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How deep-brain stimulation reshapes neural circuits in Parkinson’s disease

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Dramatic and positive rapid effects are seen with deep-brain stimulation (DBS therapy) in treatment of movement disorders. However, it is surprising to note that scientists have little understanding of why and how DBS works. Even though there are huge prospects to improve the therapy further, lack of adequate understanding and knowledge have been holding things back.

For DBS, some devices are surgically implanted in the brain which sends electrical impulses to inner brain structures that are involved in movement. It is seen that Parkinson's disease (PD) patients who receive the treatment report a significant improvement in their symptoms. Symptoms like slow movement, tremor and rigidity diminishes to a great extent after the stimulation device is activated. Also, it is seen that when it is turned off, the symptoms returns quickly.

Even though DBS therapy has been a great success, still there are certain significant issues that still remain. Customizing the therapy for each and every patient is a cumbersome and challenging process and many a times patients do not derive its maximum benefit. That is why DVS has been a subject of interest for the scientific community. With a better understanding of how DBS acts on brain circuits, researchers hope to make DBS an even more effective treatment.

A new study, published online in Nature Neuroscience says that DBS is able to keep the symptoms of Parkinson's disease in check by minimizing excessive synchronization of brain activity in the motor cortex. Motor Cortex is a region on the outer surface of the brain which is responsible for the movements of the body.

Philip Starr, MD, PhD, the Dolores Cakebread Chair in Neurological Surgery and senior author of the new study said that even though the therapy is widely used these days for not only movement disorders but also many brain disorders, no one have a clue of how it works. The results of the new study are therefore significant because it answers this question on the level of brain networks, not just addressing where you’re actually applying the stimulation in the brain. The groundwork for this study has been laid by a previous research led by Coralie de Hemptinne, PhD, a postdoctoral fellow in Starr’s laboratory. It was found that a measure of synchronized rhythmic activity in the brain, which normally varies with movement or other behaviors, is excessively high in in the cortex in PD. It was hypothesized that it is likely that PD affects the flexibility needed by the brain requires to plan and execute movements, and that DBS might work by decoupling activity patterns in the motor cortex.

For the new study, the scientists decided to find out if there was a relationship between that synchrony and symptoms, and whether synchrony is lessened when symptoms are improved by DBS.  For that they measured synchrony in the motor area of the brain before, during, and after DBS, and while the patient was resting or engaged in a movement task in which they had to reach and touch a computer screen.

Their experiment showed that DBS eliminated excessive synchrony of motor cortex activity and facilitated movement without altering normal changes in brain activity that accompany movements.

Starr said that while their 2013 research revealed how Parkinson’s disease affects the motor cortex, their latest paper showed how DBS affects the motor cortex. The information revealed in these two studies can be crucial for developing new ways for stimulators to be automatically controlled by brain activity, which is the next innovation in the treatment of movement disorders.