Love is truly an addiction if you look at how it works in the brain, scientists say. But it might be the reason why humans are still around and able to wax poetic and sing love songs.
Those who study the neurobiology of social bonding in humans and in some animals say those areas of attachment and affection share many of the same areas of the brain and the same chemical messengers as drug addiction.
That is probably not an accident, said Dr. Larry Young, the director of Emory University's Center for Translational Social Neuroscience.
"Our brain systems that are involved in love and bonding and attachment, they are not there because of drugs of abuse. Drugs of abuse are hijacking those systems that evolved to be able to promote these kinds of things," he said. "We have a brain that helps us develop an attachment to another person so that we continuously want to be with that person. And drugs of abuse simply activate those same systems."
This connection and its implications were part of Young's recent book, The Chemistry Between Us: Love, Sex and the Science of Attraction.
Bonding is likely an evolutionary development that helped humans survive by pairing up.
"It would be more difficult for a single mother with a little baby to be able to get the food and resources she needed," Young said. "It took cooperation between a male and a female, with some division of labor, to be able to create an environment that the child was likely to be able to flourish in and survive themselves."
That is particularly important for humans, who take a long time -- compared with other species -- before they can fend for themselves, Young said.
"This is one of the reasons that we think that humans developed the intellectual capacity that we have is because we developed over a much longer period of time," he said.
The actual chemical basis of this bonding can be seen in the few mammals where the male is involved in parenting, such as prairie voles, marmosets and titi monkeys, said Dr. Karen L. Bales, the vice chairwoman of psychology at the University of California, Davis.
"If you look at a prairie vole or you look at a titi monkey, there is this very strong bond between the mates," she said. "I think that the care of the babies by the male is really almost a byproduct."
The chemical messenger oxytocin, for instance, is involved in the birth process and lactation in women and causes the mother to develop a strong attachment to the baby, Young said.
"A mother really becomes addicted to her baby," he said. "Those same systems that are involved in that just got tweaked a little bit so that now the male partner is also the subject of that neurocircuitry."
While chemically similar, human attachments are just more complex than those species, Bales said.
"I think that humans just have a greater capacity to maintain simultaneous bonds of different strength," she said. "We have the ability to maintain multiple strong bonds."
The ability to understand and trace these things in the circuitry of the brain has improved.
"Fifteen years ago, people would never have thought you would be able to start to understand the biochemistry of that and the underlying circuitry," Young said. "Now we do. We know quite a bit."
For instance, withdrawal is a major problem for treating addiction and is involved in the release of stress hormones, he said. People who lose partners go through similar things in their brains and could be treated in similar ways.
Lack of attachment and social bonding in people with autism spectrum disorders and schizophrenia could pose similar challenges, and oxytocin is being studied as a potential treatment, although a recent paper by Bales showed giving chronic low-dose intranasal doses in young male prairie voles had the opposite effect.
Young, whose lab is working on drugs to induce oxytocin in the brain as a potential treatment, agrees that researchers should proceed cautiously.
Bales said she is often asked at talks: "If I give my boyfriend some oxytocin, will it make sure he wants to marry me?"
"I wouldn't count on it," Bales said with a laugh. "I don't think we have it worked out that closely."
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