Our sense of smell is often the first response to environmental stimuli. Odors trigger neurons in the brain that alert us to take action. However, there is often more than one odor in the environment, such as in coffee shops or grocery stores. How does our brain process multiple odors received simultaneously?
Barani Raman, PhD, of the School of Engineering & Applied Science at Washington University in St. Louis, set out to find an answer. Using locusts, which have a relatively simple sensory system ideal for studying brain activity, he found the odors prompted neural activity in the brain that allowed the locust to correctly identify the stimulus, even with other odors present.
The results were published in Nature Neuroscience as the cover story of the December 2013 print issue.
The team uses a computer-controlled pneumatic pump to administer an odor puff to the locust, which has olfactory receptor neurons in its antennae, similar to sensory neurons in our nose. A few seconds after the odor puff is given, the locust gets a piece of grass as a reward, as a form of Pavlovian conditioning. As with Pavlov's dog, which salivated when it heard a bell ring, trained locusts anticipate the reward when the odor used for training is delivered.
Instead of salivating, they open their palps, or finger-like projections close to the mouthparts, when they predict the reward. Their response was less than half of a second. The locusts could recognize the trained odors even when another odor meant to distract them was introduced prior to the target cue.
"We were expecting this result, but the speed with which it was done was surprising," says Raman, assistant professor of biomedical engineering. "It took only a few hundred milliseconds for the locust's brain to begin tracking a novel odor introduced in its surrounding. The locusts are processing chemical cues in an extremely rapid fashion."
"There were some interesti
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Washington University in St. Louis