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

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.

Differential effects of primary motor cortex and cerebellar transcranial direct current stimulation on motor learning in healthy individuals: A randomized double-blind sham-controlled study.

The purpose of study was to compare the effect of primary motor cortex (M1) and cerebellar anodal transcranial direct current stimulation (a-tDCS) on online and offline motor learning in healthy individuals. Fifty-nine healthy volunteers were randomly divided into three groups (n=20 in two experimental groups and n=19 in sham-control group). One experimental group received M1a-tDCSand another received cerebellar a-tDCS. The main outcome measure were response time (RT) and number of errors during serial response time test (SRTT) which were assessed prior, 35min and 48h after the interventions. Reduction of response time (RT) and error numbers at last block of the test compared to the first block was considered online learning. Comparison of assessments during retention tests was considered as short-term and long-term offline learning. Online RT reduction was not different among groups (P>0.05), while online error reduction was significantly greater in cerebellar a-tDCS than sham-control group (P<0.017). Moreover, a-tDCS on both M1 and cerebellar regions produced more long-term offline learning as compared to sham tDCS (P<0.01), while short-term offline RT reduction was significantly greater in M1a-tDCS than sham-control group (P<0.05). The findings indicated that although cerebellar a-tDCS enhances online learning and M1a-tDCS has more effect on short-term offline learning, both M1 and cerebellar a-tDCS can be used as a boosting technique for improvement of offline motor learning in healthy individuals.

Differential activation of scapular muscles, during arm elevation, with and without trigger points.

BACKGROUND: Latent Myofascial Trigger Points (LMTrPs) are defined as certain pain-free hyperirritable spots in a muscle taut band which lead to muscle activation pattern alternation in both loaded and unloaded conditions during scaption. The current study aimed to investigate the onset of upward scapular rotator muscle activations during rapid arm elevation in three planes of movement in patients with upper trapezius LMTrPs compared to healthy control participants. METHOD: Three planes of scapular movement were evaluated. The onset of Deltoid (DEL) was considered as the starting point in marking the onset of Upper Trapezius (UT) and Serratus Anterior (SA) muscle activations. RESULTS: There were significant differences in the relative muscle latencies between the LMTrPs and the control group. Those with LMTrPs showed a delayed and inconsistent activity of UT during all three planes of elevation (p < 0.05) and the same pattern happened for SA during flexion (p < 0.05). CONCLUSIONS: Both hosted and synergistic muscles experience delay in muscle activation and alterations in their recruitment pattern during rapid arm elevation in all planes of movement. These changes may serve as adaptive motor control strategies due to the presence of LMTrPs in UT muscles.

Differential effects of cathodal transcranial direct current stimulation of prefrontal, motor and somatosensory cortices on cortical excitability and pain perception - a double-blind randomised sham-controlled study.

The primary aim of this study was to assess the effects of cathodal transcranial direct current stimulation (c-tDCS) over cortical regions of the pain neuromatrix, including the primary motor (M1), sensory (S1) and dorsolateral prefrontal (DLPFC) cortices on M1/S1 excitability, sensory (STh), and pain thresholds (PTh) in healthy adults. The secondary aim was to evaluate the placebo effects of c-tDCS on induced cortical and behavioural changes. Before, immediately after and 30 min after c-tDCS the amplitude of N20-P25 components of somatosensory evoked potentials (SEPs) and peak-to-peak amplitudes of motor evoked potentials (MEPs) were measured under four different experimental conditions. STh and PTh for peripheral electrical and mechanical stimulation were also evaluated. c-tDCS of 0.3 mA was applied for 20 min. A blinded assessor evaluated all outcome measures. c-tDCS of M1, S1 and DLPFC significantly decreased the corticospinal excitability of M1 (P < 0.05) for at least 30 min. Following the application of c-tDCS over S1, M1 and DLPFC, the amplitude of the N20-P25 component of SEPs decreased for at least 30 min (P < 0.05). Compared with baseline values, significant STh and PTh increases were observed after c-tDCS of these three sites. Decreasing the level of S1 and M1 excitability, following S1, M1 and DLPFC stimulation, confirmed the functional connectivities between these cortical sites involved in pain processing. Furthermore, increasing the level of STh/PTh after c-tDCS of these sites indicated that stimulation of not only M1 but also S1 and DLPFC could be considered a technique to decrease the level of pain in patients.

