This is what jealousy does to the brain

Thomas McMullan Read more October 18, 2017

The green-eyed monster is one of the great cogs in human drama, but scientists know surprisingly little about the mechanisms of jealous minds. When jealousy rears its noxious head, what brings on those feelings of fear, insecurity and anger?

Increased brain activity in areas associated with social pain and pair bonding, is the rather prosaic answer. Eat your heart out Othello.

According to a new study, jealousy in monogamous species cause “neurological spikes” in the brain’s cingulate cortex and the lateral septum: two areas that deal with bonding and social pain. The scientists behind the research, published in Frontiers in Ecology and Evolution, say these findings could lead to a greater understanding of how monogamy evolves, and how jealousy can lead to violence in humans.

“Understanding the neurobiology and evolution of emotions can help us understand our own emotions and their consequences,” says Dr Karen Bales from the University of California, one of the authors of the study. “Jealousy is especially interesting given its role in romantic relationships – and also in domestic violence.”

A bulk of previous research on the neurochemistry of bonding has been done on prairie voles; which are socially monogamous rodents. To get closer to the brain structures of humans, Bales and her team instead sought to investigate the effect of jealousy on primates. They turned to coppery titi monkeys – a monogamous species that displays similar attitudes to romantic relationships as humans.

“Male titi monkeys show jealousy much like humans and will even physically hold their partner back from interacting with a stranger male,” says Bales.

In their experiment, the scientists made male titi monkeys jealous by placing them in view of their female partner next to an unknown male. As a control, they also placed monkeys in view of unknown females next to unknown males. They filmed all of these interactions for 30 minutes, then conducted brain scans and hormone measurements.

They found that the male monkeys in the “jealous condition” showed heightened activity in the cingulate cortex – associated with social pain in humans – and the lateral septum – associated with pair bonding in humans. Combined, it looks like the feeling of jealousy is strongly connected to a stain on bonding and feelings of social rejection.

The jealous males also showed elevated levels of the hormones testosterone and cortisol. This latter chemical, an indicator of social stress, was greatest in those that spent the most time looking at their partner next to a stranger male.

Interestingly, this neurochemistry seems similar to that in jealous prairie voles, but the locations of these areas of the brain are in different places. “Monogamy probably evolved multiple times so it is not surprising that its neurobiology differs between different species,” says Bales. “However it seems as though there has been convergent evolution when it comes to the neurochemistry of pair bonding and jealousy.”

All of this reinforces the idea that jealousy plays an important role in bonding, urging monogamous minds to protect relationships by causing social pain. A big limitation of the study, however, is that the scientists only investigated brain activity in male monkeys. Further research would need to see whether the neurochemistry of female titi monkeys differs from their male partners.

Image: From the study in Frontiers in Ecology and Evolution