Monday, July 08, 2002

Pacemaker sends a rhythm to the brain

By Peggy O'Farrell,
The Cincinnati Enquirer

        Passing small amounts of electricity into the brain can ease symptoms of depression, epilepsy, Parkinson's disease and chronic pain.

Color infographic, "Wiring The Brain."
· CAUTION: This is a large file (1.2 mb) in Adobe Acrobat format.

(Mike Royer graphic)
| ZOOM |
        Earlier this year, the Food and Drug Administration approved deep brain stimulation commonly called a brain pacemaker, for the general treatment of Parkinson's disease. It had previously been approved for tremor associated with Parkinson's and essential tremor. It's the newest of a group of treatments that apply voltage to affect electrical signals in the brain.

        When there's a glitch in those signals, disease results. Re-routing current with deep brain stimulation, stimulation of the vagus nerve (a nerve that enters the brain at the base of the neck) or other treatments helps keep diseases under control.

        Doctors don't know the exact mechanism that makes these treatments work. But most patients just want results.

        ''As long as it helps, I don't care why,'' says Sandy Lane, whose daughter, Jaimie, received an implant for vagus nerve stimulation four years ago.

        Before neuroscientists could ''wire'' the brain with neural implants and other technology, they had to rely on more invasive surgeries, such as a corpus callosotomy, to suppress epileptic seizures. In that technique, the neural connection between the brain's hemispheres is surgically severed.

        Implants don't require the destruction of brain tissue and are removable, so if they don't work, the surgeon can just take them back out.

        Dr. James L. Olds, director of the Krasnow Institute for Advanced Study, a Fairfax, Va., center that focuses on studying learning and the brain, compares using electricity to treat neurological disorders to a conductor leading a sometimes unruly orchestra.

        ''Think of a brain function, say movement or even language, as being subserved by an orchestra of nerve cells.         Now imagine that for whatever reason, they aren't playing together. The product is noise instead of music. Now imagine that we bring in a conductor or even a metronome to get all the members of that orchestra playing together once again. That logic is analagous to the logic of using electrical stimulation to treat neurological disorders. The electrical stimulation is used to re-establish the "beat,' ” Dr. Olds says.

        Others put it less poetically.

        “Usually these disorders of the brain have an abnormal electrical circuit that goes from one structure to another. When we interfere with that circuit by interrupting the signal to it, we can produce the relief of symptoms,” says Dr. Jamal Taha, a neurosurgeon at the Mayfield Clinic.

        As the baby boom generation ages, diseases such as Parkinson's are expected to grow in numbers substantially, making for increased use of neural implants and similar procedures, says Dr. Olds. He adds such procedures “may be more cost-effective than drugs.”

        But don't expect a generator to cure Alzheimer's disease., he says.

        “Continuing the orchestra analogy, Alzheimer's disease is a disease of the instruments (imaging dying violins and trombones) rather than a problem with how the orchestra plays music together,” Dr. Olds says. “With AD, we need to figure out how to fix the sick instruments (the nerve cells) and perhaps how to generate new cells.”


Relief for tremors

               An electrode placed inside the brain can help control disabling tremors caused by Parkinson's disease, dystonia and other disorders.

        Deep brain stimulation is also used occasionally to treat chronic pain, and some researchers are experimenting with the so-called brain pacemaker as a treatment for depression.

        Placement of the implant depends on what condition is being treated. A generator unit is surgically placed under the skin on the patient's upper chest, and a lead runs from the generator to the scalp and then into the brain to the implant. To treat tremor, the implant is placed in the thalamus — a large structure within the brain that relays sensory information to the cerebral cortex.

        To treat akinetic symptoms (impaired or slowed muscle movement), the implant is placed in the globus pallidus or subthalamic nucleus, brain structures which regulate involuntary movement.

        The implant can be turned off and on with a handheld magnet, and many patients turn the unit off at night.

        The electrical current “jams the signal” the brain sends out that cause tremor or other muscular reactions, says Dr. Taha. “That's probably the best way of describing it.”


