Clinical identification of the stimulus intensity to measure temporal summation of second pain.

Temporal summation of second pain (TSSP) has been suggested as a psychophysical index for central sensitization, one of the critical mechanisms in the chronification of pain. However, there is no gold standard for protocols to measure TSSP. The purpose was to establish the stimulus intensity for measuring TSSP. Female patients with chronic myofascial temporomandibular disorders pain (n = 16) and healthy female volunteers with no pain (n = 15) participated. Pain thresholds (PT °C) were measured, and repetitive heat stimuli at three stimulus intensities (PT °C, PT + 1 °C, PT + 2 °C) were applied. TSSP parameters were quantified as TSSP magnitude (TSm) and TSSP frequency (TSf). In healthy female volunteers, pain ratings significantly decreased at PT °C (p < 0.050), besides TSm and TSf at PT + 2 °C were significantly higher than those at PT °C (p < 0.025). In chronic pain patients, pain ratings significantly increased at PT + 1 °C and PT + 2 °C (p < 0.050). At PT + 2 °C, TSm and TSf in chronic pain patients were significantly higher than those in healthy volunteers (p < 0.050). It could be helpful to measure TSSP with the stimulus intensity adjusted individually to the patient's pain thresholds + 2 °C for assessing central sensitization.

Scanned optogenetic control of mammalian somatosensory input to map input-specific behavioral outputs.

Somatosensory stimuli guide and shape behavior, from immediate protective reflexes to longer-term learning and higher-order processes related to pain and touch. However, somatosensory inputs are challenging to control in awake mammals due to the diversity and nature of contact stimuli. Application of cutaneous stimuli is currently limited to relatively imprecise methods as well as subjective behavioral measures. The strategy we present here overcomes these difficulties, achieving 'remote touch' with spatiotemporally precise and dynamic optogenetic stimulation by projecting light to a small defined area of skin. We mapped behavioral responses in freely behaving mice with specific nociceptor and low-threshold mechanoreceptor inputs. In nociceptors, sparse recruitment of single-action potentials shapes rapid protective pain-related behaviors, including coordinated head orientation and body repositioning that depend on the initial body pose. In contrast, activation of low-threshold mechanoreceptors elicited slow-onset behaviors and more subtle whole-body behaviors. The strategy can be used to define specific behavioral repertoires, examine the timing and nature of reflexes, and dissect sensory, motor, cognitive, and motivational processes guiding behavior.

To safely navigate their world, animals need to be able to tell apart a gentle touch from an eye-watering pinch, detect cold water or sense the throbbing pain stemming from an infected cut. These 'somatic' sensations are relayed through thousands of nerve endings embedded in the skin and other tissues. Yet the neurological mechanisms that underpin these abilities are complex and still poorly understood. Indeed, these nerve endings can be stimulated by extreme temperatures, harmful chemicals, friction or even internal signals such as inflammation. One event can also recruit many different types of endings: a cut for example, will involve responses to mechanical pressure, tissue damage and local immune response. To disentangle these different actors and how they affect behavior, scientists need to develop approaches that allow them to deliver specific stimuli with increased precision, and to monitor the impact on an animal. To achieve this goal, Schorscher-Petcu et al. used mice in which blue light could trigger specific types of nerve endings. For instance, depending on the genetic background of the animals, a laser could either activate nerve endings involved in pain or gentle touch. Crucially, this could be done from a distance by beaming light with exquisite precision onto the paws of the mice without physically touching or disturbing the animals. How the mice responded could then be observed without any interference. Their behavior was analyzed using a combination of high-speed videos, computer-driven recording systems, and machine learning. This revealed subtle changes in behavior that had not been detected before, spotting microscopic movements of the stimulated paw and mapping simultaneous whole-body movements such as changes in posture or head orientation. The approach therefore allows scientists to assess the impact of touch, pain or temperature sensation in freely behaving mice. It could also be harnessed to develop much needed treatments against chronic pain.

Quantitative Sensory Testing to Predict Postoperative Pain.

