![enter image description here][1] **Fig. 1 Auricular stimulation.** a) Auricular ear anatomy. b) Electrode positions for taVNS and sham conditions, on the left ear. Stimulations parameters were identical between both conditions, consisting of monophasic rectangular impulses at 25Hz and 250µs pulse width, with a duty cycle of 30s ON /30s OFF. Current intensity (mA) was titrated at individual level to elicit a maximal, but non-painful, tingling sensation. Abbreviations: V3: Third branch of the trigeminal nerve (mandibular branch). C2 and C3: Second and Third cervical roots of the cervical plexus. Adapted from Peuker & Filler (2002), He et al (2012). ---------- ![enter image description here][2] **Fig 2. Overview of all experiments.** a) Experiments conducted in healthy subjects. Each participant underwent a randomized protocol, during which non-invasive taVNS and sham stimulations were delivered in a 2-day cross-over design. Experiment 1 focused on the somatosensory effects induced after 3h of taVNS/sham stimulation, while Experiment 2 focused on the immediate effects of the OFF/ON phases of the duty cycle (30s ON/30s OFF). b) Experiment 3 was conducted in epileptic patients. The experiment focused on the immediate effects of the OFF/ON phases of the duty cycle (rapid cycling: 30s ON/ 1.1min OFF) of the implanted cervical VNS in a 1-day protocol. Participants completed a minimum of 3 blocks of suprathreshold stimulations, and a fourth depending on tolerability (fading 4th arrow). Abbreviations: ERPs = Event Related Potentials, taVNS = transcutaneous auricular vagus nerve stimulation. cVNS = cervical vagus nerve stimulation T0 = baseline. T1 = during vagus nerve stimulation. T2 = after vagus nerve stimulation. ---------- ![enter image description here][4] **Fig 3. Detection thresholds.** Each diagram represents the differences in detection thresholds between T0 and T1, or between T0 and T2, for one type of sensory fibers, under one experimental condition (taVNS vs. sham stimulation). Within each diagram, individual values are shape-coded according to the experiment in which they were retrieved (circles for Experiment 1, triangles for Experiment 2), with values from a same individual linked by a grey line. Grey boxes represent group statistics, with central horizontal lines and top/bottom extremities indicating the mean ± SD values. The Y axes represent the differences in detection thresholds between T0 vs. T1 or T0 vs. T2. Detection thresholds were measured in Celsius degrees (°C) for heat- and cool-sensitive fibers, and in an arbitrary unit (A.U) for mechano-sensitive A𝛽-fibers. The X axes indicate which conditions are compared on the related Y axes. There was no significant alterations observed. ---------- ![enter image description here][5] **Fig 4: Behavioral responses: Intensity of perception.** Each diagram represents the perceived intensity for one specific somatosensory modality, under different conditions (sham, taVNS or cVNS). Within each diagram, individual values are shape-coded according to the experiment in which they were retrieved (circles for Experiment 1, triangles for Experiment 2, diamonds for Experiment 3), with values from a same individual linked by a grey line. Grey boxes represent group statistics, with the central horizontal lines and top/bottom extremities indicating the means ± SD values. The Y axes represent the differences in intensity ratings between T0 vs. T1, T0 vs. T2 or OFF vs. ON phases. Intensity ratings were collected using a numerical rating scale (NRS) from 0 (no sensation) to 10 (maximal sensation). The X axes indicate which timepoints or phases of the duty cycle are compared on the related Y axes. There was no significant alterations observed. ---------- ![enter image description here][6] **Fig 5. ERP waveforms.** Each diagram represents the ERPs obtained at group level for one somatosensory modality and one experimental condition. The colors of the waveforms are specific to one experiment, one timepoint (T0 or T2) and one phase of the duty cycle (OFF or ON). The Y axes represent the amplitude of the difference in potentials (µV) observed at the Cz electrode, when referenced to the bilateral mastoid contacts (M1M2), with negative values at the upper end and positive values at the bottom of the axes. The X axes represent the evolution of time (in seconds) relative to the onset of the somatosensory stimulus (0s). The N2 peak was defined as the most negative deflection with a latency comprised between 0.1 to 0.5s. The P2 peak was defined as the first positive deflection after N2. The black circle and asterisk represent in Experiment 1, the statistically significant alteration observed over time in the latencies of the laser-evoked N2 peaks (p=.038). To note, the low signal to noise ratio in Experiment 1 (especially on Vibrotactile- and Cool-evoked ERPs obtained from healthy subjects) and Experiment 3 (epileptic patients). ---------- ![enter image description here][3] **Figure 6: ERPs: Peak Amplitudes.** Each diagram represents the absolute difference in the amplitudes of specific peaks (N2,P2,N2P2 amplitude) of one type of somatosensory-ERP (Laser-, Vibrotactile-, Cool-ERPs), recorded at a specific timepoint (T0,T2) or phase of the duty cycle (OFF,ON) under one experimental condition (sham, taVNS or cVNS). Within each diagram, individual values are shape-coded according to the experiment in which they were retrieved (circles for Experiment 1, triangles for Experiment 2, diamonds for Experiment 3). Grey boxes represent group statistics, with the central horizontal lines and top/bottom extremities indicating the means ± SD values. The Y axes represent the absolute difference (in µV) measured between two recordings of a specific peak. The X axes indicate which timepoints or phases of the duty cycle are compared on the related Y axes. There were no statistically significant results obtained. 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