Acute effect of vagus nerve stimulation (VNS) on brain function

VNS is a non-pharmalogical neuromodulatory treatment option for difficult-to-treat depression. A pulse generator implanted in the left chest area is connected to an electrode that is wrapped around the left vagal nerve. It is presumed, that the vagal afferent network modulates neuronal activity in key monoaminergic structures. We performed MEG recording during active stimulation of the left vagal nerve. Our patient was a 60 years old female treated with VNS since December 2019 due to unipolar major depression. MEG recording and analysis were possible despite stimulation signals and the metal stimulation systems. We saw a reproducible reduction of the 10-Hz-alpha amplitude after the end of the 30 s stimulation period in wide-spread areas including parieto-occipital cortex where alpha oscillations are prominently generated. During stimulation, however, alpha oscillations remained unaffected. These findings could be reproduced in a second measurement. Increased alpha power was linked to depressive states and alterations of cortical activity. A reduction may indicate cortical activation by stimulation of the vagal nerve as a possible mechanism of action of VNS in depression.