Antinociceptive Effect of Transauricular Electrical Vagal Nerve Stimulation (TVNS_TSP)

Antinociceptive Effect of Transauricular Electrical Vagal Nerve Stimulation and Its Underlying Mechanisms

This investigation is going to study whether electrical tVNS applied at the cymba of auricular conchae reduces central sensitization of experimentally induced pain in comparison with electrical sham stimulation applied at the earlobes and whether the hypoalgesic effects of tVNS disappear after pharmacological block of muscarinic receptors. Also, this investigation will examine whether tVNS is associated with activation in brain areas, involved in processing of thermal pain stimuli and emotional and vegetative modulation of thermal pain in subjects who will respond with antinociceptive reaction to tVNS.

Real tVNS will be applied using pre-defined characteristics of tVNS device to cymba conchae of the auricle, sham procedure will be the same, however applied to tubule of the auricle

Stimulation will be applied using TENS device eco 2 (Schwa-Medico, Pierenkemper GmbH, Ehringshausen, Germany) bilaterally at the cymba conchae of the auricles for 20 minutes. Current intensity (1-max. 10 mA) will be individually adjusted for each ear separately until the maximal tVNS intensity, which is not uncomfortable or painful, will be achieved.

Same stimulation will be applied using TENS device eco 2 (Schwa-Medico, Pierenkemper GmbH, Ehringshausen, Germany) to bilaterally to the earlobes for 20 minutes. Current intensity (1-max. 10 mA) will be individually adjusted for each ear separately until the maximal tVNS intensity, which is not uncomfortable or painful, will be achieved.

Auricular electrical stimulation will be applied bilaterally using Transcutaneous Electrical Nerve Stimulation device TENS eco 2 (Schwa-Medico, Pierenkemper GmbH, Ehringshausen, Germany). tVNS will be applied bilaterally using electrical square impulses delivered in blocks of 9 impulses with a frequency of 100 Hz and a pulse width of 200 μs emitted twice per second resulting in mixed frequency pattern of 100 Hz/2 Hz with the current intensity, that will be individually adjusted for each ear separately until the maximal tVNS intensity, which is not uncomfortable or painful, will be achieved.

perceived unpleasantness of pain, which participants will rate continuously during the repetitive heat stimulation using a computerized visual analogue scale (CoVAS, Medoc Advanced Medical Systems, Ramat Yishai, Israel) ranging from 0 (= not unpleasant at all) to 100 (= intolerable pain).

Inclusion Criteria: healthy volunteers aged 18-45 years old, who have given informed consent at least two days free from consume of recreational drugs no local infection at the site of tVNS and pain stimulation Exclusion Criteria: psychiatric disorders abnormal skin conditions (infection, scars, psoriasis, eczema) at the site of tVNS contra-indications for MRI (e.g. claustrophobia, pregnancy, tattoos, metallic implants) history of coronary heart disease, cardiac arrhythmia, glaucoma, allergy to sulphates