How Deep Brain Stimulation Works

Brain Image Gallery This illustration shows how a deep brain stimulation device is positioned within the body. See more brain pictures.
Courtesy Courtesy of Medtronic, Inc.

Imagine for a moment that you have a movement disorder such as Parkinson's disease. The slight tremor that you first noticed in your fingertips has gradually worsened. Now simple tasks, like lifting a glass of water or even tying your shoes, have become nearly impossible. Your prescription medications were helpful for a time, but now the side effects are becoming a problem.

One day, your doctor suggests that you might be a good candidate for a relatively new therapy called deep brain stimulation. He describes how a small electrode would be implanted into a specific area of your brain, where it would deliver short pulses of electricity. These electrical pulses, he explains, would alter the patterns of activity in your brain responsible for your disease symptoms.

You decide to undergo the surgery required to implant the device, and just a few weeks later the difference is astonishing. Switching on the electrical stimulation immediately reduces your muscle tremors and restores your control over fine movements. Although your disease is still present, you can now manage its symptoms much more effectively.

This scenario is very real for the tens of thousands of people worldwide who have been implanted with a deep brain stimulation (DBS) device. In this article, we'll learn exactly how DBS works to achieve its therapeutic effects. We'll also explore what conditions can be treated with DBS and take a look at the risks and limitations of this form of treatment.

On the next page, we'll learn about the origins of deep brain stimulation and find out how the technology behind DBS was able to advance so quickly.

History of Deep Brain Stimulation

In the early 1950s, doctors found that lesioning, or destroying, specific areas within the brain could help treat certain movement disorders. When areas of the brain involved in the disorder were lesioned, the symptoms often improved. Soon, lesioning surgeries became a standard treatment for reducing problems in motor control caused by conditions like Parkinson's disease.

Unfortunately, lesioning surgery was not an ideal solution. They weren't always effective in reducing negative symptoms, and sometimes they resulted in damaging side effects. One of the main problems with lesioning surgeries is that their effects cannot be undone; a lesioned brain structure is permanently destroyed. As a result, unwanted side effects are usually irreversible.

In the 1970s a new drug therapy for movement disorders was introduced. Treatment with the new drug, called levodopa, could be used to control some of the same types of symptoms as lesioning, but without the risky brain surgery. Levodopa therapy quickly began to replace lesioning surgeries, mainly because of the advantages it provided patients. One of the benefits was dosages that could be adjusted to suit individual needs.

After many years, however, long-term levodopa therapy was found to cause new problems. The brain eventually compensates for the effects of the drugs. The result was often serious. Patients were developing new movement control problems that were considered worse than the original symptoms.

Then, in the late 1980s, a new discovery was made. Experts found that the same effects caused by lesioning brain tissue could be achieved by stimulating the tissue with harmless pulses of electricity. This was an exciting find, because the effects of electrical stimulation are completely reversible. In fact, when the stimulation is turned off, the brain resumes its normal behavior. Similar to drug treatments, doctors could tailor the electrical stimulation to fit the exact needs of each patient. Unlike drug treatments, the electrical stimulation could be localized so that only intended parts of the brain were affected.

Treatments with deep brain stimulation (DBS) were used on an experimental basis for several years, and positive treatment results were observed. In 2002, the use of DBS for conditions such as Parkinson's disease was approved by the Food and Drug Administration (FDA). DBS remains the standard treatment for several brain disorders similar to, and including, Parkinson's.

In the next section, we'll show you what an implantable DBS device looks like and find out how each part functions.

Deep Brain Stimulation Components

An implantable deep brain stimulation device delivers carefully controlled electrical pulses to precisely targeted areas of the brain involved in motor control.
An implantable deep brain stimulation device delivers carefully controlled electrical pulses to precisely targeted areas of the brain involved in motor control.
Courtesy of Medtronic, Inc.

