As the nation's baby boomers age, they are increasingly worried that their memories will deteriorate — and with good reason. An estimated 10 million boomers will develop Alzheimer's disease or another memory-destroying neurodegenerative condition in the coming years. Policy makers and health officials worry that the resulting bulge in the number of sufferers will burden the nation's already strained health-care system. In the wake of these concerns, a vibrant brain-fitness industry is offering a variety of ways to help people keep their brains healthy, including the use of cognition-enhancing drugs and exercise. But many experts say much of what the public is being told is of limited value, at best. Intensified brain research begun years ago at the National Institutes of Health is just now beginning to produce data that scientists hope will advance efforts to prevent memory loss, but they worry that flat federal funding since 2003 may compromise the drive for solutions.