WASHINGTON (AP) – "Exercise your brain," experts advise people hoping to stave off dementia . But how? Stretching your brain might be the better description. Do a crossword puzzle a day, and you may just get good at crosswords. Instead, research increasingly shows that a variety of habits and hobbies are like a cognitive workout, building knowledge and skills that may beef up parts of the brain as we get older. One recent study linked a lower risk of Alzheimer's disease and cognitive decline to