The Neurobiology of the “Green Monster”

The green monster. The terrible feeling of jealousy. It is the complex emotion that includes feelings of rage, fear of abandonment, and/or humiliation. The feeling is typically sparked when there is a perceived threat to the relationship from a third party. No one likes this feeling, but psychologists say that it’s not something that shouldn’t be repressed. It is said to preserve social bonds, and it motivates individuals to work at maintaining an important or valued relationship.

Humans are a mostly monogamous species. We form strong bonds and typically mate with one person, or at least that’s the goal. However, monogamy is only prevalent in a small number, 3-5%, of mammalian species, of which humans are included. Scientists have pondered this concept, and wonder how it has evolved and how is it maintained. Recently the concept of jealousy has been suggested as a “monogamy maintenance tool”, in that it motivates us to work on important relationships.

The construct of jealousy is obviously difficult to study in humans, and is rarely studied in other animals. Typically, monogamy and social bonds are studied in prairie voles, who are socially monogamous rodents, so it’s hard transfer conclusions made to more complex animals such as humans. However, on October 19th, a new study was published in the Journal, Frontiers in Ecology and Evolution, looking at the concept of jealousy in monogamous primates for the first time.

This team of researchers used the titi monkey. These monkey’s form strong attachment bonds, and after attached, they show mate-guarding behaviours and they become distressed when they are separated from their partner. This species provides an ideal model to examine a challenge to the pair bond that could elicit a jealous response.

In 1986, Ellis and Weinstein proposed that there are three conditions that are necessary for jealousy to be elicited.

  1. An attachment relationship between two individuals.
  2. Valued resources that are part of the attachment bond.
  3. Intrusion by a third individual that is perceived by one partner as wanting to become a receiver of resources.

In this study, they examined changes in neural and hormonal substrates in response to a challenge to the pair bond of male titi monkeys. They exposed the male monkeys to two conditions in which they viewed their female pair mate next to a stranger male, or they viewed a stranger female next to a stranger male. Using fMRI, they also examined areas of the brain that have been implicated in jealousy in rodents, rhesus monkeys, and humans.

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After completing the trials and performing the brain scans, the results showed that after seeing his female pair mate next to a stranger male, the male monkey showed increased activity in the cingulate cortex and the lateral septum. Interestingly, the cingulate cortex has been associated with social pain in humans.

The findings of this current study as well as previous studies suggest an important role for the lateral septum. It is known to play an important role in social memory, and in modulating stress in many species, and now there are now multiple lines of evidence suggesting that it plays a role in both pair bond formation and pair bond maintenance in titi monkeys.

There were some hormonal changes as well. There were elevated testosterone levels, probably because of its relation to mating-related aggression and competition. There were also elevated levels of cortisol, especially in those that spent more time looking at their pair mate next to a stranger male.

Taken together, the results suggest that pair bond formation involves areas that are involved in social memory and reward, and the maintenance of the bond is based on negative reinforcement; these male titi monkeys just want to avoid the pain of separation. The authors point out though, that they only studied responses in male monkeys. Therefore, to study sex differences, research on the neurobiology of jealousy needs to be conducted with female titi monkeys.

Although these discoveries are just some of the building blocks needed for understanding monogamy – how it evolved/how it is maintained – they open the doors for future research and give greater insight into our behaviours.  Humans are complex and there is so much to understand. Ultimately, research in this field of social behaviours can help us understand our own relationships, and potentially why males and females act differently. This publication gives us a better understanding of jealousy, and with further research, may shed light on how to live healthier lives and how to approach problems such as domestic violence.

Published Paper:

Nicole Maninger, Sally P. Mendoza, Donald R. Williams, William A. Mason, Simon R. Cherry, Douglas J. Rowland, Thomas Schaefer, Karen L. Bales. Imaging, Behavior and Endocrine Analysis of “Jealousy” in a Monogamous PrimateFrontiers in Ecology and Evolution, 2017; 5 DOI: 10.3389/fevo.2017.00119

Further Reading:


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