Stimulating Your Brain
By Adam P. Smith, MD, East Denver LIVING WELL Magazine
Electrical stimulation has been used since the mid-1800s when pioneers identified localized electrical activity in the brain. By applying current to the scalp, they induced movements in animals. After all, the brain is just a conglomeration of electrical circuitry. As my partner quips, we as neurosurgeons are just tradesmen… high-paid electricians.
Certain diseases, such as Parkinson’s disease (PD), are examples of how disrupted electrical circuits in the brain lead to clinical problems. The majority of PD is caused by spontaneous degeneration of a part of the brain called the substantia nigra (SN). To this date, the cause of degeneration is unknown. Regardless, this “short-circuits” the system and leads to less dopamine (DA) in the brain, which is an important chemical for movement formation. The end result is abnormal movements such as resting tremor, rigidity, bradykinesia (slow movements), and imbalance.
The earliest treatments for PD involved placing probes into the brain to “burn” specific areas or inject destructive chemicals. These areas are part of the same electric circuit in movement formation and are connected to the SN. Their destruction, in effect, compensates for the “short circuiting.” Even today, these procedures, called pallidotomy or thalamotomy, are still sometimes used. The problem with intentionally destroying part of the brain is unwanted side effects, which are irreversible. As neurosurgeons, we are preservationists and do not like routinely destroying the brain.
In the late 1960s, synthetic dopamine (L-dopa) almost completely replaced these destructive procedures. L-dopa dosage could be individualized, and this treatment strategy seemed logical since normal brain dopamine was replaced with a very close analog. One problem, however, is that the L-dopa often works too well. Dyskinesias, or excessive involuntary movements, are the result. Furthermore, when L-dopa wears off, the patients revert back to tremor, bradykinesia, and rigidity. Alternating “on” periods of dyskinesia and “off” periods of “slow” movements plagues the lives of PD patients.
Recently, destructive procedures were again re-explored and more sophisticated methods to identify the target of destruction were used. It was noted that individual brain cells actually make noise when they conduct electricity. As technology advanced, extremely small “microphones” were developed, amplifying this noise loud enough to be heard by the human ear. Furthermore, different brain areas make different and recognizable patterns of noise. Therefore neurosurgeons can listen to the cells fire, and identify the exact location. The electrodes could also be stimulated to alter movements. This is the key in deep brain stimulation (DBS). High-frequency stimulation of certain brain areas, including the subthalamic nucleus, thalamus, and globus pallidus, has been found to improve PD symptoms.
The exact mechanism in DBS is not completely understood; however, the effects are inarguable. Although it sounds contradictory, the high frequency stimulation probably inhibits the subthalamic nucleus, which counteracts the malfunctioning SN. The principle benefits of DBS are improved symptom reduction, adjustability to maximize benefits and minimize adverse effects, and reversibility.
Unfortunately, DBS only treats symptoms. PD is a neurodegenerative condition in which the SN is destroyed and the brain’s DA is depleted. DBS will not do anything to alter this progressive and destructive pathway, and the effects of DBS may vary with time. However, DBS is a terrific treatment for severe cases of PD, and is the current primary surgical treatment.
Roughly 10% of PD patients are DBS candidates. Traditionally PD patients wait four to five years before being considered for treatment, but newer studies suggest earlier surgery may be beneficial. Unfortunately, DBS does not treat all aspects of PD. Tremor and bradykinesia are the most responsive symptoms. Rigidity also improves, but imbalance poorly responds. A rule of thumb is that DBS can help symptoms improved by dopaminergic medications. However, DBS does not mean patients will stop taking their medications. DBS simply lowers medication requirements, limits the “off” time and increases the “on” time, and reduces side effects such as dyskinesias. Other areas besides the STN are sometimes targeted in PD, depending on the predominant symptoms.
The entire DBS procedure is extensive, and extends before and after the actual time spent in the operating room. Not all patients tolerate the rigorous protocol. Responsiveness to medications helps predict future response to the DBS. Psychological, cognitive, and behavioral factors are evaluated. Other diseases must be ruled out that mimic PD. This process involves a team dedicated to the individual patient’s evaluation.
Once eligible for DBS, brain imaging is used preoperatively to plan the surgery. In the operating room, the team members carefully listen to the brain cells fire, finding the optimal placement of the electrode. The patient is awake for this portion of the procedure. Often the procedure is performed on both sides of the brain. These electrodes are then connected to a battery in the chest. Postoperatively, the neurologist adjusts the stimulation to maximize symptom control. From then on, the patient’s brain is partially modulated by this external stimulator.
PD is the most common disease treated by DBS, but other movement disorders, such as dystonia and essential tremor are amenable. Newer applications of DBS are rapidly expanding. “Investigational approval” exists for obsessive-compulsive disorder. Trials are ongoing for depression, Tourette’s syndrome, obesity, cluster headache, memory, and epilepsy. This is probably the most rapidly growing aspect of neurosurgery, if not all of medicine.
If you would like to speak to a “brain electrician” and possibly be evaluated for DBS, please contact Adam P. Smith, MD, and The Neurosurgery Center of Colorado by calling 303-481-0035.