Reward-based Evaluation of Odor Stimuli Impacts Functional Connectivity in Frontal and Temporal Areas: A Longitudinal EEG Study.

Olfactory stimuli are particularly potent in triggering experiences of reward because olfactory processing in the brain directly interfaces with memory, emotional and reward-related neural pathways. Past research has focused mostly on evaluating the neural response to odor stimulation across the arousal-valence dimensions, tapping on emotion and hedonic evaluation mechanisms triggered by olfactory cues. Few studies focused on the reward-related evaluation odor stimuli and the related brain mechanisms, particularly in a longitudinal manner. To address this, in the present study participants were exposed to pleasant odor stimuli and asked to indicate their decision on having the stimuli repeated, in three experimental sessions run on consecutive days. Electroencephalography (EEG) was used to assess their neural responses to repeated stimuli presentation. Behavioral results indicated that repetitive exposure to some stimuli trigger stimulus-reward associations, and their trajectory is mediated by the rewarding value of the respective odor samples. Functional connectivity analysis and graph theoretic metrics revealed significant differences between low and high-reward stimuli in the β and γ frequency bands, over frontal and temporal regions, which tracked behavioral evaluations. These findings shed light on neural mechanisms involved in reward-related processing of olfactory stimuli during repetitive exposure and demonstrate that EEG can be used to reliably evaluate the reward value of odor stimuli.