Good friends can help keep you from losing your mind sometimes. Literally.

Case in point: Some people don't have much memory loss from Alzheimer's disease, even though their brains show physical signs of it. And the more good friends and close family they have, the less affected their memory seems to be. Coincidence?

Mental Immunity

Check your memory with this quick test.

Sometimes, the human brain can function fairly normally even when physical signs of a disease -- such as the brain "tangles" associated with Alzheimer's -- are present.

Researchers call this resilient power of the brain "neural reserve." Think of it as the brain's capacity to keep working even though it's physically injured. And it's not clear why, but having lots of close friends and family -- the kind you can call on for help or confide in about private matters -- appears to help shore up those neural reserves.

More on Your Mind
Other ways to bolster your neural reserves? Continue your education, play games (such as sudoku), and exercise regularly.

See how likely you are to have Alzheimer's by completing this questionnaire.