Embargoed for release at 2 p.m. EST, Wednesday, Nov. 13
Neural Research Shows That The Nose Needs
Time To Smell
PASADENA--New research from the California Institute of
Technology shows that it literally takes some time to
smell the roses.
In the current issue of Nature, Caltech neuroscientists
Michael Wehr and Gilles Laurent present work demonstrating
that information about odors is contained in the temporal
activity patterns of groups of neurons over an interval of
time.
"Perfumers sometimes speak of `top notes' and `medium notes'
in a bouquet," says Laurent, associate professor of biology
and computation and neural systems. "These refer to early
and late perceptions that unfold over time during long sniffs
or successive sniffs. Our new research suggests that the brain is
actually representing odors by making a neural melody of its own."
A helpful analogy Laurent offers for the research is the musical
notes that make up a tune. A listener can perceive one note in
an instant, but must listen for a time before he or she can
recognize the tune. Therefore, the specific manner in which
the notes follow one another is the very thing that gives a
song its individual character.
"It is the order in which specific neurons are activated that
appears to contain useful information about the identity of
the odor," says Laurent, adding that different odors cause
different neural "melodies."
Laurent and Wehr, a graduate student in computation and neural
systems, did their research by analyzing the brain waves of
locusts. When an odor was wafted by the olfactory organ of
the locust, the collective response of neurons in the
olfactory brain was such that specificity in the responses
arose from considerations of their temporal characteristics.
And because olfactory systems are very similar among most
animals, the researchers think that these coding principles
may be common to most, including humans.
What happens in the brain during the act of smelling is not
well understood, but has been known for a long time to
involve neural synchronization and oscillations of the EEG.
The function of oscillations, which are observed also in all
other sensory areas of the brain, remains totally speculative.
"If our hypothesis is right, oscillations are a kind of clock
for the temporal codes we observe," Laurent says.
In a parallel study by Laurent and Caltech behavioral biology
graduate student Katrina MacLeod in the November 8 issue of
Science, the authors described a method by which the neurons
representing odors can be simply desynchronized, thereby
eliminating the clock signal for the temporal codes. This
result will now allow the researchers to directly test, in
future experiments, whether these temporal codes are essential
for odor perception.
The conclusions of the researchers is that animals as primitive
as snails and as complex as humans do some mental "data crunching"
each time they pick up a smell. This allows the neurons to separate
a certain odor from the background, provided a window of time is
available.
In a manner of speaking, the research shows that time is of
the essence, and vice versa.
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