The relationship between isokinetic muscle strength and spasticity in the lower limbs of stroke patients.

OBJECTIVE: In this study the relationship between degree of spasticity and strength of knee extensor and ankle plantar flexor muscles of post stroke hemiparetic patients has been investigated. MATERIALS & METHODS: The participants of this study were 40 stroke patients whose elapsed time of stroke onset was at least 3 months. Their age averaged 59 years. Spasticity was measured with the Modified Ashworth Scale. Isokinetic muscle strength was measured with an isokinetic dynamometer. Two methods of torque normalization - subtractive and weight based normalization - were used for comparing torques among participants. RESULTS: Kendall's tau-b coefficient was calculated for investigating this relationship. This coefficient was not significant for the relationship between weight based normalized data and modified Ashworth scale (MAS) in any of each muscle groups (α = 0.05). This coefficient was significant for the relationship between the subtractive normalization method and MAS in knee extensors (P = 0.005, α = 0.01) and ankle plantar flexors (P = 0.002, α = 0.01). CONCLUSION: This study suggests a negative relationship between spasticity and muscle strength and provided evidence that spastic muscles are weaker.

Within-session repeated a-tDCS: the effects of repetition rate and inter-stimulus interval on corticospinal excitability and motor performance.

OBJECTIVE: This study investigated the effect of rate and stimulation interval of anodal transcranial direct current stimulation (a-tDCS) on CSE and motor performance. METHODS: Twelve healthy individuals participated in this study. CSE was assessed before and after five experimental conditions of one, two or three applications of 10 min of a-tDCS with an interval of 5 or 25 min. a-tDCS was applied with a constant current density of 0.016 mA/cm(2). Purdue pegboard-test was selected for motor performance assessment. RESULTS: Compared to single 10 min stimulation, the magnitude of the within-session repeated a-tDCS induced excitability was enhanced significantly after the second stimulation was performed with an interval of 25 min, but not 5 min. However, by increasing the number of a-tDCS to three repetitions the CSE was significantly increased and lasted for 2h with both 5 and 25 min intervals. Furthermore, CSE enhancement remained significant for up to 24h for within session a-tDCS repetitions with 25 min intervals. Likewise, significant improvement was seen in motor performance following three times repetition with 25 min inter-stimulus intervals. CONCLUSIONS: The results suggest that within session repeated a-tDCS with longer intervals within the lasting effects of the previous stimulations are preferable for increasing induced excitability changes with longer lasting effects. SIGNIFICANCE: It is of particular importance to increase the a-tDCS lasting effects to consolidate the neuroplastic CSE changes.

Does anodal transcranial direct current stimulation modulate sensory perception and pain? A meta-analysis study.

OBJECTIVE: The primary aim of this systematic review was to evaluate the effects of anodal transcranial direct current stimulation (a-tDCS) on sensory (STh) and pain thresholds (PTh) in healthy individuals and pain levels (PL) in patients with chronic pain. METHODS: Electronic databases were searched for a-tDCS studies. Methodological quality was examined using the PEDro and Downs and Black (D&B) assessment tools. RESULTS: a-tDCS of the primary motor cortex (M1) increases both STh (P<0.005, with the effect size of 22.19%) and PTh (P<0.001, effect size of 19.28%). In addition, STh was increased by a-tDCS of the primary sensory cortex (S1) (P<0.05 with an effect size of 4.34). Likewise, PL decreased significantly in the patient group following application of a-tDCS to both the M1 and dorsolateral prefrontal cortex (DLPFC). The average decrease in visual analogue score was 14.9% and 19.3% after applying a-tDCS on the M1 and DLPFC. Moreover, meta-analysis showed that in all subgroups (except a-tDCS of S1) active a-tDCS and sham stimulation produced significant differences. CONCLUSIONS: This review provides evidence for the effectiveness of a-tDCS in increasing STh/PTh in healthy group and decreasing PL in patients. However, due to small sample sizes in the included studies, our results should be interpreted cautiously. Given the level of blinding did not considered in inclusion criteria, the result of current study should be interpreted with caution. SIGNIFICANCE: Site of stimulation should have a differential effect over pain relief.

a-tDCS differential modulation of corticospinal excitability: the effects of electrode size.

