Researchers first tested normal flies in a chamber where a jets of air on either side brought two different odors into the container. The researchers delivered an electric shock each time a fly strayed into a particular odour stream, which taught the flies to prefer the other one: the flies learned to move in the direction of the shock-related odour 30 per cent less often [New Scientist].
Next, the researchers created a strain of genetically engineered flies with certain neurons that would be activated by a laser blast. Lead researcher Gero Miesenböck explains that with this technique, called optogenetics, researchers can use light to activate particular cell types that have been genetically engineered to express a light-responsive protein. When laser pulses hit the brain, cells expressing the light-sensitive protein activate. “It’s like sending a radio signal to a city but only those houses with a radios set to the right frequency will get the signal,” says Miesenböck [Nature News].
The flies were then put back in the chamber with the two jets of air, and every time they wandered into one of the odor streams, the laser was fired. Many of the flies were unaffected, but a select group quickly learned to avoid the odor stream associated with the laser pulse. Miesenböck says these flies feared that smell as if they had been conditioned to associate an electric shock with it. “Stimulating just these neurons gives the flies a memory of an unpleasant event that never happened,” he says [New Scientist].
In the genetic engineering process, the scientists had tweaked different neurons in different groups of flies. The contingent that did react to the laser all had 12 particular light-sensitive neurons, according to the study published in the journal Cell. Those 12 brain cells may be the root of associative learning, researchers say–at least in flies.
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