Rodent tears contain social chemosignals with diverse effects, including blocking male aggression. Human tears also contain a chemosignal that lowers male testosterone, but its behavioral significance was unclear. Because reduced testosterone is associated with reduced aggression, Agron, de March et al. tested the hypothesis that human tears act like rodent tears to block male aggression. Using a standard behavioral paradigm, they found that sniffing emotional tears with no odor percept reduced human male aggression by 43.7%. To probe the peripheral brain substrates of this effect, they applied tears to 62 human olfactory receptors in vitro, identifying 4 receptors that responded in a dose-dependent manner to this stimulus. Functional brain imaging showed that sniffing tears increased functional connectivity between the neural substrates of olfaction and aggression, reducing overall levels of neural activity in the latter. Taken together, the results imply that, as in rodents, a human tear-bound chemosignal lowers male aggression, likely dependent on the structural and functional overlap in the brain substrates of olfaction and aggression. The image depicts actual brain data and an olfactory receptor model, overlaid on a human couple, rendered using Midjourney.

Image Credit: Ofer Perl and Shani Agron