The brain normally works by sending electrical signals from one part of the brain to another. Deep brain stimulation (DBS) is a way of changing how electricity flows through the brain. Electrical impulses are transmitted through thin wire implants into carefully selected brain regions in order to achieve the desired results.
Prior to deep brain stimulation, one of the only ways to impact the electrical signal in just one part of the brain was to perform surgery to remove abnormally active brain tissue or disrupt the circuits through which neural messages flow. Unlike those methods, deep brain stimulation has the benefit of being reversible. However, deep brain stimulation is expensive and not without risks.
Deep brain stimulation is used to help various medical conditions. Perhaps the most common use is to help symptoms of Parkinson’s disease, but it has also been used for essential tremor and dystonia.
Some research suggests that deep brain stimulation may be useful outside of neurological movement disorders, and could be used to help problems like chronic pain, obsessive-compulsive disorder, or even depression. At this time, using DBS for these disorders is still considered somewhat experimental, but the practice appears to be gaining ground.
What is the Deep Brain Stimulator?
A deep brain stimulator consists of three components. The first parts are the leads. These are thin wires that run through the brain to the exact location to be stimulated. The leads are connected to extensions that run outside the brain to connect the leads to the implanted pulse generator (IPG), a device approximately the size of a stopwatch. The IPG is usually implanted near the collarbone or abdomen, and is responsible for actually triggering the electrical impulses that are then transmitted into the brain region, like a pacemaker for the brain.
Implanting a Deep Brain Stimulator
Prior to the operation in which the electrodes are implanted in the brain, an MRI scan is performed. This identifies the targeted part of the brain, and helps to ensure that the surgeon places the tips as close as possible to the desired coordinate. To further ensure that the leads are in the right position, the first part of the procedure is also done under local anesthesia rather than the general anesthesia that leads to unconsciousness. This way, the patient can let the surgeon know what they are experiencing, in order to ensure the leads are in the right spot.
After the local anesthetic is given, a small incision is made in a shaved and cleaned part of the scalp. A small hole is then made through the skull, and the dura mater that normally covers and protects the brain is opened. This leaves a small part of the brain exposed. The DBS electrode is then guided down into the appropriate location deeper in the brain.
The second part of the operation involves a general anesthetic being given so that the patient loses consciousness. An incision is made at the point where the pulse generator will be implanted, and the extensors are passed under the skin from this location up along the neck to the spot where the leads exit the brain. The pulse generator is then connected and implanted into its position, and the incisions are closed.
Sometime after the device is implanted, the patient will visit their neurologist, who will change the settings on the device to ensure that symptoms are being controlled as best as possible.
The procedures may vary depending on the location of the stimulation. For example, while the procedure may be done all in one day for most patients with dystonia, implanting stimulators into the subthalamic nucleus for Parkinson's disease requires close monitoring that is more time-consuming. For this reason, the two parts of the operation are most likely to occur on different days. Furthermore, details of the procedure vary by hospital and by physician. It is important to make sure that the details of the procedure are thoroughly discussed and understood.
Potential Complications of Deep Brain Stimulation
Complications from deep brain stimulation may develop from the surgery, from mechanical problems with the device, or as a side effect of stimulation. While some complications can occur regardless of where the leads are placed, others are more specific to certain locations in the brain.
Surgical complications from deep brain stimulator implantation are uncommon. In one review done in 2006, permanent neurologic damage occurred in 2.8% of patients who underwent the procedure, and 0.6% had complications resulting in death. Less severe complications included hemorrhage, infection, confusion, and seizures. All of these occurrences were infrequent.
Hardware problems are not uncommon following deep brain stimulation. Leads, IPGs, and extension wires may need to be replaced due to malfunctions. In thin patients, the extension wires may erode through the skin, leading to further complications. Rarely, the leads may shift from their location in the brain and stimulate a different area instead.
Many important functions of the brain are located very closely together. Stimulating one region of the brain may lead to unintentional stimulation of another. These effects vary by location, but can include changes in mood, slurring of speech, or thinking problems.
The technology surrounding deep brain stimulation is improving quickly, and one might expect the percentage of complications to have fallen since the 2006 review, with even further improvements on the horizon.
Deep brain stimulation can have profound benefits for many people with movement disorders, and is showing promise for a wide variety of other neurological conditions as well. Neurologists still don’t understand exactly how DBS causes such changes, and DBS does not change the underlying disease. Nevertheless, it’s good to have another tool to treat a patient’s symptoms, provided everyone recognizes both the potential risks and benefits involved.
Bronstein JM et al. Deep brain stimulation for Parkinson disease: an expert consensus and review of key issues. Arch Neurol 2011:68;155
Okun MS, Fotte KD. Parkinson’s disease DS: what, when, who and why? The time has come to tailor DBS targets. Expert Rev Neurother 2010:10 1847-57
Mustafa Saad Siddiqui, Ihstsham Ul Haq, Michael S Okun, Deep Brain Stimulation in Movement Disorders, Continuum : Movement Disorders Volume 16, Number 1, February 2010
Pahwa R, Factor SA, Lyons KE, et al. Practice Parameter: treatment of Parkinson disease with motor fluctuations and dyskinesia (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology 2006; 66:983.