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Before we continue, we'll need to review a few facts about the brain. You may already know that the brain is divided into many specialized areas, each responsible for different tasks. There are separate regions of your brain that play a role in controlling muscle movements, memory and even emotions. These separate regions of the brain work together to accomplish larger goals. When injury or disease prevents any one brain region from performing its role, the larger goals might not be met.
A good example of this is the basal ganglia. The basal ganglia is a group of brain structures that work together to help control body motions. As movements are planned and coordinated in the brain, information in the form of electrical brain activity flows between the structures of the basal ganglia. Each structure plays a role in modifying and refining the information to help fine tune muscle movements. When any part of the basal ganglia is impaired, the normal flow of information is altered. Widespread movement control problems are often the result, as in the case of Parkinson's disease.
To find out where deep brain stimulation comes in, let's stick with the example of the basal ganglia.
As mentioned above, the normal electrical flow of brain activity throughout the basal ganglia is disrupted by the effects of Parkinson's disease. The purpose of an implanted DBS electrode is to counteract this abnormal brain activity, altering it in a way that decreases the disease symptoms.
The electrode accomplishes this by targeting one of several possible structures within the basal ganglia. For Parkinson's disease, this is most commonly the subthalamic nucleus (STN). A deep brain stimulation electrode implanted in the STN sends out pulses of electricity, modifying its behavior. By altering the behavior of the STN, the electrode is ultimately altering all of the brain activity that the STN normally affects. This makes the DBS electrode very influential, since the STN is one of several structures in the basal ganglia that all work together.
Sounds simple enough, right? Well, what the experts haven't fully worked out yet is exactly how DBS influences the brain structures it stimulates -- although there are several likely possibilities. For example, the quickly repeating electrical signals emitted by the DBS electrode may act to block irregular brain activity. In this scenario, the effects of the electrical stimulation can be thought of as a gate blocking certain pathways of corrupted information. Another possibility is that the regular pattern of electrical pulses from the implanted DBS electrode would act to override irregular flows of information. In other words, the electrical stimulation of the DBS device acts to drown out the abnormal patterns of brain activity.
The complete story of how DBS achieves its effects is probably much more complex. It's likely that the same pattern of deep brain stimulation affects different parts of the same brain structure in completely opposite ways. Although the mechanisms of DBS aren't yet fully worked out, doctors have enough experience using DBS to feel confident of its safety and effectiveness.
Now that you have an idea of how a DBS device works, let's take a look at how it's implanted in the brain.