BACKGROUND: Novel noninvasive brain stimulation techniques such as transcranial direct current stimulation (tDCS) have been developed in recent years. tDCS-induced corticospinal excitability changes depend on two important factors: current density and electrodes size. Despite clinical success with existing tDCS parameters; optimal protocols are still not entirely set. OBJECTIVE: The current study aimed to investigate the effects of anodal tDCS (a-tDCS) with three electrode sizes on corticospinal excitability. METHODS: a-tDCS was applied with three active electrode sizes of 12, 24 and 35 cm(2) with a constant current density of 0.029 mA/cm(2) on twelve right handed healthy individuals (mean age: 34.5 ± 10.32 years) in different sessions at least 48 h apart. a-tDCS was applied continuously for 10 min, with a constant reference electrode size of 35 cm(2). The corticospinal excitability of extensor carpi radialis muscle (ECR) was measured before and immediately after the intervention and at 10, 20 and 30 min thereafter. RESULTS: We found that smaller electrode may produce more focal current density and could lead to more effective and localized neural modulation than the larger ones. Post hoc comparisons showed that active electrode of 12 cm(2) size induces the biggest increase in the corticospinal excitability compared to bigger electrode sizes, 24 cm(2) (P = 0.002) and 35 cm(2) (P = 0.000). There was no significant difference between two larger electrode sizes (24 cm(2) and 35 cm(2)) (P = 0.177). a-tDCS resulted in significant excitability enhancement lasting for 30 min after the end of stimulation in the 12 and 24 cm(2) electrode size conditions (P < 0.005). However, in 35 cm(2) electrode size condition, the MEP amplitudes of the ECR did not differ significantly from baseline value in 20 and 30 min post stimulation (P > 0.005). CONCLUSION: Reducing stimulation electrode size to one third of the conventional one results in spatially more focused stimulation and increases the efficacy of a-tDCS for induction of larger corticospinal excitability. This may be due to the fact that larger electrodes stimulate nearby cortical functional areas which can have inhibitory effects on primary motor cortex.

Does anodal transcranial direct current stimulation enhance excitability of the motor cortex and motor function in healthy individuals and subjects with stroke: a systematic review and meta-analysis.

The primary aim of this review is to evaluate the effects of anodal transcranial direct current stimulation (a-tDCS) on corticomotor excitability and motor function in healthy individuals and subjects with stroke. The secondary aim is to find a-tDCS optimal parameters for its maximal effects. Electronic databases were searched for studies into the effect of a-tDCS when compared to no stimulation. Studies which met the inclusion criteria were assessed and methodological quality was examined using PEDro and Downs and Black (D&B) assessment tools. Data from seven studies revealed increase in corticomotor excitability with a small but significant effect size (0.31 [0.14, 0.48], p=0.0003) in healthy subjects and data from two studies in subjects with stroke indicated significant results with moderate effect size (0.59 [0.24, 0.93], p=0.001) in favor of a-tDCS. Likewise, studies examining motor function demonstrated a small and non-significant effect (0.39 [-0.17, 0.94], p=0.17) in subjects with stroke and a large but non-significant effect (0.92 [-1.02, 2.87], p=0.35) in healthy subjects in favor of improvement in motor function. The results also indicate that efficacy of a-tDCS is dependent on current density and duration of application. A-tDCS increases corticomotor excitability in both healthy individuals and subjects with stroke. The results also show a trend in favor of motor function improvement following a-tDCS. A-tDCS is a non-invasive, cheap and easy-to-apply modality which could be used as a stand-alone technique or as an adds-on technique to enhance corticomotor excitability and the efficacy of motor training approaches. However, the small sample size of the included studies reduces the strength of the presented evidences and any conclusion in this regard should be considered cautiously.

Standardization of H-reflex analyses.

