Pain Threshold In Healthy Subjects Research Articles

Simultaneous measurement of intra-epidermal electric detection thresholds and evoked potentials for observation of nociceptive processing following sleep deprivation

Sleep deprivation has been shown to increase pain intensity and decrease pain thresholds in healthy subjects. In chronic pain patients, sleep impairment often worsens the perceived pain intensity. This increased pain perception is the result of altered nociceptive processing. We recently developed a method to quantify and monitor altered nociceptive processing by simultaneous tracking of psychophysical detection thresholds and recording of evoked cortical potentials during intra-epidermal electric stimulation. In this study, we assessed the sensitivity of nociceptive detection thresholds and evoked potentials to altered nociceptive processing after sleep deprivation in an exploratory study with 24 healthy male and 24 healthy female subjects. In each subject, we tracked nociceptive detection thresholds and recorded central evoked potentials in response to 180 single- and 180 double-pulse intra-epidermal electric stimuli. Results showed that the detection thresholds for single- and double-pulse stimuli and the average central evoked potential for single-pulse stimuli were significantly decreased after sleep deprivation. When analyzed separated by sex, these effects were only significant in the male population. Multivariate analysis showed that the decrease of central evoked potential was associated with a decrease of task-related evoked activity. Measurement repetition led to a decrease of the detection threshold to double-pulse stimuli in the mixed and the female population, but did not significantly affect any other outcome measures. These results suggest that simultaneous tracking of psychophysical detection thresholds and evoked potentials is a useful method to observe altered nociceptive processing after sleep deprivation, but is also sensitive to sex differences and measurement repetition.

Exercise-induced pain threshold modulation in healthy subjects: a systematic review and meta-analysis.

The use of exercise is a potential treatment option to modulate pain (exercise-induced hypoalgesia). The pain threshold (PT) response is a measure of pain sensitivity that may be a useful marker to assess the effect of physical exercise on pain modulation. The aim of this systematic review and meta-analysis is to evaluate the PT response to exercise in healthy subjects. We searched in MEDLINE, EMBASE, Web of Science, Lilacs, and Scopus using a search strategy with the following search terms: "exercise" OR "physical activity" AND "Pain Threshold" from inception to December 2nd, 2019. As criteria for inclusion of appropriate studies: randomized controlled trials or quasi-experimental studies that enrolled healthy subjects; performed an exercise intervention; assessed PT. Hedge's effect sizes of PT response and their 95% confidence intervals were calculated, and random-effects meta-analyses were performed. For the final analysis, thirty-six studies were included (n=1326). From this we found a significant and homogenous increase in PT in healthy subjects (ES=0.19, 95% CI= 0.11 to 0.27, I2=7.5%). According to subgroup analysis the effect was higher in studies: with women (ES=0.36); performing strength exercise (ES=0.34), and with moderate intensity (ES=0.27), and no differences by age were found. Confirmed by the meta-regression analysis. This meta-analysis provides evidence of small to moderate effects of exercise on PT in healthy subjects, being even higher for moderate strength exercise and in women. These results support the idea of modulation of the endogenous pain system due to exercise and highlight the need of clinical translation to chronic pain population.

Imagined and Actual Acupuncture Effects on Chronic Low Back Pain: A Preliminary Study.

