Above: Schematic of deep brain stimulation. Image courtesy of The Defeating Epilepsy Foundation.

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During deep brain stimulation, clinicians surgically implant electrodes in the brain to provide a constant current through a generator in the chest that acts like a pacemaker. This electrode stimulation can alter the normal pathway of electricity in neural networks and change the neurochemistry in the brain. Despite these impacts, the mechanisms underlying DBS are still unclear.

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In 2002, the U.S. Food and Drug Administration (FDA) approved DBS as a treatment for Parkinson’s disease that aims to prevent the decline of motor skills and tremors. It proceeded to approve DBS for obsessive-compulsive disorder only a few years later in 2009. Recent research has focused on how DBS can be used as a treatment for other mental disorders. Clinical trials have tested DBS as a potential treatment for major depressive disorder, addiction, bipolar disorder, eating disorders, and other mental illnesses. 

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A Tainted History

Neuromodulatory therapies use electrical or chemical modalities to influence the nervous system and include non-invasive treatments, like electroconvulsive therapy and transcranial magnetic stimulation, and newer invasive treatments such as responsive neurostimulation and DBS.

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Electrical therapy treatments for mental illnesses have held a negative association as a result of their past unethical uses—particularly electroconvulsive therapy (ECT), in which patients were shocked with high doses of electrical current, causing seizures and other negative side effects, without the use of general anesthesia. Medical providers still use ECT today with safer methods such as more controlled doses of electrical stimulation and proper medications. Despite ECT’s negative history, electrical stimulation therapies are gaining interest with the potential that newer neuromodulatory treatment modalities have on mental illnesses. 

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DBS Therapy

Because DBS requires open-brain surgery, doctors often use it as a last resort for people who have treatment-resistant mental illnesses, in which multiple therapeutic and pharmaceutical treatments have not helped alleviate symptoms. 1-3% of people in the US have treatment-resistant depression. Common treatments for mental illnesses include psychotherapy, brain stimulation, and residential and hospitalization programs. However, patients do not always respond to these modalities. Unfortunately, pharmaceutical medications for mental illness are not very reliable either, with 30% of patients with major depressive disorder failing to achieve remission on the medication. Mental illness increases the risk of drug abuse, suicide, disability, homelessness, incarceration, and quality of life. The World Health Organization forecasts that major depression will become the leading contributor to the global number of years lost due to disease in 2030. Suicide, often linked to depression, is the second leading cause of death for adolescents between the ages of 10-14 and adults between ages 25-34 and is the third leading cause of death for adults aged 15-24.

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Above: Disability-Adjusted Life-Years Burden for different mental illnesses in the U.S. Image courtesy of The Lancet.

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The clinical trials for DBS treatment for various mental illnesses, although still in the early stages, are promising. In a 2013 study, six out of seven patients responded to DBS treatment with an average decrease of 50% on the Montgomery-Åsberg Depression Rating Scale after just one week of stimulation. 12 to 33 weeks after the initial stimulation, four out of those six patients were in remission from depression. Several other studies have supported these findings, illustrating DBS’s potential antidepressant effects. 

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In a study targeting heroin abuse, five out of eight patients maintained abstinence over three years, two relapsed after six months, and one passed away three months after initial surgery. Additional studies targeting alcohol and nicotine addiction have likewise observed a general trend of decreased substance cravings and intake following DBS surgery.

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People experiencing treatment-resistant mental illnesses continue to struggle despite exhausting all options to improve their mental health. Mental illness can have many causes including genetic factors, trauma, chronic stress, environmental factors, and neurochemical imbalances. DBS offers a new chance to treat these multifaceted disorders. While future researchers will need to personalize DBS treatments for each patient’s unique brain and target biomarkers for specific diseases, increased access to DBS may improve the lives of many people with treatment-resistant mental illnesses. 

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