Transcutaneous vagus nerve stimulation
blindness
BLINDNESS
All subjects received active and sham tVNS treatment in a crossover design. During their first visit, participants were randomized by throwing a dice with respect to the order of active or sham intervention, resulting in a balanced assignment. Subjects received all necessary information for their participation in the study, except that the nature of the vagus nerve stimulation and the exact electrode placement were not mentioned to ensure their blindness. The inner tragus of the left ear was used as the active stimulation site, while the left earlobe served as the sham control. Previous skin preparations included a cleaning with disinfectant alcohol and the application of conductive gel. The Easy Tens + device with customized bipolar clip electrodes (both obtained from body clock, London, UK) was used to deliver continuous biphasic, rectangular pulses with a pulse width of 250 µs and a frequency of 30 Hz. The current amplitude was fixed on 20 mA, which was perceived by the subjects, but never reported as being painful.