Pacemaker electrodes – a quick fix for major depression?

Science and Technology

Major depressive disorder is a prevalent and debilitating condition. It leaves patients despondent, unable to maintain jobs and stable relationships and often leads to suicide. Treatment-resistant depressive disorder is a term used to denote a depressive condition that does not respond to two courses of typical antidepressant medication. Deep brain stimulation, a surgical treatment involving the implantation of an electronic pacemaker into the brain, is a technique that is already of considerable therapeutic benefit in several treatment-resistant movement and affective disorders including chronic pain, Parkinson’s disease and dystonia and as such, has been proposed as a putative treatment for major depression.
In a recently published paper, researchers from the Bonn University Hospital in Germany showed that deep brain stimulation of the medial forebrain bundle, a bundle of nerve cells involved in the brain’s reward system, had a remarkable effect in patients suffering from major depressive disorder. For the study, electrodes were implanted into the medial forebrain bundles of the brains of 7 patients with major depression and the electrodes were connected to a pacemaker. The neurons were then stimulated by the application of a weak electrical current. It was found that over the course of seven days, six of the seven participants noted a considerable reduction in their previous feelings of despondence and anxiety and a general elevation in mood. The speed of this improvement is in marked contrast with typically used antidepressant medication, which can take up to 6 weeks to take effect. A member of the Bonn University Hospital Department of Psychiatry said of the results: “Such sensational success both in terms of the strength of the effects, as well as the speed of the response has so far not been achieved with any other method.”
Deep brain stimulation has previously been investigated in other areas of the brain, including notably the nucleus accumbens; another part of the brain’s reward system. Electrical stimulation of this area resulted in an improvement of depressive symptoms in only half of cases, in comparison to the 85% found in this study. Further benefits of this new technique are that it requires the application of a lower current level and improvements are notable after days as opposed to weeks.
How deep brain stimulation acts to reduce depression or indeed, why the stimulation of the median forebrain bundle is found to have a greater effect than stimulation of other parts of the reward system, is currently unknown. However, it has been postulated that the positive effect is due to changing metabolic activity in different brain centres.
However, while these results are certainly promising, are pacemaker electrodes really the miracle cure that we’ve been looking for? After all, a sample size of 7 is not exactly substantial and a positive result in 85% of participants is still only a positive result in 6 patients. Furthermore, this study only looks at the effects of treatment over a short time period and further work would need to be done to support deep brain stimulation as a viable, long-term treatment. Indeed in a previous study into the efficacy of deep brain stimulation in the ventromedial cortex found that while 60% of patients achieved a reduction in symptoms in the first month post-treatment, depressive symptoms did return, with only 30% of participants maintaining an elevated mood at three months. It will therefore be important to follow up on the 6 patients in this study, to see if the positive effects are maintained.
So, while pacemaker electrodes may not be a miracle cure, this recent paper does give hope to those suffering from a greatly debilitating disorder. Further clinical trials should be undertaken, to see if the therapeutic benefit found here is more widely applicable and if this technique could one day become part of standard therapy.


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