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First Impressions Matter in Sense of Smell

Research by DIBS Faculty Network Member Kevin Franks appears in Science

If you can tell the difference between a merlot and a cabernet franc just by smell, it’s probably all in the timing.

That’s because the odor-decoding centers of the brain will pay more attention to the first smell signals to reach them, regardless of how long or strong the remainder of the sniff may be, according to a pair of Duke University neurobiologists who have teased apart the neural circuitry of smell in mice.

Humans have about 400 different types of odor receptors in their nose, each tuned to slightly different scent molecules. Whenever we inhale, the receptors most closely matched to a particular scent will signal first.

But if you take a deeper sniff in that wineglass, you will inhale many more scent molecules, which can activate less specific receptors. Those added signals should dramatically change the scent, but they don’t, a riddle sensory neuroscientists call “concentration-invariance.” 

The answer to the riddle, according to new research appearing Sept. 14 in Science, is in the timing.

A scent is routed from the nose through a structure called the olfactory bulb to the olfactory cortex, where its  signals are processed. The first signals to reach the cortex are invariably those that are most closely matched to particular odor receptors in the nose. Therefore, they provide the most precise information about the odor, said Kevin Franks, an assistant professor of neurobiology in the Duke School of Medicine.

“You’ll always activate the most specific receptors earliest,” said Franks, who is also a member of the Duke Institute for Brain Sciences.

Courtesy of Duke Today