Intervention
Participants will receive active and sham stimulation with the NEMOS © CerboMed tVNS device. Two small electrodes emit a low-voltage electric signal which permeates the skin. When the electrodes are placed at the cymba conchae of the ear, stimulation actives the afferent branch of the VN that innervates the skin of the ear (Arnold’s nerve). The electric signal consists of an 8 Hz frequency wave with participant-selected amplitudes ranging from 0.1 mA to 5 mA depending on their sensory threshold, the signal cycles of 200 ns and comes in 30 s on – 30 s off bursts. For the sham condition the electrode is placed on the earlobe which is free of vagus innervation. For the active condition it is placed on the cymba conchae of the left ear. At each stimulation study visit the device is explained to the participant and then fitted by the study researcher. Participants are given oral and written instructions at each stimulation study visit regarding how to set up and fit the device in their ear.