Variability in the H-reflex can make it difficult to identify significant changes using traditional pooled analysis techniques. This study was undertaken to introduce a normalisation approach to calculate both the relative size and the relative stimulus intensity required to elicit the H-reflex response so that comparisons can be made not only with results obtained during different experimental session but also between different subjects. This normalisation process fits the size of the measured M-responses and H-reflexes over the entire stimulus range with model curves to better facilitate the calculation of important parameters. This approach allows normalisation of not only the size of the response but also the relative stimulus intensity required to elicit the response. This eases the comparison of the reflex responses under various situations, and is capable of bringing out any genuine differences in the reflex in a reliable manner not previously possible. This study illustrates that comparison of the reflex between days is problematic, even in the same subject, as both the reflex size and the relative stimulus intensity required to obtain this reflex changed in all subjects. We suggest that H-reflex studies need to use normalisation not only for size of the reflex but also for the stimulus intensity, and also that all experiments for a single subject should be performed in the same session or during the same day using some level of background muscle activity in the muscle concerned as the variability of the muscle at rest was found to be larger.

Accuracy of an electromagnetic tracking device for measuring hip joint kinematics during gait: effects of metallic total hip replacement prosthesis, source-sensor distance and sensor orientation.

The present study sought to investigate the effects of source-sensor distance, sensor orientation and the effects of metallic total hip replacement (THR) prostheses on the accuracy of the 3Space Tracker System (3STS). Using a simulated hip joint, the angles measured by the 3STS with six different source-sensor distances and two source-sensor orientations were recorded. Then the angles measured in the absence and presence of three different THR prostheses were compared. Both source-sensor distance and sensor orientation affects the accuracy of the 3STS. Measurements were only affected by the presence of one type of prosthesis. The 3STS was equally reliable, but less accurate with source-sensor distances of more than 25 cm. The small angular error and insensitivity of this device to the presence of some metallic THR prostheses make it a useful measurement tool for gait studies performed before and after THR surgery.

Compensation of limb weight on interfaced raw torque signals from a KIN-COM dynamometer to an AMLAB workstation.

The effect of gravity should be considered when using isokinetic devices to measure human movement performance. In most isokinetic dynamometers gravity compensation is controlled by software through a gravity correction option. However in some complex research protocols the dynamometer signal acquisition and processing capability is not adequate to effectively synchronize or process a wide range of captured signals. Therefore when the force/torque signals from a commonly used dynamometer such as KIN-COM are interfaced into a signal processing workstation such as AMLAB, it is necessary to further process the received raw signals for gravity correction. The aim of this study was to evaluate the effectiveness of an AMLAB-based instrument designed for gravity compensation of raw torque signals acquired from a KIN-COM dynamometer. To check the accuracy of weight compensation within the AMLAB, environment, torque signals produced by a known weight during a 180-degree range of KIN-COM lever arm movement were compared with and without weight compensation. The results indicated that this technique is an accurate means for weight compensation when raw torque signals from a KIN-COM dynamometer are interfaced to an AMLAB workstation.

An integrated AMLAB-based system for acquisition, processing and analysis of evoked EMG and mechanical responses of upper limb muscles.

An integrated multi-channel AMLAB-based data acquisition, processing and analysis system has been developed to simultaneously display, quantify and correlate electromyographic (EMG) activity, resistive torque, range of motion, and pain responses evoked by passive elbow extension in humans. The system was designed around the AMLAB analog modules and software objects called ICAMs. Each channel consisted of a time and frequency domain block, a torque and angle measurement block, an experiment number counter block and a data storage and retrieval block. The captured data in each channel was used to display and quantify: raw EMG, rectified EMG, smoothed rectified EMG, root-mean-squared EMG, fast Fourier transformed (FFT) EMG, and normalized power spectrum density (NPSD) of EMG. Torque and angle signals representing elbow extension measured by a KIN-COM dynamometer during neural tension testing, as well as signals from an electronic pain threshold marker were interfaced to AMLAB and presented in one integrated display. Although this system has been designed to specifically study the patterns and nature of evoked motor responses during clinical investigation of carpal tunnel syndrome (CTS) patients, it could equally well be modified to allow acquisition, processing and analysis of EMG signals in other studies and applications. In this paper, we present for the first time the steps involved in the design, implementation and testing of an integrated AMLAB-based system to study and analyse the mechanically evoked electromyographic, torque and ROM signals and correlate various levels of pain to these signals. We also present samples of resistive torque ROM, and raw and processed EMG recordings during passive elbow extension.