Transcutaneous vagus nerve stimulation improves emotional processing

Invasive vagus nerve stimulation (iVNS) is approved for the treatment of major depressive disorder (MDD). The limited understanding of its underlying mechanisms, however, hinders stratification and the prediction of treatment response. Given the strong projections of the afferent vagal nucleus to brain regions involved in emotional processing, we tested whether acute transauricular VNS (taVNS) can improve emotional processing that is a core deficit in MDD.

We performed a randomized controlled trial. The facial emotion recognition task was performed by 52 participants with MDD and 44 controls during taVNS and sham stimulation. Linear mixed-effect models were used to evaluate the effect of taVNS.

At baseline, we found a negative bias across all participants with lower accuracy in detecting positive facial expressions (F(1, 173) = 17.39, p < 0.001) and more misclassification towards negative facial expressions (F(1, 173) = 13.73, p < 0.001). Acute taVNS improved the accuracy of detecting positive facial expressions across all participants (F(1, 90.26) = 6.49, p = 0.013), both at low and high intensity. Moreover, fewer negative emotional states as quantified by visual analogue scales were reported during taVNS (F(1, 85) = 5.34, p = 0.023). The effect of taVNS on ratings of positive emotional states was group-dependent (F(1, 86) = 4.20, p = 0.044), as only controls reported less positive emotions (t = 2.06, p = 0.042).

Independent of diagnosis acute taVNS has an impact on emotional processing. Future studies need to explore whether these acute effects can serve as a predictive marker for the long-term impact of taVNS.