Background Research suggests that imagined experiences can produce brain responses similar to those produced by actual experiences. Shared brain responses that support both imagination and perception may underlie the functional nature of mental imagery. In a previous study, we combined acupuncture and imagery to develop a new treatment method, video-guided acupuncture imagery treatment (VGAIT). We found that VGAIT significantly increased pain thresholds in healthy subjects. The aim of this study is to extend our previous finding by investigating whether VGAIT can relieve symptoms in patients with chronic low back pain. Methods We first performed a single-arm study in which we administered video-guided acupuncture imagery treatment (VGAIT) on patients with chronic low back pain (cLBP) (Study 1, n = 18, 12 females). We then compared our findings to those from a recently published study in which real or sham acupuncture treatment was applied on patients with cLBP (Study 2, n = 50, 31 females) using a similar protocol. All patients in Studies 1 and 2 received 6 treatments over 4 weeks. Results All three treatments (VGAIT, real, and sham acupuncture) significantly reduced pain severity as measured by a low back pain bothersomeness score. VGAIT produced similar effects to real acupuncture (p = 0.97) and nonsignificantly greater pain bothersomeness relief compared to sham acupuncture (p = 0.14). Additional analysis showed that there was no significant difference on the sensations evoked by different treatment modalities. Conclusion These findings support VGAIT as a promising method for pain management.

Noninvasive motor cortex stimulation effects on quantitative sensory testing in healthy and chronic pain subjects: a systematic review and meta-analysis.

One of the potential mechanisms of motor cortex stimulation by noninvasive brain stimulation (NIBS) effects on pain is through the restoration of the defective endogenous inhibitory pain pathways. However, there are still limited data on quantitative sensory testing (QST), including conditioned pain modulation (CPM), supporting this mechanism. This systematic review and meta-analysis aimed to evaluate the effects of noninvasive motor cortex stimulation on pain perception as indexed by changes in QST outcomes. Database searches were conducted until July 2019 to include randomized controlled trials that performed sham-controlled NIBS on the motor cortex in either the healthy and/or pain population and assessed the QST and CPM. Quality of studies was assessed through the Cochrane tool. We calculated the Hedge's effect sizes of QST and CPM outcomes and their 95% confidence intervals (95% CIs) and performed random-effects meta-analyses. Thirty-eight studies were included (1178 participants). We found significant increases of pain threshold in healthy subjects (ES = 0.16, 95% CI = 0.02-0.31, I2 = 22.2%) and pain populations (ES = 0.48, 95% CI = 0.15-0.80, I2 = 68.8%), and homogeneous higher CPM effect (pain ratings reduction) in healthy subjects (ES = -0.39, 95% CI = -0.64 to -0.14, I2 = 17%) and pain populations (ES = -0.35, 95% CI = -0.60 to -0.11, I2 = 0%) in the active NIBS group compared with sham. These results support the idea of top-down modulation of endogenous pain pathways by motor cortex stimulation as one of the main mechanisms of pain reduction assessed by QST, which could be a useful predictive and prognostic biomarker for chronic pain personalized treatment with NIBS.

Challenging the challenge: A randomized controlled trial evaluating the inflammatory response and pain perception of healthy volunteers after single-dose LPS administration, as a potential model for inflammatory pain in early-phase drug development

Background and aimsFollowing an infection, cytokines not only regulate the acute immune response, but also contribute to symptoms such as inflammatory hyperalgesia. We aimed to characterize the acute inflammatory response induced by a human endotoxemia model, and its effect on pain perception using evoked pain tests in two different dose levels. We also attempted to determine whether combining a human endotoxemia challenge with measurement of pain thresholds in healthy subjects could serve as a model to study drug effects on inflammatory pain. Methods and resultsThis was a placebo-controlled, randomized, cross-over study in 24 healthy males. Twelve subjects were administered a bolus of 1 ng/kg LPS intravenously, and twelve 2 ng/kg LPS. Before days of placebo/LPS administration, subjects completed a full study day without study drug administration, but with identical pain threshold testing. Blood sampling and evoked pain tests (electrical burst and -stair, heat, pressure, and cold pressor test) were performed pre-dose and at frequent intervals up to 10hr post-dose. Data were analysed with a repeated-measures ANCOVA. For both dose levels, LPS induced an evident acute inflammatory response, but did not significantly affect any of the pain modalities. In a post-hoc analysis, lowering of pain thresholds was observed in the first 3 h after dosing, corresponding with the peak of the acute inflammatory response around 1–3 h post-dose. ConclusionMild acute systemic inflammation, as induced by 1 ng/kg and 2 ng/kg LPS intravenous administration, did not significantly change pain thresholds in this study. The endotoxemia model in combination with evoked pain tests is not suitable to study acute inflammatory hyperalgesia in healthy males.

