BEHAVIOR
April 30, 2007

Smell: the Underrated Sense?

New research shows that the brain can learn to distinguish between very small differences in smell, to a degree far beyond what was previously thought.

Conducted using rats, this research demonstrates the importance of smell in gathering information about our surroundings.

Smell is often an undervalued sense in humans, who tend to rely on visual perceptions. Visual distractions lead people to ignore information gathered from smells, according to researchers at the University of Chicago.

"This is the first study to look at the ways in which mammals respond to challenges of distinguishing smells by studying actual activity in the olfactory bulb while varying the difficulty of the discrimination," said Leslie Kay, Assistant Professor in Psychology at the University.The olfactory bulb is the portion of the brain that processes smells, both in humans and in other mammals.

For the study, electrodes were attached to the brains of four rats and trained them to distinguish different odors. The electrodes followed the regularized motion (oscillations) of the cells in the rats' olfactory bulbs. The oscillations act as a means to carry complex information between cells.

The news was that the rats used the oscillations selectively. When smells were quite distinct, the oscillations were irregular. When the smells were similar, the oscillations became more regular. The researchers speculate that the oscillations help the rats to separate the overlapping patterns.

The findings may provide some clues about how rats are able to survive ever more determined attempts to poison them.

The study also showed that the rats' ability to distinguish scents increases if they are exposed to a new odor for one hour per day for less than two weeks. The improvement comes from an increase in the number of responsive small inhibitory neurons in the olfactory bulb, which leads to improved cooperation and increased oscillations among the cells in the olfactory bulb.

Now that researchers know that animals use these oscillations selectively for difficult discriminations and that exposure to scents over many days can improve smell, they can look more closely at how the process occurs and gain a greater understanding of how animals — including human beings — use the sense of smell.
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