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. Author manuscript; available in PMC: 2017 Apr 1.
Published in final edited form as: Pain. 2017 Apr;158(4):691–697. doi: 10.1097/j.pain.0000000000000816

Figure 1.

Figure 1

Experimental setup. Sensitization of the left or right volar forearm was induced using high frequency electrical stimulation of the skin (HFS). The stimulation consisted in five 1-s trains of 100 Hz stimuli (pulse width 2 ms), delivered to the skin using a specific electrode made of 16 blunt stainless steel pins with a diameter of 0.2 mm protruding 1 mm from the base. The pins were placed in a circle with a diameter of 10 mm and serve as cathode. A stainless steel reference electrode that served as anode was concentrically located with an inner diameter of 22 mm and an outer diameter of 40 mm. Visual stimuli were projected onto the skin of the left and right volar forearms using two green laser diodes. The two lasers were mounted on the upper part of a chin rest frame, onto which participants positioned their chin. Changes in mechanical pinprick sensitivity were tested using a 128 mN pinprick probe. Visual-evoked brain responses and mechanical pinprick sensitivity were assessed before applying HFS (T0), 20 minutes after applying HFS (T1) and 45 minutes after applying HFS (T2).