Swarming Locusts Shed Light on How Brain Processes Smells

Our sense of smell can tell us quite a bit about the environment. We can sniff out food or tell if something foul is nearby. But how does our brain process multiple odors received simultaneously? Using locusts, scientists may have just discovered the answer.

Locusts have a relatively simple sensory system that's ideal for studying brain activity. In order to better study their sense of smell, the researchers used a computer-controlled pneumatic pump to administer an odor puff to a locust, which has olfactory receptor neurons in its antennae, which are similar to the sensory neurons in our nose. A few seconds after this odor puff was given, the locust received a piece of grass as a reward.

So what did they find? With this conditioning, the locusts anticipated the grass even before it was given--similar to Pavlov's dog. What was interesting, though, was that the locusts' responses were less than half of a second; the locusts could also recognize the trained odors even when another odor was meant to distract them.

"We were expecting this result, but the speed with which it was done was surprising," said Barani Raman, one of the researchers, in a news release. "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."

The researchers also found some other interesting results. They discovered that while geraniol, which smells like a rose to us, was an attractant, citral, which smells like lemon, is a repellent to the locusts. This allowed the scientists to identify principles that are common to the odor processing.

So what could this research help with? It could potentially be used to develop a device for noninvasive chemical sensing. Such a device would be used in homeland security applications to detect volatile chemicals and in medical diagnostics. For now, though, researchers are still seeking the answers to more questions.

"Neural activity in the early processing centers does not terminate until you stop the odor pulse," said Raman in a news release. "If you have a length pulse--5 or 10 seconds long--what is the role of neural activity that persists throughout the stimulus duration and often even after you terminate the stimulus? What are the roles of the neural activity generated at different points in time, and how do they help the system adapt to the environment? Those questions are still not clear."

The findings are published in the journal Nature Neuroscience.