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About this Article
Written by: Munir Chaudhuri
Written on: December 6th, 2007
Tags: biomedical engineering, health & medicine
Thumbnail by: LadyOfHats/WIkimedia Commons
About the Author
In the fall of 2007, Munir Chaudhuri was an undergraduate student at the University Of Southern California studying Biomedical Engineering with an emphasis on neuroengineering and a hope to go to medical school.
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Volume IX Issue IV > Vagus Nerve Stimulation Therapy
Treating drug-resistant epilepsy and depression seemed impossible a few years ago. However, with the advent of Vagus Nerve Stimulation, treatment of these severe types of diseases is now possible. VNS therapy is a powerful new treatment that modulates some neural structures and functions to benefit those diagnosed with drug-resistant epilepsy and depression. Powered by an implanted battery, electrodes attached to the left vagus nerve are activated to send electric pulses to the nerve. These pulses propagate into the brain, altering the synchronous neural activity that causes epileptic seizures and affecting many areas of the brain related to depression.

Introduction

Depression is a serious medical illness that affects more than 20 million people in the United States and millions more worldwide. It's more than just feeling "blue" or "down" for a few days; it is an ongoing feeling that never leaves those with the disease. These feelings often dominate and ruin patients' lives. There are a few options for patients with depression: medications, counseling, and now Vagus Nerve Stimulation (VNS). Antidepressants work to fight the symptoms of depression by increasing the availability of neurotransmitters, molecules that propagate or inhibit neuron-to-neuron impulses in the brain. The two most common antidepressant drugs, namely serotonin-selective reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs), increase the levels of the neurotransmitters serotonin and norepinephrine. These chemicals affect many regions and structures of the brain including centers for mood, motivation, appetite, sleep, and several other areas involved in depression [1]. However, as with all drug treatments, there are adverse side effects, which often result in patients avoiding the drugs. Furthermore, the treatments do not cover everybody; cases of intractable drug-resistant depression are on the rise. Additionally, the blood-brain barrier, a very selective membrane that prevents the vast majority of small molecules from entering the central nervous system, hampers drug research.
The other option that many patients with depression seek is counseling. Despite being very effective if used properly, counseling can be expensive and time-consuming. For the most part, depression can be treated with antidepressants, counseling or a combination of the two. However, VNS offers a more simple and effective approach; in a mechanism similar to epilepsy treatment, VNS has been found to curb the effects of depression [2].
Similar to major depression, severe forms of epilepsy can be life-altering negative experiences for patients. Epilepsy is a common neurological disease, a chronic condition characterized by spontaneous, recurrent seizures. An epileptic seizure is associated with a temporary, hypersynchronous neuronal discharge [3]. During its outbreak, millions of neurons discharge simultaneously, causing an electrical overload in the brain.
Worldwide, 50 million people suffer from epilepsy, many of whom take one or more of the 15 different anti-convulsant medications. However, the drugs have painful side effects, and 50% of people with epilepsy lack adequate seizure control or continue to have disabling side effects [4]. In fact, 20-30% of all individuals with epilepsy have drug-resistant forms of the disease. Consequently, drastic measures -- such as ablative surgery in the temporal lobe of the brain -- need to be adopted in these patients; otherwise, the lack of seizure control can lead to devastating psychosocial and health consequences, including serious accidents and cognitive or behavioral deterioration [2]. The advent of Vagus Nerve Stimulation has provided a safer alternative to brain surgery for the treatment of the drug-resistant form of epilepsy.