Jan/Feb 2007 Nonfiction

When Your Brain Falls In Love

by Anju Kanumalla

(Eclectica's Science Correspondent)

Artwork by Ira Joel Haber

Roses are red
Violets are blue
My neuropeptides
Are nuts about you

New Year's is over. It's time to gear up for that next holiday: Valentine's Day. To help get you in the mood for chocolate hearts, red roses, and bad greeting card poetry, this article deals with having love on the brain.

Poetically speaking, the seat of our emotions may be the heart, but biologically speaking, our emotions come from our brains. This article focuses on the brain in love. The human brain in love is too complex to explain in a short article, but I hope by the end of it, you have a sense of why love can make us feel nervous, happy, and maybe also a little crazy.

We use the word love to mean many different things, but perhaps the most common uses refer to how we feel about our romantic partners and our children. Biologically speaking, however, these two forms of love appear to be quite similar.

For one thing, both forms of love are involved in the same important biological goal: the continuation of the species. As such, it makes sense that the areas of the brain involved in love the same as those involved in reward and motivation. Perhaps less intuitive is how love also involves biological molecules and the areas of the brain that are involved in responding to stress.


Love and Stress

Love and stress have a complex relationship. Stress can either induce people to seek out others or to isolate themselves. When people are under moderate stress, they search for comforting, pleasurable experiences. Such experiences may include food, sex, touch, and bonding with other people. The levels of stress must be manageable, however, for people to seek out other people. Under extreme stress, social relationships are more likely to break down than to be built.

When we are under stress, our bodies release cortisol. In people who have just fallen in love, the levels of cortisol in their blood tend to be higher. Cortisol, in turn, triggers the release of oxytocin and vasopressin.

Oxytocin is a small protein that acts in the brain. Such proteins are called neuropeptides. Oxytocin tends to encourage the formation of social bonds. It's released during sex and childbirth—both of which can be stressful. Oxytocin is also released during breastfeeding in both the mother's bloodstream and in breast milk.

Vasopressin is a neuropeptide very similar to oxytocin. Both oxytocin and vasopressin are the same size and have similar structures. Like oxytocin, vasopressin encourages the formation of social bonds and is released during sex. However, while oxytocin primarily induces trust, vasopressin can induce territorial behavior and aggression in males.

Vasopressin and oxytocin are not the only molecules involved in love. However, they are two of the most important and best studied. Numerous other neuropeptides and hormones, such as the sex hormones progesterone, estrogen, and testosterone, affect and are affected by vasopressin, oxytocin and the other molecules involved in love.


Love and Motivation

The parts of the brain that are involved when we fall in love are also the parts involved in motivation. There are two general types of motivation: positive and negative. Positive motivations like hunger, thirst, and the drive for sex ensure that we meet our biological needs and engage in activities required for the survival of the species, while negative motivations that steer us away from unpleasant or stressful situations. Satisfying one of these motivations usually makes us feel good.

Motivation and the emotions are both regulated by parts of the brain called the limbic system. Some parts of the limbic system include the amygdala and the hippocampus. These areas help us learn what sorts of situations to seek out and which to avoid.

The amygdala receives stimuli from the body and helps assess whether an experience is pleasant or unpleasant. Located near the amygdala is the hippocampus. The hippocampus helps record memories of what we find pleasant or unpleasant. It records such details as where the experience occurred, when it occurred, and who else was present. Sometimes this can lead a person to seek out or avoid things they would not otherwise. For example, getting sick on an airplane after eating chicken might lead us to avoid air travel, chicken, or both. Once we realize an experience is pleasant or unpleasant, the brain assesses how pleasant or unpleasant it was, and we feel a corresponding degree of reward or aversion. The amygdala is involved in remembering whether we find these stimuli pleasant or unpleasant and causing us to seek out or avoid these stimuli.

Humans tend to remember love as a pleasant experience. Oxytocin and vasopressin play a role in why we find it pleasant, but other molecules are involved as well. Among these molecules is a group of neuropeptides called endogenous opioids. These molecules act on the body in a way that is similar to morphine and related compounds. However, they are called endogenous because the body itself makes them. These molecules are responsible for the placebo effect and for why some people feel less pain when treated with acupuncture. Endogenous peptides also affect the way we remember things. They tend to increase our recall of positive things and decrease our recall of negative things.

The effect endogenous opioids have on our memory is also one of the reasons it often seems love is blind. Love reduces stress, fear, and other negative emotions, all of which can adversely affect health. However, sometimes not feeling fear or other negative emotions can reduce our ability to critically evaluate others.


The Mystery Maintained

I've heard some people say that knowing the biologic basis of love removes its mystery and thus its magic. To them, I say, "Take heart." This article can only provide a small taste of what we know about the complexity of a brain in love. There is also still much about love and the human brain that we have yet to discover. Learning about the biology of love reminds me that there's still a whole lot more mystery, and much of it is encased in the few pounds of neurons I carry around each day.


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