Changes of sensory and pain thresholds in healthy subjects after mandibular extension at maximum mouth opening: implications for temporomandibular disorders therapy.

There is evidence showing that increasing the vertical dimension of occlusion, or interocclusal distance, reduces pain symptoms in patients with temporomandibular disorders (TMD) and bruxism. The mechanism underlying the analgesic effect is still under investigation. Some researchers propose either a gate mechanism or the activation of the trigemino-cardiac reflex. In this study, sensory and pain thresholds changes in the mandibular district have been evaluated in twenty healthy subjects immediately after 5 minutes of mandibular stretching at maximum opening of the jaw. Results showed a 60% increment in sensory threshold and a 70% increment in pain threshold (p<0.001) compared with the baseline values. The magnitude of the analgesic effect seems proportional to the extent of mandibular opening. These and similar results are discussed as for the implication in the treatment of TMD related symptoms.

Analysis on the distribution of pressure- and heat-sensitive acupoints in patients with allergic rhinitis

To explore the distribution of pressure- and heat-sensitive acupoints of the Large Intestine of Hand-Yangming, Stomach Meridian of Foot-Yangming and the Lung Meridian of Hand-Taiyin below the elbow and knee joints in patients with allergic rhinitis, so as to explore the positive reaction points at the body surface of allergic rhinitis. Thirty variant rhinitis volunteer subjects and 30 healthy subjects were recruited in the present study. The subcutaneous induration, reaction points of emptiness-like feeling or pressing pain below the elbow- and knee-joints along the Large Intestine Meridian, Stomach Meridian and the Lung Meridian were inspected first, then re-examined by using heat-sensitized moxibustion method and a hand-held pain threshold tester (mechanical pressure), respectively. The frequency and coincidence rate of pressing-pain sensitive and heat-sensitive points were analyzed. In the 30 patients with allergic rhinitis, 10 positive reaction points as Kongzui (LU6), Chize (LU5), Hegu (LI4), Quchi (LI11), Shousanli(LI10), Zusanli (ST36), Shangjuxu (ST37), Fenglong (ST40), Xiajuxu (ST39), and non-acupoint of the Lung Meridian were found. Among them, the duration of heat-sensitive reaction in the LU6, LI10, ST37, ST40, and ST39 regions was obviously shorter in patients than in healthy subjects (P<0.01,P<0.005). The heat-sensitive forms of the positive reaction points were mainly heat transmission, heat-penetration and local reaction. The mechanical pain thresholds of the positive reaction points (LI4, LU6, LI10, LI11 and non-acupoint of the Lung Meridian) at the upper limbs and those (ST36, ST37 and ST40) at the lower limbs were evidently lower in patients than in healthy volunteer subjects (P<0.05). The pressure- and heat-sensitive acupoints were basically coincide in the patients, but being higher in patients than in healthy subjects in the frequency of occurrence. The mechanical pain threshold of the pressure-sensitive acupoints in patients was remarkably lower on the left side than on the right side of the upper limb, and obviously higher on the left side than on the right side of the lower limb (P<0.05). No significant differences were found between the right and left sides in the pain threshold in healthy subjects (P>0.05). There is a high overlap in the distribution of pressure- and heat-sensitive acupoints of the Lung, Large Intestine and Stomach meridians below the elbow and knee joints in patients with allergic rhinitis, and there is an imbalance between the left and right limbs in the mechanical pain threshold of the pressure- and heat-sensitive acupoints, but needing being further confirmed.

