"How on earth are you ever going to explain in terms of chemistry and physics so important a biological phenomenon as first love?—Albert Einstein
Einstein was correct—science will never clinically sterilize the wonderment of love (first or otherwise). But I think he’d also agree that it’s a mistake to confuse increased understanding with diminished meaning. No matter what we learn about love, it will continue to be one of the most meaningful and powerful forces on the planet, as it should be.
With that disclaimer, let’s jump in and discover what we've learned so far:
Thinking about one’s beloved—particularly in new relationships—triggers activity in the ventral tegmental area (VTA) of the brain, which releases a flood of the neurotransmitter dopamine (the so-called "pleasure chemical") into the brain’s reward (or pleasure) centers—the caudate nucleus and nucleus accumbens. This gives the lover a high not unlike the effect of narcotics, and it’s mighty addictive.
At the same time, the brain in love experiences an increase in the stress hormone norephinephrine, which increases heart rate and blood pressure, effects similar to those experienced by people using potent addictive stimulants like methamphetamine.
The brain in love experiences a drop in the neurotransmitter serotonin. Serotonin provides a sense of being in control; it guards against the anxiety of uncertainty and instability. When it drops, our sense of control decreases and we become obsessively fixated on things that rattle our certainty and stability cages—and since love is by definition unpredictable, it’s a prime target for obsession. The term "crazy in love" isn't too far off the truth.
The prefrontal cortex—our brain’s reasoning, command, and control center—drops into low gear when we’re in love. At the same time, the amygdala, a key component of the brain’s threat-response system, also revs down. The combination of these effects is a willingness to take more risks, even ones that would normally seem reckless to us while in another state of mind. (For more, see this study.)
Love and lust appear to be separate but overlapping neural responses in the brain. They both produce a “high”; they're both addictive; and they affect many of the same parts of the brain—but they are distinct enough that you can be in love with one person and in lust with another.
Over time, the differences become more significant. For example, the brains of people in long-term love relationships show increased activity in the ventral pallidum, a region rich with oxytocin and vasopressin receptors that facilitate long-term pair-bonding and attachment. (See researcher Helen Fisher's work in this area for more information.)
The brains of men in love show greater activity in the visual cortex than those of women in love. Add this to the fact that men seem to be more visually stimulated romantically than women in general.
The brains of women in love show greater activity in the hippocampus—a region associated with memory—than those of men in love. Add to this that a woman's hippocampus takes up a larger percentage of her brain than does the male counterpart. (Another lesson here for men in relationships: Women remember.)
Newborns and lovers have this in common: More than any other factor, eye contact is the main conduit for emotional connection. When those in love speak of their lover's “entrancing gaze," it’s not just a romantic notion—it’s a biological reality. Eye contact and a smile is an especially potent combination.
Only voice interaction comes anywhere close to eye contact in this regard. Our voice carries more information than we think, and it can help facilitate an emotional connection, but it’s still a distant second to eye contact. (Check out Barbara L. Fredrickson's book, Love 2.0, for more on all of the above.)
You may have heard about our furry little friends, the prairie voles. Scientists who study monogamy and promiscuity love the critters because they provide an excellent mirror for human relationships. One type of vole is monogamous—it bonds with one mate for life. Another type (the montane vole) is promiscuous. The key difference between the two types of voles appears to be genetic—an intriguing point when you consider that otherwise the voles are 99% genetically identical.
When researchers inject the promiscuous variety of vole with oxytocin and vasopressin—the neurochemicals linked to pair-bonding in humans (and in the monogamous voles)—the promiscuous voles become monogamous. While it’s not entirely clear if this effect would hold true to the same degree in humans, there’s good evidence that it might, if only for short periods of time. In two studies (described here) men who inhaled oxytocin became (temporarily) more empathetic, sensitive, and cuddly.
Research suggests that when it comes to managing a platonic relationship, men really don't "get it" and are far more likely to want more than just friendship. Women, on the other hand, are able to keep friendship and romantic involvement separate in their minds. So the old question, "can men and women just be friends?" appears to depend entirely on who you're asking.
You can find David DiSalvo on Twitter @neuronarrative and at his website, The Daily Brain. His latest book is Brain Changer: How Harnessing Your Brain’s Power To Adapt Can Change Your Life.