Suppressing seizures

               Tiny electrodes attached to the vagus nerve where it enters the base of the neck and heads up into the brain help suppress epileptic seizures.

        Vagus, or vagal, nerve stimulation works on the same principle as a cardiac pacemaker used to regulate heart function. A tiny generator, or battery unit, is surgically placed just under the skin on the patient's upper left chest. Plastic tubing containing electrodes runs from the implant to the vagus nerve, which winds throughout the brain. Electrical impulses from the implant are carried along the nerve into the brain to suppress seizures that can't be controlled by medication.

        “This is an alternative treatment to having to take all kinds of pills or have a brain resection,” says Dr. Michael Schmerler, a neurologist with Riverhills Healthcare Inc.

        About 2.5 million Americans have epilepsy. For one in 20, medications can't control debilitating seizures. Some patients are suitable candidates for lobectomies, the removal of tiny areas of brain tissue where seizures originate. Most aren't because doctors can't find the source of their seizures or there's more than one source in the brain.

        Jaimie Lane was 6 years old when she suffered a severe head injury in a 1982 car accident. Several months later, after surgery to relieve swelling in the brain, she began having seizures.

        Medications didn't control her seizures, said her mother. But the implant has cut the number of seizures she has each day in half, and reduced the severity of her seizures.

        “It's been a great benefit to her,” Mrs. Lane said.

        Most patients, including Jaimie, still have to take medication after vagus nerve stimulation.

        Patients can use a hand-held magnet to stimulate the generator to try to suppress a seizure if they sense one coming on. Mrs. Lane says Jaimie uses the magnet daily.

        The implant doesn't last forever: The battery lasts up to 12 years and needs to be replaced. Patients also have to have the electrical output adjusted from time to time.

        Jaimie recently had to have her implant replaced after a wire in the generator broke.

        Doctors believe that the implant works by stimulating the release of gamma-amino butyric acid (GABA) and glycine, two compounds in the brain that suppress seizures. The two compounds apparently act to interrupt the electrical signals that cause the seizures.

        The treatment isn't without side effects, says Dr. Wa-Shain Yeh, a neurosurgeon at the University of Cincinnati. He knows of two patients who asked to have the implants removed.

        “It's useful for some patients, but so far, you cannot usually tell which patients will be responsive,” Dr. Yeh says.


Shock therapy

               When Mount Auburn psychiatrist Dallas Auvil broaches the subject of electroconvulsive therapy (ECT) to patients are often surprised to learn it's still in use.

        ECT or “shock” therapy isn't as popular as it once was, but for some patients it's the only thing that works, say Dr. Auvil and Dr. James Curell, the psychiatrist who oversees the ECT program at University Hospital.

        “It's still the best treatment available for severe depression,” Dr. Curell says.

        ECT is mostly used to treat depression, less often to treat schizophrenia and the manic phase of bipolar disorder.

        “It's not the first line of treatment,” Dr. Auvil says. “It's usually after they've failed several medications.”

        Critics and former ECT patients have called the treatment torture, arguing it causes permanent memory loss. The therapy gained a bad reputation through films such as One Flew Over the Cuckoo's Nest and The Snake Pit.It was widely used in the 1950s and 60s, before effective, well-tolerated medications became available for psychiatric use.

        Doctors don't understand the exact mechanics that make ECT work. But they know it does work.

        During ECT, a mild electrical current is directed through the patient's brain, triggering a brief seizure. The seizure, in turn, causes the brain to release a flood of chemicals that somehow alleviate the patient's symptoms. Patients are sedated during the treatment.

        ECT isn't a cure, Dr. Curell says, but it can cause enough improvement in patients for medications to become effective. Dr. Curell's patients receive three ECT treatments a week for two to four weeks, depending on the severity of their symptoms. Most continue to need medication and psychotherapy after undergoing ECT. Some will require maintenance ECT treatments to continue progress.

        For most patients, ECT is a treatment of last resort.

        “It shouldn't be,” Dr. Curell says. “ECT is such a powerful treatment that many people would benefit from an earlier course.”


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