Cognition-Emotions interactions in the Olfactory modality – ICEO

The ICEO project is composed of 3 tasks and its duration is 3 years. Methods used are from discourse analysis, psychophysics and neurobiology (functional imaging, fMRI). Experiments will imply different populations (young and old healthy human subjects in task 1, patients with Alzheimer disease in task 2, and experts in olfaction in task 3). Practically, experiments 1 to 3 will consist on a single visit of the participants to the research center. Here, methods used are from linguistics, psychophysics and experimental psychology. Each experiment is composed of two sessions: in the first the subjects are screened for their olfaction, in the second one, they perceived odors and they evaluate hedonic value of the smell. In Experiment 4, we will test the influence of expertise on perception of odors that will differ in their physicochemical properties. We will set up a study in experienced subjects using fMRI. By using appropriate imaging analyses methods, we will compare neural maps in primary and secondary olfactory cortex as a function of odorant molecule types and experience level.

Using a multidisciplinary approach, data collected by our team indicate that pleasant odorant molecules whose molecular structure is complex are evaluated significantly less pleasant with age. Current models of olfactory perception refer little to the molecular structure of odor, and when this is the case, the nature of the relevant physicochemical attributes is not known. The possibility that these physicochemical properties (e.g. size, weight, complexity) that we have highlighted are relevant to the olfactory system is highly innovative and the ICEO project will help to confirm and deepen this finding. The challenge here is to achieve a thorough revision of previous models with a new approach to structure-odor (hedonic valence) relationship. The implementation of the experiments from the different tasks began a few months ago. Once the results will be established, our research program will provide to the scientific community and the industrial world, analysis tools for identifying cognitive and physico-chemical properties of odorants from verbalizations of experts and non-experts human subjects.

The aim of our project is both scientific and methodologic, in a context where understanding the impact of cognition on emotional behavior and brain activity is an issue of first order both in the international field of affective sciences and for industrial applications. The exchanges we have with manufacturers of perfumes show how challenging for this area is to better understand the effects of these odorous compounds on human behavior in order to innovate in product formulation.
The results of the ICEO project will be communicated through communication seminars, conferences, congresses and published in scientific journals.

1. Sezille C, Messaoudi B, Bertrand A, Joussain P, Thévenet M, Bensafi M. A portable experimental apparatus for human olfactory fMRI experiments. J Neurosci Methods. 2013 Aug 15;218(1):29-38
2. Joussain P, Thevenet M, Rouby C, Bensafi M. Effect of aging on hedonic appreciation of pleasant and unpleasant odors. PLoS One. 2013 Apr 24;8(4):e61376.

Affective sciences comprise a set of disciplines addressing the neural bases and behavioral display of emotions. In the last thirty years, research in this field has progressed strongly with a particular interest to the question how cognition influences emotion(s). It is in this context that the ICEO project is rooted taking the olfactory modality as window on the human emotional system.

Olfaction is a sensory system devoted to the detection and recognition of odorant molecules from the environment. In all species including humans, odors are potentially related to acts in the sense that the information they carry is generally used to decide what action to take: move away or approach the odor source. This call to action brought by the smell is a reflection of what is generally called the emotional or hedonic valence of the odor.

An important question raised by psychologists and biologists in recent decades is that of the determinants of this hedonic valence of odors. Conservation between species of a preference for certain molecules and avoidance for others argues for determinism based on the physicochemical properties of odorants. However, we all know that the hedonic perception of odor is highly variable from one individual to another. For example, while the smell of durian is popular in some Asian countries, it is much less in our Western cultures. Conversely, the smell of Saint Felicien cheese well appreciated in France can be an insult to the senses of an individual from another culture. Variations are also observed within the same culture. This implies that the hedonic valence is changed or modulated during human development, by learning and may be by aging, whether normal or pathological.

The vast majority of research on odor hedonic valence conducted in recent years has focused either on the effects of physicochemical properties of odorant molecules on perception (genetic predetermination) or on the effects of lexical and semantic knowledge acquired through experience and learning (acquired determination). Progress on the genetic predetermination is due to studies in adults or in newborns. Progresses on the effects of learning on emotional perception of odors in humans have also been published in adults and children, and each mechanism has its defenders. It seems that the proponents of an “innate” or an “acquired” determinism represent incompatible theories, and the possibility of an interaction between the physicochemical influences on the one hand and the experience and learning on the other hand is not studied today. Can learning dominate the innate physicochemical influences?

The general aim of the ICEO project is to answer this question. We will study in particular the question of the interactions between the influence of physicochemical properties of odorants and the influence of learning both in normal aging where we know that knowledge becomes difficult to access, and during pathological aging where cognitive deficits may alter these influences. Here, we will set out to examine whether there are ages or diseases such as Alzheimer's disease where physicochemical influences take precedence over culture or knowledge. On the other hand, we will look if these predetermined hedonic responses are inhibited by knowledge in experts such as perfumers or flavorists. Furthermore, to better understand the effect of cognition on perception and emotions, it is necessary to demonstrate their effect on brain activity. Thus, a neurobiological approach using fMRI will complete the project.
The project will therefore improve the understanding of human olfaction, from its emotional to its cognitive dimension. The identification of the cognitive factor modulating the hedonic valence of odors also represents a challenge in the industrial world where innovation in odorous compounds requires a better understanding of their impact.