Alzheimer's Disease is one - very common - form of senile dementia. It usually affects older people and progressively robs them of their mental faculties. It occurs because a protein called beta amyloid builds up in the brain forming harmful deposits called plaques, which are toxic to nerve cells. What's confusing though is that the brain naturally makes beta amyloid all the time but seems to wash most of it away when we go to sleep. But what aspect of sleep is important for this clean-up process, and what are the implications for people who are chronically poor sleepers? At Washington University, in St Louis, Yo-El Ju recruited a small group of volunteers to find out.