Paris, 8 March 2011
We are all able to visualize our own living room, move about virtually or mentally hum a catchy tune. But can we recall the smell of toast or a fig to the point of actually smelling their odor? Olfactory mental imagery is a much more difficult exercise than visual or auditory mental imagery and most people say they do not have this capacity. However, perfumers, olfactory experts used to smelling, evaluating and creating odors, claim they are capable of smelling an odor even in its absence. Where does the truth lie?
To answer this question, the researchers used functional Magnetic Resonance Imaging (fMRI). They compared the spatial organization of the cerebral activations of students from the Ecole de Parfumerie de Versailles (ISIPCA) to that of professional perfumers, a rare species (there are no more than 500 throughout the world, of which some 120 are in France and Switzerland). While placed in a scanner, the subjects were asked to mentally conjure up the smell of odorous substances (1), whose chemical name appeared on a screen.
The results show that in the experts of both groups, olfactory mental imagery activates the primary olfactory cortex (piriform cortex) a zone of the brain ordinarily stimulated during perception. This proves that similar areas are activated during the perception and imagination of odors. Like visual or auditory mental imagery, olfactory imagery depends on the reactivation of olfactory images via an internal cognitive process (our own brain generates this sensation) and not in response to an odor.
Another finding is that, in perfumers, intense olfactory training influences the activation level of the neuronal network involved in the mental imagery of odors. Surprisingly, the greater the level of expertise, the more the activity of the olfactory and mnesic (hippocampus) regions is reduced. Thus, when the brain is trained, “communication” at the neuronal level takes place more easily, rapidly and efficiently, and the message is more specific, resulting in reduced activation. This shows that regular training enhances olfactory mental imagery, which does not stem from an innate faculty.
In this study, the perfumers were able to imagine the odors rapidly, sometimes instantaneously, whereas the students experienced some difficulties and needed to concentrate their attention. By easily reactivating the mnesic representations of odors, perfumers can mentally compare and combine scents with the aim of creating new fragrances. These results demonstrate the brain's extraordinary capacity to adapt to environmental demand and to reorganize itself with experience.
© JP Royet
The cerebral activity of professional and student perfumers was recorded in an MRI scanner when they mentally imagined odors whose chemical names (dihydromyrcenol, aldehyde C11, triplal, alpha-damascone, methyl anthranylate, linalyl acetate, etc.) were presented to them via a mirror placed above the antenna.
© JP Royet
The primary olfactory cortex is activated in both hemispheres when the subjects mentally imagine odors. The activations are represented in horizontal and frontal sagittal sections of the brain.
1 - Dihydromyrcenol, aldehyde C11, triplal, alpha-damascone... just some of the chemical names of the twenty or so odorants selected for the experiment among the 300 with which student perfumers normally work.
Plailly J., Delon-Martin C., Royet J.P. (2011) Experience induces functional reorganisation in brain regions involved in odor imagery in perfumers. Human Brain Mapping, in press.
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