Deep brain stimulation, currently used to treat tremors, may one day be able to preserve and restore memories.
What would you think if I told you I was going to shock your brain with electricity? You might first have a flashback to Jack Nicholson's "shock shop" in One Flew Over the Cuckoo's Nest or to a crazed Dr. Frankenstein energizing his new creation. But those tales are fiction. In reality, we have harnessed electricity to treat a variety of brain disorders. Much like 70 years ago, when we educated people that when it came to cooking, electricity was their best friend, we are beginning to explore the many benefits of stimulating the deeper parts of the brain with electricity.
Last week, I taught second-year medical students how to perform a neurologic examination. I always enjoy this part of the year, since the medical students are waist-deep in course work and hungry to see a real patient. Our patient had a long history of an essential tremor. When he tried to hold his arms straight out in front of him, his arms and hands moved wildly up and down. It was dramatic. He couldn't bring a glass of water to his lips without soaking himself or anyone within a few feet. It took him 30 minutes to button his shirt. Medications didn't help him, and his degree of disability depressed him.
As I told the students about his operation six years prior, he slowly held a small device that looked like a TV remote control over his chest to turn on the small electrical current at the tip of the wires deep inside his brain. He once again slowly raised his hands, and this time, they were rock solid. Not a tremor, not even a wiggle. The initial collective gasp of the students was followed by a universal exclamation: "Wow." This was why they were becoming physicians -- to change people's lives. It looked like magic, to just flip a switch and change a life. But, this man's "miracle" was the end result of many years of research.
The next day my eye caught a headline on CBS News that read, "Electric brain stimulation may treat Alzheimer's." This is exciting news. Deep brain stimulation (DBS) is highly effective for the treatment of Parkinson's disease, essential tremor, and dystonia. Currently, we're also studying its effect on people with depression, obsessive-compulsive disorder, chronic pain, and obesity. However, the ability to alter the course of Alzheimer's disease would change the lives of tens of millions of people and their families.
So, if DBS is such a "miracle worker," what is it really, and how does it work? Clinical trials that placed stimulating wires (electrodes) deep in the brain to control abnormal movements started in the 1980s and were first approved for clinical use in the United States in 1997. The actual procedure is fascinating. The patient is awake throughout most of the procedure so that they can supply feedback on how they feel and the surgeon can see the results of the stimulation on any abnormal movements. Before the surgery begins, a stereotactic frame is screwed into the skull under local anesthesia. It is not as bad as it sounds -- the patient experiences little to no pain. With the frame in place, the surgeon performs an MRI scan, which allows him to calculate within 1mm where he should place the wire deep inside the brain. The patient is briefly put to sleep, and the surgeon drills a small hole on each side of the skull.
It looked like magic, to just flip a switch and change a life.
The brain itself does not feel pain, so with the patient awake and with the guidance system of the frame attached to the skull, the surgeon passes a small wire with a stimulating electrode at its tip precisely to the desired location. The stimulator attaches to the wire and the wire is positioned so that the patient obtains the desired response without side effects. The hardware is then secured to the skull and the small battery powered implanted pulse generator (IPG) is placed under the skin just below the collarbone. The patient turns the stimulator on and off using a small controller that they place over their skin above the IPG.
Typically, the doctor doesn't turn on the stimulator for 2 to 4 weeks, so everything can heal. The physician "programs" the device to deliver the precise type of electric stimulation by placing another device over the skin and IPG. It may take several months and programming trials to get the desired effects.
To be truthful, we are not totally certain how DBS works, but it does help if you understand a few basic facts about the brain. It is simplistic to think that right side of the brain only controls the left side of the body and vice versa. The brain is a complicated collection of neural "networks" that connect distant areas of the brain. Imagine that you are sitting in your air-conditioned office on a warm summer day. The lights, AC, computers and elevators all hum along without a glitch. You hear a light rain hitting the windows, but ten miles away a lightning bolt strikes the relay transformers on the power grid. Your computer blinks off, and suddenly you realize that all the power is gone. Nothing happened at your office that would have cut the power, but since you are on the same power grid as where the lightning struck, all your services shut down. The same thing can happen in your brain.