Ed Boyden, a researcher at MIT, is at the forefront of a new science that aims to map and even heal the brain with light. It’s called optogenetics, and the journal Science has called it one of the great insights of the 21st century. It’s in its early days, but the goal is to one day be able to take a disease like depression, PTSD, or epilepsy and, using bursts of light, just turn it off -- the same way you’d fix a software glitch in a computer.