Semantic Congruence Alters Functional Connectivity during Olfactory-Visual Perception

Previous research has shown that humans struggle to interpret multiple perceptual signals when the information provided by these signals is incongruent. In the context of olfactory-visual integration, behavioral and neuronal differences in response to congruent and incongruent stimulus pairs have been established. Here, we explored functional connectivity of the human brain with regard to the perception of congruent and incongruent food stimuli. Participants were simultaneously presented olfactory and visual stimuli of 4 different food objects, 2 healthy and 2 unhealthy objects. Stimulus pairs were grouped into "congruent" (olfactory and visual presentation of the same object), "semi-congruent" (stimuli of similar "healthiness"), and "incongruent" (healthy-unhealthy stimulus combination). Using functional magnetic resonance imaging and psychophysiological interaction (PPI) analyses, we revealed part of a neural network, the nodes of which show differential connectivity depending on the level of congruency of the presented stimulus combinations. This network relies strongly on, mostly left, inferior frontal gyrus. The analysis of such network transcends standard subtractive designs and indicates the need for more detailed formulations of neuronal models and increased specificity in functional imaging.