PURPOSE OF REVIEW: We review the relevance of quantitative sensory testing (QST) in light of acute and chronic postoperative pain and associated challenges. RECENT FINDINGS: Predicting the occurrence of acute and chronic postoperative pain with QST can help identify patients at risk and allows proactive preventive management. Generally, central QST testing, such as temporal summation of pain (TSP) and conditioned pain modulation (CPM), appear to be the most promising modalities for reliable prediction of postoperative pain by QST. Overall, QST testing has the best predictive value in patients undergoing orthopedic procedures. Current evidence underlines the potential of preoperative QST to predict postoperative pain in patients undergoing elective surgery. Implementing QST in routine preoperative screening can help advancing traditional pain therapy toward personalized perioperative pain medicine.

Dependence of the filled-space illusion on the size and location of contextual distractors.

For most observers, the part of the stimulus that is filled with some visual elements (e.g., distractors) appears larger than the unfilled part of the same size. This illusion of interrupted spatial extent is also known as the \'filled­space' or 'Oppel­Kundt' illusion. Although the continuously filled­space illusion has been systematically studied for over a century, there is still no generally accepted explanation of its origin. The present study aimed to further develop our computational model of the continuously filled­space illusion and to examine whether the model predictions successfully account for illusory effects caused by distracting line­segments of various lengths that are\r\nattached to different endpoints (i.e., terminators) of the reference spatial interval of the three­dot stimulus. Our experiments confirm that the illusion manifests itself along a distracting segment located both inside and outside of the reference interval. In the case of two distractors arranged symmetrically with respect to the lateral terminator, we found that the magnitude of the illusion is approximately equal to the sum of the relevant values obtained with separate distractors. The results of experiments using vertical shifts of distractors supported the model's assumption regarding the two­dimensional Gaussian profile of hypothetical areas of weighted spatial summation\r\nof neural activity. A good correspondence between the experimental and theoretical results supports the suggestion that perceptual positional biases associated with the context­evoked increase in neural excitation may be one of the main causes of the continuously filled­space illusion.

The relation of peripheral and central sensitization to muscle co-contraction: the MOST study.

OBJECTIVE: To examine the relation of pain sensitization to altered motor activity in knee OA as assessed by hamstrings muscle co-contraction during maximal effort knee extension. DESIGN: Medial, lateral, and overall hamstring co-contraction was assessed in the Multicenter Osteoarthritis (MOST) Study cohort using electromyography during isokinetic knee extension at 60°/second. Mechanical temporal summation of pain (TS) was assessed at the right wrist and pressure pain thresholds (PPT) were assessed at the patellae; PPTs were categorized into sex-specific tertiles. Muscle co-contraction was categorized into age- and sex-specific tertiles. We evaluated the relation of measures of sensitization to muscle co-contraction using a generalized logistic regression model. RESULTS: 1633 participants were included: mean age and BMI was 67.3 ± 7.7 years and 30.3 ± 5.6 kg/m2, respectively; 58% were female. Presence of TS was associated with higher overall (OR 1.3, 95% confidence interval (CI) (1.0-1.8)), medial (1.4 (1.0-1.9), and lateral (1.3 (1.0, 1.9)) hamstring co-contraction. The lowest PPT tertile (greater sensitivity) was associated with higher overall (1.5 (1.0, 2.3)) and medial (1.5 (1.0, 2.3)) hamstring co-contraction compared with those in the highest PPT tertile. CONCLUSION: Greater pain sensitization, as assessed by presence of TS at the wrist and low patellar PPT, was associated with greater overall and medial hamstring co-contraction during knee extension. This provides support to the possibility that peripheral and/or central nervous system alterations may not only affect pain sensitivity, but also motor function.

Non-specific analgesia during a clinical trial in fibromyalgia.

BACKGROUND: When patients suffering from fibromyalgia undergo a therapeutic trial, a non-negligible part of analgesia is not explained by the drug itself. The mechanisms of this non-specific effect need to be understood. MATERIALS AND METHODS: We undertook secondary analyses of a double-blind randomized trial in fibromyalgia patients in which 100 mg/day milnacipran was not found superior to placebo. Data from 49 patients belonging to both groups were pooled. Both before treatment and one month after treatment, all patients underwent a CaNTAB® neuropsychological test (related to spatial planning, reaction time, decision-making and risk-taking, and ability to name objects), and measurements of sensation and pain thresholds to heat and cold, supraliminal heat pain threshold, punctuate mechanical pain threshold and temporal summation, mechanical allodynia to skin brushing, and response to conditioned pain modulation. We studied the baseline predictors of analgesia and the indicators of change associated to analgesia separately. A stepwise approach was used to select the factors to enter into the final ANCOVAs, in which age, body mass index, treatment group and pain at baseline were covariates. RESULTS: No baseline predictor of non-specific analgesia other than pain at baseline was found to be predictive. Conversely, several neuropsychological (higher performance) or psychophysical (lower sensitivity) changes correlated with analgesia in unadjusted analyses. Multivariable analyses identified increases in warm/heat thermal thresholds and an increased ability to name objects, as factors associated with analgesia. CONCLUSIONS: The changes observed concomitantly to non-specific pain analgesia might be related to mild changes in brain functioning, based on convergent literature data.

