Neural representation of allegedly sex-specific human body odor compounds

Body odors play an important role in nonverbal communication, and particularly in one's attractiveness. However, their central processing remains underexplored, especially as a function of gender. This study aims at identifying the neural networks involved in the processing of two allegedly sex-specific human body odor compounds (3-hydroxy-3-methylhexanoic acid, HMHA, and 3-methyl-3-sulfanylhexan-1-ol, MSH). We hypothesized that i) these body odors would be processed by different brain regions than non-body odors, and that ii) their role in attractiveness, if any, would be indicated by the activation of specific regions and by differential verbal and neurophysiological responses in men and women. Thirty participants (15 men, 15 women) performed a functional Magnetic Resonance Imaging (fMRI) session during which they rated the attractiveness of HMHA, MSH, and 5 non-body odorants. At the end of the session, participants rated all odors on multiple perceptual scales. HMHA activated visual (striate area and occipital gyrus) rather than olfactory brain regions. Men rated HMHA as more masculine than women did, and presented greater neural activity in the superior and medial frontal gyri while women activated the inferior frontal gyrus significantly more than men in response to this odor. MSH was processed as the other non-body odors, and not subject to gender differences. The results suggest that HMHA (not MSH) bears specific social information, resulting in a neural processing outside the main olfactory network. It is also processed differently in men and women, although our findings do not provide clear evidence in favor of relevance for one's attractiveness.