The vagus nerve in psychiatry: From theories to therapeutic neurostimulation in neuropsychiatric disorders

The vagus nerve (VN) plays an important role in the modulation of the autonomic nervous system, inflammatory system, and interoception, therefore connecting the cardiovascular and gastrointestinal systems to the central nervous system. Dysregulation of the VN is implicated in several psychiatric disorders. The recent availability of safe and non-invasive transcutaneous VN stimulation (tVNS) techniques opens new opportunities to evaluate the role of the VN in psychiatric disorders. We briefly review the basic anatomy and physiology of the VN, extensively discuss various theories linking VN dysfunction to health and illness, give details of the probable neurochemical underpinnings of VN activity, delineate its dysfunction in psychiatric disorders and put forward the current state and future directions of VNS, specifically focusing on tVNS.