Test–retest reliability of subjective supra-threshold scaling of multiple pressure-pain sensations among healthy individuals: a study using hydraulic pressure algometry

Abstract

Background: Supra-threshold scaling of multiple pressure-pain sensations involves delivery of varied stimulus intensities, either via stimulus-dependent or response-dependent manner, and recording of subjective pain ratings by participants. The focus of this study was to determine the intra- and inter-session reliability of pain intensity and pain unpleasantness ratings related to pressure-pain thresholds (PPTs) of just noticeable pain (JNP), weak pain (WP) and moderate pain (MP) among healthy individuals.

Methods: Fourteen healthy participants (eight women, six men) participated in three sessions of testing at varied intervals over the course of 72?h. In session one, a multiple random staircase method using hydraulic pressure algometry was used to measure PPT of JNP, WP and MP on thumbnail bed. In session 2, ratings of pain intensity and pain unpleasantness were recorded when stimuli at levels corresponding to PPT of JNP, WP and MP were repeatedly applied before and after 20?min of no intervention.

Results: Interclass correlation coefficient (ICC) values for pain ratings of JNP, WP and MP in intra-session reliability were 0.810, 0.826 and 0.881, respectively, whereas the values were 0.817, 0.792 and 0.910, respectively, for inter-session reliability. ICC values for pain unpleasantness were also highly consistent and repeatable. Temporal summation of pain intensity and pain unpleasantness were not related to the repeated application of pressure stimuli.

Conclusions: The findings indicate that the pain intensity and pain unpleasantness ratings for stimuli at levels equal to the thresholds of JNP, WP and MP have good intra- and inter-session reliability.

Significance: This study showed that both pain intensity and pain unpleasantness of JNP, WP and MP have good intra- and inter-session reliability and agreement. Furthermore, the temporal summation of pain or unpleasantness is not related to repeated application of pressure stimuli.

Abbreviations: JNP: Just noticeable pain; WP: Weak pain; MP: Moderate pain; PPTs: pressure-pain thresholds; HPA: Hydraulic pressure algometry; MRSM: multiple random staircase method     

Barrels IX-proceedings

The properties of a newly developed tonic heat pain model (THPM), which makes use of pulsating contact heat, were investigated in 18 young men. The most important feature of this model is that repetitive heat pulses with an intensity of 1°C above the individual pain threshold are employed. This approach was used to tailor the tonic pain stimulation to the individual pain sensitivity. In the first of two experiments, the effects of pulse frequencies ranging from 5 to 30 pulses per minute (ppm) on ratings of pain intensity and pain unpleasantness (visual analogue scales) were examined. At all frequencies, both ratings increased steadily over the 5-min test period. Frequencies of 15 ppm or more appeared to enhance pain intensity throughout the test period compared to the lower frequencies, but did not appear to alter pain unpleasantness. This suggests that only pain intensity is influenced by slow temporal summation and that a sort of frequency threshold exists for this kind of summation. In the second experiment, the THPM was compared to a well-established form of tonic pain stimulation, the compressor test (CPT); visual analogue scales were again used, and in addition the McGill Pain Questionnaire was employed. The CPT appeared to produce stronger tonic pain than the THPM. However, as is typical with tonic pain, both tonic pain models induced relatively higher values on the affective pain dimension than on the sensory pain dimension. The time course of pain was dynamic in the CPT, with an increase followed by a plateau phase, at least in those subjects who could tolerate the CPT for more than 60 sec. In contrast, as in the first experiment, the pain ratings in the THPM were characterized by a slow and steady increase over time. Moreover, there was absolutely no indication of a dichotomy between “pain-sensitive” and “pain-tolerant” individuals in the THPM, although such a dichotomy was evident in the CPT. This implies that the distinction between pain-sensitive and pain-tolerant individuals can be made only with the CPT, and that this distinction represents individual differences in peripheral vascular reactions to cold rather than in pain perception. In conclusion, the THPM appears to produce a stable and predictable temporal pattern of tonic pain with a predominant affective component, and to be suitable for application in the majority of individuals without causing undue discomfort.     

