During the weeklong session, researchers will give more than 1,600 presentations of scientific work that deals with diseases of the brain and nervous system.

"This is the largest meeting ever," Catherine Rydell, executive director of the academy, told United Press International. "We are up about 20 percent over attendance at last year's meeting in San Diego."

In one study discussed in Boston, Harvard Medical School doctors tested how sleep affects memories. They recruited 48 healthy people who were given standard word-pairing tests at 9 a.m. and then were asked to recall the parings at 9 p.m. after being awake for 12 hours.

Another group of subjects took the test at 9 p.m., got normal rest and then were asked to recall the list at 9 a.m. The study found that people who slept after learning the information performed best, successfully recalling more words, or a 12-percent greater recall overall.

"This is the first study to show that sleep protects memories," said Dr. Jeffrey Ellenbogen, a clinical fellow in medicine at the Center for Sleep and Cognition at Brigham and Women's Hospital in Boston.

"These results provide important insights in to how the sleeping brain interacts with memories: It appears to strengthen them. Perhaps then, sleep disorders might worsen memory problems seen in dementia."

Other researchers said that vigorous recreational activities and exercise may reduce the impact of Parkinson's disease.

"This study does not prove that exercise caused the lowered risk of Parkinson's disease; it's possible that something else lowers the risk," said Evan Thacker, a research assistant at Harvard's School of Pubic Health. "But considering all of the other benefits of exercise, it certainly doesn't hurt to make sure you get some moderate or vigorous exercise several times a week."

Thacker and colleagues reviewed data on 63,348 men and 79,977 women in the Cancer Prevention Study II Nutrition Cohort from 1992 to 2001 and calculated the amount of exercise reported by the participants.

Compared with people who did little daily activity, people who performed daily vigorous exercise had about a 40-percent lowered risk of developing Parkinson's disease, Thacker reported.

Recreational activities also trended to be protective, he said, indicating those activities such as walking or dancing had a 20-percent reduction in the risk of developing Parkinson's disease later in life.

In the battle against multiple sclerosis, doctors who checked demographic records said they are still seeing the trend of women developing the disease at a higher rate than men. At one point in the early 20th century, multiple sclerosis was thought to be almost strictly a disease that affected men, but better diagnosis techniques found that by 1940, twice as many women as men developed the disease.

By the year 2000, that disproportion had grown to more than four to one, said Gary Cutter, professor of biostatistics at the University of Alabama at Birmingham.

"That's an increase in the ratio of women to men of nearly 50 percent per decade," he said. "We don't know yet why more women are developing multiple sclerosis than men. More research is needed."

He said researchers are considering numerous possibilities such as changes in women over the decades in use of oral contraceptives, earlier menstruation, obesity rates, changes in cigarette smoking, later age of first births, use of hair dyes or use of sunscreens that may block vitamin D absorption.

"At this point we are just speculating on avenues of research that could be pursued," Thacker said.

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