A new medical technique, tested so far only on two monkeys with a form of Parkinson's disease, has dramatically eased their symptoms, researchers report in today's issue of the journal Science. The procedure also sheds new light on the nature of the disease.

The new technique reduced the disease's characteristic tremors and muscle rigidity, according to Mahlon DeLong of Emory University in Atlanta and two researchers from Johns Hopkins University.

"We think the finding is very exciting. It gives us a much more concrete idea about the basis of the disease," DeLong said.

The treatment involved destroying a small part of the brain, called the subthalamic nucleus.

"It is rather strong support for the hypothesis that the subthalamic nucleus -- a small structure deep within the brain just below the thalmus -- plays an important role in Parkinson's," DeLong said.

But he said it was too early to tell whether the technique would prove useful in treating Parkinson's in humans.

Delong said this demonstrates that Parkinson's symptoms are at least partially due to excessive electrical activity in the nerve cells in the portion of the brain they destroyed.

"It provides strong support for the view that the pathway through the subthalamic nucleus is overactive and if you can block that pathway by some means you can reduce the symptoms dramatically," he said.

"We have blocked it in the most obvious way by injecting a chemical that kills the nerve cells in that structure, and this could conceivably be done in man as well but we feel it needs to be more fully explored in animal models before we can contemplate using it in humans," he said.

DeLong said the next step is to study the long-term effects of the procedure and how it interacts with various drug therapies already used for Parkinson's.

Parkinson's, which mostly strikes people over 40, causes tremors and gradual loss of muscle control. About 500,000 Americans suffer from it.

It results from a gradual loss of nerve cells in an area of the brain known as the substantia nigra. These cells produce a brain chemical called dopamine that is vital for normal coordinated muscle movement.

The new findings suggest that the dopamine somehow keeps cells of the subthalamic nucleus under control. Without the dopamine, they become overactive and cause the muscle problems of Parkinson's disease. But by destroying this overactive region, the muscles are prevented from receiving its uncontrolled signals.