Decreasing Pain Ratings in Chronic Arm Pain Through Changing a Virtual Body: Different Strategies for Different Pain Types

Modifying the visual aspect of a virtual arm that is felt as one's own using immersive virtual reality (VR) modifies pain threshold in healthy subjects, but does it modify pain ratings in chronic pain patients? Our aim was to investigate whether varying properties of a virtual arm co-located with the real arm modulated pain ratings in patients with chronic arm/hand pain because of complex regional pain syndrome (CRPS) type I (without nerve injury) or peripheral nerve injury (PNI). CRPS (n = 9) and PNI (n = 10) patients were immersed in VR and the virtual arm was shown at 4 transparency levels (transparency test) and 3 sizes (size test). We evaluated pain ratings throughout the conditions and assessed the virtual experience, finding that patients with chronic pain can achieve levels of ownership and agency over a virtual arm similar to healthy participants. All 7 conditions globally decreased pain ratings by half. Increasing transparency decreased pain in CRPS but did the opposite in PNI, whereas increasing size slightly increased pain ratings only in CRPS. We conclude that embodiment in VR can decrease pain ratings in chronic arm pain, although the type of pain determines which strategy to decrease pain is most useful. We discuss this through the interactions between body image and pain perception. Perspective“Embodiment” in VR is useful to decrease pain ratings in chronic pain patients, but the best strategy needs to be tuned to the pain etiology. This approach could potentially help patients with chronic pain and clinicians who seek alternatives to pain management for patients.

The acute effect of Bowen therapy on pressure pain thresholds and postural sway in healthy subjects

ObjectiveThe purpose of the study is to determine the immediate effect of Bowen Therapy in pressure pain threshold and postural sway of healthy individuals. DesignCrossover, randomized, and double blinded study. SettingUniversity. ParticipantsParticipants aged 18 years old or over, naïve to Bowen therapy were recruited among university students. An a priori sample size calculation determined that 34 participants were needed. MethodsEach participant attended two sessions and received Bowen Therapy and a sham procedure. The order in which Bowen or the sham procedure were administered was randomized. All participants had their postural control and pressure pain thresholds assessed in sessions 1 and 2 both at baseline and at the end of the session. Main outcome measurementsPostural control was assessed using a force plate and centre of pressure antero-posterior and medio-lateral displacement, velocity and total sway area were calculated. Pressure pain threshold was measured at 10 different body sites on the paraspinal muscles from C1 to S1 using an electronic algometer. ResultThe results showed a significant increase in the anteroposterior displacement (p = 0.04) and a significantly lower decrease in the mean velocity (p = 0.01) of the centre of pressure and a significant increase in the pressure pain thresholds of two (out of ten; p ≤ 0.04) body sites in the group receiving Bowen Therapy compared to the group receiving the sham. No other significant differences were found. ConclusionsThe findings suggest that Bowen Therapy has inconsistent immediate effects on postural control and pain threshold in healthy subjects. Further studies are needed using symptomatic participants.

The influence of electrode placement of Transcutaneous electrical nerve stimulation (TENS) and trait anxiety on pressure pain threshold in healthy subjects―ipsilateral or bilateral stimulation―

The influence of electrode placement of Transcutaneous electrical nerve stimulation (TENS) and trait anxiety on pressure pain threshold in healthy subjects―ipsilateral or bilateral stimulation―

Effects of two different intensities of transcutaneous electrical nerve stimulation on pain thresholds of contralateral muscles in healthy subjects.

[Purpose] This study aimed to investigate the differential effects of high-intensity and low-intensity transcutaneous electrical nerve stimulation on the contralateral side on the pain threshold in healthy subjects. [Subjects and Methods] Twenty-five healthy adults, volunteers received two intensity levels (motor-level, 1.5 times the muscle motor threshold; sensory-level, sensory threshold of the common peroneal nerve), for 30 s on separate days. Pressure pain threshold was recorded on the contralateral tibialis anterior and deltoid muscle before, during, and after stimulation. [Results] Motor-level stimulation significantly increased the pressure pain threshold at both muscle sites, while effects of sensory-level stimulation on pressure pain thresholds were significant only at the deltoid site. The percent change in pressure pain thresholds at both sites was significantly higher during motor-level stimulation. [Conclusion] Motor-level stimulation, applied unilaterally to one leg, produced immediate contralateral diffuse and segmental analgesic effects. This may be of therapeutic benefit in patients for whom transcutaneous electrical nerve stimulation cannot be directly used at the painful site.

