Karl Deisseroth uses a combination of green algae, blue lasers, gene therapy and fiber optics to map neural circuits deep inside the brain. The technique is called optogenetics.
The technique begins with the placing of light-sensitive proteins from green algae inside specific types of brain cells. The cells can then be turned on or off with pulses of blue and yellow light.
According to Deisseroth: "Optogenetics is the combination of genetics and optics to control well-defined events within specific cells of living tissue. It includes the discovery and insertion into cells of genes that confer light responsiveness; it also includes the associated technologies for delivering light deep into organisms as complex as freely moving mammals, for targeting light-sensitivity to cells of interest, and for assessing specific readouts, or effects, of this optical control." (see Scientific American)
You can find a number of videos on the internet. Here's one link
Read more at: http://www.youtube.com/watch?v=C8bPbHuOZXg