studies, suggesting different temporal dynamics for threat and safety learning and extinction, respectively. Perspective: The present results demonstrate the challenge to maintain safety in the presence of acute pain and suggest more research on the interaction of affective learning mechanism and pain processing.

The role of chronic pain and pain anxiety in delay discounting of pain and monetary losses

Pain may alter intertemporal decisions by modifying the value of pain-related outcomes. For example, a person with chronic back pain may be faced with two choices: undergo surgery that could provide long-term relief but would involve additional short-term pain and discomfort during recovery; or continue living with the chronic pain and avoid the surgery, thus leading to overall deteriorated health. Such choices are well captured by delay discounting, which is defined as the decline in the subjective value of an outcome as the delay of its receipt increases. We investigated general pain anxiety and delay discounting of monetary losses and pain in 255 individuals with and without chronic pain. We found that people with chronic pain tend to discount the value of pain outcomes more than those without chronic pain, suggesting that chronic pain may contribute to impulsivity in decision-making related to pain. Moreover, the effect of chronic pain on delay discounting was mediated through general pain anxiety. This result, however, should be taken with caution, because the effect sizes were small, and the path model was underpowered. In conclusion, people with chronic pain might be more likely to prioritize avoiding immediate discomfort and may undervalue the potential long-term benefits of actions that could alleviate their pain in the future.

A narrative review of the literature on illness uncertainty in hypermobile ehlers-danlos syndrome: implications for research and clinical practice

BACKGROUND

Hypermobile Ehlers-Danlos syndrome (hEDS) is characterized by joint and skin laxity, and often accompanied by chronic pain, dysautonomia, increased distress and, functional limitations. The journey to accurate diagnosis is often prolonged due to unclear etiology of symptoms. This manuscript is a narrative review of the literature on illness uncertainty (IU) in hEDS, highlighting the unique facets of IU in this population, as compared to the broader chronic pain population (given symptom overlap between these two disease groups), that warrant additional investigation. Additionally, we considered the unique challenges associated with IU in the context of the developmental nuances of pediatric populations. Specifically, we aimed to (1) map the extant literature of the IU experience in chronic pain conditions broadly including the pediatric and adult research to identify key concepts related to IU and incorporate potential developmental considerations in IU; (2) delineate and describe the IU experience specifically in patients with hEDS, with the goal of identifying gaps in the literature based on aspects of presentation in hEDS that do and do not differ from the broader chronic pain population; and (3) elucidate the potential areas of adverse impact of IU in both general chronic pain populations, and those with hEDS specifically, to provide actionable areas for future research and clinical care of individuals with hEDS. Results of this review indicate that IU has been well-studied in chronic pain generally, but inadequately evaluated in hEDS specifically. Specific features of hEDS (complexity of the disorder, involvement of multiple bodily systems, contribution of organic pathology) may uniquely contribute to IU in this population. This review suggests that ambiguities surrounding the diagnosis of hEDS, symptom course, and treatment recommendations, along with misdiagnosis, perceived dismissal of symptoms, or attribution of symptoms to mental health concerns might increase risk for IU and related distress in patients.

CONCLUSION

Findings from the present review suggest that distinct features of hEDS yield a set of driving factors for IU that may be somewhat different than those faced by patients with chronic pain or other medical conditions. The development of a validated measure of IU to appropriately assess this construct in patients with hEDS is a research priority. In the clinical setting, providers should be attentive to the potentially aversive diagnostic and treatment experiences reported by patients and attempt to provide clear explanations based on the extant knowledge of hEDS, and implement best-practice recommendations for multidisciplinary treatment.

Quantitative sensory testing in a magnetic resonance environment: considerations for thermal sensitivity and patient safety

Introduction

Quantitative sensory testing (QST) is often used to understand the perceptual basis of acute and chronic conditions, including pain. As the need grows for developing a mechanistic understanding of neurological pathways underlying perception in the basic and clinical sciences, there is a greater need to adapt techniques such as QST to the magnetic resonance (MR) environment. No studies have yet evaluated the impact of the MR environment on the perception of thermal stimuli. This study aimed to evaluate the differences in temperature sensitivity outside an MR environment and during an MRI scanning session. We hypothesized that there would be a difference in how participants reported their pain sensitivity between the two environments.

Methods

Healthy participants underwent thermal QST outside the MR scanning environment, where they were asked to rate the temperature of a noxious stimulus at which they perceived their pain to be 7/10, using a Likert scale ranging from 0 to 10. Participants repeated this procedure inside a 3.0 T MRI approximately 30 min later. We repeated our investigation in a clinical cohort of participants with a chronic pain condition.

Results

There were statistically significant changes of 1.1°C in thermal sensitivity between environments. This increase in pain threshold was found in healthy participants and replicated in the clinical cohort.

Discussion

Findings can be applied toward improving MR safety, the resolution of brain pathways underlying pain mechanisms, and to more broadly comment on the impact of the MR environment on investigations that integrate perception-influenced processes.