Electromagnetic effects on forearm disuse osteopenia: a randomized, double-blind, sham-controlled study

A randomized, double‐blind, sham‐controlled, feasibility and dosing study was undertaken to determine if a common pulsing electromagnetic field (PEMF) treatment could moderate the substantial osteopenia that occurs after forearm disuse. Ninety‐nine subjects were randomized into four groups after a distal radius fracture, or carpal surgery requiring immobilization in a cast. Active or identical sham PEMF transducers were worn on the distal forearm for 1, 2, or 4 h/day for 8 weeks starting after cast removal (“baseline”) when bone density continues to decline. Bone mineral density (BMD) and bone geometry were measured in the distal forearm by dual energy X‐ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT) at entry (“baseline”) and 8, 16, and 24 weeks later. Significant average BMD losses after baseline were observed in the affected forearm at all time points (5–7% distally and 3–4% for the radius/ulna shaft). However, after adjusting for age, gender, and baseline BMD there was no evidence of a positive effect of active versus sham PEMF treatment on bone loss by DXA or pQCT for subjects completing all visits (n = 82, ～20 per group) and for an intent‐to‐treat analysis (n = 99). Regardless of PEMF exposure, serum bone‐specific alkaline phosphatase (BSAP) was normal at baseline and 8 weeks, while serum c‐terminal collagen teleopeptide (CTX‐1) was markedly elevated at baseline and less so at 8 weeks. Although there was substantial variability in disuse osteopenia, these results suggested that the particular PEMF waveform and durations applied did not affect the continuing substantial disuse bone loss in these subjects. Bioelectromagnetics 32:273–282, 2011. © 2010 Wiley‐Liss, Inc.     

Responsibility and the sense of agency enhance empathy for pain

Being held responsible for our actions strongly determines our moral judgements and decisions. This study examined whether responsibility also influences our affective reaction to others'' emotions. We conducted two experiments in order to assess the effect of responsibility and of a sense of agency (the conscious feeling of controlling an action) on the empathic response to pain. In both experiments, participants were presented with video clips showing an actor''s facial expression of pain of varying intensity. The empathic response was assessed with behavioural (pain intensity estimation from facial expressions and unpleasantness for the observer ratings) and electrophysiological measures (facial electromyography). Experiment 1 showed enhanced empathic response (increased unpleasantness for the observer and facial electromyography responses) as participants'' degree of responsibility for the actor''s pain increased. This effect was mainly accounted for by the decisional component of responsibility (compared with the execution component). In addition, experiment 2 found that participants'' unpleasantness rating also increased when they had a sense of agency over the pain, while controlling for decision and execution processes. The findings suggest that increased empathy induced by responsibility and a sense of agency may play a role in regulating our moral conduct.     

Sex differences in nociceptive withdrawal reflex and pain perception

Experimentally induced pain often reveals sex differences, with higher pain sensitivity in females. The degree of differences has been shown to depend on the stimulation and assessment methods. Since sex differences in pain develop anywhere along the physiological and psychological components of the nociceptive system, we intended to compare the nociceptive flexion reflex (NFR) as a more physiological (spinal) aspect of pain procession to the verbal pain report of intensity and unpleasantness as the more psychological (cortical) aspect. Twenty female and twenty male healthy university students were investigated by use of nociceptive flexion reflex threshold (staircase method) after electrical stimulation of the N. suralis. Furthermore, we assessed supra-threshold reflex responses (latency, amplitude and area) by applying 10 stimuli 5 mA above reflex threshold. Following each stimulation, the subjects provided pain ratings of intensity and unpleasantness on a visual analogue scale. Females exhibited marked lower nociceptive flexion reflex thresholds than males, while the supra-threshold reflex response tailored to the individual reflex threshold did not show any significant differences. The verbal pain ratings, corrected for NFR threshold, were not found to differ significantly. The large sex differences in nociception that were present in NFR threshold but not in the pain ratings corroborate the hypothesis that spinal processes contribute substantially to sex differences in pain procession.     

Spatial summation of heat pain in males and females

Sex differences in pain sensitivity have been found to vary between considerable and negligible. It has appeared that the pain stimulation method is critical in this context. It was assumed this might be due to the different degrees of spatial summation associated with the different pain stimulus modalities. Hence, sex differences were investigated in spatial summation of heat pain in 20 healthy women and 20 healthy men of similar age. Pain thresholds were assessed by a tracking procedure and responses to supra-threshold pain stimulation by numerical ratings. Heat stimuli were administered by a thermode with contact areas of 1, 3, 6 and 10 cm2. Pain thresholds were significantly higher with smaller areas stimulated than with larger ones. No significant effect of area was found for the ratings of the supra-threshold stimuli, the intensities of which were tailored to the individual pain threshold. Consequently, spatial summation of heat pain appeared to result mainly in a shift of the pain threshold on the ordinate and not a change of slope of the stimulus-response function in the pain range. In neither of the two pain parameters were there any sex differences. Therefore, the present study demonstrated that sex differences in spatial summation of heat pain are unlikely.     

