 Blinding will be performed before the start of the study. Every participant will be given a number pseudonym, which will be programmed into the stimulator. Each number will be randomly assigned to sham or verum treatment and the same treatment will then be performed at every session. The stimulator can be programmed beforehand to assign numbers randomly to the verum or sham group, so that the respective patient data are unknown to both the person who performs the stimulation and the course leaders. Half of the participants will be randomly assigned to the sham group and half to the verum group. The stimulator will be programmed at the start of the study. 