Research on myofascial temporomandibular disorder (mTMD) has often focused on potential dysfunction in endogenous pain modulation. However, studies on the specific inhibitory and facilitatory components of endogenous pain modulation using conditioned pain modulation (CPM) and temporal summation of second pain (TSSP) have shown mixed results. This study aimed to 1) examine whether women with mTMD demonstrated efficient CPM compared to controls; 2) explore the association between independent measures of CPM and TSSP in women with mTMD relative to controls; and 3) determine whether resulting modulatory profiles differentially predicted pain intensity among cases. All participants were recruited from dental clinics. Cases were women who met the research diagnostic criteria for mTMD. Controls did not have facial pain on exam and were selected to be sociodemographically similar to cases. CPM and TSSP were assessed via independent psychophysical protocols. CPM was examined in linear mixed models predicting pain thresholds adjusted for age and stratified by TSSP. Mean CPM was estimated at a 2.2 (SD = 2.8) degree increase in pain thresholds (P ≤ .001), similar in cases and controls (P = .67). CPM was less efficient in cases with enhanced TSSP (P = .031), but not in controls. Although the double-pronociceptive profile of both low CPM and high TSSP trended higher among cases than controls, it did not predict higher levels of pain intensity among cases. This study does not support deficient inhibitory endogenous pain modulation in mTMD, but results suggest that inhibitory and facilitatory pain modulation should be examined concomitantly in the study of endogenous pain modulation. PERSPECTIVE: This manuscript presents a novel examination of inhibitory modulation by the level of facilitatory modulation in mTMD. The findings and approach may prove useful for mechanistic researchers studying endogenous pain modulation and clinical researchers seeking to jointly examine conditioned pain modulation and temporal summation in future research on chronic pain.

C-tactile (CT) fibers, responsible for the so-called \"affective\" touch (AT), have drawn a fair amount of attention within the scientific community for their marked social dimension. However, while the pain-relieving potential of discriminative touch (DT) has been documented, proofs of the analgesic properties of AT are still scarce. Additionally, no study has so far tested its possible pain-relieving effects on a clinically-relevant model. Temporal summation of second pain (TSSP), otherwise referred to as \"wind-up,\" relies on repetitive stimulation of C-nociceptors and it is thought to reflect central sensitization, a process linked to many chronic pain conditions. In the present experimental, within participants, design we induced TSSP through trains of ascending and descending repetitive heat stimulation. Forty-two healthy participants\' pain was measured during 2 different tactile stimulations (stroking velocities AT: 10 cm/s; DT: 0.3 cm/s) or without concomitant tactile input. Since measures of pleasantness of the tactile stimulation have been found to strongly correlate with C-tactile fibers\' firing rate, these, together with participants\' body awareness, were also taken into account. Our results show that AT brought about a decrease of our participants\' pain as opposed to both DT and no touch, while DT did not produce any significant pain reduction. Thus, only AT successfully modulated wind-up. As expected, AT was perceived as more pleasant than DT, while a clear relationship between body awareness and pain was found only during DT. Targeting CT fibers could pave the way to new treatments for chronic pain conditions whose aetiology depend on abnormal C-nociceptors\' physiology. PERSPECTIVE: This study extends previous findings on the analgesic potential of affective touch, documenting a clear pain reduction during temporal summation of second pain (TSSP). Since TSSP is thought to reflect central sensitization, the psychophysiological mechanisms of affective touch could be exploited for new chronic pain treatments.

Quantitative sensory testing (QST) is used to systematically interrogate normal responding and alterations of nervous system function, including pain-related central sensitization (CS). However, up to now, QST of CS in human subjects has been mostly focused on temporal summation of second pain (TSSP), has been difficult to perform, and has been associated with low reliability. In contrast, slow ramp & hold (RH) procedures are simpler tests of temporal summation and easier to perform. We examined the usefulness of RH procedures as reliable generators of CS using 2 validated QST procedures: decay of pain aftersensations and wind-down. Twenty-seven pain-free subjects (74% female) were enrolled into the study. Trains of sensitivity-adjusted TSSP or RH heat stimuli were applied to the hands of participants to achieve moderate temporal pain summation (50 Numerical Rating Scale [NRS] [0-100]). Fifteen-second aftersensations and 30-second wind-down related to TSSP or RH were used for CS comparisons. Reliability of all test procedures was tested over 24 hours. Use of sensitivity-adjusted TSSP and RH heat stimuli resulted in average pain ratings of 48.2 and 49.6 NRS, respectively. Aftersensations or wind-down decay were not significantly different after either TSSP or RH, (all P > .05), indicating that each procedure achieved similar levels of short-term CS. Sensitivity-adjusted RH stimuli were well tolerated and resulted in reliable pain increases of ∼50 NRS. The magnitude of short-term CS, determined by aftersensations and wind-down was similar after sensitivity-adjusted TSSP and RH stimuli (P > .05), suggesting that pain facilitation of healthy participants and likely chronic pain patients can not only be tested with TSSP but also with RH procedures. PERSPECTIVE: This article examines the ability of RH procedures to generate similar central sensitivity augmentation than TSSP. The results suggest that RH is similarly well suited as TSSP to explore central pain mechanisms in healthy subjects and most likely also in chronic pain patients.

Individuals with greater borderline personality features may be vulnerable to chronic pain. Because pain is an unpleasant sensory and emotional experience, affect dysregulation as the core personality feature may be linked to pain hypersensitivity. Studies have found that greater borderline features are associated with increased intensity in clinical and experimental pain, and that depression mediates this increase. The current study further examined the association between borderline features and heat pain sensitivity, the contribution of affect dysregulation and the other borderline personality factors (identity problems, negative relationships, self-harming/impulsivity) to the association, and depression as a mediator. Additionally, we examined whether blunted sympathetic responses mediate the association between borderline features and temporal summation of second pain (TSSP). Thermal pain threshold, thermal TSSP and aftersensations pain were assessed in 79 healthy individuals with varying degrees of borderline features. TSSP is a proxy measure for central sensitization and refers to the gradual increase in pain to repeated nociceptive stimuli. A regression analysis showed that greater borderline features predicted greater TSSP (β = .22, p = .050, R2 = .05). Borderline features were unrelated to pain threshold and TSSP decay. A stepwise regression showed greater TSSP in individuals with greater borderline features was accounted for by the negative relationships factor rather than the affect dysregulation factor. The results of mediational analyses showed depression and blunted sympathetic skin conductance responses mediated the positive association between TSSP and borderline features.