Nm 983 w

For nociceptive stimulation, IES method was adopted using a disposable concentric bipolar needle electrode (NM‐983W; Nihon Kohden Corporation, Tokyo, Japan), connected to a specific stimulator for cutaneous Aδ and C fibers, as previously described (PNS-7000, Nihon Kohden).12 (link) The stimulator consisted of an outer ring anode (1.3 mm diameter) and the cathode of an inner needle that protruded 0.025 mm from the level of the outer ring. IES electrode was placed onto the skin of the instep (over the extensor digitorum brevis) to deliver weak continuous electrical stimulations. This stimulation can evoke a local pricking sensation. In instances where the keratinized layer of the skin was too thick and likely to interrupt the electronic stimulation, the electrode was moved elsewhere on the same foot to locate an area of seemingly no thick layer. The participants were instructed to push the button as quickly as possible only when they felt a sensation. Stimulation intensity was decreased by 0.05 mA stepwise from 0.4 mA until the participants reported a pricking sensation. The current intensity is directly proportion to the intensity of stimulation. PINT was defined as the minimum intensity at which the participants felt a pricking sensation in more than two trials. Therefore, PINT can basically evaluate the degrees of hypoalgesia toward electrical pain stimulation.