Introducing the brain: how odors are interpreted (Introduction)

by David Turell , Thursday, July 02, 2020, 20:11 (1388 days ago) @ David Turell

A different approach using mouse brain again:

https://medicalxpress.com/news/2020-07-reveals-brain-odors.html

"By delivering odors with carefully selected molecular structures and analyzing neural activity in awake mice, the team showed that neuronal representations of smell in the cortex reflect chemical similarities between odors, thus enabling scents to be placed into categories by the brain. Moreover, these representations can be rewired by sensory experiences.

"The findings suggest a neurobiological mechanism that may explain why individuals have common but highly personalized experiences with smell.

"'All of us share a common frame of reference with smells. You and I both think lemon and lime smell similar and agree that they smell different from pizza, but until now, we didn't know how the brain organizes that kind of information," said senior study author Sandeep Robert Datta.

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"The experiments revealed that similarities in odor chemistry were mirrored by similarities in neural activity. Related odors produced correlated neuronal patterns in both the piriform cortex and olfactory bulb, as measured by overlaps in neuron activity. Weakly related odors, by contrast, produced weakly related activity patterns.

"In the cortex, related odors led to more strongly clustered patterns of neural activity compared with patterns in the olfactory bulb. This observation held true across individual mice. Cortical representations of odor relationships were so well-correlated that they could be used to predict the identity of a held-out odor in one mouse based on measurements made in a different mouse.

"Additional analyses identified a diverse array of chemical features, such as molecular weight and certain electrochemical properties, that were linked to patterns of neural activity. Information gleaned from these features was robust enough to predict cortical responses to an odor in one animal based on experiments with a separate set of odors in a different animal.

"The researchers also found that these neural representations were flexible. Mice were repeatedly given a mixture of two odors, and over time, the corresponding neural patterns of these odors in the cortex became more strongly correlated. This occurred even when the two odors had dissimilar chemical structures.

"The ability of the cortex to adapt was generated in part by networks of neurons that selectively reshape odor relationships. When the normal activity of these networks was blocked, the cortex encoded smells more like the olfactory bulb.

"'We presented two odors as if they're from the same source and observed that the brain can rearrange itself to reflect passive olfactory experiences," Datta said.

"Part of the reason why things like lemon and lime smell alike, he added, is likely because animals of the same species have similar genomes and therefore similarities in smell perception. But each individual has personalized perceptions as well.

"'The plasticity of the cortex may help explain why smell is on one hand invariant between individuals, and yet customizable depending on our unique experiences," Datta said.

"Together, the results of the study demonstrate for the first time how the brain encodes relationships between odors. In comparison to the relatively well-understood visual and auditory cortices, it is still unclear how the olfactory cortex converts information about odor chemistry into the perception of smell. (my bold)
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"'We don't fully understand how chemistries translate to perception yet," Datta said. "There's no computer algorithm or machine that will take a chemical structure and tell us what that chemical will smell like."

"'To actually build that machine and to be able to someday create a controllable, virtual olfactory world for a person, we need to understand how the brain encodes information about smells," Datta said. "We hope our findings are a step down that path.'"

Comment: It is amazing how our senses work translating what is received by each organ type into electrical impulses that we interpret as color, noise of speech, odors, etc.