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| © PETER PARKS Des scientifiques américains ont étudié la manière dont les mammifères perçoivent et distinguent les différentes odeurs. |
In the United States, scientists have created for the first time an electronic signature capable of being identified as an odor by the brain of mice, although it is completely synthetic.
The purpose of the study, published in the journal Science on Thursday, is to analyze how mammals perceive and distinguish different odors.
Edmund Chong, a doctoral student at the Grossman School of Medicine at NYU, who led these experiments, explained that there were many things that scientists did not yet understand about smell and its main characteristics.
To explore this issue, the researchers set up experiments with genetically modified mice so that their neurons could be activated by a light projected using an optical fiber, a technique called "optogenetics".
Experiments focused on the olfactory bulb, a structure behind the nose in animals and humans.
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 glomerule. The signals are finally sent to the neurons in the brain.
The team trained the mice to recognize the signal of a synthetic odor created using light to activate six nerve beams in a particular order. Mice were rewarded with water when they pushed a lever after recognizing "smell."
If they pushed this lever after activating another combination of nerve beams, they did not receive water.
The melody of smells
With this experiment, scientists were able to subtly change the timing and combination of activated nerve beams to determine which ones were most important, i.e. what aspect of a particular smell defines it and differentiates it from another scent.
In particular, the researchers realized that by changing the order of the beams activated at the beginning of the sequence of an odor, this reduced the recognition of the scent by 30%.
Making changes later in the sequence, on the other hand, had a much smaller impact on the degree of odor identification.
Nervous activation functioned as "the notes of a melody," the scientists reported. As if to recognize a song, the changes at the beginning of the sequence have a more significant impact on the identification of an odor, than a change at the end of the sequence.
"Our results for the first time determine a code of how the brain transforms sensory information into perception, in this case, smell," notes one of the study's authors, Dmitry Rinberg.