dr. ronald petersen, director of the alzheimerss disease research center. in our washington studio, gale hunt, president and c.e.o. of the national alliance for care giving and from chicago, angela, chief strategy officer of the alzheimerss association. dr. fielder sen, we talk add little bit about rest, but help us understand what is it? what is the actual stuff of rest? >> well, rest is a protein that starts to protect the brain. seven against various toxins. so as you indicated many people who live throughout the life span have am lloyd in the brain. some of them become clinically impaired and some do not. it's always been a mystery as to why people with the same amount of this toxic protein in the brain can do well. this study indicates that perhaps this rest protein, is active at different levels in those individuals. so people who have the protein in the brain, but do not become demented may have higher levels of this protein, than individuals who do become clinically impairs and that may give office therapeutic window. that may predispose them. >> ad