Comparison of hyperalgesia induced by capsaicin injection and controlled heat injury: effect on temporal summation

The relationship between induction of central sensitization and facilitation of temporal summation to repetitive stimulation is still unclear. The aim of this study was to investigate temporal summation before and after the induction of secondary hyperalgesia by two different experimental methods: capsaicin injection and controlled heat injury. The effect of each injury model was assessed on a separate day with an interval of at least 5 days. Twelve healthy volunteers participated. Each experiment was performed using electrical, radiant heat, mechanical impact, and punctuate stimuli consecutively. The pain threshold (PT) to a single stimulus and the summation threshold to five repetitive stimuli for electrical (2?Hz) and radiant heat (0.83?Hz) were assessed within the secondary hyperalgesic area. The degree of temporal summation for stimulus intensities of 0.8, 1.0, and 1.2 times the baseline pain thresholds were evaluated by the increase in visual analogue scale (VAS) scores from the first to the fifth stimulus of the train. Further, the degrees of temporal summation were assessed for mechanical impact and punctuate stimuli within the primary and secondary hyperalgesic areas. The contra-lateral forearm served as control (no injury). The pain threshold and the summation threshold to electrical and heat stimuli decreased significantly within the secondary hyperalgesic area after the injury induced by both heat injury or capsaicin injection. However, there was no temporal summation for heat and electrical stimuli in either model. In contrast, for the mechanical impact and punctuate mechanical stimuli the degree of temporal summation was significantly facilitated in the secondary hyperalgesic areas compared with the baseline and the control arm in both models. In the primary hyperalgesic area, the degree of temporal summation was facilitated to mechanical impact and punctuate stimuli but only following the capsaicin injection. In conclusion, the temporal summation mechanism for mechanical stimuli was facilitated in the secondary hyperalgesic area.     

A Psychophysical Comparison of Sensory and Affective Responses to Four Modalities of Experimental Pain

It is generally accepted that the sensory and affective components of pain may be differentially associated with various acute and chronic diseases, and that some treatment regimens are best directed toward certain aspects of the pain experience. In addition, experimental animal models have been described that presume to assess either the sensory-discriminative aspects of phasic pain or the affective responses associated with tonic pain. The present psychophysical experiment directly compares the perceived intensity and unpleasantness of sensations evoked by four types of experimental noxious stimuli: contact heat, electric shock, ischemic exercise, and cold-pressor pain. A novel pain measurement technique is described that incorporates unbounded magnitude-estimation/category scales; this technique allows precise ratio responses, while minimizing within- and between- subject variability. We observe that, relative to the perceived intensity of the individual stimuli, subjects consistently differentiate among the degrees of unpleasantness evoked by the four stimulus modalities. Ischemic exercise and cold-pressor pain evoke higher estimates of unpleasantness, and thus may better mimic the pain of chronic disease. The relative unpleasantness produced by contact heat is significantly less than that of the other modalities tested, and therefore contact heat stimuli may be ideally suited for assessing sensory-discriminative aspects of pain perception. Possible neurophysiological mechanisms underlying the observed differences in perceived unpleasantness are discussed in relation to the growing body of literature concerning tonic and phasic pain stimuli.     

