Synthetic odors recognized by mice (study) - France 24

Washington (AFP)

Scientists in the United States have for the first time created an electronic signature capable of being identified as an odor by the mouse brain, although it is completely synthetic.

The aim of the study published in the journal Science on Thursday is to analyze the way in which mammals perceive and distinguish the different odors.

Edmund Chong, a doctoral student at the Grossman School of Medicine at NYU, who led these experiments, explained that there was a lot that scientists did not yet understand about smell and its main characteristics.

To explore this question, the researchers set up experiments with genetically modified mice so that their neurons can be activated by a light projected using an optical fiber, a technique called "optogenetics".

The experiments focused on the olfactory bulb, a structure located behind the nose in animals and humans.

The odor-related molecules activate receptor neurons in the nose, which pass information as an electrical signal to bundles of nerve fibers in the bulb, called the glomerulus. The signals are finally sent to the neurons of the brain.

The team trained the mice to recognize the signal for a synthetic odor created by using light to activate six nerve beams in a particular order. Mice were rewarded with water when they pushed a lever after recognizing "the smell".

If they pushed this lever after activating another combination of nerve beams, they received no water.

- The melody of smells -

With this experiment, the scientists were able to subtly change the timing and the combination of the activated nerve beams to determine which ones were the most important, i.e. what aspect of an odor defines it in particular and differentiates it from another scent.

The researchers notably realized that by changing the order of the activated beams at the start of the odor sequence, this reduced the recognition of the scent by 30%.

Making changes later in the sequence, for its part, had a much smaller impact on the degree of identification of the odor.

Nerve activation worked like "the notes of a melody," the scientists reported. As with recognizing a song, changes at the start of the sequence have a more significant impact on identifying an odor than a change at the end of the sequence.

"Our results determine for the first time a code of how the brain transforms sensory information into perception, in this case, into odor," notes one of the study's authors, Dmitry Rinberg.

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