Reliability of Measuring the Area and Intensity of Secondary Hyperalgesia Induced by High Frequency Stimulation

High-frequency stimulation will be applied on the volar forearm (6-10 cm distal to the cubital fossa). To avoid any confounding effect of handedness, the arm onto which HFS will be applied twice (dominant vs nondominant) will be counterbalanced across participants. HFS will consist of 12 trains of 42 Hz electrical pulses lasting 1 s each. The time interval between each train will be 10 s. The intensity of stimulation will be 5mA. Electrical pulses will be delivered to the skin using a specifically-designed electrode designed: the cathode consists of 16 blunt stainless-steel pins with a diameter of 0.2 mm protruding 1 mm from the base. The 16 pins are placed in a circle with a diameter of 10 mm. The anode consists of a surrounding stainless-steel ring having an inner diameter of 22 mm and an outer diameter of 40 mm. This procedure induces secondary pinprick hyperalgesia (an increase in pinprick sensitivity in a large area of the skin).