Does deep brain stimulation have a future in the treatment of depression?

Photo courtesy: Dr. Curtis Cripe via Flickr

Deep brain stimulation (DBS) is a neurosurgical intervention aimed at regulating neuron activity within the brain. The procedure is done under anaesthetic, where surgeons typically place electrodes into the brain through two small holes in the skull. A thin wire lead with several electrodes is then implanted, with a follow-up surgery done to implant the pulse generator near the collarbone. 

After the surgeries, the consultant will activate the generator through the use of specialist programmes. This is done to help relieve the symptoms of the condition, but it cannot cure the disease. The application of this technology has speculative benefits in treating severe forms of depression. So, just how effective is this surgery for affected patients? 

Treatment-Resistant Depression 
Depression is a common but serious mental health disorder. It causes an individual to have a persistent feeling of sadness and loss of interest in their day-to-day activities. It can affect people from a range of different backgrounds, regardless of race, age, or gender. Within the UK, around 4.5% of all adults are estimated to suffer from depression, with 70% of those accounting for mild depression. For the 16-24 age category, the figure could be as high as a third who are affected by some form of depression, based on a survey carried out by mental health charity Mind. 

The most severe form of the condition is treatment-resistant depression (TRD). TRD belongs to a subset of major depressive disorders. The symptoms exhibited in TRD are extreme mirrors of text-book depression e.g., insomnia or frequent suicidal ideation, but resist standard antidepressant medication treatment. Categorisation of the condition has been difficult, owing to its “multidimensional” nature. Some have even suggested the name “difficult-to-treat depression” as individuals may see benefit from a multimodal intervention, however, achieving an adequate remission in symptoms is rare.

Patients with TRD are offered a range of pharmacological approaches to attempt remission. For example  lithium when used in combination with tricyclic antidepressants has been found to improve the outcome of patients' moods when compared to standard and placebo treatments. However, their true success rate is hard to determine as the relative amount of lithium provided is fairly low. Another option for TRD patients is the use of second-generation antipsychotics (SGAs). They act in combination with first-generation medications by  inhibiting reuptake of serotonin and norepinephrine, with medications such as Risperidone offering symptomatic relief as a result. These interventions have been successful in nonpsychotic unipolar depression. However, these treatments are not always guaranteed to work for patients, prompting the search for new modes of treatment. 

Use of DBS for Depression
DBS has previously been considered for use in other neuropsychiatric conditions. One of them is obsessive-compulsive disorder. The exact placement of the electrodes is important in providing a clinically significant benefit for patients. Targeting is also critical when aiming to treat TRD, with most focus aimed at the subcallosal cingulate (SCC). This region of white matter is connected to the limbic system and regulates emotional behaviour, especially the feeling of sadness. 

The SCC has been one of the most studied regions for targeted DBS. In double-blind studies, remission has been found to be induced for periods of up to 3 years when using prolonged stimulation. Adverse effects have not been reported within the literature for either short- or long-term stimulation of the areas. Additionally, no cognitive impairments were noted upon multiple periods of stimulation, with benefits seen when the treatment strategy was not continued for a period of time before restarting again. 

However, there are still ethical concerns associated with this intervention. Overstimulation of an individual through prolonged electrode use may lead to the induction of neurological disorders or even mania. As the treatment aims to improve mood, an over-exertion of the treatment may lead to a reliance on the intervention to provide a state of euphoria. Extremes of overstimulation have even been noted to induce hypersexuality in patients, resulting in an inability to control their libido..

Progress for the Future
DBS is only being considered for the use of extreme cases of depression. Mild depression, where the effects are primarily on mood and behaviour, is responsive to conservative forms of treatment. The NHS website recommends talking-based therapies and regular exercise to assist wellbeing before a formal doctor’s appointment. 

Whilst the surgery may only be applicable for a small portion of those suffering from depression, the advancements that have led to this should be recognised. As patients hope for novel approaches to treat their chronic conditions without pharmacotherapies, the possibility of improving many patients’ experiences should not be ignored. Though optimum outcomes from DBS take time to be seen, the prospect of a new treatment provides hope for those suffering from a truly debilitating condition..  

Writers’ Note: Around 3 in 100 people are diagnosed with depression every week in England alone. It is a debilitating condition that still does not receive the recognition it deserves. As we approach the end of term, please know that Christmas can be the loneliest time of the year for many. So please, do reach out to your friends, even if it is for a quick conversation. You never know whose day you could make better. Samaritans are available 24 hours a day at 116 123 and Nightline is available from 6pm-8am at 02076310101.