The method for sensory TENS was described previously. Briefly, a J5 Myomonitor TENS Unit device (Myotronics-Noromed, Inc., Tukwila, WA, USA) with disposable electrodes (Myotrode SG Electrodes, Myotronics-Noromed, Inc., Tukwila, WA, USA) will be used. This low-frequency neurostimulator generates a repetitive synchronous and bilateral stimulus delivered at 1.5 s intervals. The stimulus has adjustable amplitude of approximately 0-24 mA, duration of 500 μs, and frequency of 0.66 Hz. Two TENS electrodes will be placed bilaterally over the cutaneous projection of the notch of the fifth pair of cranial nerves, which is located between the coronoid and condylar processes and will be retrieved by manual palpation of the zone anterior to the tragus. Additionally, a third grounding electrode will be placed in the center of the back of the neck. The amplitude of TENS stimulation started at 0 mA, with the stimulator turned on and the rheostat, which controls the amplitude, positioned at 0. The amplitude of stimulation will be progressively increased at a rate of 0.6 mA/s until the patients reported a pricking sensation. The duration of each stimulation will be 40 minutes. Particular attention will be paid to avoid reaching the threshold of motor stimulation; if any movement of the investigated muscles will be observed, the amplitude of stimulation will be immediately reduced.