The mystery of odour-cued perception

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Olfactory experiment: while the proband breathes in various scents, electrodes m
Olfactory experiment: while the proband breathes in various scents, electrodes measures his physiological reactions. The result: before classifying a scent as pleasant or unpleasant, the brain checks whether it is familiar or not. (Photo: Bibliothèque Nationale de France)

Odours are powerful stimulants for the human brain. Now, for the first time, researchers have succeeded in demonstrating that the evaluation of olfactory perceptions actually follows a very strict order.

New or familiar? Pleasant or unpleasant? When met with an odour, the brain evaluates it within seconds in this order and not the other way around. In other words, first the brain determines whether, for example, a perfume is familiar or not. Only then does it categorise the scent as pleasant or unpleasant. Whether it is considered exhilarating, aggressive, repulsive or intoxicating, an odour is first perceived in terms of its novelty. 

Researchers at the University of Geneva working on the subject of olfactory perception as part of the NCCR Affective Sciences have discovered this sequential process for the first time. Olfactory information is processed according to an organised sequence that can be divided into two phases: first, detection of novelty, then categorisation as pleasant or unpleasant. These two phases were identified in an experiment testing physiological reactions to the perception of different odours.

Eighteen test persons were attached with electrodes to specific areas of their face and body and then asked to breathe in pairs of aromatic samples of different types (floral, fruity or animal). Researchers measured the electrical activity of facial muscles, the perspiration on hands and heart rates and then recorded the data on a comparative timescale. The results brought researchers a big step closer to revealing the origins of the emotional mechanisms linked to the senses and to odours in particular.

These mechanisms, frequently mentioned in literature – from Baudelaire’s Flacon to the famous Proustian ‘madeleine phenomenon’  - attract a great deal of interest from the cosmetics industry today. The research work conducted at the Affective Sciences Centre of the University of Geneva is partially funded by the perfume multinational, Firmenich, with headquarters in Geneva.

One of the aims of the partnership is to develop reliable tools for assessing the emotional effects of scents. It is very attractive at a commercial level to come closer to the origins of olfactory memory by solving the mystery of odour-cued perception. Who, indeed, could resist an anti-wrinkle cream that evokes childhood memories or a lipstick reminiscent of the unforgettable taste of a first kiss?