TheClockworkSoul writes "Researchers at the University of Oxford have devised a way to write memories onto the brains of flies, revealing which brain cells are involved in making bad memories. The researchers said that in flies, just 12 brain cells were responsible for what is known as 'associative learning.' They modified these neurons by adding receptors for ATP, so that the cells activate in the presence of the chemical, but since ATP isn't usually found floating around a fly's brain, the flies generally behave just like any other fly. Most interestingly, however, is that the scientists then injected ATP into the flies' brains, in a form that was locked inside a light-sensitive chemical cage. When they shined a laser on the fly brains, the ATP was released, and the 'associative learning' cells were activated. The laser flash was paired with an odor, effectively giving the fly a memory of a bad experience with the odor that it never actually had, such that it then avoided the odor in later experiments. The researchers describe their findings in the journal Cell."