New Brain Briefs on the Senses

Do you know that emotions increase activity in the visual cortex, so “colors look more vivid and details stand out when we’re happy, angry, or frightened”?  Or that hair cells play a vital function in hearing and that as we get older the “progressive loss of hair cells means less acute hearing, particularly in higher frequencies”? How about that olfactory receptor cells are themselves neurons that are “on one end in direct contact with the external world and the other in direct contact with the brain”?  Have you ever wanted to learn more about how our senses function?

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From the Archives: Smells

I associate many smells with spring—flowers blooming, strawberries arriving at the farmer’s market, horseradish, matzo, and wine (Passover’s nearly here).

A few days ago, a tweet from @FragrantMoments reminded me of a Cerebrum article from 2001, “Ah, Sweet Skunk! Why We Like or Dislike What We Smell,” by Rachel S. Herz.

Our reactions to smells, writes Herz, are not innate (except, maybe, my aversion to those flowers thanks to the resulting itchy eyes and sneezing):

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Garbage or roses?

Saturday’s BrainWave
program at the Rubin Museum in New York City was an experiential event hosted
by Columbia University neurobiologist Stuart
Firestein
and award-winning French perfumer Christophe Laudamiel (who was
integral in the Guggenheim’s recent “scent opera”
). While learning about the basic science behind scent creation and our sense
of smell, we in the audience also were invited to sniff different scents that
Laudamiel concocted. 

To lead off the conversation, Firestein dispelled a popular
notion that humans
don’t have a strong sense of smell
in comparison with other animals. In
fact, we have one of the most discriminating palates. And the reason a dog may
pick up an odor before we do is mainly because we walk on two legs and our
noses are placed high on our bodies, while most smells emanate from below, he
said.

Humans have more than 340 receptors in their nose, which can
discriminate thousands of odors. Compared with the other senses, the sense of
smell reaches the brain quickly—olfaction is the only major sensory pathway
that projects directly to the cortex.

The olfactory receptors are also uniquely hardy—they have a
singular ability among neurons to regenerate throughout an animal’s life. In
his lab,
Firestein and his colleagues found that mice with severed olfactory nerves regenerated
these receptors in five to six weeks, regardless of the age of the mouse. This
ability has made the olfactory system an important model for the study of
neural regeneration.

With our new basic understanding of how the brain processes odors,
we were invited to smell several scents, including geranio (one of the 300
molecules that make up the scent of a rose), aldehyde (often used in cleaning
products), and Paris 1738. While people stopped to sniff the first two scents a
second and third time, Paris 1738, based on the smell of Parisian streets of
that year and inspired
by the 2006 movie “Perfume
,” prompted wrinkled noses and waving program
cards. Suddenly a strong sense of smell didn’t seem like a blessing, as the
smell of manure, a musty room, and body odor prevailed. Thankfully, the program
closed with the delicious scent of cardamom, and I left craving Indian food.

—Ann
L. Whitman

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