Quantitative sensory testing in feline osteoarthritic pain - a systematic review and meta-analysis.

Quantitative sensory testing (QST) is a psychophysical test used to quantify somatosensory sensation under normal or pathological conditions including osteoarthritis (OA). OBJECTIVE: This study aimed to conduct a systematic review and meta-analysis of studies using QST in healthy and osteoarthritic cats, registered at Systematic Review Research Facility (#26-06-2017). DESIGN: Hierarchical models with random intercepts for each individual study extracted through the systematic review were fit to subject-level data; QST measures were contrasted between healthy and osteoarthritic cats. Four bibliographic databases were searched; quality and risk of bias assessment were performed using pre-established criteria. RESULTS: Six articles were included; most were of high quality and low risk of bias. Punctate tactile threshold (n = 70) and mechanical temporal summation (n = 35) were eligible for analysis. Cats with OA have lower punctate tactile threshold [mean difference (95%HDI): -44 (-60; -26) grams] and facilitated temporal summation of pain [hazard ratio (95%HDI): 5.32 (2.19; 14) times] when compared with healthy cats. The effect of sex and body weight on sensory sensitivity remained inconclusive throughout all analyses. Due to the correlation between age and OA status, it remains difficult to assess the effect of OA on sensory sensitivity, independently of age. CONCLUSIONS: Clear and transparent reporting using guidelines are warranted. Similar to people, centralized sensitization is a feature of OA in cats. Future studies should try to elucidate the age effect on feline OA. Research with natural OA in cats is promising with potential to benefit feline health and welfare, and improve translatability to clinical research.

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

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

Temporal Summation in Chronic Pelvic Pain.

OBJECTIVE: This study sought to characterize central sensitization further among women with chronic pelvic pain by identifying temporal summation using a cotton-tipped applicator test that can be used at the bedside. METHOD: A total of 36 women (18 with chronic pain and allodynia; 18 without pain) were recruited. Both groups were randomly assigned to receive 3 strokes of a benign stimulus on the abdomen at differing frequencies: 10, 30, or 100 seconds. Each group included 6 women. Pain was assessed using a rating scale of 1 to 10. Data were analyzed using the multivariate approach to repeated measures analysis of variance. RESULTS: The pattern of pain scores differed significantly between women with and without chronic pain (P = 0.002). Women with chronic pelvic pain and allodynia showed a statistically significant increase in pain with successive strokes of the cotton-tipped applicator (P = 0.012 for stroke 1 vs. 2, P = 0.026 for stroke 2 vs. 3, and P = 0.005 for stroke 1 vs. 3). CONCLUSION: Women with chronic pelvic pain and allodynia showed significant worsening of pain with successive strokes of a cotton-tipped applicator. This finding indicates that pain wind-up and central sensitization are present in women with chronic pelvic pain and allodynia. Identification of summation is further evidence of neuroplasticity, which is helpful in innovative therapies for chronic pelvic pain.

How Much Is Needed? Comparison of the Effectiveness of Different Pain Education Dosages in Patients with Fibromyalgia.

