Why do we need sleep? This October, researchers at the University of Rochester reported to Science a new potential answer: to flush out microscopic─though over time, potentially insidious─build-up of proteins that become stuck to brain cells during the waking day. Few would consider rest an active or exciting exercise─there is little adrenaline involved─but without that consistent cleanse, people stand a greater change of developing dementia or Alzheimer's disease later on, the research suggests