Exploration of Parameters of Transcranial Direct Current Stimulation (tDCS) in Chronic Pain

Experimental: Active Anodal HD-tDCS

Subject will receive one 20-minute session of active anodal HD-tDCS.

Dispositivo: High Definition Transcranial Direct Current Stimulation (HD-tDCS)

Subject will receive active anodal/cathodal and sham HD-tDCS in a randomized, counterbalanced order. Each stimulation session will be separated by at least one week to avoid carryover effects. For both active and sham HD-tDCS the electrodes will be placed over the primary motor cortex, at an intensity of 2mA.

• For active anodal stimulation, the anode will be over the primary motor cortex, and the cathodal electrodes (4) will surround the anode in a 3 inch square, duration will be 20 minutes.
• For active cathodal stimulation, the cathode will be over the primary motor cortex, and the anodal electrodes (4) will surround the cathode in a 3 inch square, duration will be 20 minutes.
• For sham stimulation, the same procedure will be used, however, current will only be active for 30 seconds (current ramping up, then ramping down)

Experimental: Active Cathodal HD-tDCS

Subject will receive one 20-minute session of active cathodal HD-tDCS.

Dispositivo: High Definition Transcranial Direct Current Stimulation (HD-tDCS)

Subject will receive active anodal/cathodal and sham HD-tDCS in a randomized, counterbalanced order. Each stimulation session will be separated by at least one week to avoid carryover effects. For both active and sham HD-tDCS the electrodes will be placed over the primary motor cortex, at an intensity of 2mA.

• For active anodal stimulation, the anode will be over the primary motor cortex, and the cathodal electrodes (4) will surround the anode in a 3 inch square, duration will be 20 minutes.
• For active cathodal stimulation, the cathode will be over the primary motor cortex, and the anodal electrodes (4) will surround the cathode in a 3 inch square, duration will be 20 minutes.
• For sham stimulation, the same procedure will be used, however, current will only be active for 30 seconds (current ramping up, then ramping down)

Comparador falso: Sham HD-tDCS

Subject will receive one sham session of HD-tDCS

Dispositivo: High Definition Transcranial Direct Current Stimulation (HD-tDCS)

Subject will receive active anodal/cathodal and sham HD-tDCS in a randomized, counterbalanced order. Each stimulation session will be separated by at least one week to avoid carryover effects. For both active and sham HD-tDCS the electrodes will be placed over the primary motor cortex, at an intensity of 2mA.

• For active anodal stimulation, the anode will be over the primary motor cortex, and the cathodal electrodes (4) will surround the anode in a 3 inch square, duration will be 20 minutes.
• For active cathodal stimulation, the cathode will be over the primary motor cortex, and the anodal electrodes (4) will surround the cathode in a 3 inch square, duration will be 20 minutes.
• For sham stimulation, the same procedure will be used, however, current will only be active for 30 seconds (current ramping up, then ramping down)

Change in pain scales

Determine whether anodal or cathodal hd-tDCS is effective in reducing pain in subjects with chronic musculoskeletal pain as measured by changes in the Visual Analogue Scale (VAS) for pain. The VAS scale will be measured immediately before the hd-tDCS stimulation sessions and after the hd-tDCS stimulation sessions for each subject for the duration of their participation in the trial. This outcome will also be measured at their baseline visit, and follow-up visit.

Change in cutaneous hyperalgesia/allodynia

To investigate whether treatment with active anodal hd-tDCS alters the phenomenon of central sensitization as indexed by cutaneous allodynia and hyperalgesia by measuring whether anodal tDCS changes the threshold for pain and perception as compared with sham and cathodal hd-tDCS. The subject's pain threshold will be measured immediately before the hd-tDCS stimulation sessions and after the hd-tDCS stimulation sessions for the duration of their participation in the trial. This outcome will also be measured at their baseline visit, and follow-up visit.