Pair- bonding and the Brain

Pair – Bonding and the Brain

Medical Institute Science Department Staff

August 2018

In the book, Hooked, authored by Medical Institute’s (MI) founder, Joe S. McIlhaney, Jr., MD and our current President and CEO, Freda McKissic Bush, MD, the science of bonding with a sexual partner and the effects related to that bonding is discussed.  As the authors and the MI science staff have been reviewing the book for updates, it is encouraging to see that further studies on pair- bonding, including research on the neurochemicals oxytocin, vasopressin and dopamine, continue to support the precepts presented in Hooked. This article presents a review of some of the current literature specifically relating to the brain and bonding.

The term pair-bonding is a scientific term used to describe a mating pattern in which a male and female partner together in a relatively permanent manner.  The term is used for many species of animals, including humans. In monogamous systems, pair-bonding is associated not only with relatively permanent partnering, but also with an exclusive mating relationship.1

Many studies done on pair-bonding have used prairie voles as research animals. Critics of Hooked have argued that what happens in prairie voles has little to do with humans. They also argue that although prairie voles are considered monogamous, some individual voles are promiscuous. However, researchers continue to use prairie voles in search of answers to questions about bonding in humans. It is not simply that prairie voles are monogamous creatures, but rather that the neuroscience of bonding involves the same areas in the brain and the same neurochemicals that are found both in humans and prairie voles. 2

The neurophysiology of pair-bonding is very complex, which makes it difficult to explain in layman’s language. That is one reason that Hooked has been such a popular read. The authors were able to break down for parents and other concerned adults these difficult brain processes in an understandable, relatable way.  However, as the explanations get passed on by word of mouth, the pitfall of oversimplification can turn quickly to misunderstanding and inaccuracy. As people became familiar with Oxytocin, a neurochemical that is critically involved with bonding, a common erroneous theme emerged that Oxytocin production decreased with repeated sexual intercourse and thus people who had repeated sex or multiple sexual partners no longer had the ability to bond with partners due to a lack of Oxytocin. The truth is that people can damage their ability to bond, but it is not because of a decrease in Oxytocin production.  It is a much more complicated process involving brain molding, other neurochemicals and higher brain functions.

Our behavior actually changes our brain. The connections between neurons that are stimulated by our actions, increase with more use and decrease with less use.  When a couple engages in sexual behavior, neurotransmitters, such as oxytocin, vasopressin and dopamine stimulate formation of synaptic connections in the brain, associating the pleasure of sex with the partners involved, encouraging  them to bond and to have more sex together, leading to the beginning of a family unit.

In 2014 another prairie vole study dealt with broken pair-bonds. The loss of a partner resulted in anxiety-like and depression-like behaviors, disrupted bond-related behaviors and altered neuropeptide systems that regulate such behaviors.  The authors state that the prairie vole may well provide a model for us to better understand partner loss and grief.3 In 2016, a study on separation of pair-bonded titi monkeys also showed similar neural pathways and neurochemicals to be altered.4 So, again we see that newer research has continued to show that breaking partner bonds is not only a painful emotional experience, but that it also alters brain function and neurochemicals such as Oxytocin.

However, when an individual choses to engage in casual sex, breaking bond after bond with each new sexual partner, the brain forms a new synaptic map of one-night –stands. This pattern becomes the “new normal” for the individual. When and if the individual later desires to find a more permanent partner, the brain mapping will have to be overcome, making a permanent bond more difficult to achieve. Often the individual is not aware that the brain has adapted to the behavior pattern and he/she begins to think, “That’s just the way I am”, further reinforcing the pattern. In conclusion, research on bonding continues to support previous research showing that the brain is strongly influenced by sexual behaviors.  Dopamine pathways as well as oxytocin and vasopressin and other neural systems are important factors in the formation of pair-bonds. When a person engages in sexual behavior there are consequences above and beyond the possibility of unwanted pregnancy and sexually transmitted infections. Bonding with a sexual partner is one of those results.



  1. Fletcher GJO, Simpson JA, Campbell L and Overall NC, “Pair-Bonding, Romantic Love, and Evolution: The Curious Case of Homo sapiens, “ Perspectives on Psychological Science 2015, Vol. 10(1) 20-36.
  2. Johnson ZV and Young LJ, “Neurobiological mechanisms of social attachment and pair-bonding,” Curr Opin Behav Sci. 2015 Jun; 3: 38-44
  3. Sun P, Smith AS, Lei K, et al, “Breaking bonds in male prairie vole: Long-term effects on emotional and social behavior, physiology, and neurochemistry,” Behav Brain Res. 2014 May 15; 265: 22-31
  4. Hinde K, Muth C, Maninger N, et al, “Challenges to the Pair Bond: Neural and Hormonal Effects of Separation and Reunion in a Monogamous Primate,” Frontiers in Behavioral Neuroscience, Nov 2016, Volume 10, Article 221.