Social Anxiety, Social Support, and Quality of Life in Patients With Epilepsy at a Tertiary Care Hospital in Saudi Arabia

Objectives The objectives of this study were to measure the prevalence of social anxiety disorder and its association with quality of life (QoL) in patients with epilepsy (PWE) in King Khalid University Hospital, Riyadh City, Saudi Arabia. Methodology A self-administrated, online, questionnaire-based, cross-sectional study was conducted at King Khalid University Hospital, Riyadh, Kingdom of Saudi Arabia on PWE 18 years of age and above from February 2021 to January 2022. Social anxiety and the five domains of QoL were measured using the validated Arabic versions of the Liebowitz social anxiety scale and European quality-of-life 5-dimensions 3-levels (EQ-5D-3L), respectively. Information was collected on sociodemographic characteristics, social support, and adverse life events. Results This study included 246 patients, of which approximately 25% and 15% had mild/moderate and severe/very severe levels of social anxiety, respectively. Severe social anxiety was significantly associated with poor QoL domains, namely, restricted mobility (2.65 [1.00, 6.99]), inability to perform usual activities (3.88 [1.61, 9.36]), pain or discomfort (3.21 [1.38, 7.48]), and anxiety and depression (5.77 [2.45, 13.61]). Similarly, the lack of social support was also significantly associated with poor QoL, such as restricted mobility (2.42 [1.12, 5.22]), restricted self-care (3.64 [1.18, 11.17]), inability to perform usual activities (2.86 [1.42, 5.75]), pain/discomfort (2.53 [1.38, 4.66]), and anxiety and depression (1.93 [1.04, 3.57]). Females showed higher odds for restricted mobility (2.79 [1.29, 6.03]) and low education with limited self-care (7.38 [1.49, 36.71]). Conclusion Patients with epilepsy reported high levels of social anxiety that have a negative effect on their QoL. Healthcare providers should be able to provide counseling to the patient and their family members. In addition, social support is important to improve their mobility and socialization with friends and neighbors.

Suffering from chronic tinnitus, chronic neck pain, or both: Does it impact the presence of signs and symptoms of central sensitization?

Chronic subjective tinnitus is a prevalent symptom, which has many similarities with chronic pain. Central sensitization is considered as a possible underlying mechanism of both symptoms. Central sensitization has already been investigated in chronic pain populations but not in patients with chronic subjective tinnitus. Therefore, the main objective of this cross-sectional study was to compare signs and symptoms, indicative for central sensitization, in tinnitus patients with and without chronic idiopathic neck pain, patients with chronic idiopathic neck pain only, and healthy controls. Also, differences in psychological and lifestyle factors, possibly influencing the association between central sensitization and tinnitus, were examined as well as correlations between signs and symptoms of central sensitization, and tinnitus, pain, psychological and lifestyle factors. Differences in signs and symptoms of central sensitization were examined using the self-report Central Sensitization Inventory and QST protocol (local and distant mechanical and heat hyperalgesia, conditioned pain modulation). Tinnitus, pain, psychological and lifestyle factors were evaluated using self-report questionnaires. Symptoms of central sensitization and local mechanical hyperalgesia were significantly more present in both tinnitus groups, compared to healthy controls, but were most extensive in the group with chronic tinnitus+chronic idiopathic neck pain. Distant mechanical hyperalgesia, indicative for central sensitization, was only observed in the group with both chronic tinnitus+chronic idiopathic neck pain. This group also displayed a significantly higher psychological burden and poorer sleep than patients with chronic tinnitus only and healthy controls. Signs and symptoms of central sensitization were also shown to be associated with tinnitus impact, pain-related disability, psychological burden and sleep disturbances. This study shows preliminary evidence for the presence of central sensitization in patients with chronic tinnitus+chronic idiopathic neck pain. This could be explained by the higher perceived tinnitus impact, psychological burden and sleep problems in this group. Trial registration: This study is registered as NCT05186259 (www.clinicaltrials.gov).

The Value of Pain Sensitivity Questionnaire in Predicting Postoperative Pain in Living Kidney Donors: A Prospective Observational Study

Purpose

This study aimed to investigate the value of the Pain Sensitivity Questionnaire (PSQ) for the prediction of postoperative pain and the relationship between pain sensitivity and postoperative pain in kidney donors undergoing living-related kidney transplantation.

Patients and Methods

A total of 148 kidney donors were selected and the preoperative pain sensitivity questionnaire was administered the day before surgery. Kidney donors were assigned to low PSQ group (PSQ < 6.5, n = 76) or high PSQ group (PSQ ≥ 6.5, n = 72). The primary endpoint was the number of patient-controlled analgesia (PCA). Other outcomes included: the incidence of acute pain, flurbiprofen axetil remediation rate, the incidence of chronic pain, neuropathic pain assessment scale (Douleur Neuropathique 4 Questions, DN4), visual analog scale (VAS) at rest after surgery as well as the correlation between PSQ and QST (Quantitative Sensory Testing).

