What's Going On in a Jealous Man's Brain

Source: Syda Productions/Shutterstock

Jealousy triggers an increase of neural activity in brain areas associated with pair bonding and social pain, along with an uptick in testosterone and cortisol, according to a new study from the University of California, Davis, of male Coppery titi monkeys, who are hardwired for monogamy. These findings were recently published in the journal Frontiers in Ecology and Evolution. According to the researchers, this is the first study to use a monogamous primate model to better understand the neurobiology of jealousy.

Only about 4 percent of mammalian species are socially monogamous. Until recently, most animal research on pair bonding and monogamy focused on prairie voles. However, findings on monogamy in rodents may not be as applicable to humans as monogamy-based research on primates. Learning more about the neurobiology of pair bonding in non-human primates significantly advances our understanding human monogamy.

Typically, socially monogamous animals develop their pair bond with a significant other during an adult phase of attachment. This monogamous relationship is marked by the onset of social buffering and mate-guarding in both males and females toward both same- and opposite-sex individuals.

Coppery titi monkeys are notorious for displaying a variety of monogamous behaviors that correlate to human jealousy. For example, males become visibly agitated upon separation from their significant other, and this agitation is coupled with physiological stress biomarkers. This psychophysiological response makes the male titi monkey an ideal non-human primate for examining the neurobiology of both monogamy and jealousy.

If given the opportunity, a male titi monkey will physically restrain or block his partner from interacting with another male who might make unsolicited sexual advances. For this study, the researchers used functional neuroimaging to illuminate changes in regional cerebral glucose metabolism of male titi monkeys while remotely viewing their pair mate in close proximity to a strange male "intruder" who represented a monogamy threat for 30 minutes.

After eliciting the “jealousy” response in the males, the researchers observed heightened activity in the cingulate cortex, an area of the brain associated with social pain, and the lateral septum, an area associated with pair bond formation.

In addition to pinpointing neural changes associated with jealousy, the researchers were also interested in identifying hormonal changes in jealous male monkeys. During the jealousy condition, males had higher levels of testosterone and plasma cortisol concentrations. The hormonal increases triggered by jealousy weren’t surprising, given testosterone's association with mating-related aggression and cortisol’s role as a stress hormone.

In a statement, senior author Karen Bales of the California National Primate Research Center and the Department of Psychology at the University of California, Davis, said, "Understanding the neurobiology and evolution of emotions can help us understand our own emotions and their consequences. Jealousy is especially interesting given its role in romantic relationships — and also in domestic violence."

Bales is also the director of The Laboratory for Comparative Neurobiology of Monogamy at UC Davis. She is optimistic that gaining a better understanding of the neurobiology of jealousy in the animal kingdom may provide important clues on how to approach health and welfare problems in human relationships, such as addiction and domestic violence.

One significant limitation of this research is that it only examined jealousy in males. The question remains as to whether the neurobiology of jealousy is the same in both male and female titi monkeys. Future research by Bales and her colleagues will address this question.