Stopped at a red light on his drive home from work, Karl
Deisseroth contemplates one of his patients, a woman with
depression so entrenched that she had been unresponsive to drugs
and electroshock therapy for years. The red turns to green and
Deisseroth accelerates, navigating roads and intersections with
one part of his mind while another part considers a very
different set of pathways that also can be regulated by a system
of lights. In his lab at Stanford University’s Clark Center,
Deisseroth is developing a remarkable way to switch brain cells
off and on by exposing them to targeted green, yellow, or blue
flashes. With that ability, he is learning how to regulate the
flow of information in the brain. Deisseroth’s technique, known
broadly as optogenetics, could bring new hope to his most
desperate patients. In a series of provocative experiments, he
has already cured the symptoms of psychiatric disease in mice.
Optogenetics also shows promise for defeating drug addiction.
When Deisseroth exposed a set of t