The Science Of Love: How Romance Changes Our Brain And Body

-Analysis-

PARIS — “To love is a bad fate like that in fairy stories, against which nothing avails until the enchantment has ceased,” Marcel Proust wrote in Time Regained. Good or bad — black or white — the “magic” of love no longer escapes the libido sciendi of scientists. The “intermittences of the heart” and the convulsions of the body are no longer left — with a touch of disdain — to writers and poets.

Since the early 2000s, and thanks to advances in brain imaging, people in lab coats become metaphorical flies on the wall with their experimental protocols and MRI machines. This is the first observation made by Aurore Malet-Karas, a sexologist and doctor in cognitive neuroscience, in her fascinating 2024 essay on the subject “Cerveau, sexe et amour” (Brain, Sex and Love): “111 scientific publications bearing the term “love” are listed in Pubmed between 1980 and 2000, compared to over 900 between the year 2000 and now,” she writes in the introduction.

Nearly 1,000 publications in just a quarter of a century is not insignificant. So what have we learned from this avalanche of recent studies about what happens in our bodies, and particularly in our brains, when we fall in love?

Love lasts three years 

One of the most striking of these studies was carried out by the recently deceased American anthropologist Helen Fischer. In 2005, she came up with the idea of putting different photos, including one of a loved one, in front of people undergoing MRI scans. She was able to show that two brain regions were activated only when the photo visualized was that of the partner and not, for example, of a mere friendly acquaintance.

This is especially true in the early stages of a new relationship, when both members of the couple are still in, what Anglo-Saxon specialists rather prosaically call, the lust phase (which, according to Fischer, lasts an average of three years).

This result becomes even more interesting when we consider that the two regions in question, the ventral tegmental area and the nucleus accumbens, are at the heart (so to speak) of our reward and motivation circuit, whose fuel is a neuromodulator well known for its involvement in the addiction phenomenon: dopamine.

The same low serotonin levels are observed in new lovers as in those suffering from OCD.

So when someone tells you they’re “hooked” on a recent acquaintance, you can take their word for it. The euphoria provoked by their company or the mere sight of them, as well as the obsessive, intrusive thoughts of which this person becomes the object, all stem from the dopamine discharges circulating in our reward circuit.

Surprisingly, it has since been shown that another key neuromodulator, the famous serotonin, sees its levels drop in the lover’s brain at these first signs of new love. The same low serotonin levels are observed in new lovers as in those suffering from obsessive-compulsive disorder, which is no doubt linked to the obsessive nature of the lust phase.

Why the drop in serotonin? The answer is still a matter of debate, Malet-Karas explains. “Some people have suggested that it might enable us to be more alert, better able to encode information during this critical period, but we don’t know for sure. We’re still in the early days of love research.”

Having a crush

Let’s go back to dopamine, whose role is just as complex as that of serotonin. Researchers have shown that an orgasm is accompanied, among many other biochemical phenomena, by a large burst of dopamine. But this neuromodulator is not confined to pleasure and excitement. Produced by just 0.0005% of neurons (one in 2 million), it nevertheless has a disproportionate influence on our biology and behavior.

In the late 1990s, neuroscientist Wolfram Schultz revealed an astonishing phenomenon in monkeys. After a certain number of iterations of the same expected event (for example, finding your new crush in the university cafeteria after a boring Friday afternoon economics class), the dopaminergic discharge subsides: the crush is there, smiling, as expected, the heart racing slows down compared to the early days.

This is the phenomenon of habituation, well known in neuroscience. But if the chosen one misses the appointment, the worry and unease arise, “what if he/she doesn’t love me anymore?” Economics class had finally finished, signaling the coming reward but the reward didn’t come.

They are the biochemical basis of the attachment we feel for our long-term partner.

In this case, the dopaminergic neurons react, “marking” this disappointment by reducing their activity. More generally, dopamine not only encodes the pleasure born of presence: it also encodes, via its depletion, absence along with its afflictions.

Let’s pretend to be in a fairytale and be optimistic, assuming that our two Friday-night sweethearts have finally moved in together, becoming a stable, solid couple. The reward circuit and the dopaminergic system continue to act, albeit in a less uneven way than before (habituation).

But two other substances are increasingly taking over: two hormones. One, oxytocin, has the function of relaxing the smooth muscles surrounding the organs and the other, vasopressin, is an antidiuretic, instructing the body to slow down the rate of filtration so as not to eliminate too much water.

After some time

But together, they are the biochemical basis of the attachment (no longer passionate, but calm and serene) we feel for our long-term partner and even of our tendency toward monogamy, as shown by an amusing and instructive experiment on rodents by neurobiologist Larry Young.

“The role of the oxytocin-vasopressin couple is a perfect illustration of the central notion in biology of ‘evolutionary tinkering,’ which means that we have understood nothing about living things if we talk about a molecule in overly simplistic and reductive terms,” Malet-Karas writes.

To complete the picture, let’s add that the oxytocin-vasopressin couple is already involved in the early stages of romance, during the passionate lust phase. We secrete it just after the massive discharge of dopamine that occurs at the height of sexual pleasure, during the “resolution” (the technical term) of the orgasm.

Lower heart rate, muscle relaxation, reduced stress and anxiety all combine to create the feeling of well-being and security we experience fleetingly in our partner’s arms.