Cortical Excitability and Heart Rate Variability in Response to Short Duration Transauricular Vagus Nerve Stimulation...

Vagus nerve stimulation (VNS) is approved as an adjunctive therapeutic intervention in neurologic conditions, including epilepsy and primary headache disorders. Transauricular VNS (tVNS) is increasingly used as a method for noninvasively activating the vagus nerve. However, the central neurophysiologic effects of tVNS are not well understood.

We evaluated the effects of tVNS on selected paired-pulse transcranial magnetic stimulation (TMS) tests and heart rate variability (HRV) in a group of healthy participants.

In this cross-over study design, we randomized healthy participants into either the tVNS or no-stimulation groups. Electrophysiologic assessments (short-interval intracortical inhibition [SICI], intracortical facilitation [ICF], and short-latency afferent inhibition [SAI], using TMS, and HRV) were performed before and after one hour of tVNS or no-stimulation. The same participants were allocated to the opposite treatment arm after a one-week wash-out period. tVNS was delivered to the tragus of the left ear using a portable electrical stimulation device with a custom-made clip electrode. An electrode was placed for an hour on the left ear lobe without stimulation as the control intervention.

tVNS increased SICI (reflected by the reduced motor-evoked potential amplitude) but had no significant effect on ICF or SAI. The HRV low-to-high-frequency ratio showed a greater reduction, and the normalized high-frequency power exhibited a greater increase after tVNS than did no-stimulation; these are markers of cardiovagal activity. None of the participants reported pain or discomfort during or after the tVNS. No adverse events were reported.

This study establishes enhanced cortical inhibition and cardiovagal activity in response to tVNS and its safety in healthy adult participants.