6533b855fe1ef96bd12b0eb3

RESEARCH PRODUCT

Discrimination des expressions faciales et environnement olfactif - Corrélats cérébraux en électroencéphalographie (EEG) chez l'adulte et le très jeune enfant

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This thesis examines the mechanisms subtending the perception of emotional facial expressions and their early development using a Fast Periodic Visual Presentation (FPVS) approach coupled with electroencephalography (EEG). More specifically, we tried to characterize brain responses reflecting facial expression discrimination and to determine whether hedonic odor contexts influence these responses in adults (studies 1 and 2), and in infants at different developmental stages (studies 3 and 4). We showed specific responses to the discrimination of every facial expression in the adult brain, indicating rapid and automatic categorization of basic facial expressions (study 1). In addition, we revealed that hedonic odor contexts influence these expression-specific brain responses. While the response to happiness is unchanged, the response to disgust is weaker in both pleasant and unpleasant odor contexts. The odor effect is strong for the response to neutrality, this response being nearly absent in the unpleasant odor context vs. larger in the pleasant context. Hedonic odors could thus orient facial expression perception toward their own emotional valence, or toward the valence of the odor for the emotionally ambiguous neutral expression, hampering or facilitating their discrimination from the other mainly negative expressions (study 2). In infants, a first study isolated brain responses to the discrimination of facial expressions in 3.5- and 7-month-olds (study 3). In particular we observed that the response to happiness evolves between 3.5- and 7-month-old (additional fronto-central activity), suggesting the progressive integration of the emotional meaning of this positive expression. The second study has been initiated in 7-month-old infants to test the influence of a pleasant hedonic odor context on the specific brain response to happiness (study 4, ongoing study). This study seems to indicate that the response is larger in a pleasant rather than neutral odor context. These results reveal that facial expressions are readily discriminated in adults, hedonic odor contexts orienting perception toward emotional valence rather than related basic emotions. Emotional valence may be acquired early in development, before 7 months, since the discrimination of happiness (positive) from other expressions (mainly negative) evolves at this age. Moreover, at 7 months, the perception of happiness seems facilitated by the presence of a pleasant odor context. Hence, due to the early functional maturity of the olfactory system, odors may actively participate in acquiring the emotional meaning of facial expressions during early development and facilitate the perception of expressions whose emotional meaning is ambiguous in adults. Overall, our work sheds new light on the role of multisensory integration during early perceptual development and opens interesting perspectives to investigate typical and atypical socio-cognitive and affective development.