A study carried out on mice deciphers the cerebral mechanism which makes it possible to perceive and distinguish odors.
Create a synthetic smell to better understand the sense of smell. A research team from the NYU Grossman School of Medicine (United States) took this bet. The scientists created an artificial smell that they tested on mice to be able to analyze the brain mechanisms linked to this sense. In the review Sciencethey publish their results.
A complex process
“Decoding how the brain differentiates between odors is complicatedbelieves one of the main authors of the study Edmund Chong, in particular because unlike other senses, such as sight, we do not yet know the characteristic elements of each of the smells.” To understand sight, scientists can rely on specific elements such as the eyes: a person can recognize someone only thanks to them. Science has yet to find equivalents for smell.
The importance of the olfactory bulb
The researchers created an electronic signature, which the mice’s brains identified as an odor. They analyzed nerve responses in the brain to understand how smell works. The team focused on the olfactory bulb, located behind the nose. According to previous research, the molecules linked to the scents activate receptor cells in the nose, which will themselves send electrical signals to fibers located in the bulb, called glomerulus, then they are transmitted to neurons.
A system similar to auditory recognition
In this new study, the researchers wanted to follow the “journey” of a specific odor through the different types of neurons. Using optogenetics, which activates neurons with light, they were able to train mice to recognize the synthetic smell. The experiment involved activating six different nerve bundles in a specific order. The mice had a reward when they managed to distinguish the artificial scent.
After this first step, the researchers changed the order of activation of the nerve bundles to understand how the brain manages to analyze the smell. They found that it is the first beams that take precedence: when these are reversed, the success rate in recognizing odors was reduced by 30%. Conversely, there was little change when the order of the last beams was changed.
Further research needed
For researchers, the recognition of odors in the olfactory bulb works a bit like the notes of a melody: it is the first notes that allow us to identify it. “Now that we have a model for the order and timing of glomerulus activation, we can begin to examine the type and number of receptors needed by the olfactory bulb to identify an odor.”concludes Dmitry Rinberg, co-author of the study.
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