Electrical Stimulation of the Brain Reverses
Symptoms of Parkinson's Disease

The Toronto Hospital - first in Canada - to perform
deep brain stimulation for treating Parkinson's disease

Toronto June 1, 1997 ... Toronto researchers have shown that part of the brain that is underactive in Parkinson's disease patients improves its function when electrical stimulation is applied deep in the brain. As a result, the symptoms of Parkinson's disease are reversed.

The study, which is published today in Nature Medicine, found that stimulating the globus pallidus, a part of the brain that regulates movement, leads to improved activity in another part of the brain that co-ordinates muscle movements, the supplementary motor and pre-motor areas.

The finding explains why patients who undergo a procedure known as deep brain stimulation have improvements in their Parkinson's disease symptoms, says Dr. Andres Lozano, a neurosurgeon at The Toronto Hospital and principle investigator of the study.

The Toronto Hospital was the first in North America to perform this procedure for the treatment of Parkinson's disease, a chronic, slowly progressive disease of the nervous system. Its causes are unknown. But its major symptoms, which may include tremors, muscle rigidity, slowness of movement, difficulty with balance and movement, are caused by a lack of the chemical neurotransmitter dopamine. For some reason, cells that normally produce dopamine gradually die. Approximately 100,000 Canadians have the disease.

"Previous research has shown that patients with Parkinson's disease have underactive or diminished function in their supplementary and pre-motor areas of the brain. What was not known, however, was why patients who undergo deep brain stimulation have improvements in their symptoms. With this study, we have shown that the underactive part of the brain becomes active, or is like a dimmed light bulb that shines brighter after stimulation."

More interesting is that the electrical stimulation is not applied directly to the underactive part of the brain but another part deep in the brain, the globus pallidus. "We can stimulate from a remote part of the brain and have an effect on a different part of the brain that is underactive," Dr. Lozano says, "It's like a domino effect."

In deep brain stimulation, electrodes are placed in either the globus pallidus, to control movement, or the thalamus, to control tremors. The electrodes are then connected to a stimulator, much like a heart pacemaker, located under the collarbone. The stimulator, which is battery operated, sends electrical currents to the brain interrupting the abnormal signal sent from the diseased brain cells. The electrical stimulation, which is reversible, can be altered to suit individual patient's needs.

The study also found that deep brain stimulation appears to work by electrically inhibiting or blocking the globus pallidus.

"In patients with Parkinson's disease, the globus pallidus has become overactive because of the lack of dopamine. As a result, it acts like a brake on the car which is pushed down all the time resulting in diminished movement in patients. Our studies suggest, however, that the stimulation decreases the activity of the brake by inhibiting the globus pallidus."

Fifteen patients were enrolled in the study nine who had undergone deep brain stimulation in the globus pallidus and six in the thalamus. The thalamus group was the control group. Using positron emission tomography (PET), blood flow in the brain was monitored while the stimulators were turned off, turned on halfway and turned on completely.

"This study indicates that deep brain stimulation offers a promising approach to treating Parkinson's disease," Dr. Lozano says. "It also shows that the globus pallidus is certainly one of the most important parts of the brain to place stimulating electrodes. There are other areas we can place the electrodes and we are exploring those as well.

The study was done in collaboration with the Department of Physiology at the University of Toronto and the Clarke Institute.

For more information, contact Josey Panetta, Senior Media Relations Officer, The Toronto Hospital, 416 340-3303.

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