Vagus nerveThe most commonly used treatments for major depressive episodes are pharmacotherapy and psychotherapy. - Although the majority of patients suffering from a major depressive episode improve significantly with these treatments, a minority does not achieve adequate symptom reduction.These minority are described as having treatment-resistant depression (TRD).Although the definition of TRD is itnpetfect, the (STARD) data suggest that patients who have major depression and who have failed to respond to three or four medication trials are treatment resistant.Until recently, few treatments for major depression other than pharmacotherapy, psychotherapy, and electroconvulsive therapy (ECT) have been available.Now days somatic therapies are being used for TRP.- These new treatments are device-related and/or surgical interventions .for major depression and other psychiatric illnesses, and the field associated with these new treatments often is referred to as "neurotherapeutics" or "neuromodulation".These treatments are typically (but not always) used in TRD patients.Examples of neurotherapeutic interventions for major depression include :- Ablative limbic system surgeries- Vagus nerve stimulation (VNS),- Transcranial magnetic stimulation (TMS), and- Deep brain stimulation (DBS).Ablative limbic system surgery Procedures used include - Anterior cingulotomy - Subcaudate tractotomy - Limbic leucotomy - Anterior capsulotomyThese procedures have been found to be efficacious in patients suffering .from intractable mood and anxiety disorders with response rates ranging .from 35% to 70% over a period of several weeks to several months, depending upon the response criteria.Vagus nerve stimulation (VNS) Vagus nerve stimulation (VNS) was initially approved for use in treatment-resistant epilepsy in 1994 in Europe and in 1997 in the United States. During the treatment it was noted that many patients with treatment-resistant epilepsy being treated with VNS experienced improved mood. This led to its use for treatment-resistant depression and bipolar disorder.VNS device is surgically implanted around the left vagus nerve an incision in the neck (only the left vagus nerve is used for VNS because the right vagus nerve has parasympathetic branches to the hea)The exact mechanism of VNS is not completely understood. The fibres of vagus have widespread connections to many areas throughout the CNS that are implicated in feeding, arousal, mood, and other "reflex" behaviors.It is impoant to note that the FDA-approval language states that VNS is an adjunctive treatment for TRD and that it should be used in patients with severe, chronic, recurrent TRD who have failed at least four adequate antidepressant trials.Transcranial magnetic stimulationRepetitive trans-cranial magnetic stimulation (rTMS) uses a strong magnetic field introduced on the scalp surface to generate .focal electrical stimulation of the coical surface.To date in the United States, this procedure remains experimental, not approved .for general clinical use with regard to this indication i.e. treatment resistant depression.Deep brain stimulationDBS involves the placement of electrodes in specified brain regions so that electrical stimulation can be delivered in a targeted manner.To date, one clinical trial of DBS for depression has been published.