Vagus Nerve Stimulation (VNS) and Treatment of Depression: To the Brainstem and Beyond

Abstract

Neuromodulation appears to be emerging gradually as a new therapeutic field in psychiatric treatment. It encompasses neuropsychiatric medical devices, such as vagus nerve stimulation (VNS), transcranial magnetic stimulation (TMS), deep brain stimulation (DBS), and electroconvulsive therapy (ECT). As a therapeutic approach to affective disorders, neuromodulation shifts the focus from the monoamine synapse to neural circuitry of the brain, which is dysregulated in depression. This neural circuitry has been elaborated on over the course of 15 years of neuroimaging research in mood disorders and is now believed to encompass disturbances in a frontolimbic network. These include reduced metabolism and blood flow in the prefrontal cortex and anterior cingulate and pathologically increased activity in the subgenual cingulate and amygdala.VNS is an implanted device that has established efficacy in pharmaco-resistant epilepsy. It was approved by the FDA for the treatment of severe, recurrent unipolar and bipolar depression in July of 2005. VNS adopts a bottom-up approach to modulating the neural circuitry of depression by stimulating vagal afferent fibers in the neck, which carry impulses to the brain stem to target there the locus ceruleus and dorsal raphe nucleus. Now that VNS has moved beyond the experimental phase and into the clinic, psychiatrists are faced with deciding who is an appropriate patient for this surgical implant and how to integrate VNS into existing treatment in order to optimize both efficacy and safety.This review of VNS will assess the efficacy and safety data that led to the FDA approval. We will also review for the busy clinician how VNS is likely to translate into clinical practice as a treatment option for patients in need who are suffering from severe depression.

Keywords: VNS; frontolimbic network; neuromodulation.

Figure 1

Schematic illustrating implanted pulse generator in chest wall and electrode attached to the left vagus nerve in the neck

Figure 2

VNS system with pulse generator (2” diameter and 2oz weight) and electrode lead with helical windings that the surgeon wraps around the left vagus nerve