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Emotion makes nose a sharper smeller1
By LAURAN NEERGAARD - AP Medical Writer Published 2:38 pm PDT Friday, March 28, 2008
Know how a whiff of certain odors can take you back in time, either to a great
memory or bad one? It turns out emotion plays an even bigger role with the nose,
and that your sense of smell actually can sharpen when something bad happens.
Northwestern University researchers proved the surprising connection by giving volunteers electric
shocks while they sniffed novel odors. The discovery, reported in Friday's edition of the journal
Science, helps explain how our senses can steer us clear of danger. More intriguing, it could shed
light on disorders such as post-traumatic stress syndrome(PTSD).
"This is an incredibly unique study," said Dr. David Zald, a Vanderbilt University neuroscientist who
studies how the brain handles sensory and emotional learning. "We're talking about a change in our
perceptual abilities based on emotional learning."
Scientists long have known of a strong link between the sense of smell and emotion. A certain
perfume or scent of baking pie, for instance, can raise memories of a long-dead loved one.
Conversely, a whiff of diesel fuel might trigger a flashback for a soldier suffering PTSD.
Could an emotionally charged situation make that initial cue be perceived more strongly in the first
place? The research team recruited 12 healthy young adults to find out. Volunteers repeatedly
smelled sets of laboratory chemicals with odors distinctly different from ones in everyday life. An
"oily grassy" smell is the best description that lead researcher Wen Li, a Northwestern postdoctoral
fellow in neuroscience, could give.
Two of the bottles in a set contained the same substance and the third had a mirror image of it,
meaning its odor normally would be indistinguishable. By chance, the volunteers correctly guessed
the odd odor about one-third of the time.
Then Li gave the volunteers mild electric shocks while they smelled just the odd chemical. In later
smell tests, they could correctly pick out the odd odor 70 percent of the time. MRI scans showed the
improvement was more than coincidence. There were changes in how the brain's main olfactory
region stored the odor information, essentially better imprinting the shock-linked scent so it could be
distinguished more quickly from a similar odor.
In other words, the brain seems to have a mechanism to sniff out threats. That almost is certainly a
survival trait evolved to help humans rapidly and subconsciously pick a dangerous odor from the sea of scents
constantly surrounding us, Li said. Today, that might mean someone who has been through a kitchen fire can tell
immediately if a whiff of smoke has that greasy undertone or simply comes from the fireplace.
But the MRI scans found the brain's emotional regions did not better discriminate among the different
odors, Li noted. That discrepancy between brain regions is where anxiety disorders may come in. If
someone's olfactory region does not distinguish a dangerous odor signal from a similar one, the
brain's emotional fight-or-flight region can overreact. Researchers say that is a theory not yet
tested. For now, Northwestern neuroscientist Jay Gottfried, the study's senior author, says the
work illuminates a sense that society too often gives short shrift.
"People really dismiss the sense of smell," said Gottfried, who researches "how the brain can put
together perceptions of hundreds of thousands of different smells. ... Work like this really says that
the human sense of smell has much more capacity than people usually give it credit."
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1
People recall smells with a 65% accuracy after a year, while the visual recall of photos
sinks to about 50% after only three months. 2
Our odor memories frequently have strong emotional qualities and are
associated with the good or bad experiences in which they occurred.
Olfaction is handled by the same part of the brain (the limbic system)
that handles memories and emotions. Therefore, we often find that we
can immediately recognize and respond to smells from childhood such
as the smell of clean sheets, cookies baking in the oven, the smell of
new books or a musty room in Grandma’s house. Very often we cannot
put a name to these odors yet they have a strong emotive association
even if they cannot be specifically identified.
No two people smell the same odor the same way. In other words, a rose may smell
sweeter to some people than to others.
In fact, according to neuropsychologist, Robert Bonkowski, a person never experiences one
smell the same way twice. Furthermore, an individual’s ability to detect odors changes from day
to day, depending on his or her physiological condition.
Every time we inhale, currents of air swirl up through the
nostrils, over the bony turbinates, to a “sheet” about the size
of a small postage stamp that contains millions of olfactory
receptor neurons. This is the olfactory epithelium.
Each of the millions of olfactory neurons has minuscule
filaments (cilia) extending from its knob. This knob is
located at the tip of the olfactory neuron and the cilia project
from the knob directly into the atmosphere. This is the only
part of the brain that projects into the atmosphere. The
cilia contain olfactory receptors, specialized proteins that
bind low molecular weight molecules (odorants).
One of the big breakthroughs of the past 15 years was the
discovery by L. Buck and R. Axel of a large multi-gene family
that encode for these olfactory receptors. Each receptor has
a pocket (binding site) that is just the right shape to bind
either a specific molecule or a group of structurally similar
molecules. The interaction of the right molecule with the
right receptor causes the receptor to change its shape
(structural conformation). This conformational change gives
rise to an electrical signal that goes first to the olfactory bulb
and then to the areas of the brain that convert the electrical
signal to a smell.
Nearly everyone who has experienced a bad cold has familiarity with temporary smell loss or disruption
of the sense of smell, but imagine if the inability to smell persisted and you could no longer enjoy the
aroma of freshly baked cookies or the scent of newly cut flowers. Although loss of the sense of smell is
not nearly as detrimental as the loss of sight or hearing, interruption of a person’s ability to smell,
whether it be partial or total loss, severely diminishes a person’s quality of life. Millions of Americans
2
http://www.senseofsmell.org/
suffer from a muted, distorted, or absent sense of smell. In recent years, researchers have shown an
increased interest in smell disorders and changes to quality of life due to olfactory interruptions.
What is Smell Loss and what happens if you lose it?
Total loss of the sense of smell, known as Anosmia, results from various causes and can have a
profound effect on a person’s quality of life. Olfactory damage is a significant sensory loss that
affects 1-2% of the American population. Approximately 200,000 people seek medical attention
related to smell disorders each year in the United States (Doty, 2003). Occasionally damage to
the sense of smell goes undetected, even though smell dysfunction can severely alter a person’s
quality of life and even put them at risk for many dangers.
Studies show that the majority of the two million Americans that experience smell loss are age
65 or older, as the sense of smell tends to decrease with age.
Write a one paragraph summary in your own words about what you thought was most
interesting and how the sense of smell occurs.
Emotion makes nose a sharper smeller
- The Associated Press
Published 3:45 pm PDT Thursday, March 27, 2008
SNIFFING OUT THREATS: Researchers at Northwestern University discovered that
our sense of smell can sharpen when something bad happens. It might explain
how our senses can help us avoid danger.
THE STUDY: Researchers gave volunteers mild electric shocks while they smelled
an odd chemical. In later smell tests, the volunteers' ability to pick out the odd
odor was greatly improved.
PHYSICAL CHANGES: MRI scans showed changes in how the brain's main
olfactory region stored the odor information, essentially better imprinting the
shock-linked scent so it could be distinguished more quickly from a similar odor.