The Vagus Nerve as a Gateway to Body Ownership: taVNS Reduces Susceptibility to a Virtual Version of the Cardiac and Tactile Rubber Hand Illusion

Figures

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  FIGURE 1. taVNS setup. Panel A: neurostimulation electrodes were cut into shape to fit participants' ears. Panel B: Electrodes were placed on the cymba conchae during active taVNS (blue) and on the earlobe during sham taVNS (red). We delivered continuous current stimulation with a pulse width of 200–300 μs at 25–30 Hz with stimulation amplitude tailored to individual perceptual threshold (between 0.5 and 50 μA).

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  FIGURE 2. Electrode setup for neuECG recording. The setup was conducted according to the procedures described by Kusayama et al. (2020). Lead I on the right and left subclavicular areas (cathode and anode, respectively) for Channel 1, and Lead II on the right subclavicular area (cathode) and left abdomen (anode) for Channel 2. The reference electrode is placed on the right abdomen.

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  FIGURE 3. Setup and procedure for the virtual rubber hand illusion. Panel A: Participants sit at a black desk with their left hand on the table. They wear an Oculus Rift head‐mounted display with a LeapMotion hand tracking device on its front. Panel B: In the VR setting, participants are seated at a desk, and they can see a virtual hand that mirrors their hand movements in real time.

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  FIGURE 4. Procedure for the virtual rubber hand illusion. The experiment is composed of eight trials: Four tactile trials (two synchronous and two asynchronous) and four cardiac trials (two synchronous and two asynchronous) which were presented in pseudo‐randomized order. During each trial, after an initial resting period, participants (1) complete a first proprioceptive drift test, (2) focus on their virtual hand during a 2‐min induction period in which the hand is stroked by a paintbrush or flashes red, (3) complete a second proprioceptive drift test, and (4) complete the final 5‐item questionnaire.

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  FIGURE 5. Output data for neuECG from one participant on Labchart 8. Channels 1 and 2 display raw data. Channels 3 and 4 display the SKNA (μV); Channels 5 and 6 display iSKNA; Channels 7 and 8 display aSKNA; Channel 9 displays ECG, and Channel 10 displays the tachogram of the HR.

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  FIGURE 6. Violin plots displaying significant differences in HR and SKNA between baseline and (active and sham) taVNS. Our findings suggest that HR was lower compared to baseline for active but not for sham stimulation, whereas SKNA increased with the stimulation both during active and sham conditions.

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  FIGURE 7. Violin plots displaying significant differences in PDD between active and sham taVNS. In both cardiac and tactile trials, the stimulation seemed to affect susceptibility to the rubber hand illusion. PDD (in cm) was greater for synchronous trials compared to asynchronous trials only during sham stimulation but not during active stimulation.

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  FIGURE 8. Violin plots displaying significant differences in subjective ownership between active and sham taVNS. In both cardiac and tactile trials, subjective ownership was greater for synchronous trials compared to asynchronous trials only during sham stimulation but not during active stimulation.