Here's a story from the New York Times reporting on work from Gero Miesenböck at the University of Oxford and published recently in Cell. In the study, the biologists used light to activate a group of cells in the fly brain to lay down a bad memory and assess how flies respond to the reminder of a negative experience. "Dr. Miesenböck’s team was able to distinguish, by their genetics, different classes of the dopamine-making neurons.