OBJECTIVE: To assess the effect of different dosages of pain neuroscience education (PNE) programs on central nociceptive processing in patients with fibromyalgia. Second, to compare the effects of different dosages of PNE programs on numerical pain rating scale (NPRS), disability, and psychological variables. DESIGN: Single-blind randomized controlled trial. SETTING: Three fibromyalgia centers in Spain (Valencia, Alcorcón, Alcalá de Henares). SUBJECTS: Seventy-seven patients with fibromyalgia. METHODS: Participants were randomized to four groups of PNE: 1) high-dose PNE (N = 20), 2) low-concentrated dose PNE (N = 20), 3) diluted low-dose PNE (N = 20), and (4) control treatment (N = 17), conducted in two 30-50-minute sessions in groups of four to six participants. Conditioned pain modulation (CPM), temporal summation (TS), and pressure pain thresholds (PPTs) were assessed at baseline and at three-month follow-up. Secondary outcome measures were the Fibromyalgia Impact Questionnaire, Pain Catastrophizing Scale, and Pain Anxiety Symptoms Scale. RESULTS: There were significant between-group differences for NPRS in favor of the groups receiving high-dose PNE, with a large effect size at three-month follow-up (P < 0.01, η2p = 0.170), but there were no significant differences between groups for the remaining variables (P > 0.05). All groups improved for central nociceptive processing, psychological variables, disability, and pain intensity (NPRS). CONCLUSIONS: In patients with fibromyalgia, higher dosages of PNE produced a larger improvement in pain severity at three-month follow-up than other dosages of PNE and biomedical education. However, PNE was not superior to biomedical education in the central nociceptive processing, disability, or psychological variables in patients with fibromyalgia.

Experimentally induced spinal nociceptive sensitization increases with migraine frequency: a single-blind controlled study.

The nitric-oxide donor nitroglycerin (NTG) administration induces a facilitation of nociceptive pathways in episodic migraine. This study aims to test the hypothesis that induced spinal sensitization could be more pronounced in patients affected by high-frequency migraine (HF-MIG) with respect to low-frequency migraine (LF-MIG). We enrolled 28 patients with LF-MIG (1-5 migraine days/month), 19 patients with HF-MIG (6-14 migraine days/month), and 21 healthy controls (HCs). Spinal sensitization was evaluated with the neurophysiological recording of the temporal summation threshold (TST) of the nociceptive withdrawal reflex at the lower limb. Temporal summation threshold was recorded at baseline and 30, 60, and 120 minutes after NTG administration (0.9 mg sublingual). Spinal sensitization was detected in LF-MIG at 60 (P = 0.010) and 120 minutes (P = 0.001) and in HF-MIG at 30 (P = 0.008), 60 (P = 0.001), and 120 minutes (P = 0.001) after NTG administration. Temporal summation threshold did not change in HC (P = 0.899). Moreover, TST reduction was more pronounced in HF-MIG with respect to LF-MIG (P = 0.002). The percentage of patients who developed a migraine-like headache after NTG was comparable in the 2 migraine groups (LF-MIG: 53.6%, HF-MIG: 52.6%, P = 0.284), whereas no subjects in the HC group developed a delayed-specific headache. Notably, the latency of headache onset was significantly shorter in the HF-MIG group when compared with the LF-MIG group (P = 0.015). Our data demonstrate a direct relationship between migraine frequency and both neurophysiological and clinical parameters, to suggest an increasing derangement of the nociceptive system control as the disease progresses, probably as a result of the interaction of genetic and environmental factors.

Stereoscopic depth adaptation from binocularly correlated versus anti-correlated noise: Test of an efficient coding theory of stereopsis.

Stereoscopic, or "3D" vision in humans is mediated by neurons sensitive to the disparities in the positions of objects in the two eyes' views. A disparity-sensitive neuron is typically characterized by its responses to left- and right-eye monocular signals, SL and SR, respectively. However, it can alternatively be characterized by sensitivity to the sum of the two eyes' inputs, S+ = SL + SR, and the difference, S- = SL - SR. Li and Atick's theory of efficient binocular encoding proposes that the S+ and S- signals can be separately weighted to maximize the efficiency with which binocular information is encoded. This adaptation changes each neuron's sensitivity and preferred binocular disparity, resulting in predicted effects on the perceived stereoscopic depth of objects. To test these predictions, we measured the apparent depth of a random-dot stereogram with an 'in-front' target following adaptation to binocularly correlated or anti-correlated horizontally-oriented grating stimuli, which reduce sensitivity to the S+ and S- signals, respectively, but which contain no conventional stereo-depth signals. The anti-correlated noise adaptation made the target appear relatively closer to the background than the correlated noise adaptation, with differences of up to 60%. We show how this finding can be accommodated by a standard model of binocular disparity processing, modified to incorporate the binocular adaptation suggested by Li and Atick's theory.

