Title: The Neuroscience of Love: What’s Going on in the Lovestruck Brain?

Love may not be a choice. It may just be your brain on autopilot intoxicated by the love potion.

That’s according to Tom Sherman, a neuroendocrinologist and professor in Georgetown’s School of Medicine who studies the endocrine system and how hormones shape human physiology and behavior.

“Falling in love is a fascinating phenomenon,” Sherman said. “It’s wonderful if you’ve experienced it and can remember it.”

When a person falls in love, the brain triggers a series of complex mechanisms involving multiple chemicals and hormones that heavily influence a person’s behavior. So is love real or is it an uncontrollable brain reaction?

This Valentine’s Day, Sherman answers this question and breaks down what’s happening to the human brain in love as well as how the brain responds to short-term flings and lifelong loves.

Ask a Professor: Thomas Sherman on Your Brain in Love

How does love activate the brain’s reward circuit?

There are areas of the brain that together comprise the mesolimbic system, that make up the reward circuit. Love can be accurately described as a reinforcing — not quite an addiction, yet — but a reinforcing action in which you are activating your reward circuit to enact an extremely pleasurable experience.

How do cortisol and dopamine affect the human brain in love?

There are multiple components to a reward circuit, but two main ones are an increase in cortisol and an increase in dopamine. These are seen as reinforcing. And because falling in love often has an uncertainty to it that can be perceived as stressful, this is where the rise in cortisol as part of the stress response is going to impact your physiology to heighten your sense of awareness. Meanwhile, when your mesolimbic system associates certain sensations with something pleasurable, such as meeting a promising prospective mate, it stimulates the release of dopamine in order to reinforce that feeling and stimulate behaviors to seek more contact.

There are also areas of your brain that would ordinarily be saying, “Be careful, you don’t know much about this man or woman.” But those areas are being turned down, whereas other areas that are saying, “I can only think about this person,” are being turned on.

How is love different from other pleasurable activities? Is more dopamine released?

I don’t know that I would say more dopamine is released. I think perhaps the contributions of hormones such as norepinephrine that cause the racing heart and sweaty palms or because of the combination of testosterone and estrogen or the influence of oxytocin and vasopressin, it’s a different kind of reinforcing reward that you experience more strongly than by simply eating a bar of chocolate or something like that.

How do oxytocin and vasopressin work together in the human brain when it comes to love?

Oxytocin and vasopressin are peptide hormones secreted from the pituitary into the blood to regulate endocrine functions: oxytocin regulates milk ejection during breastfeeding and uterine contractions during childbirth, and vasopressin stimulates water retention and urine concentration during dehydration. But both of these hormones are also secreted from hypothalamic neurons projecting throughout the brain to regulate maternal and paternal behaviors. Oxytocin acting within the brain is essential for mother-infant bonding, pair bonding, empathy and sexual behavior in females; whereas vasopressin acting centrally reinforces territorial aggression, mate guarding and pair bonding in males. Not surprisingly, the secretion of both of these hormones in the brain and blood is stimulated during sexual activity, thus reinforcing pair bonding, monogamy and social cognition.

I have to carefully monitor my emotions when I lecture on the role of oxytocin during pregnancy because I retain these lovely images of my wife, before the birth of our daughters, standing in the child’s room repeatedly folding and unfolding baby clothes. This is a great example of oxytocin-induced nest-building behavior and these memories can easily make me cry!

How does someone’s brain chemistry change as a new romantic relationship evolves into a long-term partnership?

I think the stress component of early love goes away. The apprehension goes away, so it may no longer feel euphoric. You could say that love begins as a stressor, but then love becomes a buffer against stress. This is actually part of why a stable relationship is evolutionarily conserved because people in a stable relationship are healthier and live longer.

How does evolution factor into the role of human love?

Long-term relationships are better for us. An enduring preferential association formed between two sexually mature adults is evolutionarily adaptive. Couples live longer than their unpaired counterparts. Intimacy between pairs is inversely correlated with negative psychological states, such as depressed mood, and positively correlated with a stronger immune function and cardiovascular health. We’re going to be happier, we’re going to be more reproductively active, and therefore we’re going to pass our genes on more successfully. It’s always hard to know how our actions are influenced by evolution, but they undoubtedly still are.

There is evidence for genes in male animals who are not capable of forming a stable pair bond and have a mutation in the vasopressin receptor in that part of the brain, and it is reasonable to suspect that something like this is true in human males as well. Unable to form a stable pair bond, these men are in unhappy relationships, are typically unmarried or partnered with somebody equally unhappy. You would think with time that these mutations are going to be excluded or minimized from future generations.

Is love really a choice, or is it just a product of uncontrollable brain chemistry?

I tend to lean toward the latter. ln one of my neuroscience classes, we talked about circadian rhythms and the concept of long night breeders versus short night breeders. A long night breeder is an animal that breeds in the late fall or early winter because it’s advantageous to have their young in the spring. If you are a short night breeder, like a hamster or a mouse, your gestation time is so short that you can breed in the spring and still give birth in the spring. These behaviors are all governed by circadian rhythms and how animals attune themselves to the diurnal cycle on earth.

We like to think that we are independent of that. We will acknowledge we’re animals, but we believe we’re much more independent than that. And yet humans more often than not give birth in the summer. And so chances are with a nine-month gestation time, we are more frequently breeding in the late fall and winter and giving birth in the spring and summer. So whether that’s because it’s cold out and we’re going to bed more or because it’s part of our circadian rhythms is not clear. But I think for some behaviors like falling in love, we have no real control over it. I think that when somebody says, “You are the one,” it’s not because you decided you’re going to fall in love with that person, but that there was an attraction that you acted upon, and it’s that attraction that is somewhat outside of our control.