Two days ago it was S. Valentine’s day and as I promised in my previous post, this week I will talk about monogamy and falling in love in humans and their possible molecular correlates. However, if you also want to have a more comprehensive view about monogamy in animals and you missed my previous post about the hormone of monogamy, you can find it here. Then after this small premise, let’s start!
In the human brain, the oxytocin receptors are concentrated in areas that are rich in dopamine (have a look here if you want to know more about oxytocin and dopamine). Even if this distribution pattern is similar to that of monogamous species, the receptors of oxytocin and vasopressin are not present in areas that are full of these receptors in the praire voles and monkeys that show a monogamous behaviour (have a look below for a schematic of what happens in our brain when we fall in love).
An MRI study testing adult subjects that were looking at pictures of their partners or pictures of their friends showed an activation of areas that are different from the ones activated when we look at faces of strangers or areas related to visual attention, sexual arousement and other emotional states. However, this study showed that the areas that were firing up while looking at a picture of the beloved ones were showing analogies with the results of a preliminary MRI study of mothers that were listening to the cries of their babies. These studies on human affection show a strong overlap between the activation pattern that we have when we see or listen to our loved ones and the activation pattern of euphoric states induced by psychostimulants. Therefore, these data suggest how the circuits that regulate human attachment might have evolved from the circuits of gratification.
Moreover, it has been recently seen a positive and statistically significant correlation between the plasma levels of oxytocin and the anxiety related to the romantic attachment, that means the levels of oxytocin were increasing along with the scores on the anxiety levels, in accordance with the literature already present showing the anxiolytic properties of oxytocin in animals, thus leading to a role of the oxytocin in humans so that it might decrease the level of anxiety present during a loving relationship, contributing to the wellbeing that normally accompanies a romantic partnership.
Quite recently, few studies are showing the role of the peripheral levels of neurotrophins in people that are in love. Researchers analysed if the initial phase of a loving relationship was correlated to alterations in the levels of circulating neurotrophins. They studied 58 subjects that recently fell in love with a control group composed by single individuals or people that were already in a long-lasting relationship: surprisingly, the neurotrophin levels are significantly higher in the recently fell in love subjects compared to those of the control group. Even more interesting is the fact that there was a significant positive correlation between the levels of neurotrophin and the intensity of romantic love measured via the “Passionate love scale” by Hatfield and Sprecher (1986). 12/24 months after, 39 of these in love subjects that were still in the same romantic relationship claimed that they were not experiencing the same mental disposition as they had at the beginning of the study and their neurotrophins were analysed again: surprisingly, their plasma levels were decreased back to the ones of the control groups.
All these data point towards the relationship between the increase of circulating neurotrophine levels and falling in love behaviors and psychological manifestations. Indeed, neurotrophines could be a main character in the molecular mechanism of romantic love, acting as a fine modulator of different endocrine functions. Or more in general, it is possible to hypothesize that neurotrophines are involved in social relationships, directly or indirectly via the modulation of symptoms that regulate the stress response.
However, the more we investigate the science behind monogamy and falling in love, the more I realise we are nothing more than chemical reactions and electricity passing through our bodies. As detached as this can be, more and more signs are pointing towards the fact that we are regulated by neurotransmitters and neuromodulators that can bind to different receptors in different areas (as it is the case for oxytocin and vasopressin) and therefore generate an electric stimulus that makes us feel in love: making sense out of these signals and chemicals in our bodies, that we then translate into behaviours, as it is the case for falling in love, is what made me fall in love with neuroscience. I hope this post gave you a good hint of some of the cool studies out there correlating human behaviour and what is actually happening in our bodies. Stay tuned for more.