Vagus nerve stimulation (VNS) is a procedure that was originally developed for the treatment of severe epilepsy (seizures). In this procedure, which does require surgery, a “pacemaker” is implanted in a pouch in the left chest wall, and a “lead” is attached to the vagus nerve in the neck.
A connection is made between the two devices by a thin “wire” under the skin. The “pacemaker” then delivers an electrical stimulation to the vagus nerve, which runs up to the brain and has many connections with different structures in the brain. It has been found that this kind of electrical stimulation can stop seizure activity. An external magnet allows the patient to stop the stimulation of the vagus nerve if it becomes uncomfortable (main complaints are hoarseness, cough and throat pain).
Researchers observed that there was a sharp improvement in mood in patients with seizure disorder after they were treated with VNS. Researchers also knew that some of the medications used in the treatment of seizures can have beneficial effects on mood, for reasons which are only partially understood. One of the main theories at this point is that the parts of the brain that are often involved in severe seizure disorders are also the parts of the brain that are involved in the regulation of mood.
Because of these observations, researchers have tried VNS in a small group of patients with treatment-refractory depression (TRD) — depression that is not responding to the usual medication treatments currently available. They have found that a subgroup of these patients have responded very well to the VNS. Interestingly, like with antidepressant medications, there is a short time period after starting the VNS before the depression symptoms start to improve. This suggests that VNS causes a process of adaptation or “re-balancing” in the brain which then leads to improvement in mood and functioning.
We need to await larger trials of VNS in depression (especially “double-blind” trials, where the patients do not know whether they are getting true VNS or “pretend” stimulation of the vagus nerve) before we can say for sure that this is an effective treatment for severe depression. But the initial results look very promising. One of the most useful outcomes of this kind of research will be that it helps us to learn more about how the brain malfunctions in depression and how we can design better treatments.