Auricular vagus nerve stimulation for stress reduction: Evidence from alpha prefrontal asymmetry

This study explores auricular vagus nerve stimulation (aVNS) within the context of stress. Five healthy subjects underwent a pulsed mode aVNS (with a frequency of 25 Hz and pulse width of 200 μs) using a custom made current stimulation device. The device triggered the auricular vagus nerve branch through the tragus for 15 minutes, with prefrontal EEG data collected pre and post aVNS (each for 5 minutes) to capture stress indicators. Given that the frontal location is prone to noise, EEG signal pre-processing through independent component analysis (ICA) was used to reduce eye movements and other artifacts. Alpha (8-14 Hz) asymmetry in prefrontal location in both hemispheres was computed from locations Fp1 and Fp2 for one second segments of EEG; these asymmetry values were normalised by subtracting the post aVNS (or placebo) from pre aVNS (placebo). The normalised alpha frontal asymmetries were assessed for statistical significance using T-test. Results showed increased aVNS alpha prefrontal asymmetry compared to placebo, indicating reduced stress. This was statistically significant ( ) for all five subjects. It is therefore concluded that the pulsed mode aVNS stimulation at the tragus may represent a potential approach for stress relief.