MEntal Representation of ODors: from physical features to perceptual processing – MEROD

Three sets of experiments embedded in 3 Tasks combining the efforts of a German team (Hummel lab at the Technical Unversity of Dresden) and a French team (Bensafi lab at the University of Lyon and CNRS) will be conducted. In the first experimental Task, we shall realize a series of extensive psychophysical experiments in both France and Germany in a large sample of participants to define a set of odorants varying in chemical and perceptual properties. This odor database will enable selection of odors used in the two following, independent experimental tasks performed in Dresden and Lyon. In the second experimental Task, the role of central olfactory areas (piriform cortex, amygdala and orbitofrontal cortex) in extracting both chemical and perceptual similarities across odorants and odors will be tested in novices (non-experts) and experts in olfaction (perfumers, who have higher discrimination abilities about odors). In the third Task, the role of the human olfactory bulb (the first relay of odor information) in extracting chemical similarities across odorants will be explored. In a second aim, we will promote scientific culture and communication on olfaction in the general public and in higher education based on the original findings from the project.

The first findings from the experiments performed in the first experimental task allowed us to develop a database containing 105 odorants characterized by a large number of chemical and perceptual properties. It was on the basis of these data that the experiments of the other experimental tasks could be done. Thus, 3 different brain imaging studies were performed. In the first, we revealed a hierarchy in the treatment of chemical and perceptual attributes of odors: while the former are represented within the primary olfactory areas, the latter are represented within the secondary olfactory cortex. In the second study, we have shown that learning modulates the way odors are represented especially in associative brain regions. Finally, in the third study, we observed that the hedonic component of odors was represented at an early stage of treatment, within the olfactory bulb. Studies involving expert individuals (perfumers) and using larger sets of odors are currently carried out.

*Mental representation of odors is multidimensional, involving primary sensory areas to process chemical attributes of smells and secondary areas for perceptual features. *The hedonic component of odors is represented very early, at the level of the olfactory bulb. *Learning induces neural changes in the representation of odors, especially in heteromodal and associative areas.

* Fournel A, Ferdenzi C, Sezille C, Rouby C, Bensafi M. Multidimensional representation of odors in the human olfactory cortex. Hum Brain Mapp. 2016 Jun;37(6):2161-72. *Fournel A, Sezille C, Licon C, Sinding C, Gerber J, Ferdenzi C, Hummel T, Bensafi M. Learning to name smells increases activity in hetero-modal semantic areas. Hum Brain Mapp. 2017 sous presse.

Around the turn of the century the idea that civilized human beings might do without olfaction became outdated: this inarticulate sense, hitherto considered superfluous to cognition, became a focus of study in its own right. It was acknowledged as an object of science by Nobel prizes; in addition, society ecame more hedonistic, and hence more attentive to the emotional effects of odors. Odors are sources of both pleasure and social bonding; they influence our sexuality and relations with others in general and with our children in particular. They contribute to our emotional balance: olfactory damage impairs this equilibrium. An important issue in cognitive psychology is to understand how the human brain represents odor objects. Representation of visual objects is far better understood; we know that physical and perceptual attributes of visual stimuli are represented in a distributed and hierarchical manner, but it is still unclear how chemical properties of odorant molecules and perceptual aspects of odors are represented along the human olfactory pathway.
In the present project, we hypothesize that the multidimensional representation of odors is the result of a neural mechanism that processes similarities of chemical information and perceptual information at various stages of the olfactory system. Three sets of experiments embedded in 3 Tasks combining the efforts of a German team (Hummel lab at the Technical Unversity of Dresden) and a French team (Bensafi lab at the University of Lyon and CNRS) will be conducted. In the first Task, we shall realize a series of extensive psychophysical experiments in both France and Germany in a large sample of participants to define a set of odorants varying in chemical and perceptual properties. This odor database will enable selection of odors used in the two following, independent experimental tasks performed in Dresden and Lyon. In the second experimental Task, the role of central olfactory areas (piriform cortex, amygdala and orbitofrontal cortex) in extracting both chemical and perceptual similarities across odorants and odors will be tested in novices (non-experts) and experts in olfaction (perfumers, who have higher discrimination abilities about odors). In the third Task, the role of the human olfactory bulb (the first relay of odor information) in extracting chemical similarities across odorants will be explored. In a second aim, we will promote scientific culture and communication on olfaction in the general public and in higher education based on the original findings from the project. Thus, the present project aims to position itself in international competition with original objectives. It combines expertise in human olfaction and cognitive psychology. It aims to better understand mental representation of smells, in a fundamental perspective for deciphering their neural organization, and in an educational perspective for providing original courses i the field of psychology of smells.