dr., always good to see you. >> great to see you. martha: it is a fear of all of ours and you forget something and you say, gosh is it an early onset of alzheimer's happening in my brain and why would having ambition in life stave it off. >> alzheimer's is the most common dementia and there are over 5 million people in the u.s. that have it and it is a build-up of abnormal proteins in the brain and they tend to involve the part of the brain that has to do with reasoning, and add advanced reasoning and language, and, knowing where you are, and that is why alzheimer's patients get lost, and we have come a long way, in towards diagnosing this with pet scans and functional mris and very sophisticated ways to see it before you got it and we don't know what to do about it when you have it. what is really interesting about the study, out of chicago, martha, is it looks like, if you have a purpose in life, you cut down your risk of getting alzheimer's, by twice, in other words you are half as likely to