Effects of transcutaneous electrical nerve stimulation and cryotherapy on pain threshold by induced pressure

Studies have shown that cryotherapy, transcutaneous electrical nerve stimulation (TENS) and the association of them promotes analgesia, but the effectiveness of this association is unclear. The objective was to evaluate the effects of single and combined application of TENS and cryotherapy on pressure-induced pain threshold in healthy subjects. The sample consisted of 40 subjects, randomly assigned into four groups: (1) cryotherapy group - CG, (2) TENS group - GT; (3) cryotherapy + TENS group - GCT; (4) placebo group - GP. The pain threshold was determined by an algometer before (T1), immediately after (T2) and in the instants 10 (T3), 20 (T4) and 30 (T5) minutes after application of the analgesic techniques. TENS (100 Hz, 40 μs) and cryotherapy (cold compress) were applied for 20 minutes in the GC, GT and GTC, while in the GP was simulated electrical stimulation for the same period of time. Repeated measures ANOVA and Bonferroni post hoc test were employed, considering a significance level of 5%. All experimental groups showed an increase in pain threshold when compared to GP: GC (p<0.001), GT (p<0.009) and GCT (p<0.008). In relation to the time of analgesia, there was an increase in pain threshold in T2 for all experimental groups (p <0.001) up T3 to GCT (p <0.001) and only in the GC analgesia lasted up to T5. We concluded that under the conditions studied, the three experimental groups had an increase in pain threshold compared to the GP, but cryotherapy had more prolonged effect.

Pressure and cold pain threshold in healthy subjects undergoing interferential current at different amplitude modulated frequencies

BACKGROUND AND OBJECTIVES:The interferential current is an electrical stimulation method widely used with analgesic purposes; however, there are controversies regarding their usage parameters. The aim of this study was to compare different amplitude modulated frequencies of the interferential current on the pressure and cold pain threshold in healthy volunteers.METHODS:This is a crossover, randomized and blinded evaluators and evaluated in quantitative character test. Participants were 20 volunteers divided into four groups, who for four weeks were subject to different modulated frequencies. Thresholds of pressure and cold pain in four different times were evaluated - at the beginning, right after electric stimulation, 20 and 60 minutes after. As a form of electrical stimulation, interferential current was used at modulated amplitude frequencies of 1Hz, 10Hz and 100Hz with base frequency of 4,000Hz, being that in a particular week volunteers received placebo (0Hz).RESULTS:There has been no significant difference in comparisons within frequencies or between them and the placebo group.CONCLUSION:The use of amplitude modulated frequencies of interferential current of 1Hz, 10Hz and 100Hz did not change cold and pressure pain thresholds, similar to what has been found for the placebo group

Effects of Motor Cortex Modulation and Descending Inhibitory Systems on Pain Thresholds in Healthy Subjects

