Fig. 4From: Treatment of chronic migraine with transcutaneous stimulation of the auricular branch of the vagal nerve (auricular t-VNS): a randomized, monocentric clinical trialMean course of number of headache days per 28 days during t-VNS treatment. Results of the per protocol set are shown (1 Hz: n = 17, 25 Hz: n = 22). Values are mean ± SEM. Mean values are also given in the figureBack to article page