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Love and behaviour: a party of hormones


Love is perhaps one, if not the best feeling we are able to experience. It is a feeling so powerful and so universal, that humans have invested thousands of hours writing, painting, singing, sculpting, and even creating gods around the feeling, or representing love. It is in our blood, therefore, to feel love, and to desire the feeling of being loved. And as the associate professor of psychiatry at McLean Hospital - Richard Schwartz put it: “there's good reason to suspect that romantic love is kept alive [in societies and through human history] by something basic to our biological nature”. However, some questions remain: What is the precise definition of love? And even more important, can we study it in a scientific way?

Love and the reward system

The answer to the first question is a matter of much debate in the philosophical community, but by escaping from the grandiose philosophical question, and taking a more naturalistic and simplistic way of looking at love, this feeling we all seem to understand and enjoy can be summarised in a few words – molecules in our brain and the way we, as sentient beings, interpret them. In 2005, Helen Fisher published a study that compared the brains of people in different situations – using functional MRI (fMRI images). In the first situation, people described as in the throes of romantic love were shown images of their loved ones. Almost immediately the scientists could see activity in parts of the brain rich in dopamine, the so called “feel good neurotransmitter”. Pictures of other people didn't spark the same areas of the brain. Moreover, two other brain regions that also saw increased activity were the caudate nucleus, and ventral tegmental area. The latter is part of the brains´ reward circuit which is considered a primitive neural network. “We know” – said Jacqueline Olds, HMS associate professor of psychiatry at Boston’s Massachusetts General Hospital – “that primitive areas of the brain are involved in romantic love”. Love is, therefore, something more ancient that we could have thought.

Love’s effect on behaviour

In terms of behaviour, there are many changes because of the hormones released when we are in love. The molecule mentioned before, Dopamine, is responsible for the feeling of addiction and is released in situations related to drug and alcohol use. Love can therefore create a pleasant experience compared with those of these substances and can be highly addictive. Dopamine is also responsible for an accelerated heart rate, flushed cheeks, sweaty palms, and the feeling of compassion and anxiety. And other hormones which are also prevalent when we are in love, like cortisol – the stress hormone -, might explain why in the initial parts of romantic interaction feel like a test- our brain is merely "marshaling"our bodies to cope with the crisis at hand”. If everything mentioned above wasn't enough, the same study concluded that parts of the brain responsible for negative emotion were shut off when people were in love. When we are in love, the romantic machinery responsible for making critical assessment of those around us literally turns off - finally giving sense to the old and prevailing proverb: “Love is blind”

Lasting love

As a passionate relationship evolves, after 1 or 2 years, the stress levels are reduced whereas the areas associated with reward are still active. Romantic love is evolving towards a love that is also compassionate, so the craving for love is less intense and the caring for the partner becomes more important. This could be explained by a decrease in the levels of cortisol and serotonin (stress inducing hormones) to attain the usual levels in the body, whereas the levels of dopamine remain high. The decrease in cortisol allows for the couple to be more comfortable and less stressed when they are together. The serotonin hormone is a contributing factor to the concentration and obsession with a partner. As serotonin levels go back to normal, obsession over the relationship progress will decrease and therefore love has no longer a stressful impact but is perceived as a support for the couple.

Some studies (2011 study conducted at Stony Brook University in New York, by Bianca P. Acevedo, 1 Arthur Aron, Helen E. Fisher and Lucy L. Brown) compared the levels of dopamine emitted by newlywed couple and couples that had been married for around 21 years and found that the couples had the same intensity levels of dopamine activating the areas of the brain. Hence, this evolution towards a more compassionate love allows the couple to feel less nervous and more trusting with each other. This change from romantic to compassionate love can make some long-term couples fall into a routine type of love. This phenomenon is called the “rustiness phenomenon”, when couples no longer are intimate and forget what they felt like when they first met each other, which may be due to valid external motives such as raising children, work, etc. However, the passionate love felt in the beginning of the relationship could be reignited by an increase of oxytocin levels. The increase of production of this happy hormone has positive impacts in the behaviour such as relaxation, decrease of stress and increase of trust in the partner. Sexual activity, for example, can increase oxytocin levels and activate the brain’s reward circuit, making couples desire as they did in the beginning of the relationship.


All in all, love is a strange feeling. A very complex mess of molecules can create a wide range of emotions and can change the way we interact with other people. It can be the root for addictive behaviour, while at the same time making us feel anxious and nervous. Love has a positive impact in our lives and lets us have a support system allowing us to feel safe, if with the right partner. It apparently moves with ancient and well-studied parts of our brains, yet it feels incomprehensible. Love is truly one of the great mysteries of humanity and the human experience, and it should certainly continue to serve as inspiration for a lot of our artistic endeavour, perhaps a simpler way of understanding ourselves.


Rita Cordovil & João Castanheira


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