Randomized crossover study of transcutaneous auricular vagus nerve stimulation compared with sham stimulation on high-frequency stimulation–induced secondary mechanical hypersensitivity in healthy women
Experimental secondary mechanical hypersensitivity induced by high-frequency stimulation in healthy women.
The study uses a randomized within-subject crossover laboratory design with two conditions: transcutaneous auricular vagus nerve stimulation (taVNS) and sham stimulation. Participants attend two laboratory visits conducted on separate days. In one session, participants receive taVNS and in the other session, sham stimulation. The order of the two conditions is counterbalanced across participants. Randomisation of condition order was performed using block randomisation. Before the experiment, a list was generated in LibreOffice Calc in which each row contained the order of conditions and a random number generated by LibreOffice Calc’s random number generator. The random numbers were then ordered from low to high and this new sequence of ordered conditions was followed, with the first signed-up participant assigned to the first row, the second to the second row, and so on. At the beginning of each session, three electrocardiogram (ECG) electrodes are attached to monitor cardiac activity throughout the experiment. After a 5-minute baseline recording period, participants report their affective state and rate the intensity and unpleasantness of mechanical pinprick stimulation applied to the volar forearm of both arms. High-frequency electrical stimulation (HFS; 2.5 mA) is then applied to one forearm to induce secondary mechanical hypersensitivity. Affective state ratings are collected again following HFS. Electrical stimulation of the left ear is delivered using a DS5 constant-current stimulator (Digitimer Ltd., UK) controlled by MATLAB. In the taVNS condition, a modified NEMOS® electrode is used, with its contacts combined into one pole, while an EEG electrode serves as the second pole. The electrodes are positioned at the cymba conchae and cavum concha to stimulate auricular regions innervated by the vagus nerve. In the sham condition, two EEG electrodes are attached to the earlobe. Stimulation intensity is individually calibrated using a 0–100 sensation scale to re
1. Healthy women aged 18–35 years 2. Able to understand spoken and written English 3. Able and willing to comply with study procedures and provide informed consent
1. Bradycardia, cardiac arrhythmia, or any cardiac disease 2. History of or current neurological disorder 3. Current psychiatric disorder 4. Other serious medical condition 5. Use of chronic and ongoing medication (women using contraceptive pills are allowed) 6. Pregnancy 7. Use of recreational drugs within the past week 8. Recovery from serious trauma or an operation 9. Previous participation in studies using the same stimulation device