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scientists have deciphered how the brains of mammals perceive the smells -despite the smells, in reality, do not exist – and they are one among thousands. In experiments on mice, researchers from the NYU Grossman School of Medicine (EE. UU.) created for the first time an electrical signature which is perceived as a smell in the processing center of the olfactory of the brain, the olfactory bulb.

that Is to say, they created a brain stimulation mimicking the sensation a given odor . It, by its artificial nature, could be manipulated in time and order to be able to identify what changes were most important for the ability of the mice to identify with precision the ” smell inner “. Something like a “melody” of the brain related to the sense of smell that lets you know how the brains of mammals to recognize a specific smell.

Many scents

“Decoding how the brain discriminates among odors is complicated, in part, because unlike other senses such as vision, we still do not know the most important aspects of the single odors,” explains the principal investigator of the study, Edmund Chong , MS, a doctoral student at NYU Langone Health. “In the face recognition , for example, the brain can recognize people based on visual cues, such as the eyes, even without seeing the nose and the ears of someone. But these distinguishing characteristics, as registered by the brain, have not yet been found for each odor,” he says.

The results of the study, published in the journal “Science”, focus on the olfactory bulb , located just behind the nose in mammals, incluisos the human. Previous studies had already shown that the molecules in the air are linked to smells to activate recipient cells lining the nose to send the electrical signals to the nerves in the bulb , called glomeruli . From there, are transmitted to the brain cells (neurons).

it Is known that the time and the order of activation of the glomeruli are unique for each odor, with signals that are then transmitted to the cerebral cortex, which controls how an animal perceives, reacts to and remembers a smell. But there is a pitfall quite important: the odors can vary with time and mixed with other , so isolate with precision a single sign of smell in various neurons it has been a scientific challenge for a long time.

The experiment

For the new study, the researchers used mice genetically modified so that their cells to glow when activated , a technique called optogenetics . After, he trained the mice to recognize a signal generated by light activation of six glomeruli, which are similar to a pattern evoked by a smell. That is to say, provoked in the olfactory bulb the feeling that she was sniffing something concrete, and the researchers were able to see the reaction the brain of the mouse. In addition, it gave them a rewards only when they saw the “smell” right , and pressed a lever. If the mice pressed the lever after the activation of a different set of glomeruli (mimicking a different smell), did not receive a reward.

Using this model, the researchers changed the time and the combination of activated glomeruli -i.e., activating a succession or the other of activation of the glomeruli, creating the sensation of an odor or other in the brain of mice – and noted how each change had an impact on the perception of each mouse and was reflected in a different behaviour: pressing or not the shift lever.

is Not the same the beginning to the end of the “song”

Specifically, the researchers found that change the first of the glomeruli that triggered the feeling of course smell -let us remember that in every experience were six – led to a fall of up to 30% of the capacity of the mouse to detect an odor correctly and operate the lever. On the contrary, the changes in the latest glomeruli only did it lower the effectiveness of the ability of the mice to 5%.

“Now that we have a model for breaking down the time and the order of activation of the glomeruli, we can examine the minimum number and type of receptors that need the olfactory bulb to identify a particular smell,” explains the principal investigator of the study and a neurobiologist Dmitry Rinberg . That is, this method uses a kind of some musical patterns, varying the type of notes and the “tempo” of the piece to be able to define each of the odors as if it were a song.

Rinberg, associate professor at NYU Langone and its Institute for Neuroscience, explains that knows that the human nose has about 350 different types of odorant receptors , while the mice , whose sense of smell is much more specialized, have more than 1.200 : “Our findings identify for the first time a code of how the brain converts sensory information into perception of something, in this case a scent,” adds Rinberg. “This brings us closer to answering the long questions in our field of how the brain extracts sensory information to evoke the behavior.”

What the nose can teach us against the coronavirus

And this progress not only brings us closer to understand the functioning of the sense of smell in mammals, but that can be applied in specific cases, such as new advances in the fight against the current pandemic of coronavirus that has scarred the planet.

“figure out how the sense of smell works has recently received a new interesting twist for two reasons: an early symptom robust Covid-19 is a loss of the sense of smell, and trained animals can potentially be trained to detect diseases,” says another of the main authors, Edmund Chong . “Therefore, a better understanding of the mechanisms of smell can potentially help to the design of powerful tools for the detection and treatment of disease during a pandemic.”