When atherosclerosis affects the arteries supplying blood to the brain, a stroke can result. One type of stroke, called a cerebral thrombosis, occurs when a blood clot forms on top of an arterial plaque in a blood vessel in the neck or head.

This shuts off or seriously restricts the blood supply to a part of the brain, killing the tissue there in a matter of min¬utes. This type of stroke typically causes paralysis on one side of the body or disturbances of speech, vision, hearing, or memory.

The exact signs and symptoms of the stroke depend on the specific parts of the brain that are affected. With physical therapy, another part of the brain can sometimes be trained to take over the task once controlled by the damaged area, restoring most or all of the lost functions.

A cerebral throm¬bosis can be fatal, however, if the damage occurs in an area of the brain responsible for breathing.

Atherosclerosis can also cause a second type of stroke— a cerebral hemorrhage—if a plaque-covered artery becomes weak enough to rupture.

This happens more frequently in people with high blood pressure, and large parts of the brain can die if the bleeding is severe enough. Cerebral hemor¬rhage strokes have many of the same symptoms as strokes caused by blood clots, but cerebral hemorrhages are more likely to be fatal.

About 2.7 million people in the United States have ath¬erosclerosis of brain arteries, and in 1987 nearly 150,000 people died from a stroke, making it the third leading cause of death.

Another 350,000 survive a stroke each year, and all told there are about 2 million stroke survivors in the United States.

The risk of death from stroke is twice as great in blacks as whites. Even more than heart attacks, the number of deaths from stroke has declined greatly in the last 20 years, mainly due to effec¬tive control of hypertension.