Cul3 and insomniac are required for rapid ubiquitination of postsynaptic targets and retrograde homeostatic signaling.

At the Drosophila neuromuscular junction, inhibition of postsynaptic glutamate receptors activates retrograde signaling that precisely increases presynaptic neurotransmitter release to restore baseline synaptic strength. However, the nature of the underlying postsynaptic induction process remains enigmatic. Here, we design a forward genetic screen to discover factors in the postsynaptic compartment necessary to generate retrograde homeostatic signaling. This approach identified insomniac (inc), a putative adaptor for the Cullin-3 (Cul3) ubiquitin ligase complex, which together with Cul3 is essential for normal sleep regulation. Interestingly, we find that Inc and Cul3 rapidly accumulate at postsynaptic compartments following acute receptor inhibition and are required for a local increase in mono-ubiquitination. Finally, we show that Peflin, a Ca2+-regulated Cul3 co-adaptor, is necessary for homeostatic communication, suggesting a relationship between Ca2+ signaling and control of Cul3/Inc activity in the postsynaptic compartment. Our study suggests that Cul3/Inc-dependent mono-ubiquitination, compartmentalized at postsynaptic densities, gates retrograde signaling and provides an intriguing molecular link between the control of sleep and homeostatic plasticity at synapses.

Association Between Pain Sensitivity and Endogenous Supraspinal Pain Modulation in Patients with Orofacial Pain.

Address correspondence to: Dr. Carla S. Enriquez, Physical Therapy Program, Stockton University School of Health Sciences, 101 Vera King Farris Drive, Galloway, NJ 08205-9441, USA. Tel 609-626-3508, fax 609-652-4858. carla.enriquez@stockton.edu. PURPOSE: To investigate the association between pain sensitivity and endogenous supraspinal pain modulation activity using quantitative sensory tests (QST) in patients with orofacial pain. METHODS: Temporal summation (TS) testing and conditioned pain modulation (CPM) are QSTs used to quantify individual pain processing mechanisms. TS testing was used to assess pain sensitivity which correlates to central sensitization and CPM for endogenous pain modulation. These tests were administered to a convenience sample of patients with orofacial pain (n=40) seen for initial examination in an orofacial pain clinic. Bivariate correlation analyses were conducted on TS and CPM scores, including age and gender. RESULTS: A strong linear correlation was found between pain sensitivity and endogenous pain modulation (r=0.69, p<0.001). QST outcomes suggest that inefficient endogenous pain modulation is positively correlated with the magnitude of pain sensitivity among individuals who seek treatment for orofacial pain. A weak linear correlation was also found between TS and age (r=0.37, p=0.02). CONCLUSION: QSTs demonstrated a strong association between heightened pain sensitivity and inefficient endogenous pain modulation revealed from higher pain report on TS and CPM testing in patients with orofacial pain. Our findings provide supporting evidence on the impairments in pain-processing mechanisms that require consideration when evaluating orofacial pain etiology, where increased pain sensitivity and aberrant pain modulation appear to significantly contribute in prolonged and persistent pain experience.

Functional Specialization of ON and OFF Cortical Pathways for Global-Slow and Local-Fast Vision.

Visual information is processed in the cortex by ON and OFF pathways that respond to light and dark stimuli. Responses to darks are stronger, faster, and driven by a larger number of cortical neurons than responses to lights. Here, we demonstrate that these light-dark cortical asymmetries reflect a functional specialization of ON and OFF pathways for different stimulus properties. We show that large long-lasting stimuli drive stronger cortical responses when they are light, whereas small fast stimuli drive stronger cortical responses when they are dark. Moreover, we show that these light-dark asymmetries are preserved under a wide variety of luminance conditions that range from photopic to low mesopic light. Our results suggest that ON and OFF pathways extract different spatiotemporal information from visual scenes, making OFF local-fast signals better suited to maximize visual acuity and ON global-slow signals better suited to guide the eye movements needed for retinal image stabilization.

Peripheral and Central Sensitization of Pain in Individuals With Hand Osteoarthritis and Associations With Self-Reported Pain Severity.

