So you thought that smell was cheese!

Researchers in the UK have found that visual words can influence the perception of smells, with pleasant words influencing olfactory brain regions to perceive an odour as pleasant, an interesting idea that might hold particular relevance for restaurateurs and advertisers.

In their experiments, researchers at the University of Oxford presented subjects with a cheddar cheese odorant and showed them labels that read either "cheddar cheese" or "body odour." They found that the subjects rated the odour significantly more pleasant when it was labelled "cheddar cheese" than "body odour."

Then they scanned the subjects' brains using functional magnetic resonance imaging (fMRI) during the presentation of labels and doors to explore which brain regions were activated. They also analysed brain activity when the subjects were presented with clean air labelled either "cheddar cheese" or "body odour." 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 led by Edmund T. Rolls found that labelling the odour "cheddar cheese" produced an activation in a specific part of the brain region that processes olfactory information. Clean air labelled as "cheddar cheese" activated the same area, but to a lesser extent. The "body odour" label, however, did not produce activation in this area, either with the cheddar cheese odour or clean air.

The researchers also used correctly labelled pleasant ("flowers") and unpleasant ("burned plastic") doors as reference doors to test the subjects' responses to such doors and to identify areas of the brain activated by either pleasant or unpleasant doors, they also tested whether a change in the amount of "sniffing" in response to an odour label might influence the results, and found no effect.

The team emphasize that word labels were used so that the cognitive input would be "high level and semantic," as opposed to a picture, which could have been a lower-level association in the brain.

Both de Araujo and Rolls say the results show that cognitive inputs can be very important in influencing subjective responses, including affective responses to olfactory stimuli, and show that some of the brain areas activated by doors, show an effect of this high-level cognitive influence. They also noted that their inclusion of clean air in the study showed that semantic labels influenced judgment, even when the absence of odour was paired with the labels.

Whether the words caused subjects to imagine a smell or simply affected their brain's processing of doors the sight of a word, can influence the activity in brain regions that are activated by olfactory stimuli.

The research is published in the May 19 issue of Neuron.