Functional magnetic resonance imaging shows that vagus nerve stimulation (VNS) modulates activity in brain regions associated with mood control in patients with treatment-resistant depression who respond to therapy, according to an article in the August issue of Neuropsychopharmacology.

The current study, led by Ziad Nahas, MD, associate professor, Medical University of South Carolina Department of Psychiatry, enrolled nine adults with unipolar or bipolar depression (severe depressed type) who had received a stimulation device for adjunct therapy. Serial evaluation of cortical brain activity was done with a three-month, double-blind, placebo-controlled study period and an open 20-month follow-up.

The study was also designed to identify variables that affected functional response such as length of use, strength of stimulation and level of depression, in order to better understand the impact of vagus nerve stimulation therapy.

"These data provide further insight into VNS therapy's distinct mechanism of action and support its previously demonstrated long-term, sustained efficacy," Nahas said. "We are encouraged to see the unique benefit VNS therapy may bring to patients with one of the most difficult-to-treat forms of depression and are excited to continue neurostimulation research at MUSC."

The study illustrated that therapy modified activity of the medial prefrontal cortex, the same area of the brain targeted by many antidepressant medications and electroconvulsive therapy.

A critical time for such effective modulation occurs at approximately 30 weeks of treatment. Such modulation could support this unique mechanism of action as a long- term treatment for chronic or recurrent depression that would directly correspond with the timeframe in which patients typically experience a decrease in symptoms.

Further analysis of the data demonstrated that modulation of brain activity was a dynamic process that led to indirectly related improved response with continued use. These findings corroborate an earlier study at the same institution that revealed approximately two thirds of patients who respond to therapy continue to experience significant clinical benefit at 24 months, making it the only treatment for treatment-resistant depression to demonstrate such long-term improvements.

The U.S. Food and Drug Administration approved this form of device therapy in 2005 as an adjunctive long-term treatment of chronic or recurrent depression for patients 18 years of age or older who are experiencing a major depressive episode and have not had an adequate response to four or more antidepressant treatments.
It is the only device ever studied and approved for treatment-resistant depression. Therapy is delivered from a small pacemaker-like device implanted in the chest area that sends mild pulses to the brain via the vagus nerve in the neck.