They then used a process called optogenetics, whereby they shined beams of light into the brains of the rats to suppress activity in the ventral pallidum.
Sure enough, when they "switched off" that region of the brain, the rats were far less likely to go after the sugar water when the sound played. And when they did, they did so more slowly. The rats were not as interested in the things that had appeared rewarding before.
Richard pointed out the ventral pallidum activity was not just registering the sounds the rats were hearing. It was actually driving their reward-seeking behavior.
Richard's team carried out a laboratory study with rats — not humans living their everyday lives — so important limitations come to bear: There are, for example, huge biological and behavioral differences between the two species. In addition, Richard said, the rats were not "especially unhappy." They weren't starved for food, and there was no reason to think they were emotionally distressed or depressed. So a human addict out in the world may experience psychological or outside factors that bear different results.