Some of the neurons responsible for behavioral decisions in rats have been identified in a new study. Using a technique that employs light to control nerve cell activity, researchers inactivated a region of the brain and showed that it caused the rats to behave more flexibly while trying to get a reward. The technique, called optogenetics, allows researchers to “show that the firing or inhibition of certain neurons has a causative relationship with a given behavior, whereas previous methods only allowed us to correlate neuronal activity with behavior,” says one researcher.