I and my colleagues Art Aron and Lucy Brown and others, have put 37 people who are madly in love into a functional MRI brain scanner. 17 who were happily in love, 15 who had just been dumped, and we're just starting our third experiment: studying people who report that they're still in love after 10 to 25 years of marriage. So, this is the short story of that research.

In the jungles of Guatemala, in Tikal, stands a temple. It was built by the grandest Sun King, of the grandest city-state, of the grandest civilization of the Americas, the Mayas. His name was Jasaw Chan K'awiil. He stood over six feet tall. He lived into his 80s, and he was buried beneath this monument in 720 AD. And Mayan inscriptions proclaim that he was deeply in love with his wife. So, he built a temple in her honor, facing his. And every spring and autumn, exactly at the equinox, the sun rises behind his temple, and perfectly bathes her temple with his shadow. And as the sun sets behind her temple in the afternoon, it perfectly bathes his temple with her shadow. After 1,300 years, these two lovers still touch and kiss from their tomb.

Around the world, people love. They sing for love, they dance for love, they compose poems and stories about love. They tell myths and legends about love. They pine for love, they live for love, they kill for love, and they die for love. As Walt Whitman once said, he said, "Oh, I would stake all for you." Anthropologists have found evidence of romantic love in 170 societies. They've never found a society that did not have it.

But love isn't always a happy experience. In one study of college students, they asked a lot of questions about love, but the two that stood out to me the most were, "Have you ever been rejected by somebody who you really loved?" And the second question was, "Have you ever dumped somebody who really loved you?" And almost 95 percent of both men and women said yes to both. Almost nobody gets out of love alive.

So, before I start telling you about the brain, I want to read for you what I think is the most powerful love poem on Earth. There's other love poems that are, of course, just as good, but I don't think this one can be surpassed. It was told by an anonymous Kwakiutl Indian of southern Alaska to a missionary in 1896, and here it is. I've never had the opportunity to say it before. "Fire runs through my body with the pain of loving you. Pain runs through my body with the fires of my love for you. Pain like a boil about to burst with my love for you, consumed by fire with my love for you. I remember what you said to me. I am thinking of your love for me. I am torn by your love for me. Pain and more pain -- where are you going with my love? I am told you will go from here. I am told you will leave me here. My body is numb with grief. Remember what I said, my love. Goodbye, my love, goodbye." Emily Dickinson once wrote, "Parting is all we need to know of hell." How many people have suffered in all the millions of years of human evolution? How many people around the world are dancing with elation at this very minute? Romantic love is one of the most powerful sensations on Earth.

So, several years ago, I decided to look into the brain and study this madness. Our first study of people who were happily in love has been widely publicized, so I'm only going to say a very little about it. We found activity in a tiny, little factory near the base of the brain called the ventral tegmental area. We found activity in some cells called the A10 cells, cells that actually make dopamine, a natural stimulant, and spray it to many brain regions. Indeed, this part, the VTA, is part of the brain's reward system. It's way below your cognitive thinking process. It's below your emotions. It's part of what we call the reptilian core of the brain, associated with wanting, with motivation, with focus and with craving. In fact, the same brain region where we found activity becomes active also when you feel the rush of cocaine.

But romantic love is much more than a cocaine high -- at least you come down from cocaine. Romantic love is an obsession. It possesses you. You lose your sense of self. You can't stop thinking about another human being. Somebody is camping in your head. As an eighth-century Japanese poet said, "My longing had no time when it ceases." Wild is love. And the obsession can get worse when you've been rejected.

So, right now, Lucy Brown and I, the neuroscientist on our project, are looking at the data of the people who were put into the machine after they had just been dumped. It was very difficult actually, putting these people in the machine, because they were in such bad shape. (Laughter) So anyway, we found activity in three brain regions. We found activity in the brain region, in exactly the same brain region associated with intense romantic love. What a bad deal. You know, when you've been dumped, the one thing you love to do is just forget about this human being, and then go on with your life -- but no, you just love them harder. As the poet Terence, the Roman poet once said, he said, "The less my hope, the hotter my love." And indeed, we now know why. Two thousand years later, we can explain this in the brain. That brain system -- the reward system for wanting, for motivation, for craving, for focus -- becomes more active when you can't get what you want. In this case, life's greatest prize: an appropriate mating partner.

We found activity in other brain regions also -- in a brain region associated with calculating gains and losses. You know, you're lying there, you're looking at the picture, and you're in this machine, and you're calculating, you know, what went wrong. How, you know, what have I lost? As a matter of fact, Lucy and I have a little joke about this. It comes from a David Mamet play, and there's two con artists in the play, and the woman is conning the man, and the man looks at the woman and says, "Oh, you're a bad pony, I'm not going to bet on you." And indeed, it's this part of the brain, the core of the nucleus accumbens, actually, that is becoming active as you're measuring your gains and losses. It's also the brain region that becomes active when you're willing to take enormous risks for huge gains and huge losses.

Last but not least, we found activity in a brain region associated with deep attachment to another individual. No wonder people suffer around the world, and we have so many crimes of passion. When you've been rejected in love, not only are you engulfed with feelings of romantic love, but you're feeling deep attachment to this individual. Moreover, this brain circuit for reward is working, and you're feeling intense energy, intense focus, intense motivation and the willingness to risk it all to win life's greatest prize.