Modulation of oral heat and cold pain by irritant chemicals

Common food irritants elicit oral heat or cool sensations via actions at thermosensitive transient receptor potential (TRP) channels. We used a half-tongue, 2-alternative forced-choice procedure coupled with bilateral pain intensity ratings to investigate irritant effects on heat and cold pain. The method was validated in a bilateral thermal difference detection task. Capsaicin, mustard oil, and cinnamaldehyde enhanced lingual heat pain elicited by a 49 degrees C stimulus. Mustard oil and cinnamaldehyde weakly enhanced lingual cold pain (9.5 degrees C), whereas capsaicin had no effect. Menthol significantly enhanced cold pain and weakly reduced heat pain. To address if capsaicin's effect was due to summation of perceptually similar thermal and chemical sensations, one-half of the tongue was desensitized by application of capsaicin. Upon reapplication, capsaicin elicited little or no irritant sensation yet still significantly enhanced heat pain on the capsaicin-treated side, ruling out summation. In a third experiment, capsaicin significantly enhanced pain ratings to graded heat stimuli (47 degrees C to 50 degrees C) resulting in an upward shift of the stimulus-response function. Menthol may induce cold hyperalgesia via enhanced thermal gating of TRPM8 in peripheral fibers. Capsaicin, mustard oil, and cinnamaldehyde may induce heat hyperalgesia via enhanced thermal gating of TRPV1 that is coexpressed with TRPA1 in peripheral nociceptors.     

Low frequency therapeutic EMF differently influences experimental muscle pain in female and male subjects

Effects of a pulsating, half sine wave magnetic field (MF) with a frequency of 100 pps and 15 mT rms flux density, generated by the MD TEMF device (EMF Therapeutics, Inc., Chattanooga), on subjective pain rating, heart rate, and arterial blood pressure were tested in a double blind, crossover design study employing experimental muscle pain. Each of 24 healthy volunteers (12 females and 12 males, 24.7 +/- 3.2 years of age) received painful stimulation induced by the infusion of 5% hypertonic saline (HS) into the erector spinae muscle during real and sham MF exposure, in counterbalanced order. Exposure to MF differently affects subjective pain estimates in females and males. MF exposure increased averaged pain level and time integral of pain ratings in females, whereas no statistically significant difference for these characteristics was found in males. Pain related elevation of systolic and diastolic blood pressure was observed during both real and sham EMF exposure in female and male subjects.     

Does Anthropomorphism of Dogs Affect Pain Perception in Animal-Assisted Interventions? An Exploratory Study

The purpose of this exploratory study was to determine the effects of anthropomorphism of a therapy dog on pain perception during an animal-assisted intervention. Participants were 32 college women who were randomly assigned to the anthropomorphism condition or the control condition. All participants engaged in a pretest cold pressor task to measure base-line individual differences in pain tolerance and perceptions of pain intensity and pain unpleasantness. After completing this task, participants in the anthropomorphism group engaged in a task intended to prime them to view a therapy dog anthropomorphically. Specifically, they rated photos of dogs on a series of humanlike traits (e.g., “this dog would be a good listener”). Participants in the control condition rated photos of dogs on a series of canine traits (e.g., “this dog would make a good watchdog”). After this experimental manipulation, participants engaged in a second cold pressor task in the presence of a therapy dog and the therapy dog handler. We hypothesized that participants in the anthropomorphism group would demonstrate greater pain tolerance and report lower levels of pain intensity and pain unpleasantness during the second cold pressor task than participants in the control group. Results provide partial support for these hypotheses. Participants in the anthropomorphism group reported lower posttest pain intensity than participants in the control group. In addition, they demonstrated greater posttest pain tolerance than participants in the control group—but only under conditions of medium or high pretest pain tolerance. The two groups did not differ with respect to posttest pain unpleasantness. The results of this exploratory study provide preliminary evidence that prompting individuals to view a therapy dog anthropomorphically may augment their experience of pain relief from a therapy dog visit.     

Thermosensory intensity and affect throughout the perceptible range

The thermosensory system was evaluated psychophysically in 12 healthy volunteers, spanning the full range of tolerable temperatures. Subjects provided ratings of (1) perceived thermal intensity, (2) perceived pleasantness or unpleasantness, and (3) perceived pain intensity after placing either one hand or foot in a temperature controlled water bath. Of particular interest were the interrelationships among the three perceptual measures, and differences between heat and cold. The relationship between perceived intensity and (un)pleasantness was different for hot vs cold stimuli. Specifically, for a given perceived thermal intensity, cold stimuli were rated as less pleasant or more unpleasant than hot stimuli. Similarly, for a given pain intensity, cold stimuli were rated as more unpleasant than hot stimuli. As warm temperatures increased and as cold temperatures decreased, stimuli were perceived as being unpleasant before they were perceived as being painful. The difference in transition temperatures for unpleasantness vs pain for heat averaged 1.4 degrees C, while the same difference for cold averaged 5.6 degrees C. Thus, there was a fourfold difference in the range of unpleasant but non-painful cold vs hot temperatures. Pain intensity and unpleasantness ratings were significantly higher for heat stimuli applied to the foot vs hand. In contrast, there was no significant body site difference for pain intensity or unpleasantness ratings of cold stimuli. All of these results reveal important differences in the processing of cold vs hot stimuli. These differences could be exploited to differentiate processing relevant to discriminative vs affective components of somesthetic perception, in both the innocuous and noxious ranges.     

