Sniff... Sniff...

What's that Smell?

Ever entered a room and noticed a pleasing smell? Then, after taking a second whiff, realized the smell was floral? And after a third sniff, you knew the smell was roses?

Researchers from the Center for the Neural Basis of Cognition (CNBC) — a joint project of Carnegie Mellon University and the University of Pittsburgh — now know what makes this refining of the senses possible. It's a mechanism in the brain they're calling "dynamic connectivity."

In a paper published in Nature Neuroscience, Carnegie Mellon Professor Nathan Urban and his colleagues explain the mechanism, showing how neuronal circuits are rewired "on the fly." This means they allow the brain to quickly sort through stimuli to determine exactly what is being sensed.

"If you think of the brain like a computer, then the connections between neurons are like the software that the brain is running," said Urban, who is an associate professor of biological sciences. "Our work shows that this biological software is changed rapidly as a function of the kind of input that the system receives."

In order to understand dynamic connectivity, the researchers looked at a process called lateral inhibition. In lateral inhibition, encountering a stimulus — such as an odor — causes many neurons to fire.

When many neurons fire at the same time, the signals can be difficult for the brain to interpret. During lateral inhibition, the stimulated neurons send "cease-fire" messages to the neighboring neurons, reducing the noise and making it easier for the brain to precisely identify the stimulus.

Results of their study showed that dynamic connectivity allows lateral inhibition to be enhanced when a large number of neurons initially respond to a stimulus. By filtering out the noise, the stimulus can be more clearly recognized and separated from similar stimuli.

"By understanding how the brain does this, we can then apply this mechanism to other problems faced by the brain," said Urban.

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