President Obama today lifted an eight-year-old ban on embryonic stem cell research, signing an executive order that he called "an important step in advancing the cause of science in America."

"We will vigorously support scientists who pursue this research," Obama said at a signing ceremony in the White House. "And we will aim for America to lead the world in the discoveries it one day may yield."

Obama's order ends former President George W. Bush's limit on federally funded embryonic stem-cell research to cell lines created before Aug. 9, 2001. Congress tried twice to reverse that ban, and his National Institutes of Health (NIH) director, Elias Zerhouni, urged an end to the restrictions, but Bush vetoed the legislation both times.

A bizarre disorder that causes people to physically act out their dreams while sleeping is associated with a dramatically increased risk of developing dementia, and Alzheimer's and Parkinson's diseases, according to new research that suggests the sleep disorder may actually be an early symptom of those conditions.

People with REM sleep behavior disorder, a condition caused by the brain's failure to immobilize a person's muscles while they're dreaming, have an estimated 52 percent risk of developing one of those neurological diseases within a dozen years, according to a study published in today's Neurology. Among people without REM sleep behavior disorder, that risk is about 5 percent, according to study author Ron Postuma, an associate researcher in neurology at the Sleep Disorders Center at Sacre-Coeur Hospital in Montreal.

A large-scale study released this week showed that the herb gingko biloba has no effect in preventing dementia or Alzheimer’s disease. But alternative medicine aficionados may find hope in a new research touting the bennies of another "herb" in preserving memory.

Scientists from Ohio State University report that marijuana, contrary to the conventional wisdom,  may help ward off Alzheimer's and keep recall sharp. Their findings, released today at the Society for Neuroscience meeting in Washington D.C.:  chemical components  of marijuana reduce inflammation and stimulate the production of new brain cells, thereby enhancing memory.

The team suggested that a  drug could be formulated that would resemble tetrahydroannibol, or THC, the psychoactive  ingredient in pot sans making the user high. But the research  may ultimately drive those who fear impending dementia to roll their own solution to the problem.

A drug called PBT2, developed by Australian company Prana Biotechnology, appears to improve cognitive abilities in patients with early-stage Alzheimer's disease.  Researchers report in Lancet Neurology, that it was also successful in reducing protein buildup associated with the debilitating neurodegenerative illness, which plagues up to 4.5 million Americans.

Craig Ritchie, a neuroscientist at Imperial College London and Prana consultant, says that the success of the recent 12-week trial (which had 78 participants) -- must be replicated in a larger longer-term trial before the company would consider seeking approval to sell it as an Alzheimer's therapy. "Our hope is that we might be able to see treatments that can substantially improve the lives of people with Alzheimer's disease within the next five or so years," he said in a statement.