A Novel Magnetic Stimulator Increases Experimental Pain Tolerance in Healthy Volunteers - A Double-Blind Sham-Controlled Crossover Study

The ‘complex neural pulse’^TM (CNP) is a neuromodulation protocol employing weak pulsed electromagnetic fields (PEMF). A pioneering paper reported an analgesic effect in healthy humans after 30 minutes of CNP-stimulation using three nested whole head coils. We aimed to devise and validate a stimulator with a novel design entailing a multitude of small coils at known anatomical positions on a head cap, to improve applicability. The main hypothesis was that CNP delivery with this novel device would also increase heat pain thresholds. Twenty healthy volunteers were enrolled in this double-blind, sham-controlled, crossover study. Thirty minutes of PEMF (CNP) or sham was applied to the head. After one week the other treatment was given. Before and after each treatment, primary and secondary outcomes were measured. Primary outcome was heat pain threshold (HPT) measured with thermal quantitative sensory testing. Other outcomes were warmth detection threshold, and aspects of cognition, emotion and motor performance. As hypothesized heat pain threshold was significantly increased after the PEMF stimulation. All other outcomes were unaltered by the PEMF but there was a trend level reduction of cognitive performance after PEMF stimulation as measured by the digit-symbol substitution task. Results from this pilot study suggest that our device is able to stimulate the brain and to modulate its function. This is in agreement with previous studies that used similar magnetic field strengths to stimulate the brain. Specifically, pain control may be achieved with PEMF and for this analgesic effect, coil design does not appear to play a dominant role. In addition, the flexible configuration with small coils on a head cap improves clinical applicability.

Trial Registration

Dutch Cochrane Centre NTR1093     

Horizontal Body Position Reduces Cortical Pain-Related Processing: Evidence from Late ERPs

The present study investigated the influence of short-term horizontal body position on pain-related somatosensory processing, by measuring subjective and cortical responses to electrical pain stimulation. Twenty-eight healthy women were randomly assigned to either the experimental horizontal group (Bed Rest, BR) or to the sitting control group (Sitting Control, SC). After 90 minutes in either horizontal or sitting position, the individual pain thresholds were assessed and EEG/self-evaluations recorded during the administration of 180 stimuli delivered to the left forearm. Electrical pain stimuli, calibrated to subjects’ individual pain thresholds, consisted of two different intensity levels: no pain (40% below pain threshold) and pain (40% above pain threshold). Compared with control, BR condition significantly inhibited subjective sensitivity to painless stimuli, whereas electrophysiological results pointed to a reduced slow cortical wave (interval: 300-600 ms) at all stimulus intensities, and smaller amplitude in BR’s right vs. left prefrontal sites. sLORETA analysis revealed that cortical responses were associated with a decreased activation of superior frontal gyrus and anterior cingulate cortex (BA 6/24). Interestingly, BR group only showed significant negative correlations between self-evaluation of painful intensities and frontal cortical negativity, revealing increasingly differentiated responses in bed rest: indeed those BR participants who reported lower pain ratings, displayed reduced negativity within anterior regions. Taken together, results indicate that short-term horizontal position is able to inhibit a fronto-parietal pain network, particularly at the level of central prefrontal regions typically involved in cognitive, affective and motor aspects of pain processing.     

