Berkeley - Any wine connoisseur knows the nose can learn to
recognize subtle new aromas, but where does that learning
take place?
A new study by a team of neuroscientists at the University
of California, Berkeley, has determined that we learn new
smells in an area of our brains, not just in our noses,
which have neural nasal receptors previously thought to
be solely responsible for a person's ability to detect new
odors.
This finding has prompted the team, led by graduate student
Joel Mainland and Noam Sobel, assistant professor of psychology,
to conclude that the adult brain has more capabilities to
change than previously thought. The study appears in the
Oct. 24 issue of Nature.
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Video:
Noam Sobel, assistant professor of psychology,
discusses the brain's surprising role in deciphering
smells, and the potential for healing after
strokes.
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The discovery may have implications for how the brain recovers
from injury. Lately, there has been a lot of evidence that
activity in damaged regions of the body results in regeneration
in the brain. For example, in stroke patients, tying down
the unaffected limbs to force patients to try use their
affected arms or legs has resulted in recovery of some use
of those limbs.
The researchers conducted their work through a very simple
mechanism using the chemical androstenone. Androstenone
cannot be detected by approximately 30 percent of the population.
However, about half of such non-detectors can develop the
capability to detect the odorant following repeated exposure
to it. For those who can smell it, there is a wide range
of reactions to its odor. The people who are most sensitive
to it find the smell extremely foul and reminiscent, Sobel
said, "of dirty laundry."
Sobel and his colleagues conducted an extensive screening
to find subjects who could not detect this smell. The screening
yielded 12 people. In the test subjects, one nostril was
completely blocked, and the open nostril was exposed to
androstenone every day for 21 days. After the 21 days, both
nostrils were tested for detection. Both nostrils doubled
their detection accuracy due to this exposure.
The unexposed nostril detected the androstenone at the
same level as the exposed nostril. Because there is no neural
link between the nostrils at the peripheral level, the researchers
concluded that this exposure-induced learning must have
occurred in the olfactory structures in the brain that share
information from both nostrils.
"Since the unexposed nostril learned just as well, the
brain is definitely involved. This contradicts a previous
theory that olfactory learning occurred in the nose only,"
said Sobel, a member of UC Berkeley's Health Sciences Initiative,
a broad effort bringing together campus researchers from
many disciplines to work on health problems of the 21st
century.
"Our results suggest there must be a central component
in the brain at work," Sobel said, though he added the researchers
have not ruled out peripheral neural changes occurring as
well. Ongoing research is being conducted to determine if
peripheral neural plasticity - the nervous system acquiring
a capability it didn't have before - is involved.
In children, the nervous system is constantly changing
and developing, "but in adults, it's a question as to how
much it can change," Sobel said. "If you want to repair
a damaged nervous system, the best way to go about doing
this is to figure out how it regenerates on its own."
Further studies by the team will investigate the difference
between people who can learn to detect an odor through exposure
to that odor and those who cannot. The researchers also
will use Magnetic Resonance Imaging to localize regions
in the brain to see where learning and change is occurring.
