Making Sense of Scents: How Animals Sniff Out Odors from Background Smells

What smells good and what smells bad? Making sense of scents can mean the difference between a meal and avoiding certain death for many animals. Now, scientists have taken a closer look at exactly how animals separate objects of interest from background information.

"There is a continuous stream of information constantly arriving at our senses, coming from many different sources," said Venkatesh Murthy, one of the researchers, in a news release. "The classic example would be a cocktail party-though it may be noisy, and there may be people talking, we are able to focus our attention on one person, while ignoring the background noise. Is the same true for smells? We are bombarded with many smells all jumbled up. Can we pick out one smell 'object'-the smell of jasmine, for example-amidst a riot of other spells?"

In order to find out, the researchers trained mice to detect specific scents. The scientists presented the animals with a combination of smells, sometimes including the "target" scent and other times not. In the end, the researchers found that the mice were able to identify when a target scent was present with 85 percent accuracy or better.

"Although the mice do well overall, they perform progressively poorer when the number of background odors increases," said Murthy.

In order to find out why this was, the scientists used fluorescent proteins to create images that showed how each of 14 different odors stimulated neurons in the olfactory bulb. In the end, they found that the ability of mice to identify a particular smell was markedly diminished if background smells activated the same neurons as the target odor.

"This study is interesting because it first shows that smells are not always perceived as one whole object-they can be broken down into their pieces," said Murthy. "This is perhaps not a surprise-there are in fact coffee or wine specialists that can detect faint whiffs of particular elements within the coplex mixture of flavors in each coffee or wine. But by doing these studies in mice, we can now get a better understanding of how the brain does this."

The findings are published in the journal Nature Neuroscience.