Comparison of hyperalgesia induced by capsaicin injection and controlled heat injury: effect on temporal summation

The relationship between induction of central sensitization and facilitation of temporal summation to repetitive stimulation is still unclear. The aim of this study was to investigate temporal summation before and after the induction of secondary hyperalgesia by two different experimental methods: capsaicin injection and controlled heat injury. The effect of each injury model was assessed on a separate day with an interval of at least 5 days. Twelve healthy volunteers participated. Each experiment was performed using electrical, radiant heat, mechanical impact, and punctuate stimuli consecutively. The pain threshold (PT) to a single stimulus and the summation threshold to five repetitive stimuli for electrical (2 Hz) and radiant heat (0.83 Hz) were assessed within the secondary hyperalgesic area. The degree of temporal summation for stimulus intensities of 0.8, 1.0, and 1.2 times the baseline pain thresholds were evaluated by the increase in visual analogue scale (VAS) scores from the first to the fifth stimulus of the train. Further, the degrees of temporal summation were assessed for mechanical impact and punctuate stimuli within the primary and secondary hyperalgesic areas. The contra-lateral forearm served as control (no injury). The pain threshold and the summation threshold to electrical and heat stimuli decreased significantly within the secondary hyperalgesic area after the injury induced by both heat injury or capsaicin injection. However, there was no temporal summation for heat and electrical stimuli in either model. In contrast, for the mechanical impact and punctuate mechanical stimuli the degree of temporal summation was significantly facilitated in the secondary hyperalgesic areas compared with the baseline and the control arm in both models. In the primary hyperalgesic area, the degree of temporal summation was facilitated to mechanical impact and punctuate stimuli but only following the capsaicin injection. In conclusion, the temporal summation mechanism for mechanical stimuli was facilitated in the secondary hyperalgesic area.     

Utilizing Repetitive Transcranial Magnetic Stimulation to Improve Language Function in Stroke Patients with Chronic Non-fluent Aphasia

Transcranial magnetic stimulation (TMS) has been shown to significantly improve language function in patients with non-fluent aphasia¹. In this experiment, we demonstrate the administration of low-frequency repetitive TMS (rTMS) to an optimal stimulation site in the right hemisphere in patients with chronic non-fluent aphasia. A battery of standardized language measures is administered in order to assess baseline performance. Patients are subsequently randomized to either receive real rTMS or initial sham stimulation. Patients in the real stimulation undergo a site-finding phase, comprised of a series of six rTMS sessions administered over five days; stimulation is delivered to a different site in the right frontal lobe during each of these sessions. Each site-finding session consists of 600 pulses of 1 Hz rTMS, preceded and followed by a picture-naming task. By comparing the degree of transient change in naming ability elicited by stimulation of candidate sites, we are able to locate the area of optimal response for each individual patient. We then administer rTMS to this site during the treatment phase. During treatment, patients undergo a total of ten days of stimulation over the span of two weeks; each session is comprised of 20 min of 1 Hz rTMS delivered at 90% resting motor threshold. Stimulation is paired with an fMRI-naming task on the first and last days of treatment. After the treatment phase is complete, the language battery obtained at baseline is repeated two and six months following stimulation in order to identify rTMS-induced changes in performance. The fMRI-naming task is also repeated two and six months following treatment. Patients who are randomized to the sham arm of the study undergo sham site-finding, sham treatment, fMRI-naming studies, and repeat language testing two months after completing sham treatment. Sham patients then cross over into the real stimulation arm, completing real site-finding, real treatment, fMRI, and two- and six-month post-stimulation language testing.     

Effectiveness of Pulsed Electromagnetic Fields on Bone Healing: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

The effect of pulsed electromagnetic field (PEMF) on bone healing is still uncertain and it has not been established as a standardized treatment. The aim of this systematic review and meta-analysis is to evaluate the effect of PEMF on bone healing in patients with fracture. We searched CNKI, Wan Fang, VIP, EMbase, PubMed, CENTRAL, Web of Science, Physiotherapy Evidence Database, and Open Grey websites for randomized controlled trials (published before July 2019 in English or Chinese) comparing any form of PEMF to sham. Reference lists were also searched. Related data were extracted by two investigators independently. The bias risk of the articles and the evidence strength of the outcomes were evaluated. Twenty-two studies were eligible and included in our analysis (n = 1,468 participants). The pooled results of 14 studies (n = 1,131 participants) demonstrated that healing rate in PEMF group was 79.7% (443/556), and that in the control group was 64.3% (370/575). PEMF increased healing rate (RR = 1.22; 95% confidence interval [CI] = 1.10–1.35; I² = 48%) by the Mantel–Haenszel analysis, relieved pain (standardized mean difference (SMD) = −0.49; 95% CI = −0.88 to −0.10; I² = 60%) by the inverse variance analysis, and accelerated healing time (SMD = −1.01; 95% CI = −2.01 to −0.00; I² = 90%) by the inverse variance analysis. Moderate quality evidence suggested that PEMF increased healing rate and relieved pain of fracture, and very low-quality evidence showed that PEMF accelerated healing time. Larger and higher quality randomized controlled trials and pre-clinical studies of optimal frequency, amplitude, and duration parameters are needed. © 2020 Bioelectromagnetics Society.     

