CHICAGO (AP) -- Brisk walking led to slight improvements on mental tests for older people with memory problems in what is billed as the first rigorous test of exercise on the aging brain. The results from the small Australian study were only modest. But they back up observational studies showing potential mental benefits from physical activity.

WASHINGTON (AP) -- Scientists for the first time have peered into people's brains to directly measure the ebb and flow of a substance notorious for its role in Alzheimer's disease.

WASHINGTON (AP) -- Nearly three years into the Medicare drug benefit, federal officials have yet to ensure that private drug plans enacted programs to deter fraud and abuse, government investigators say.