Falling in love is a truly strange experience.
You become utterly, inexplicably obsessed with one person. You feel a spike of pleasure whenever you get a text or email from them, and spend as much time with them as humanly possible. You see the good in them, but not the bad. When you're with them, the world shrinks, telescoping down to a bubble the size of two people.
Not everyone goes through the experience of being in love, but many do, and it's one of the most distinctive parts of being a human. Until recently, though, neuroscience largely ignored love as a topic of research.
"Most neuroscientific research has been devoted to negative symptoms — depression and addiction, instead of joy," says Donatella Marazziti, an Italian psychiatrist who has studied neurotransmitter levels in the brains of people who've recently fallen in love.
Helen Fisher, a Rutgers University researcher who's used MRI and other brain imaging techniques to examine both romantic love and long-term attachment, says that "it's a new idea to accept that there are even brain systems associated with love in the first place."
As a result, the study of love is pretty new, and the phenomenon is still largely a mystery. The studies that have been conducted are relatively small, and they only hint at the neurological basis of love — they don't fully define it.
Still, here are a few interesting things that scientists have learned so far.
1) The first stage of romantic love is a bit like a drug addiction
Fisher distinguishes the early torrent of romantic love and the longer-term, calmer attachment phase that follows. And she's found that a brain in the initial stage of love looks surprisingly like a brain experiencing a drug addiction.
"When we put people who've just fallen happily in love into a brain scanner, we find heightened activity in a few different brain regions," she says. "The big ones are the ventral tegmental area — the VTA — and the caudate nucleus." The scans compared participants' brains when looking at photos of their lovers, versus photos of random acquaintances. And participants who'd scored higher on a survey that measured feelings of love, moreover, had proportionately more activity in the VTA and caudate nucleus.
These are both core parts of the brain's reward system: areas that release the neurotransmitter dopamine to other parts of the brain, triggering feelings of pleasure. Heightened activity in the VTA in particular has been associated with all sorts of addictions — whether nicotine, alcohol, heroin, or gambling — with each dose causing a fresh spike of dopamine.
This, Fisher says, explains the feeling of obsession many people experience when falling in love. "It's what gives you the elation and the craving that is basic to romantic love." She sees the early stages of love as more of a drive to be fulfilled — like hunger and thirst — than a stable, permanent emotion.
2) Falling in love seems to reduce your ability to be judgmental
Other brain-imaging work by Samir Zeki, a neurobiologist at University College London, might explain a related aspect of falling in love: the way new lovers only see the positives in each other.
When Zeki has put people who have fallen in love inside of fMRI machines and shown them photos of their lovers, he's detected reduced activity in the amygdala — a pair of brain regions that are involved in decision-making. Amygdala activity is typically heightened during fearful or stressful situations, and research suggests that we use it when making social judgements and trying to determine if other people are lying.
Reduced amygdala activity in lovers, Zeki believes, may make them less prone to making negative judgements and distrusting each other, facilitating a sense of intimacy.
3) There are some similarities between falling in love and OCD
In experiments at the University of Pisa, Marazziti and colleagues have studied levels of serotonin — a neurotransmitter associated with feelings of contentment — in the brains of people who said they fell in love in the previous six months.
Given that we think of love as a positive emotion, it's a bit surprising that she found reduced levels of serotonin in these people, compared to controls. Even more surprising, though, is that they were as low as other study participants who had obsessive compulsive order — so low, she says, that "my biologists came back to me and assumed that the readings were from people who suffered from OCD."
It's well-established that people who suffer from obsessive compulsive order have reduced serotonin levels, likely contributing to extreme feelings of anxiety. When it comes to love, Marazziti writes, a lack of serotonin may lead to the obsessive, irrationally jealous behavior we see in some people.
4) Getting rejected is a bit like going through withdrawal
Fisher has also scanned the brains of people who said they were in love with people who'd rejected them. Given that love shares some characteristics with addiction, it might not be a surprise that when they looked at photos of their beloveds, their brains looked like addicts going through withdrawal.
"When you're rejected in love, we still find activity in the VTA — you're still madly in love with that person, after all," she says. "But we also find elevated activity in other brain regions linked with craving, and in a part of the brain associated with the distress that goes along with physical pain."
Rejected lovers, in other words, appear to retain the same obsessive focus on their object of desire, but are unable to have it fulfilled. One positive aspect of the study, though, was that the more time that had passed since the participants' rejection, the lower activity was in another brain region associated with attachment.
5) Long-term attachment is neurologically different from early-stage love
Fisher and other researchers distinguish between these successive phases of love for a good reason — in terms of both behavior and brain activity, they look somewhat different.
Her fMRI studies of couples who'd been happily married for decades found that, when they looked at photos each other, activity increased in brain areas distinct from those identified in the study of new lovers. Activity was elevated in the VTA — just like in new lovers — but also the ventral pallidum, an area associated with maternal attachment in animal studies.
This, Fisher says, may be what's responsible for the long-term, persistent feeling of attachment between people in a committed relationship. "The feeling of attachment is really very different from the feeling of romantic love," she says. "Romantic love is giddiness, elation, euphoria, energy. When you're feeling a deep sense of attachment, you're much more calm, and contented."
It's still uncertain why people transition from the first phase of love to the second phase of attachment, but Fisher hypothesizes that they're driven by separate evolutionary mechanisms. The initial flood of obsessive love evolved, she thinks, in order to get you to focus on a single person in order to reproduce. The second phase of attachment, by contrast, evolved to link you to another person for an extended period of time, in order to raise a child.