Some researchers have speculated that optogenetics could eventually improve on deep brain stimulation, a therapy in which surgeons implant electrodes in a patient’s brain to treat movement disorders, drug-resistant depression, and other conditions. The metal electrodes they use now can’t target a specific type of neuron, but optogenetics can. Conceivably that could allow doctors to target just the neurons that are malfunctioning and cut down on side effects by leaving normally-functioning neurons alone.

http://www.wired.com/wiredscience/2013/04/light-brain/