Scientists decode how the brain senses smell

Date:
June 18, 2020
Source:
NYU Langone Health / NYU School of Medicine
Summary:
Scientists have further decoded how mammalian brains perceive
odors and distinguish one smell from thousands of others.



FULL STORY ========================================================================== Scientists have further decoded how mammalian brains perceive odors and distinguish one smell from thousands of others.


==========================================================================
In experiments in mice, NYU Grossman School of Medicine researchers have
for the first time created an electrical signature that is perceived
as an odor in the brain's smell-processing center, the olfactory bulb,
even though the odor does not exist.

Because the odor-simulating signal was humanmade, researchers could
manipulate the timing and order of related nerve signaling and identify
which changes were most important to the ability of mice to accurately
identify the "synthetic smell." "Decoding how the brain tells apart odors
is complicated, in part, because unlike with other senses such as vision,
we do not yet know the most important aspects of individual smells,"
says study lead investigator Edmund Chong, MS, a doctoral student at
NYU Langone Health. "In facial recognition, for example, the brain can recognize people based on visual cues, such as the eyes, even without
seeing someone's nose and ears," says Chong. "But these distinguishing features, as recorded by the brain, have yet to be found for each smell."
The current study results, published online in the journal Science
on June 18, center on the olfactory bulb, which is behind the nose in
animals and humans.

Past studies have shown that airborne molecules linked to scents trigger receptor cells lining the nose to send electric signals to nerve-ending
bundles in the bulb called glomeruli, and then to brain cells (neurons).

The timing and order of glomeruli activation is known to be unique to
each smell, researchers say, with signals then transmitted to the brain's cortex, which controls how an animal perceives, reacts to, and remembers
a smell. But because scents can vary over time and mingle with others, scientists have until now struggled to precisely track a single smell
signature across several types of neurons.



==========================================================================
For the new study, the researchers designed experiments based on the availability of mice genetically engineered by another lab so that their
brain cells could be activated by shining light on them -- a technique
called optogenetics. Next they trained the mice to recognize a signal
generated by light activation of six glomeruli -- known to resemble a
pattern evoked by an odor -- by giving them a water reward only when
they perceived the correct "odor" and pushed a lever.

If mice pushed the lever after activation of a different set of glomeruli (simulation of a different odor), they received no water. Using this
model, the researchers changed the timing and mix of activated glomeruli, noting how each change impacted a mouse's perception as reflected in a behavior: the accuracy with which it acted on the synthetic odor signal
to get the reward.

Specifically, researchers found that changing which of the glomeruli
within each odor-defining set were activated first led to as much as
a 30 percent drop in the ability of a mouse to correctly sense an odor
signal and obtain water.

Changes in the last glomeruli in each set came with as little as a 5
percent decrease in accurate odor sensing.

The timing of the glomeruli activations worked together "like the notes
in a melody," say the researchers, with delays or interruptions in the
early "notes" degrading accuracy. Tight control in their model over when,
how many, and which receptors and glomeruli were activated in the mice,
enabled the team to sift through many variables and identify which odor features stood out.

"Now that we have a model for breaking down the timing and order of
glomeruli activation, we can examine the minimum number and kind of
receptors needed by the olfactory bulb to identify a particular smell,"
says study senior investigator and neurobiologist Dmitry Rinberg, PhD.

Rinberg, an associate professor at NYU Langone and its Neuroscience
Institute, says the human nose is known to have some 350 different
kinds of odor receptors, while mice, whose sense of smell is far more specialized, have more than 1,200.

"Our results identify for the first time a code for how the brain
converts sensory information into perception of something, in this case an odor," adds Rinberg. "This puts us closer to answering the longstanding question in our field of how the brain extracts sensory information to
evoke behavior." Funding support for the study was provided by National Institutes of Health grant R01 NS109961.


========================================================================== Story Source: Materials provided by NYU_Langone_Health_/_NYU_School_of_Medicine. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Edmund Chong, Monica Moroni, Christopher Wilson, Shy Shoham, Stefano
Panzeri, Dmitry Rinberg. Manipulating Synthetic Optogenetic Odors
Reveals the Coding Logic of Olfactory Perception. Science, 2020 DOI:
10.1126/ science.aba2357 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200618150304.htm

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