Multimodal Integration of Olfactory and Visual Processing through DCM analysis: Contextual Modulation of Facial Perception

This study examines the modulatory effect of contextual hedonic olfactory stimuli on the visual processing of neutral faces using event-related potentials (ERPs) and effective connectivity analysis. The aim is to investigate how odors' valence influences the cortical connectivity underlying face processing, and the role arousal enhanced by faces plays on such visual-odor multimodal integration. To this goal, a novel methodological approach combining electrodermal activity (EDA) and dynamic causal modeling (DCM) was proposed to examine cortico-cortical interactions changes. The results revealed that EDA sympathetic responses were associated with an increase of the N170 amplitude, which may be suggested as a marker of heightened arousal to faces. Hedonic odors had an impact on early visual ERP components, with increased N1 amplitude during the administration of unpleasant odor and decreased vertex positive potential (VPP) amplitude during the administration of both unpleasant and neutral odors. On the connectivity side, unpleasant odors strengthened the forward connection from the inferior temporal gyrus (ITG) to the middle temporal gyrus (MTG), involved in processing changeable facial features. Conversely, the occurrence of sympathetic responses was correlated with an inhibition of the same connection, and with an enhancement of the backward connection from ITG to the fusiform face gyrus. These findings suggest that negative odors may enhance the interpretation of emotional expressions and mental states, while faces capable of enhancing sympathetic arousal prioritize the processing of identity. The proposed methodology provides insights into the neural mechanisms underlying the integration of visual and olfactory stimuli in face processing.