Why we love

Love is a huge part of the human experience, but what can neuroscience reveal about the mechanisms which drive it?

Written by: Joe Reynolds

Art by: Winnie Lei

The study of love is not a recent undertaking; for centuries it has been the subject of great poets, novelists and philosophers. Stories of love from literature around the world all share a commonality; the unity to be found in love. This theme could be called an inherited neural concept, something we are simply born with. Some will view love as a Darwinian mechanism used to spread our genes: however, we must also reconcile an apparent paradox in love. Why do some dejected lovers take their own lives, or live in despair for years before thinking about finding another partner? Regardless of the philosophies applied to understanding love, modern medical imaging allows us to elucidate the neurobiological mechanisms that drive it.

Many of us will experience romantic love during our lives and the effects it brings about – for novelist Gabriel Garcia Marquez, falling in love was like contracting cholera, with physical manifestations like cold sweats and debilitating nausea. Marazziti’s 1999 study compared the binding of serotonin (a neurotransmitter involved with sexual desire and anxiety) to its transporter in a control group, a group of patients with OCD, and a group who were in the early phase of romantic love. In their results, the love group had significantly lower binding of serotonin than the control, and were similar to those with OCD. It could be said that this obsession with a partner evolved to help us concentrate our time and resources on one partner to maximise chance of reproductive success. Furthermore, an fMRI study by Fisher at the Albert Einstein College of Medicine found great increases of activity in the ventral tegmental area (associated with dopamine release and reward) of a group who were in ‘a passionate stage of romantic love’ compared to a control group. This was further confirmed in a study by Zeki et al in 2009, in which PET was used to measure dopamine levels in cortical areas. The study found an increase of dopamine release in the medial orbitofrontal cortex and the medial prefrontal cortex, areas associated with reward and encoding facial beauty. It is no wonder why those who claim to be passionately in love begin to obsess over their partner and crave their attention.

Like other addictions, when a lover is rejected feelings of despair, melancholy and rage are often found. In a study of 114 men and women rejected in the previous 8 weeks, 40% were found with clinically measurable depression. As the reward of the partner disappears, the dopamine circuits in the reward centres decrease in activity, producing this depressive effect. Several similar reward pathways activated by substances such as alcohol, opioids and amphetamines are also activated in people who are in love or have been rejected.

How else do we fall in love? Undoubtedly, one of the reasons is sexual attraction. In 2006 at the University of Zurich, Ishai used MRI to scan the orbitofrontal cortex of 40 hetero- and homosexual men and women while they were viewing 200 pictures of men and women, and asked to rate their facial attractiveness. In homosexual men and heterosexual women, attractive male faces elicited a stronger activation than attractive female faces; similarly, in homosexual women and heterosexual men, attractive women elicited a stronger activation. Combined with the increased dopamine response and connectivity with areas associated with reward, this suggests sexual attractiveness is crucial to romantic love.

Humans are not the only animals to have been found with this neurochemistry. Dopamine and other neurotransmitters such as vasopressin and oxytocin have been found to mediate pair bonding mechanisms in prairie voles. These voles are strongly monogamous and will not mate with another vole, and when a female prairie vole expresses attraction to a male, there is a 50% increase in activity associated with reward areas. In comparison, the montane vole is highly polygamous, and does not experience the same kind of dopamine increases as the prairie vole.

Love has defined our society for the entirety of recorded history. To many it is crucial to the concepts of marriage and family. It has influenced our culture through its expression in music, art and literature. It will shape each of our lives through the people we meet, spend time with, and cherish. Although science may not be able to explain Romeo and Juliet, we are able to study our brain chemistry and begin to piece together possible causes of the highs and lows experienced as we love.


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