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Biology 202
2002 Second Paper
On Serendip

I Love You From the Bottom of My Brain: The Neurobiology Behind Love

Miranda White

You're at a typical weekend party. You spot someone across the room. They look over in your direction. "Wow, they're so beautiful," you think. You want desperately to go over and talk to them, but at the very thought of it, your heart starts racing and your palms begin to sweat. Looking over at them again, you see that amazingly enough they are coming over to you. Even before speaking to them, you feel like you have just fallen in love. Is this feeling really love at first sight? Or is it merely the release of hormones in the brain? What causes the feeling of being in love? How can we know for sure if we really are in love?

Love is one of the strongest and most elusive emotions. Nearly every person seeks to experience the feeling of being in love. And once it is achieved, one's life is forever changed. Yet, most people would have extreme difficulty describing what exactly love is, how they know for sure that they are in love, or why love is so universally important. Understanding the neurobiology behind love might help to give us a more clear perspective on social bonding and raises the question of whether love is nothing more than the release of certain chemicals.

The hormone oxytocin plays a significant role in many animals' instinct to love and form social bonds. In fact, it has been called jokingly, "the cuddle hormone." (1) Oxytocin is a small protein composed of nine amino acids. It is produced in the hypothalamus and is released by the pituitary gland. (2) Oxytocin is also produced in the ovaries of women and the testes of men. However, the hormone's most well known function is specific to females. (3) First, it plays an integral role in the delivery of a baby. When a woman goes into labor, oxytocin levels increase. This stimulates contraction in the smooth muscle of the uterine walls, thereby facilitating delivery. Secondly, oxytocin plays a role in milk letdown in nursing mothers. Milk is initially released into small sacs, called alveoli, which are surrounded by smooth muscle cells. Oxytocin stimulates contractions of this smooth muscle, causing the milk to be released to the mouth of a nursing baby. (3) Lastly, and most importantly, oxytocin causes the formation of maternal behavior. Successful reproduction and survival for many species relies upon a mother's attachment to and caring for her offspring. There is a drastic increase in the levels of oxytocin in the body and brain of a woman who is in labor. This upsurge is the main cause of the establishment of the strong bond of love a mother initially feels for her child. (4)

It is very strange to think that mothers nurture and care for their children mainly due to the release of a hormone at the moment of birth. We tend to believe that the relationship between a mother and a child goes beyond biology - that there is something much deeper than merely instinct or the release of chemicals that causes a mother to love. However, there is very convincing evidence that proves that hormones like oxytocin are largely the cause of maternal behavior. A number of experiments have been done, showing the importance of oxytocin in the formation of the mother-child relationship. In many species (for example sheep and rats), blocking the release of oxytocin caused mothers to abandon their young. Similarly, when virgin female rats were injected with oxytocin, they exhibited mother-like behavior. They cared for and cuddled with the offspring of other females as if they were their own. (1)

Oxytocin does not only play a role in the bond between mother and child but also between two mates. The attachment formed between sexual partners is predominantly caused by the release of oxytocin during sexual intercourse. Oxytocin is intricately tied with the biology of sex - it causes penile erections and shortens both the time for ejaculation and the refractory period after ejaculation. (4) The release of oxytocin can be learned. In other words, after repeatedly having sex with the same partner, simply seeing him or her could set off the release of oxytocin. As a result, one becomes attached to that particular partner and learns to prefer them to other possible mates. Thus the monogamy practiced by humans and other species is also the result of the release of oxytocin.

To prove that oxytocin creates monogamy and social bonding, an experiment was conducted using a mouse-like rodent called a prairie vole. Prairie voles, much like humans, form life-long monogamous relationships. Both parents live together and meticulously care for their offspring. Both males and females show a strong preference to their mate over other voles, and the male aggressively guards the female from possible harm. On the other hand, montane voles do not form lasting bonds nor do they protect and care for their young. They are promiscuous maters, showing no loyalty to one partner over another. Researchers blocked the release of oxytocin in prairie voles to test if it was the key ingredient in their monogamous preferences. Not so surprisingly, mating pairs formed no lasting bonds. In a similar experiment, scientists did not allow the prairie voles to mate, but they administered oxytocin to the females and vasopressin (a hormone much like oxytocin found mainly in males) to the males. Even without sex, the voles still created monogamous social bonds and strong preference to their mate over other voles. (5)

Unfortunately, there has been no real data regarding oxytocin levels in humans in relation to the formation of relationships. And there are, of course, some very significant differences between voles and humans. Obviously the vole brain and the human brain are not identical, nor are their mating habits or reasons for forming social attachments. (5) However, studying the biology behind love and social bonding in other animals could help us in understanding our own species. The vole experiments show how extraordinarily important oxytocin is in the formation of social relationships. (6)

Knowing that love is so chemically influenced and based brings up many interesting issues. It is strange to think that motherly love and romantic or sexual love are so intricately related, both caused by the release of the same hormone. We tend to see our mother's love for us as completely different from her love for her husband. In much the same way, there is something uneasy about that thought that merely one hormone could be the reason behind our most intimate social relationships and one of our most intense emotions. Is love nothing more than instinct? Does the way we feel about the people we love really have anything to do with that person or is it simply connected to hormones? Are there really no emotions that are beyond the brain? Understanding the role that hormones like oxytocin play will be very instrumental in our figuring out just how much neurobiology dictates the perception of our emotions.


1)Oxytocin Web Site, a rich resource with a lot of information about oxytocin

2)Oxytocin Web Site, the structure of oxytocin

3)Oxytocin, The Hormone of Love, an in depth look at oxytocin

4)The Chemistry of Love, a look at the chemicals that cause all the manifestations of being in love

5)Why do Voles Fall in Love

6)Love and Sex: The Vole Story

6)What is Love, Medically Speaking?

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