By directly manipulating the activity of individual neurons, scientists have given flies memories of a bad experience they never really had, according to a report in the October 16th issue of the journal Cell, a Cell Press publication.
“Flies have the ability to learn, but the circuits that instruct memory formation were unknown,” said Gero Miesenböck of the University of Oxford. “We were able to pin the essential component down to 12 cells. It's really remarkable resolution.” Those dozen cells are sufficient to manage what is a difficult cognitive problem: learning to associate a particular odor with something bad, like an electric shock. In essence, these cells create memories that the fly then uses to avoid that odor.
To pinpoint the exact neurons responsible for this memory among thousands in the fly brain, the researchers used a clever technique they developed, called optogenetics, in which a simple flash of light is used to release caged-molecules present in selective neurons that then stimulate the activity of those neurons. An analogous situation, says Miesenböck, is if you wanted to send a message only to certain inhabitants of a city, you would give those you wanted to reach a radio tuned to the right frequency and send the message publicly, over the airwaves