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Glenn D. Braunstein, M.D. Headshot

The Biochemistry of Love's Ecstasy and Agony

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For most of us, it just wouldn't be Valentine's Day if we didn't offer a heart-shaped expression of heart-felt love to someone we care about. And whether we're celebrating a long-time relationship or we're newly smitten, the ups and downs of the experience are universal: the thrill of attraction, the joy of connection, the despair of rejection, the warmth of an ongoing union.

Love is one of the most fundamental of all human conditions. But considering its all-consuming nature, how it changes so many parts of our lives -- and even results in the creation of life -- it's noteworthy how many questions about love remain unanswered. How does it work? And if we knew its physiological function, could we make it occur more often? Could we stop bad relationships? Can we make good ones last?

With all the heart strings that will be tugged at on this special day in February, new findings in a growing body of research, both on animals and humans, show that it's not so much the heart but the brain and its biochemistry that play a big role in how we fall in love, with whom and for how long.

Love's brain chemistry: millions of years in the making

Research into "the brain chemistry of love" indicates that when a person sees a potential mate, it takes as little as a fifth of a second for the brain to launch a complex "love-related" chain reaction involving multiple areas of the cortical and more primitive subcortical portions of the brain. Activation of some of these areas launches a host of neurotransmitters, hormones and proteins into action. Studies in humans have shown a great deal of similarity with the processes that occur in lower species, suggesting that the systems have evolved over millions of years in order to maintain procreation.

The cerebral cortex receives inputs from all the senses. Attractiveness noted through visual cues, a pleasing voice transmitted through the hearing apparatus, touch through nerves in the skin, and, possibly, the detection of pheromones through the sense of smell are instantly integrated by the cortex, which then signals other areas of the brain. The main area of the brain responsible for the early, swift love response is the caudate nucleus, a large C-shaped region near the center. This area is almost primordial, thought to be part of the "reptilian brain" that evolved before mammals took the main stage. It plays a key role in the brain's reward system and is responsible for general arousal and pleasure sensations.

When this area of the brain gets activated, we're not only flooded with positive feelings and sensations, we're motivated to keep getting them; we do and say whatever seems appropriate to keep compliments and positive reinforcement coming our way. When researchers, using functional magnetic resonance imaging (fMRI), scanned brain activity of test subjects who described themselves as "madly in love," the more passionate they were about their new partners, the more active were their caudate regions. Of interest, activity in the prefrontal cortex of the brain, which is hyperactive in depression, is turned down during this phase of early romantic love.

The other region central to the "love response" is the ventral tegmental area, also a key component of the brain's reward circuitry and home to cells that manufacture dopamine, the neurotransmitter that enables obsessive focus, feelings of elation and even mania. Dopamine is most prevalent in one particular part of the love process. And though not every relationship evolves in the same way and feelings seem to rage out of control, the release of particular brain chemicals seems to be present in three distinct phases of love that optimize the continuation of the species.

Three stages of love

The first phase often is the all-important sex drive, which is part of procreation and includes the cultivating of an optimum number of partners. The hypothalamus and pituitary, which lie at the base of the brain, signals the gonads to release testosterone and estrogen which stimulate libido, an important component during the "lust" phase of a relationship.

Research recognizes the second phase as intense romantic love, an evolutionary step that seems to support monogamy as a way to achieve efficient use of mating time. This is the phase for all those inexplicable behaviors: obsessive thinking and focus on the loved one; the racing heart; diminished attention span; the need to ascribe significance to even minor encounters or communications; and the ability to see only positive qualities of the new partner. This is the phase in which the neurotransmitters dopamine and norepinephrine come into play, as well as the "stress hormone" cortisol and a substance called nerve growth factor. As brain scans show, these substances can be as powerful as addicting amphetamines. MRI scans show the brains of lovers, like cocaine users, "light up" in this phase, leading researchers to conclude that romantic love can be addictive. And as occurs with many addictions, in intense romantic love, the brain experiences: tolerance, which makes it need more exposure to the love object; withdrawal, the pain that occurs when the love object is gone; and even relapse; if a break-up occurs and -- even months later -- if the other person reappears, thanks to a resurgence of dopamine and norepinephrine, the partner is once again in love.

In attachment, the research-identified third phase of human relationships when couples bond and rear children, studies find that the hypothalamus and pituitary release hormones like oxytocin. In women, oxytocin stimulates uterine contraction during birth and allows milk to flow during an infant's suckling, and is important for maternal bonding. The biochemical objective in this phase appears to be to foster calm, peace and security for the young.

Therapeutic biochemistry

As researchers on human attraction and relationships begin to see love, not merely as a fickle, indecipherable emotion but as a highly developed motivation and reward system wired into the human brain, they can try to apply their research to real life. They're investigating if, by knowing that dopamine is triggered by novel situations, they can help long-time couples find ways to keep the romantic spark alive. Their studies may also lead to new treatments and therapies for couples in the military who endure long, painful separations, or for lovers who suffer debilitating insecurities or depressions after break-ups. And for those who tend to get hooked on the high of intense romantic attraction, the research may underscore that, while we may hope for the person who will make us feel all "lit up" in that crucial fifth of a second, well, try to keep your head about you.

Around the Web

The Science of Romance: Why We Love - TIME

The science of love | Science | guardian.co.uk

Forbes.com: The Science Of Love

The Science Behind True Love