An anonymous reader writes "The prelimbic region of the prefrontal cortex in the human brain is thought to play a key role in drug addiction, and researchers at the National Institute on Drug Abuse wanted to see if manipulating cells there had a positive or negative impact on that addiction. They got some rats addicted to cocaine but not before loading them up with light sensitive proteins called rhodopsins that were placed in their prefrontal cortex, attaching to the neurons there. By shining a tuned laser light on to the prefrontal cortex, it was possible to activate and deactivate the cells. By turning them on with the laser, the addictive behavior of the rats was removed. Turning them off, even in non-addicted rats, saw the addictive behavior return or introduced."