Indeed, researchers have now identified three brain systems that are at work in mating and reproduction: lust, which is primarily mediated by the sex hormone testosterone; romantic love, which is primarily mediated by dopamine, a neurotransmitter that drives the brain’s reward and pleasure centers, and is characterized by craving and focused attention for just one person at a time; and attachment, which is primarily mediated by the hormones oxytocin and vasopressin and is associated with the bonding and security you often feel with a long-term partner.
These systems vary from person to person and can function discretely, together, or in all sorts of combinations, says one of the researchers, Helen Fisher, a biological anthropologist at Rutgers University and the author of “Why We Love: The Nature and Chemistry of Romantic Love.”
“That’s why you can feel deep attachment for one person, then swing into wild romantic love for someone else, then switch on the Internet, look at pornography and feel a sex drive that has nothing to do with any of those,” she says. “You can also look across the table and feel all of that for the same person, which is what we want on Valentine’s Day.”
Fisher adds that the interplay of such brain systems, along with the neurotransmitter serotonin, clearly lead to variations in temperament, which help explain why you can walk into a crowded room and fall madly in love with one person rather than another. “The reality is that we’ve got a very strong, powerful brain system for romantic love, and it can get triggered at any moment, but we will not fall in love with everyone that comes along: We have preferences, and those have to do, in part, with the way that our brain is built,” she explains.
However, it remains to be seen how big a part neurochemicals and brain circuits play in love and relationships.
“It’s hard to weed out how much is sociological and how much is biological,” says Lisa Diamond, an associate professor of psychology and gender studies at the University of Utah. “We know that there are huge cultural differences in the way we socialize women and men [about love and relationships], and now we know from animal research that there are biological differences.”