Lasers Impart Life Lessons in Flies

By beaming a laser into the brains of fruit flies, scientists have created new memories from scratch. It's an "amazing piece of work," says neuroscientist Simon Schultz of Imperial College London.

The memories are very simple: just the association that a particular stimulus is bad and should be avoided. As a first step to creating this association, neuroscientist Gero Miesenböck of the University of Oxford in the United Kingdom and colleagues studied fruit flies that preferred the odor of either 3-octanol (OCT) or 4-methylcyclohexanol (MCH). Next, the team electrically shocked the flies when one or the other odor was present. Naturally, the flies began to avoid the odor associated with the shock, even if they had preferred that odor in the first place.

Miesenböck and colleagues then wanted to see whether they could program the flies to dislike an odor without shocking them first. To do this, they injected an engineered version of ATP--a source of cellular energy--into various neural circuits in the flies' brains. This time, when the flies encountered either OCT or MCH, the researchers flashed laser light into their brains. This released the engineered ATP, which activated neurons that release dopamine, a neurotransmitter believed to create aversive memories in flies. Sure enough, flies exposed to the laser light in the presence of OCT or MCH began to avoid that odor, just as though they had been shocked.

Further experiments allowed the researchers to narrow down this negative reinforcement to a mere 12 neurons in the fruit fly brain. The team reports its findings tomorrow in Cell.

Researchers are beginning to use the laser-light approach in mice, Schultz says, so it won't be long before these findings can be tested in mammals. And although it's a distant prospect, Schultz is already thinking about how this work could help humans: "Imagine being able to take a pill ... while you are briefly exposed to information you might want to remember later, such as a Shakespeare sonnet or your car-repair manual."

Posted in Brain & Behavior