Results

The low PSQ group had a significantly lower number of PCA than high PSQ group (P < 0.0001). The incidence of acute pain was 75% in low PSQ group and 100% in high PSQ group (P < 0.0001). Furthermore, flurbiprofen axetil remediation rate was lower in low PSQ group than that in high PSQ group (P = 0.042). The incidence of chronic pain was significantly lower in low PSQ group than in high PSQ group (6.6% vs 61.1%, P < 0.001). Moreover, DN4 was significantly lower in low PSQ group than that in high PSQ group (P < 0.001). The PSQ-mean was significantly negatively correlated with QST in kidney donors. VAS at rest for the low PSQ group were lower than those of the high PSQ group.

Conclusion

The PSQ was found to be associated with the intensity or postoperative pain and might be used to screen patients prior to living-kidney transplantation.

Pain related to intravitreal injections for age-related macular degeneration: a qualitative study of the perspectives of patients and practitioners

OBJECTIVES

Ocular pain is a commonly reported finding in the intravitreal injection procedure, but post-injection experiences and patient adherence to treatment remain underexplored. We therefore aimed to identify key variations in the intravitreal injection procedure that may influence pain, and to gain insights into the post-injection experience and treatment adherence from the perspective of patients and practitioners.

DESIGN

Qualitative semistructured interview study using reflexive thematic analysis of transcripts.

SETTING

Hospital Eye Clinic in Wales, UK. Interviews were conducted between May and September 2019.

PARTICIPANTS

Purposive sample of patients aged ≥50 years with neovascular age-related macular degeneration and no other retinal pathology who had received at least six intravitreal injections, and practitioners including ophthalmologists, registered nurses and optometrists who performed intravitreal injections at the research site.

RESULTS

Data saturation was reached with 21 interviews: 14 patients and 7 practitioners. Three main themes were identified from the analysis: fear of losing eyesight and treatment anxiety influence patient adherence to treatment, variability in pain experience during treatment, and post-injection experience and impact on patient recovery. To reassure patients feeling apprehensive about the injections, practitioners promoted safety and trust, and used techniques to manage anxiety. Key variations that may influence pain identified were application of antiseptic or anaesthetic, injecting methods and communication. During injection, patients reported a dull-aching and sharp pain, contrary to practitioners' perspective of feeling a 'pressure'. Patients described prolonged soreness and irritation of up to 36 hours post-injection affecting their sleep and recovery.

CONCLUSION

Establishing rapport supported patients to recognise the necessity of ongoing treatment to prevent sight loss; however, inadequate pain management led to undesirable outcomes. Practitioners should use pain assessment tools during and immediately after injection and provide ongoing consistent information to help patients manage pain at home.

Patients with neuropathic pain from lumbosacral radiculopathy demonstrate similar pressure pain thresholds and conditioned pain modulation to those with fibromyalgia

OBJECTIVE

The purpose of the study was to evaluate pain thresholds, impairment of the endogenous pain modulatory system, and self-reported cognitive-emotional and central sensitization-related symptoms among three subject groups: a rarely studied patient cohort with neuropathic pain from lumbosacral radiculopathy (NPLSR), patients with fibromyalgia (FM) and healthy controls (HC).

METHODS

Patient-reported pain-related symptomology was evaluated with psychometricallyvalidated questionnaires. Pressure pain threshold (PPT), heat pain threshold (HPT), and cold pain threshold (CPT) were assessed in the low back and contralateral forearm. Conditioned pain modulation (CPM) was evaluated with a recently introduced methodology that accounts for a standard error of measurement.

RESULTS

Compared to the HC subjects, the FM and NPLSR subjects had significantly lower pain thresholds and more CPM impairment. No significant differences in PPT and CPM were observed between the FM and NPLSR groups. Significant group differences were found in self-reported symptoms of depression, anxiety, stress, and central sensitization. Self-reported symptom severity increased in a stair-step fashion, with the HC group scoring lowest and FM group scoring highest.

CONCLUSION

The NPLSR group manifested CPM dysfunction and pressure hyperalgesia at similar levels to the FM group, indicating that these two chronic pain syndromes, likely based on different pathophysiological mechanisms, in fact share some common pain processing features. However, though both patient groups demonstrated similarities in pain processing, self-reported cognitive-emotional and central sensitization-related symptom severity was significantly higher in the FM cohort, which distinguished them from the chronic NPLSR cohort.

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.

Identification of brain-to-spinal circuits controlling the laterality and duration of mechanical allodynia in mice

Mechanical allodynia (MA) represents one prevalent symptom of chronic pain. Previously we and others have identified spinal and brain circuits that transmit or modulate the initial establishment of MA. However, brain-derived descending pathways that control the laterality and duration of MA are still poorly understood. Here we report that the contralateral brain-to-spinal circuits, from Oprm1 neurons in the lateral parabrachial nucleus (lPBNOprm1), via Pdyn neurons in the dorsal medial regions of hypothalamus (dmHPdyn), to the spinal dorsal horn (SDH), act to prevent nerve injury from inducing contralateral MA and reduce the duration of bilateral MA induced by capsaicin. Ablating/silencing dmH-projecting lPBNOprm1 neurons or SDH-projecting dmHPdyn neurons, deleting Dyn peptide from dmH, or blocking spinal κ-opioid receptors all led to long-lasting bilateral MA. Conversely, activation of dmHPdyn neurons or their axonal terminals in SDH can suppress sustained bilateral MA induced by lPBN lesion.