In their experiments, researchers led by Edmund T. Rolls of the University of Oxford presented subjects with a cheddar cheese odorant and showed them labels that read either "cheddar cheese" or "body odor." They found that the subjects rated the odor significantly more pleasant when it was labeled "cheddar cheese" than "body odor."
They then scanned the subjects' brains using functional magnetic resonance imaging (fMRI) during the presentation of labels and odors to explore which brain regions were activated. They also analyzed brain activity when the subjects were presented with clean air labeled either "cheddar cheese" or "body odor." The widely used analytical technique of fMRI uses harmless magnetic fields and radio waves to measure blood flow in regions of the brain, which reflects brain activity.
The researchers found that labeling the odor "cheddar cheese" produced an activation in a specific part of the brain region that processes olfactory information. Clean air labeled as "cheddar cheese" activated the same area, but to a lesser extent. The "body odor" label, however, did not produce activation in this area, either with the cheddar cheese odor or clean air.
The researchers also used correctly labeled pleasant ("flowers") and unpleasant ("burned plastic") odors as reference odors to test the subjects' responses to such odors and to identify areas of the brain activated by either pleasant or unpleasant odors. Also, they tested whether a change in the amount of "sniffing" in response to an odor label might influence the results, finding no effect.