HD-tDCS: Effects on the Somatosensory System

Study Overview
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Brief Summary
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The purpose of this study is to investigate the efficacy of high definition tDCS on different cortical targets in modulating the nociceptive system in the healthy subjects.

Detailed Description
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The investigators aim to investigate the efficacy of different HD-tDCS electrode configurations on modulating the somatosensory/nociceptive system. This is done to investigate the hypothesis, that different stimulation protocols can be used to modulate the somatosensory and nociceptive system, as shown in the previous studies, but that it is necessary to uncover the most efficient way to do so. The study uses a double-blinded, sham-controlled, longitudinal design, where quantitative sensory testing will be used to assess the somatosensory function of the participants before and after a receiving a specific configuration of HD-tDCS on three consecutive days.

Official Title
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High Definition Transcranial Direct Current Stimulation: Effects on the Somatosensory System

Conditions
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Acute Pain, Neuroplasticity, Brain Modulation, Somatosensory Function

Intervention / Treatment
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* Device: Primary Motor Cortex Stimulation
* Device: Dorsolateral Prefrontal Cortex Stimulation
* Device: Multimodal Stimulation (DLPFC+M1)
* Device: Sham stimulation


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Healthy men and women. Able to speak, read and understand English or Danish. Exclusion Criteria: Pregnancy Drug addiction defined as the use of cannabis, opioids or other drugs Current use of opioids, antipsychotics, benzodiazepines Previous or current neurological, musculoskeletal, rheumatic, malignant, inflammatory or mental illnesses Current or prior chronic pain conditions Lack of ability to cooperate

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 60 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Parallel Assignment
Interventional Model Description: Longitudinal, sham-controlled, parallel groups design.
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: Primary motor cortex<br> | Device: Primary Motor Cortex Stimulation<br>* Using the Starstim 32, HD-tDCS equipment we provide 20 minutes of 2 mA anodal stimulation of primary motor cortex (M1) using a ring-cathode configuration<br>|
| Active Comparator: Dorsolateral prefrontal cortex<br> | Device: Dorsolateral Prefrontal Cortex Stimulation<br>* Using the Starstim 32, HD-tDCS equipment we provide 20 minutes of 2 mA anodal stimulation of dorsolateral prefrontal cortex (DLPFC) using a ring-cathode configuration<br>|
| Active Comparator: Multi-modal stimulation (DLPFC+M1)<br> | Device: Multimodal Stimulation (DLPFC+M1)<br>* Using the Starstim 32, HD-tDCS equipment we provide 20 minutes of 2 mA anodal multimodal stimulation of dorsolateral prefrontal cortex (DLPFC) and primary motor cortex simultaneously using ring-cathode configurations around the two anodes.<br>|
| Sham Comparator: Sham-stimulation<br> | Device: Sham stimulation<br>* Using the Starstim 32, HD-tDCS equipment we provide sham stimulation with 30 seconds of ramping up to 2 mA intensity, then turning off for 19 minutes and then ramping down from 2 mA intensity to 0 in the last 30 seconds.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in pressure pain threshold | A hand-held pressure algometer (Somedic, Hörby, Sweden) with a 1-cm2 probe will be used to record the pressure pain threshold. The pressure is increased gradually at a rate of 30 kPa/s. The measurement is repeated three times on on flexor carpi radialis. | Six assessments over three days: Baseline is assessed before any intervention at day one, and then the pain thresholds are assessed before and after each intervention on the subsequent two days. | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in tactile detection threshold | Tactile threshold will be measured using an anaesthesiometer consisting of a set of Von Frey filaments. The filaments are made of nylon fibre of various diameters so as to provide a range of forces of up to 300 grams. The minimum force that the subject can detect will be identified. This will be assessed on flexor carpi radialis on the right hand arm. | Six assessments over three days: Baseline is assessed before any intervention at day one, and then the sensory thresholds are assessed before and after each intervention on the subsequent two days. | 
| Change in mechanical pain threshold | Mechanical pain threshold (MPT) will be measured using a set of weighted pinprick stimulators with a flat contact area of 0.25 mm diameter that exert forces between 8 and 512 mN. Threshold procedures will use a method of limits with up to five series of ascending and descending stimulus intensities. This will be assessed on flexor carpi radialis on the right hand arm. | Six assessments over three days: Baseline is assessed before any intervention at day one, and then the sensory thresholds are assessed before and after each intervention on the subsequent two days. | 
| Change in Thermal Sensory Detection | A 3×3 cm (9 cm2) contact thermode (Medoc Advanced Medical Systems, Israel) will be used to apply thermal stimulation. Each stimulus will be started at 32°C and thresholds of heat and cold sensory detection will be assessed by ascending or descending ramps in temperature to the cutoffs of 0-50 °C. This will be assessed on flexor carpi radialis on the right hand arm. | Six assessments over three days: Baseline is assessed before any intervention at day one, and then the sensory thresholds are assessed before and after each intervention on the subsequent two days. | 
| Change in Thermal Pain Detection | A 3×3 cm (9 cm2) contact thermode (Medoc Advanced Medical Systems, Israel) will be used to apply thermal stimulation. Each stimulus will be started at 32°C and thresholds of heat and cold pain detection will be assessed by ascending or descending ramps in temperature to the cutoffs of 0-50 °C. This will be assessed on flexor carpi radialis on the right hand arm. | Six assessments over three days: Baseline is assessed before any intervention at day one, and then the sensory thresholds are assessed before and after each intervention on the subsequent two days. | 
| Change in conditioned pain modulation (CPM) | A computer-controlled cuff pressure algometer (Nocitech, Denmark) with an air-filled tourniquet cuff (VBM, Germany) will be used to record cuff pressure-induced pain thresholds over the muscle bulk on the calfs. The pressure is increased gradually at a rate of 1 kPa/s to assess pain tolerance on a 0-10 VAS scale, where 0 is no pain at all and 10 is the worst pain imaginable. During CPM testing, the pain tolerance is first assessed on one leg marking the baseline. The pressure pain tolerance is then assessed on the same leg again, while the contralateral calf is applied a simultaneous painful pressure stimulus. The outcome of the CPM testing is the difference in pressure pain tolerance measured in kPA between the first and the second assessment. The larger the positive difference is between the baseline and the second assessment, the stronger CPM effect the subject has. | Six assessments over three days: Baseline is assessed before any intervention at day one, and then the sensory thresholds are assessed before and after each intervention on the subsequent two days. | 
| Change in vibration detection threshold. | Vibration detection threshold (VDT) will be determined with a Rydel-Seiffer tuning fork (64 Hz, 8/8 scale), which will be placed three times over a bony prominence of the distal part of the ulna on the right arm. Subjects are to indicate the disappearance of vibratory sensations. | Six assessments over three days: Baseline is assessed before any intervention at day one, and then the sensory thresholds are assessed before and after each intervention on the subsequent two days. | 
| Change in temporal summation of pain (TSP). | TSP will be applied using cuff pressure algometry. A total of 10 repeated mechanical pressure stimuli will be delivered at 0.5 Hz (1-s stimuli duration and 1-s interval between stimuli) to the test area. During the 10 repeated stimuli, subjects will continuously rate the pain intensity on a 10-cm continuous VAS. TSP is assessed on the calf of the right leg. | Six assessments over three days: Baseline is assessed before any intervention at day one, and then the sensory thresholds are assessed before and after each intervention on the subsequent two days. | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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tDCS, HD-tDCS, Somatosensory function, QST, quantitative sensory testing, Non-invasive brain stimulation, NIBS, Transcranial Direct Current Stimulation