OBJECTIVE: Pain sensitization, an important osteoarthritis (OA) pain mechanism, has not been substantially investigated in patients with hand OA. It is unknown how peripheral and central sensitization are related to self-reported hand pain. METHODS: Individuals with verified hand OA in the Nor-Hand study underwent quantitative sensory testing of pressure pain thresholds (PPTs) locally (painful and nonpainful finger joints) and remotely (wrist, trapezius, and tibialis anterior muscles), and testing of temporal summation (TS), a manifestation of central sensitization. We examined cross-sectional associations of PPT tertiles and TS with hand pain using the Numerical Rating Scale (NRS) (range 0-10) and the Australian/Canadian Osteoarthritis Hand Index (AUSCAN) pain subscale (range 0-20). Linear regression models were adjusted for demographics, psychosocial factors, and radiographic severity. RESULTS: This study included 282 participants (88% female) with a median age of 61 years (interquartile range [IQR] 57-66). Participants with the lowest PPTs in their finger joints and in most remote locations reported higher NRS pain values, compared to patients with the highest PPTs, with adjusted ß values ranging from 0.6 (95% confidence interval [95% CI] 0.0, 1.2) to 0.9 (95% CI 0.3, 1.5). The 118 participants (42%) with TS reported higher mean ± SD NRS pain values compared to those without TS (4.1 ± 2.4 versus 3.1 ± 1.7; adjusted ß = 0.6 [95% CI 0.2, 1.1]). Neither PPTs nor the presence of TS were associated with AUSCAN pain. CONCLUSION: Central sensitization was common in patients with hand OA. Lower local and widespread PPTs and the presence of TS were associated with higher hand pain intensity, even after adjustment for demographics, psychosocial factors, and radiographic severity. Sensitization may therefore represent a possible treatment target.

The type of sport matters: Pain perception of endurance athletes versus strength athletes.

BACKGROUND: Studies assessing athletes' pain sensitivity yield inconsistent data, which demonstrate either increased pain threshold and tolerance in athletes than controls or similar thresholds. This inconsistency may result from the variability in the type of sport practiced by the athletes and its effect on pain perception. For example, endurance athletes perform continuous intense exercise for prolonged durations, whereas strength athletes perform short bouts of extreme efforts. Consequently, endurance athletes may tolerate and modulate pain better than strength athletes. This hypothesis was tested by comparing pain perception of endurance athletes with that of strength athletes. METHODS: Subjects were 19 endurance athletes (triathletes), 17 strength athletes (weightlifters and throwers) and 17 non-athlete controls. Quantitative measurements included heat-pain threshold, heat-pain tolerance, cold pressor pain ratings, temporal summation of pain (TSP) and conditioned pain modulation (CPM). Fear of pain and pain catastrophizing were also assessed. RESULTS: The two athlete groups had lower pain ratings than non-athletes. However, strength athletes had higher heat-pain threshold than endurance athletes, whereas endurance athletes had higher heat-pain tolerance and stronger CPM than strength athletes and lower fear of pain levels. Longer training time correlated with TSP in endurance athletes but with CPM and heat-pain tolerance in strength athletes. CONCLUSIONS: Although athletes in general seem less responsive to noxious stimuli than non-athletes, the type of sport differentially affects pain perception; whereas endurance-based sport is associated with improved pain inhibition, strength-based sport is associated with reduced pain sensitivity. These characteristics may be considered when sport is recommended for pain management. SIGNIFICANCE: This study shows that different sport types are associated with different characteristics of pain perception and modulation, as well as of thoughts towards pain.

Enhanced facilitation and diminished inhibition characterizes the pronociceptive endogenous pain modulatory balance of persons living with HIV and chronic pain.

Chronic pain in persons living with HIV (PLWH) may be related to alterations in endogenous pain modulatory processes (e.g., high facilitation and low inhibition of nociception) that promote exaggerated pain responses, known as hyperalgesia, and central nervous system (CNS) sensitization. This observational study examined differences in endogenous pain modulatory processes between 59 PLWH with chronic pain, 51 PLWH without chronic pain, and 50 controls without HIV or chronic pain. Quantitative sensory testing for temporal summation (TS) of mechanical and heat pain as well as conditioned pain modulation (CPM) were used to assess endogenous pain facilitatory and inhibitory processes, respectively. Associations among TS, CPM, and self-reported clinical pain severity were also examined in PLWH with chronic pain. Findings demonstrated significantly greater TS of mechanical and heat pain for PLWH with chronic pain compared to PLWH without chronic pain and controls. CPM effects were present in controls, but not in either PLWH with or without chronic pain. Among PLWH with chronic pain, greater TS of mechanical pain was significantly associated with greater average clinical pain severity. Results of this study suggest that enhanced facilitation and diminished inhibition characterizes the pronociceptive endogenous pain modulatory balance of persons living with HIV and chronic pain.

