Influence of Vagus Nerve Stimulation on Mood and Associated Disorders

There is growing interest in the application of neuromodulatory therapies to the treatment of psychiatric conditions, such as mood and anxiety disorders. Vagus nerve stimulation (VNS) was approved by the United States Food and Drug Administration in 2005 as an adjunctive, long-term therapeutic option for adults with treatment-resistant depression. Clinical studies have demonstrated that augmenting standard antidepressant treatments with VNS is associated with greater reductions in depressive symptoms and improvements in remission rates compared to using standard treatments alone in this population. Moreover, the clinical benefits of VNS appear to increase over time with long-term treatment. Potential mechanisms underlying the antidepressant effects of VNS include effects on neurotransmitter systems, inflammation, and neurogenesis. Despite these demonstrated benefits, the invasive nature of surgically-implanted VNS has limited its clinical application. Noninvasive forms of VNS have recently been developed, including transcutaneous vagus nerve stimulation (tVNS). Although research on clinical applications of tVNS is in its early stages, there is some evidence to suggest that tVNS may improve symptoms of depression, anxiety, and related conditions, such as posttraumatic stress disorder and insomnia. This chapter provides a review of the clinical and preclinical literature exploring the effects of VNS and tVNS on mood and anxiety symptoms. In addition, it discusses potential mechanisms underlying these effects and highlights limitations of available research and important avenues for continued investigation.