In the middle of a pitch-black room, a very special mouse lies motionless on a microscope stage. Months before, the mouse had two small holes cut out of its skull, revealing the dura--the brain's outer membrane--and the blood vessels below. The holes have been permanently covered with clear glass so that scientists can peer directly into the mouse's brain, where some of its neurons glow green under the laser light of a microscope.

For images of this brain-watching lab, click here.