Pain modulation can be achieved using neuromodulatory tools that influence various levels of the nervous system. Transcranial direct current stimulation (tDCS), for instance, has been shown to reduce chronic pain when applied to the primary motor cortex. In contrast to this central neuromodulatory technique, diffuse noxious inhibitory controls (DNIC) refers to endogenous analgesic mechanisms that decrease pain following the introduction of heterotopic noxious stimuli. We examined whether combining top-down motor cortex modulation using anodal tDCS with a bottom-up DNIC induction paradigm synergistically increases the threshold at which pain is perceived. The pain thresholds of 15 healthy subjects were assessed before and after administration of active tDCS, sham tDCS, cold-water-induced DNIC, and combined tDCS and DNIC. We found that both tDCS and the DNIC paradigm significantly increased pain thresholds and that these approaches appeared to have additive effects. Increase in pain threshold following active tDCS was positively correlated with baseline N-acetylaspartate in the cingulate cortex and negatively correlated with baseline glutamine levels in the thalamus as measured by magnetic resonance spectroscopy. These results suggest that motor cortex modulation may have a greater analgesic effect when combined with bottom-up neuromodulatory mechanisms, presenting new avenues for modulation of pain using noninvasive neuromodulatory approaches. PerspectiveThis article demonstrates that both noninvasive motor cortex modulation and a descending noxious inhibitory controls paradigm significantly increase pain thresholds in healthy subjects and appear to have an additive effect when combined. These results suggest that existing pain therapies involving DNIC may be enhanced through combination with noninvasive brain stimulation.

BDNF as an effect modifier for gender effects on pain thresholds in healthy subjects

BDNF is an important marker of neuronal plasticity. It has also been associated with pain processing. Increased BDNF levels are observed in chronic pain syndromes. In order to understand the role of BDNF associated with other factors such as gender on experimental pain we aimed to determine whether experimental heat or pressure pain threshold is correlated with brain derived neurotrophic factor (BDNF) level, gender and age. Heat pain threshold and pressure pain threshold were measured in 49 healthy volunteers (27 females). The multivariate linear regression models (on heat and pressure pain thresholds) revealed a significant effect of gender (p=0.001 for both models), serum BDNF (p<0.004 for both models) and interaction between BDNF and gender (<0.001 for both models). In fact, when adjusting for BDNF levels and age, heat and pressure pain thresholds were significantly reduced in women as compared to men (p<0.001 for both models). These effects were not observed when gender was analyzed alone. These finding suggests that experimental heat and pressure pain threshold is gender-related and BDNF dependent. In fact BDNF has a facilitatory effect on pain threshold in females but has an opposite effect in males; supporting the notion that BDNF is an effect modifier of the gender effects on pain threshold in healthy subjects.

S34-01 - Putative cerebral correlates of abberant pain processing in depression

The complex sensory experience of pain involves cognitive, behavioural and emotional aspects which are closely interrelated. While patients suffering from major depressive disorder (MDD) mainly exhibit increased thresholds towards experimentally induced thermal pain applied to the skin, the induction of sad mood increases pain perception in healthy controls.Neurobiological underpinnings of the discrepancy of pain perception in depression and after sad mood induction in healthy volunteers will help to understand aberrant pain perception in the disease. Patients and controls were rated on mood scales and results were correlated to brain activity assessed in fMRI sessions. Similarly, autonomic modulation in respect to pain perception was assessed in patients.We found a highly significant reduction in heat pain threshold on the left hand after sad mood induction in patients and controls. Subjects were scanned twice, one group before and after sad-mood induction and another group before and after neutral-mood induction, respectively. Our main finding was a significant group×mood induction interaction bilaterally in the ventrolateral nucleus of the thalamus indicating a BOLD signal increase after sad-mood induction and a BOLD signal decrease in the control group.We present evidence that induced sad affect leads to reduced heat pain thresholds in healthy subjects and depressed patients. This is probably due to altered lateral thalamic activity, which is potentially associated with changed attentional processes. Furthermore we present evidence for similar changes in depressed patients after sad mood induction. Autonomic modulation is less likely to interfere with pain perception in the disease.

