Study federally funded

Merck holds patents on the drug but did not sponsor the study, which is one of many being funded by the federal government. This year, Alzheimer's disease research received about $647 million from the federal government.

Some scientists believe that lowering cholesterol levels in the body changes chemical reactions in the brain and slows the progression of Alzheimer's disease. Already, studies have shown that controlling blood pressure, cholesterol and weight can help reduce the risk of the disease.

Previously, small-scale studies with 20 to 50 patients have shown that cholesterol-lowering drugs, such as Lipitor and Zocor, may slow the progression of Alzheimer's disease.

The disease, sometimes referred to as "the long goodbye," attacks the minds of the elderly over the course of decades. Alzheimer's patients typically begin by losing their memory. Eventually dementia takes over. As their minds degenerate, Alzheimer's patients can regress to the point of babbling like a baby and being unable to stand or swallow.

With the aging baby-boom generation, the number of Alzheimer's patients is likely to increase. Currently, an estimated 220,000 people in Northern California struggle with the disease, according to the Alzheimer's Association, a national research and advocacy group based in Chicago.

By 2050, the association estimates that more than 600,000 Northern Californians will be diagnosed with the disease.

Clumps and tangles

Alzheimer's disease has been studied for nearly a century.

As Germany was enjoying an industrial boom before World War I, Alois Alzheimer, a neurologist in Munich, first identified the disease. He interviewed a woman who was losing her memory and spatial skills. Before she died a few years later, the woman had started hallucinating and had lost the ability to write.

Alzheimer performed an autopsy on her brain in 1906. He found protein plaques, clumps of tiny biological molecules, and also found that parts of the nerve cells in her brain had become tangled. Those clumps and tangles have come to define Alzheimer's disease.

Like Alzheimer, scientists today still do not know what causes the disease. Some believe the clumps and tangles are a result of Alzheimer's, not its cause. But many studies have shown that the clumps and tangles cause brain decay. Alzheimer's research is therefore often aimed at reducing the number of clumps in the brain.

There is no cure for Alzheimer's disease, nor is there a way to stop it from progressing. The few drugs that are available mostly help ease some symptoms of the disease, such as insomnia, anxiety and depression. The nationwide study now under way aims to determine whether lowering the cholesterol in Alzheimer's patients is enough to slow the progress of the disease by slowing the accumulation of clumps in the brain.

The clumps are formed from the biological molecules, called beta-amyloid particles, that float around in the brain. Because the particles are slightly sticky, they eventually start clinging to each other. Studies have shown that high levels of cholesterol can trigger the brain to produce lots of beta-amyloid particles, which occur naturally in the brain but become dangerous when clumped together -- ''Like when you are cooking spaghetti and it all sticks together,'' said William Seavey, a geriatrician and internist at UC-Davis who has also been involved in the nationwide study.