Society is showing increasing concern for disorders related to aging that lead to a loss of brain function. In view of the enormous proportion of elderly people in our society today, brain aging is more than ever subject to challenge to us all, not only politicians and health authorities, but every individual who is confronted with the difficult situation of watching the mental powers of apparently healthy elderly friends, neighbours, or relatives fail, often with alarming rapidity. This challenge is directed especially toward us scientists. As one of our colleagues succinctly put it 2 years...