Love and biology are deeply entwined. Love can make a heart race and a lack of chemistry can turn romance into friendship. But just what is the nature of this link? Can biochemistry cause love?

Dr. Hagop Akiskal won the Ig-Nobel prize in Chemistry for trying to answer this very question. The Ig-Nobel prizes are organized by the Annals of Improbable Research and distributed by Nobel Prize winners. They are designed to celebrate research that “makes people laugh and then makes them think." Akiskal’s work on how love looks a lot like obsessive-compulsive disorder does just that.

Akiskal is the director of the International Mood Center at the University of California, San Diego. Much of his career has been devoted to understanding and redefining illnesses such as depression and bipolar disorder. These topics may seem a long way off from love, but after meeting Akiskal it is easy to imagine why he was drawn to researching romance. Part scientist, part poet, Akiskal has always been fascinated by love and determined to understand the things that fascinate him.

Born in Armenia just one generation after the Armenian Holocaust of the early 1900s, Akiskal’s natural curiosity and interests drove him toward literature and other intellectual fields that were considered controversial at the time. His family pushed for him to go into a career that would be less dangerous. “They were more for me to do something solid like become a doctor or an engineer, fields where there was no controversy. Intellectuals are dangerous, they go to dangerous places or say dangerous things and I was known for that,” says Akiskal.

Akiskal landed in medical school but this did nothing to deter him from saying controversial things. Disillusioned by the way psychiatry was approached in the 1960s and worried by the chasm that existed between biology and psychiatry, Akiskal developed a radical theory stating that behavior, emotion, neurochemistry and neurophysiology were all related. Akiskal submitted his “Integrative Theory” to Science. “I had the daring idea of sending it to Science. I thought it was important enough. Science, even in those days, was the standard. It was mainly astrophysics and biology. I think there had only been one psychiatrist published in Science before. They liked it and there it is; it’s history. At the age of 26, I became very famous.” This notoriety led to his appointment as Senior Science Advisor to the Director of the National Institute of Mental Health.

It was during this time that Akiskal met Dr. Donatella Marazziti, an Italian scientist who had become interested in obsession and how much it resembled another human condition: love. The similarities between the early stages of love and obsession are easy to see. People are often preoccupied with the object of their affection and unable to focus on daily activities. Marazziti’s group had recently implicated a particular seratonin transporter in obsessive-compulsive disorder. With Akiskal’s help they wanted to see if this transporter might also play a role in the preoccupation that can accompany love.

To do this they talked to participants who claimed to be in love. Importantly, these participants were preoccupied with their love object for four hours or more every day. People preoccupied by an object of obsession for four or more hours a day are considered to have moderately severe obsessive-compulsive disorder.

Levels of the 5-HT seratonin transporter were found to be significantly decreased in participants in love and participants suffering from obsessive-compulsive disorder when compared to a normal “control” group (Marazitti et al, 1999). This evidence supported the theory that obsessive-compulsive disorder and love have a lot in common biochemically. It also implicated serotonin as the chemical behind romantic love.

One of the hallmarks of romantic love is that it is fleeting. Even when couples stay together they generally settle into a more comfortable stage in which preoccupation decreases and they are able to function more normally outside of the relationship. “Romantic love is something that starts at one point and ends at one point. Mercifully it ends because it’s such an intense emotion that it must end at some point,” says Akiskal. What does this mean for the biology? In the follow up to this study Akiskal and Marazitti found that when these participants were re-tested 12-18 months later their 5-HT levels had returned to normal. The participants reported that they no longer felt distracted and preoccupied with the object of their affection. If serotonin is the biochemistry of love, and if it fades, how does anyone stay together?

Research from the prairie vole, a mammal that mates for life, suggests this may be the work of yet another chemical: vasopressin. After sex male prairie voles express high levels of vasopressin. They become devoted to their partner and protect her from the attention of other males, but if vasopressin expression is blocked the male prairie vole fails to become devoted after mating and leaves the female vulnerable to the attention of other males. Vasopressin isn’t just released after sex. It’s elevated in both the male and female during pregnancy and has been shown to increase in males just from holding a baby. Human males with a particular variant of the vasopressin receptor have been shown to be less likely to get married and more likely to have spouses who are unsatisfied with the marriage when they do. Vasopressin may have evolved as a way to bind couples together to care for young. Serotonin may be the chemical behind love, but vasopressin seems to be the chemical of monogamy (Young, 2009).

In the last decade a multitude of hormones have been implicated in regulating the type and intensity of love that a person experiences. Dopamine and endorphins play their own role in romantic love, and oxytocin and testosterone can affect long-term love. These biochemicals not only interact with the cells of the brain; they interact with one another. In addition to this complicated biochemistry there is another factor, which Akiskal is the first to point out: “Romantic love is much more than a serotonin receptor. It’s immensely more; it’s somewhere between the atoms of the cells, the subatomic particles, all the way beyond poetry and music and joy and intense happiness which is intangible.”

References:

Marazitti D, Akiskal HS, Rossi A, Cassano GB. Alteration of the platelet serotonin transporter in romantic love. Psychol. Med. 1999 May;29(3):741-5.

Young LJ. Being human: love: neuroscience reveals all. Nature. 2009 Jan 8, 457(7226):14

Author: Jennifer Rust for MySDscience

March 24, 2009