Responses to tonic heat pain in the ongoing EEG under conditions of controlled attention

To confirm the existence of an ongoing electroencephalogram (EEG) pattern that is truly suggestive of pain, tonic heat pain was induced by small heat pulses at 1?°C above the pain threshold and compared to slightly less intense tonic non-painful heat pulses at 1?°C below the pain threshold. Twenty healthy subjects rated the sensation intensity during thermal stimulation. Possible confounding effects of attention were thoroughly controlled for by testing in four conditions: (1) focus of attention directed ipsilateral or (2) contralateral to the side of the stimulation, (3) control without a side preference, and (4) no control of attention at all. EEG was recorded via eight leads according to the 10/20 convention. Absolute power was computed for the frequency bands delta (0.5–4?Hz), theta (4–8?Hz), alpha1 (8–11?Hz), alpha2 (11–14?Hz), beta1 (14–25?Hz), and beta2 (25–35?Hz). Ratings were clearly distinct between the heat and pain conditions and suggestive for heat and pain sensations. Manipulation of attention proved to be successful by producing effects on the ratings and on the EEG activity (with lower ratings and lower EEG activity (theta, beta1, 2) over central areas for side-focused attention). During pain stimulation, lower central alpha1 and alpha2 activity and higher right-parietal and right-occipital delta power were observed compared to heat stimulation. This EEG pattern was not influenced by the manipulation of attention. Since the two types of stimuli (pain, heat) were subjectively felt differently although stimulation intensities were nearby, we conclude that this EEG pattern is clearly suggestive of pain.     

Double-Cone Coil TMS Stimulation of the Medial Cortex Inhibits Central Pain Habituation

Objective

The aim of this study was to investigate whether Transcranial Magnetic Stimulation (TMS) applied over the medial line of the scalp affects the subjective perception of continuous pain induced by means of electric stimulation. In addition, we wanted to identify the point of stimulation where this effect was maximum.

Methods

Superficial electrical stimulation was used to induce continuous pain on the dominant hand. At the beginning of the experiment we reached a pain rating of 5 on an 11-point numeric rating scale (NRS; 0 = no pain and 10 = maximum tolerable pain) for each subject by setting individually the current intensity. The TMS (five pulses at increasing intensities) was applied on 5 equidistant points (one per session) over the medial line of the scalp in 13 healthy volunteers using a double-cone coil to stimulate underlying parts of the brain cortex. In every experimental session the painful stimulation lasted 45 minutes, during which pain and distress intensities NRS were recorded continuously. We calculated the effect of adaptation and the immediate effect of the TMS stimulation for all locations. Additionally, an ALE (Activation Likelihood Estimation) meta-analysis was performed to compare our results with the neuroimaging literature on subjective pain rating.

Results

TMS stimulation temporarily decreased the pain ratings, and pain adaptation was suppressed when applying the TMS over the FCz site on the scalp. No effect was found for distress ratings.

Conclusions

The present data suggest that the medial cortex in proximity of the cingulated gyrus has a causal role in adaptation mechanisms and in processing ongoing pain and subjective sensation of pain intensity.     

Effect of eccentric strength testing on delayed-onset muscle pain

This investigation was designed to determine the effect of eccentric strength testing on delayed-onset muscle pain in 20 untrained university students. Initially, eccentric strength testing (5-repetition maximum [5RM]) was performed bilaterally. Next, 1 arm completed 3 sets of 10 eccentric repetitions to induce delayed-onset muscle pain. Then, in a subsequent session, whichever arm previously performed only the 5RM test completed the 5RM test a second time and the 3 sets of 10 eccentric repetitions. Statistical analyses supported significantly increased pain intensity and unpleasantness across 48 hours post-5RM test alone. However, pain intensity and unpleasantness after the eccentric training bouts were significantly lower in the arm that performed 2 5RM tests than the arm that performed only 1. Thus, the eccentric strength testing produced delayed-onset muscle pain and protected against future delayed-onset muscle pain. These effects should be considered when such testing is used in baseline strength assessments.