What drives people to do the strangest things?

The Science of Love…

Like with many universities across the UK, the study of psychology and neuroscience is very popular at Oxbridge. These topics are attractive and difficult to master, a result of their breadth of scope that spreads itself over the spectrum of human sociology, cell biology and biochemistry. As ever, when preparing for any subject interview at Oxbridge, it pays to spend time learning about and preparing answers for particular hot topics. One such example for these topics would be emotions and how and why we have them. Of course, of all emotions, one of the most discussed and treasured and debated is that of love. What is love? Can it be quantified and can science explain an emotion which can drive people to do the strangest things?

Of course scientists love a challenge and some interesting research has happened over the years looking into love. Before any experiments could happen, scientists required a model organism to work on and the usual suspects of fruit flies, mice and zebra fish (with their promiscuous mating behaviours) do not meet the standard of animals in “love”. However, of all the animals in the mammal class, very, very few (just three percent, according to one survey) display the romantic behaviour known as “lifelong pair bonding” — or, as it is more commonly known, monogamy. To better understand this phenomenon as it manifests in humans, scientists have taken to studying our brethren in this till-death-do-them-part project, and one of the best model animals is a tiny rodent that lives throughout the American plains known as the prairie vole.

Like many human relationships, prairie voles form monogamous commitments, called pair-bonds. Prairie vole couples mate and affiliate exclusively with each other, share nests, and even raise their offspring together! Male prairie voles often display intense aggression toward strangers for defence of territory, nest, and mate. All in, prairie voles make for valuable models for investigating the neurobiological mechanisms for pair-bonding – the ability to form intense, exclusive social attachments with a mate.

Molecules in Love

But not all voles exhibit pair-bonding. The close relatives of prairie voles, montane voles, prefer a rather free approach to relationships. They are more promiscuous, do not pair-bond, and do not exhibit aggressive behaviors to defend a mate or their offspring. Intrigued by this difference, neuroscientists compared neuropeptide expression, receptor distribution, and nerve pathways between prairie voles and montane voles. Two molecules were hypothesised to be implicated in pair-bonding behaviour: oxytocin and vasopressin.
In a now classic experiment by researchers from the National Institute of Mental Health, the mechanism underlying their pair bonding was identified. (For an excellent and humorous synopsis of this experiment, watch this short video by Oxford grad and occasional Oxbridge Applications tutor, Ali Jennings:

Male prairie voles were injected with an antagonist (a chemical that binds to the receptor but does not activate it) of either the oxytocin or vasopressin receptor. They found that blocking the prairie voles’ oxytocin receptors with the antagonist had no effect in mating-induced aggression and partner preference over other new potential mates (they still exhibited pair-bonding). However, male prairie voles injected with the vasopressin antagonist failed to exhibit aggression to defend the female partner, and did not spend as much time with the original mate as with new potential mates (they no longer pair-bonded). When researchers administered vasopressin to these male prairie voles, the effects were reversed; they became aggressive toward other males and preferred to spend time with their partner than with strangers. It was almost as if he fell in love with her all over again!

And your interview question…

This study implicated vasopressin as the neuropeptide that facilitates the social cues necessary for protective aggression and pair-bonding in males. In other studies, it has also been found that oxytocin promotes bonds and trust between parents and children and between couples in committed, monogamous relationships. Together, oxytocin and vasopressin form part of the molecular and neural mechanisms that allow for the social cues necessary for individual recognition and behaviour that we describe as loving. In the larger neural architecture of pair-bonding and attachment, vasopressin and oxytocin act in the reward centres of the brain, similar to dopamine. However, as we begin to unravel the science underlying emotions like love, we are of course forced to ask, is love just some biochemical interaction, or is there more to it than that?