An implantable deep brain stimulation (DBS) device is made up of three main parts: the electrode, the pulse generator and the extension. Here's what each part of the device is designed to do:

The electrode is a small tip-shaped device (imagine the plug for a pair of headphones) that is implanted deep into the region of the brain involved with the disease symptoms. The surface of the electrode has four metal pads used to transmit pulses of electricity. These pulses of electricity are small and only stimulate the brain tissue within close range of the electrode. This allows the electrical stimulation to specifically target only the brain region closest to where the electrode is implanted.

The pulse generator (also called the stimulator) is a small, box-shaped device that generates the electrical signals that are sent to the electrode. The pulse generator is usually implanted under the skin in a space near the patient's chest. It includes a battery with a lifespan that ranges anywhere from two to seven years. The electrical patterns are generated in quick on-off pulses delivered at very high frequencies -- usually over 100 times per second. Only at these high frequencies does the stimulation help reduce the unwanted symptoms.

The last component of an implanted DBS device is the extension, which is simply an insulated cable that carries the electrical signals from the pulse generator to the electrode implanted in the brain. Having any part of the DBS device go through the skin would create a risk of infection, so the surgeon typically tunnels a small path under the skin from the pulse generator to the electrode.

Patients are typically given a handheld device that uses a magnet to communicate through their skin to the pulse generator. This allows the patient to control the dosages of electrical stimulation he or she receives. A doctor sets the range of stimulation dosages within certain limits, but the patient actually does the fine-tuning of the device based on his or her own individual needs.

Now that you know what parts make up a DBS device, let's find out how it produces the desired effect.

Influencing the Brain Through Deep Brain Stimulation

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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.

Implanting the Deep Brain Stimulation Device

MRI scans are used to help the surgeon accurately locate structures within the patient's brain.
MRI scans are used to help the surgeon accurately locate structures within the patient's brain.
Luis Carlos Torres/iStockphoto

One of the most challenging goals for a surgeon implanting a deep brain stimulation device is to safely implant the electrode in the precise target location within the brain. Because not everyone's brain is shaped the same, the task of locating and accessing a specific brain structure without disturbing the surrounding structures requires the use of special tools and techniques.

One standard tool that is used for most delicate brain surgeries is a stereotactic frame. This device is basically a metal structure that holds the patient's head very still and gives the doctors a stable starting point to make their measurements. The surgeon will also rely on sophisticated imaging techniques to help pinpoint the location of specific structures within the brain. For example, the surgeon may rely on magnetic resonance imaging (MRI) or computerized tomography (CT scan) imaging, which can both be loosely thought of as three-dimensional X-ray scans.

The best way for the surgeon to be sure that the electrode is in the right place is to turn on the device and observe its effects on the patient's symptoms. For this reason, the patient is usually kept awake for the electrode implantation portion of the surgery. Because the brain itself has no pain receptors, the patient won't feel any pain. Only local anesthesia is required to numb the location where a small hole is made in the skull. The patient will also be required to discontinue the use of all medications prior to the surgery. This requirement is so that the effects of the electrical stimulation alone on the disease symptoms can be observed.

After the electrode is firmly in place, the pulse generator is implanted elsewhere in the patient's body where there's more space. Usually, this is in a location within the patient's chest. Since there's no longer any need for the patient to be awake, the patient is placed under general anesthesia for this part of the surgery. One other step involved in the surgery is to tunnel a wire under the skin from the pulse generator to the electrode in the brain.

Several days after the surgery, the doctors switch on the deep brain stimulation device and program it to suit the individual needs of the patient. Different aspects of the electrical stimulation pattern, such as its pulse strength, shape and frequency, can be adjusted as necessary. The patient is also required to come in every few months so that doctors can adjust this pattern to ensure optimal performance of the device.

