In this video, a mouse with a fiberoptic cable implanted into his brain explores a four-arm maze. The animal has been genetically engineered to express light-sensitive proteins in a specific part of the amygdala, a brain region linked to fear. Mice are naturally afraid of open spaces, and at the beginning of the video, the mouse spends most of his time in one corner of the maze, occasionally dashing out to explore his environment. Turning on the light (as indicated by blue text) activates a specific neural circuit, which appears to make the mouse much braver, continually exploring all the parts of the maze. The video is shown at ten times normal speed.