A comparison of the analgesic efficacy of medium-frequency alternating current and TENS

Objective To compare the analgesic efficacy of burst-modulated medium-frequency alternating current (BMAC) and transcutaneous electrical nerve stimulation (TENS) using an experimental cold pain model. Design Within-group crossover study. Setting A university research laboratory. Participants Twenty healthy subjects. Interventions BMAC (4-kHz AC applied in 4-millisecond bursts at 50 Hz) and TENS (125-microsecond phase duration applied at a frequency of 50 Hz) administered to each participant on separate occasions. Main outcome measure Time to cold pain threshold. Results The mean time to cold pain threshold with the BMAC intervention was no different than with TENS. Statistical analysis showed that both interventions elevated the cold pain threshold significantly [BMAC: increase = 15.2 seconds, 97.5% confidence interval (CI) 3.1 to 27.2, P = 0.01; TENS: increase = 15.4 seconds, 97.5%CI 2.5 to 28.4, P = 0.02], and the difference between interventions was not simply insignificant but the intervention effects were ‘significantly the same’ (mean difference = 0.3 seconds, 95%CI −15.3 to 15.9, P = 0.97). Conclusions BMAC is as effective as TENS in increasing cold pain thresholds in healthy subjects. Since BMAC has been shown to be more comfortable than TENS in previous studies and is likely to be better accepted and tolerated by patients, clinical investigation is warranted.

Reduced heat pain thresholds after sad-mood induction are associated with changes in thalamic activity

Negative affective states influence pain processing in healthy subjects in terms of augmented pain experience. Furthermore, our previous studies revealed that patients with major depressive disorder showed increased heat pain thresholds on the skin. Potential neurofunctional correlates of this finding were located within the fronto-thalamic network. The aim of the present study was to investigate the neurofunctional underpinnings of the influence of sad mood upon heat pain processing in healthy subjects. For this purpose, we used a combination of the Velten Mood Induction procedure and a piece of music to induce sad affect.Initially we assessed heat pain threshold after successful induction of sad mood outside the MR scanner in Experiment 1. We found a highly significant reduction in heat pain threshold on the left hand and a trend for the right. In Experiment 2, we applied thermal pain stimuli on the left hand (37, 42, and 45°C) in an MRI scanner. Subjects were scanned twice, one group before and after sad-mood induction and another group before and after neutral-mood induction, respectively. Our main finding was a significant group×mood-induction interaction bilaterally in the ventrolateral nucleus of the thalamus indicating a BOLD signal increase after sad-mood induction and a BOLD signal decrease in the control group. We present evidence that induced sad affect leads to reduced heat pain thresholds in healthy subjects. This is probably due to altered lateral thalamic activity, which is potentially associated with changed attentional processes.

Modulatory effects of anodal transcranial direct current stimulation on perception and pain thresholds in healthy volunteers

We aimed to evaluate whether transcranial direct current stimulation (tDCS) is effective in modulating sensory and pain perception thresholds in healthy subjects as to further explore mechanisms of tDCS in pain relief. Twenty healthy subjects received stimulation with tDCS under four different conditions of stimulation: anodal tDCS of the primary motor cortex (M1), dorsolateral prefrontal cortex (DLPFC), occipital cortex (V1), and sham tDCS. The order of conditions was randomized and counterbalanced across subjects. Perception threshold and pain threshold to peripheral electrical stimulation of the right index finger were evaluated by a blinded rater. The results showed a significant effect of the interaction time versus stimulation condition for perception (P = 0.046) and pain threshold (P = 0.015). Post hoc comparisons revealed that anodal stimulation of M1 increased both perception (P < 0.001, threshold increase of 6.5%) and pain (P = 0.001, threshold increase of 8.3%) thresholds significantly, whilst stimulation of the DLPFC increased pain threshold only (P = 0.046, threshold increase of 10.0%). There were no significant effects for occipital or sham stimulation. These results show that both M1 and DLFPC anodal tDCS can be used to modulate pain thresholds in healthy subjects; thus, the mechanism of tDCS in modulating pain involves pathways that are independent of abnormal pain-related neural activity.

P059 Repeatability of cold pain and heat pain thresholds in healthy subjects

P059 Repeatability of cold pain and heat pain thresholds in healthy subjects