The researchers, led by Martin Giurfa, first trained thousands of bees to associate a specific chemical, such as the alcohol 1-nonanol, with a sucrose reward. Then the researchers tested the bees' response to a set of different smells, varying in chemical composition. By watching how often the bees responded positively to a particular scent when they'd been trained on another, the researchers could assign perceptual "distances" between pairs of chemicals. Drawing together all these distances, they created a preliminary map of the bees' "perceptual space," similar to how surveyors measure distances between landmarks to map a landscape. From this comparison they found, for example, that the bees generalized more by functional group than by carbon-chain length.
Previously, another group had recorded bees' brain responses to the same pairs of scents, assigning distances within centers of activity for each scent. Giurfa's team compared these two sets of data and found that the perceptual and neural distances correlated well, which suggests there's a species-specific code that ties together the insects' brain and behavior. Future studies should only improve our ability to investigate the correlations between brain and behavior, the authors say. Such studies would go even further toward cracking the codes underlying animals' perception and memory.