So, what have I learned from this experiment that I would like to tell the world? Foremost, I have come to think that romantic love is a drive, a basic mating drive. Not the sex drive -- the sex drive gets you out there, looking for a whole range of partners. Romantic love enables you to focus your mating energy on just one at a time, conserve your mating energy, and start the mating process with this single individual. I think of all the poetry that I've read about romantic love, what sums it up best is something that is said by Plato, over 2,000 years ago. He said, "The god of love lives in a state of need. It is a need. It is an urge. It is a homeostatic imbalance. Like hunger and thirst, it's almost impossible to stamp out." I've also come to believe that romantic love is an addiction: a perfectly wonderful addiction when it's going well, and a perfectly horrible addiction when it's going poorly.

And indeed, it has all of the characteristics of addiction. You focus on the person, you obsessively think about them, you crave them, you distort reality, your willingness to take enormous risks to win this person. And it's got the three main characteristics of addiction: tolerance, you need to see them more, and more, and more; withdrawals; and last, relapse. I've got a girlfriend who's just getting over a terrible love affair. It's been about eight months, she's beginning to feel better. And she was driving along in her car the other day, and suddenly she heard a song on the car radio that reminded her of this man. And she -- not only did the instant craving come back, but she had to pull over from the side of the road and cry. So, one thing I would like the medical community, and the legal community, and even the college community, to see if they can understand, that indeed, romantic love is one of the most addictive substances on Earth.

I would also like to tell the world that animals love. There's not an animal on this planet that will copulate with anything that comes along. Too old, too young, too scruffy, too stupid, and they won't do it. Unless you're stuck in a laboratory cage -- and you know, if you spend your entire life in a little box, you're not going to be as picky about who you have sex with -- but I've looked in a hundred species, and everywhere in the wild, animals have favorites. As a matter of fact ethologists know this. There are over eight words for what they call "animal favoritism:" selective proceptivity, mate choice, female choice, sexual choice. And indeed, there are now three academic articles in which they've looked at this attraction, which may only last for a second, but it's a definite attraction, and either this same brain region, this reward system, or the chemicals of that reward system are involved. In fact, I think animal attraction can be instant -- you can see an elephant instantly go for another elephant. And I think that this is really the origin of what you and I call "love at first sight."

People have often asked me whether what I know about love has spoiled it for me. And I just simply say, "Hardly." You can know every single ingredient in a piece of chocolate cake, and then when you sit down and eat that cake, you can still feel that joy. And certainly, I make all the same mistakes that everybody else does too, but it's really deepened my understanding and compassion, really, for all human life. As a matter of fact, in New York, I often catch myself looking in baby carriages and feeling a little sorry for the tot. And in fact, sometimes I feel a little sorry for the chicken on my dinner plate, when I think of how intense this brain system is. Our newest experiment has been hatched by my colleague, Art Aron -- putting people who are reporting that they are still in love, in a long-term relationship, into the functional MRI. We've put five people in so far, and indeed, we found exactly the same thing. They're not lying. The brain areas associated with intense romantic love still become active, 25 years later.

There are still many questions to be answered and asked about romantic love. The question that I'm working on right this minute -- and I'm only going to say it for a second, and then end -- is, why do you fall in love with one person, rather than another? I never would have even thought to think of this, but Match.com, the Internet-dating site, came to me three years ago and asked me that question. And I said, I don't know. I know what happens in the brain, when you do become in love, but I don't know why you fall in love with one person rather than another. And so, I've spent the last three years on this. And there are many reasons that you fall in love with one person rather than another, that psychologists can tell you. And we tend to fall in love with somebody from the same socioeconomic background, the same general level of intelligence, the same general level of good looks, the same religious values. Your childhood certainly plays a role, but nobody knows how. And that's about it, that's all they know. No, they've never found the way two personalities fit together to make a good relationship.

So, it began to occur to me that maybe your biology pulls you towards some people rather than another. And I have concocted a questionnaire to see to what degree you express dopamine, serotonin, estrogen and testosterone. I think we've evolved four very broad personality types associated with the ratios of these four chemicals in the brain. And on this dating site that I have created, called Chemistry.com, I ask you first a series of questions to see to what degree you express these chemicals, and I'm watching who chooses who to love. And 3.7 million people have taken the questionnaire in America. About 600,000 people have taken it in 33 other countries. I'm putting the data together now, and at some point -- there will always be magic to love, but I think I will come closer to understanding why it is you can walk into a room and everybody is from your background, your same general level of intelligence, your same general level of good looks, and you don't feel pulled towards all of them. I think there's biology to that. I think we're going to end up, in the next few years, to understand all kinds of brain mechanisms that pull us to one person rather than another.

So, I will close with this. These are my older people. Faulkner once said, "The past is not dead, it's not even the past." Indeed, we carry a lot of luggage from our yesteryear in the human brain. And so, there's one thing that makes me pursue my understanding of human nature, and this reminds me of it. These are two women. Women tend to get intimacy differently than men do. Women get intimacy from face-to-face talking. We swivel towards each other, we do what we call the "anchoring gaze" and we talk. This is intimacy to women. I think it comes from millions of years of holding that baby in front of your face, cajoling it, reprimanding it, educating it with words. Men tend to get intimacy from side-by-side doing. (Laughter) As soon as one guy looks up, the other guy will look away. (Laughter) I think it comes from millions of years of standing behind that -- sitting behind the bush, looking straight ahead, trying to hit that buffalo on the head with a rock. (Laughter) I think, for millions of years, men faced their enemies, they sat side by side with friends. So my final statement is: love is in us. It's deeply embedded in the brain. Our challenge is to understand each other. Thank you.