What do you expect? Catastrophizing mediates associations between expectancies and pain-facilitatory processes.

BACKGROUND: Pain expectancies are associated with altered pain sensitivity in individuals with chronic pain. However, little is known about the processes by which pain expectancies impact pain processing. This study assessed the association between pain expectancies and temporal summation (TS) of pain, and examined whether pain catastrophizing mediated this association. METHODS: In this cross-sectional study, participants (437 chronic low back pain [CLBP] patients, 115 controls) completed self-report measures of pain intensity, pain expectancies and pain catastrophizing before undergoing psychophysical pain-testing procedures designed to assess mechanical TS of mechanical pain. Pearson's correlations examined the associations between study variables in CLBP patients and controls. Bootstrapping mediation analyses assessed the mediating role of pain catastrophizing on the association between pain expectancies and TS of pain. RESULTS: Temporal summation of pain was significantly associated with pain expectancies (r = 0.113) and pain catastrophizing (r = 0.171) in CLBP patients. Results of mediation analyses revealed that pain catastrophizing mediated the relationship between pain expectancies and TS of pain in CLBP patients (ab = 0.309, 95% CI = 0.1222-0.5604), but not in healthy controls (ab = -0.125, 95% CI = -0.5864 to 0.0244). CONCLUSIONS: The findings from this study suggest that compared to controls, CLBP patients show increased sensitivity to mechanical pain procedures and enhanced pain-facilitatory processing, proving further evidence for changes in central nervous system pain processing in CLBP patients. Our results also suggest that pain catastrophizing may be the mechanism by which pain expectancies are associated with TS of pain in CLBP patients. SIGNIFICANCE: Individuals with chronic low back pain who expect higher levels of pain and catastrophize about their pain are more likely to experience altered pain sensitivity. Our results point to catastrophizing as a mechanism of action through which psychological factors may operate and lead to the development and maintenance of chronic low back pain.

STarT Back Tool risk stratification is associated with changes in movement profile and sensory discrimination in low back pain: A study of 290 patients.

BACKGROUND: Investigation of movement and sensory profiles across STarT Back risk subgroups. METHODS: A chronic low back pain cohort (n = 290) were classified as low, medium or high risk using the STarT Back Tool, and completed a repeated spinal bending task and quantitative sensory testing. Pain summation, time taken and the number of protective behaviours with repeated bending were measured. Sensory tests included two-point discrimination, temporal summation, pressure/thermal pain thresholds and conditioned pain modulation. Subgroups were profiled against movement and sensory variables. RESULTS: The high-risk subgroup demonstrated greater pain summation following repeated forward bending (p < 0.001). The medium-risk subgroup demonstrated greater pain summation following repeated backward bending (p = 0.032). Medium- and high-risk subgroups demonstrated greater forward/backward bend time compared to the low-risk subgroup (p = 0.001, p = 0.005, respectively). Medium- and high-risk subgroups demonstrated a higher number of protective behaviours per forward bend compared to the low-risk subgroup (p = 0.008). For sensory variables, only two-point discrimination differed between subgroups, with medium- and high-risk subgroups demonstrating higher thresholds (p = 0.016). CONCLUSIONS: This study showed altered movement characteristics and sensory discrimination across SBT risk subgroups in people with CLBP. Membership of the high SBT risk subgroup was associated with greater pain and disability levels, greater pain summation following repeated bending, slower bending times, a greater number of protective behaviours during forward bending, and a higher TPD threshold. Treatment outcomes for higher risk SBT subgroups may be enhanced by interventions specifically targeting movement and sensory alterations. SIGNIFICANCE: In 290 people with chronic low back pain movement profile and two-point discrimination threshold differed across risk subgroups defined by the STarT Back Tool. Conversely, pain sensitivity did not differ across these subgroups. These findings may add further guidance for targeted care in these subgroups.