Deep Brain Stimulation Results

Actor Michael J. Fox attends "A Funny Thing Happened On The Way To Cure Parkinson's" -- A benefit evening for the Michael J. Fox Foundation for Parkinson's Research.
Actor Michael J. Fox attends "A Funny Thing Happened On The Way To Cure Parkinson's" -- A benefit evening for the Michael J. Fox Foundation for Parkinson's Research.
Matthew Peyton/Getty Images

DBS is perhaps most famously used in the treatment of Parkinson's disease. Prominent actor Michael J. Fox helped to bring Parkinson's to the eyes of the public when he revealed his diagnosis with the disease. Essential tremor and dystonia are two other movement disorders that are also commonly treated with DBS. Essential tremor is characterized by tremors during muscle movements and is actually the most common movement disorder in the United States. Usually medication alone is sufficient to treat essential tremor, but sometimes severe cases require treatment with DBS.

Dystonia is a disorder resulting in unwanted muscle contractions. Notably, the DBS implantation surgery is performed differently in the case of dystonia. Because dystonia patients are unable to suppress the head and neck movements that are part of their symptoms, the patients must be placed under general anesthesia during the electrode implantation surgery. As we'll later learn, this situation can make proper electrode implantation more challenging for the doctor.

Parkinson's disease, essential tremor and dystonia are all movement disorders that share symptoms treatable by DBS stimulation to the basal ganglia. DBS can also be used on brain regions outside the basal ganglia to treat other conditions caused by abnormal brain function. The most common use of DBS is actually for the treatment of chronic pain.

DBS has also shown promising results in the experimental treatment of other conditions including Tourette syndrome, multiple sclerosis (MS), depression, epilepsy and obsessive compulsive disorder (OCD). A wide range of other possible future applications for deep brain stimulation therapy exists as well. The treatment of certain types of headaches, depression and even obesity are just a few of the possible applications of DBS that are currently being explored.

We've seen what a DBS device looks like and what conditions it can treat, but what are some of the risks and side effects?

Risks and Side Effects of Deep Brain Stimulation

The surgery required to implant a DBS device is an expensive and potentially risky procedure that doctors will recommend only for certain patients. First of all, the patient must be in healthy physical condition and able withstand the stresses caused by a major surgery.

It's also important to ensure that DBS therapy will have a good chance of producing effective results. One indication that DBS will be an effective treatment is if the patient's symptoms are responding to drug therapy. Drug therapies act on some of the same brain pathways as DBS, so if the drugs are having a good effect, deep brain stimulation might be beneficial as well.

So at what stage should deep brain stimulation be considered? Most specialists agree that DBS implantation should occur after drug therapies begin to produce their negative side effects but before the patient begins to experience a major decrease in quality of life. Quality of life is sometimes measured by the patient's ability to perform activities of daily living.

The patient must also have realistic expectations regarding the outcomes of DBS therapy. It must be clear to the patient that DBS is not a cure for his or her condition, but rather a treatment that might alleviate the condition's symptoms. Of course, the patient should also be fully aware of the risks and possible side effects involved with DBS implantation.

Although DBS is generally recognized as a very safe treatment, any major surgery -- especially brain surgery -- carries certain risks. One of the major risks is hemorrhaging, or excessive bleeding caused by damage to blood vessels. Brain tissue is very delicate, and navigating through the brain to implant a device can be challenging. The probability of major damage due to hemorrhaging is low, but if hemorrhaging occurs, the resulting complications can be severe and permanent.

Infection is another risk associated with DBS implantation surgery. The problems caused by infection are usually mild and treatable, but sometimes infections can cause serious problems. One more risk worth mentioning is breakage of the device. Breaks in the extension wire or movement of the stimulating electrode are two of the major causes of device failure.

The side effects caused by the electrical stimulation from the DBS electrode vary from patient to patient and commonly include minor sensory or motor control problems. Psychological side effects might include mood changes or feelings of depression. Fortunately, all of these side effects are usually temporary or can be reversed by turning off the stimulation. In most cases, the doctor can adjust the device's electrical stimulation patterns to minimize side effects.

If you found this article interesting and would like to know more about deep brain stimulation, follow the links on the next page. They can provide you with plenty of great information.

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Sources

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