The chemistry of love
Couples fall in love in different ways. Some lock eyes across a crowded room and experience a powerful mutual attraction, "love at first sight", others are friends for years and over time their friendship matures first into affection and later into passion. Everyone has a different story but many aspects of our experience and expectations for love are similar. We expect that for most of us the first flush of passionate love will in time temper into something more familar and stable. But why?
Nothing is truly known but Neuroscientists have some interesting theories that help explain our universal experiences of love. How we feel and the biological basis for why we feel that way.
Neuroscientists have identified 3 distinct systems of the brain that control romantic love, the sex drive and partner bonding. Key among these systems are the glands that control the release of hormones in the brain.
When we "fall in love" we are experiencing romantic love in it's strongest form. It's no surprise that this kind of love is also known as "passionate love" or "obsessive love". Falling in love is characterized by an obsession with the object of our desire, an intense possessiveness over them, feelings of ecstasy when things are going well, wild mood swings, anger and despair when they are going badly. At the same time our ability to concentrate on every detail of our beloved and remember everything about them also comes to the fore. We need less sleep, have more energy, and feel more vibrantly alive. We become more impulsive. Separation from our loved-one causes us anxiety and we are consumed with a longing for emotional fusion with our beloved.
There is strong sexual desire wrapped up in falling in love but it is less important than the deep personal connection we long to feel with the beloved.
So what is going on in the brain of someone in love? Magnetic Resonance Imaging (MRI) scans of the brains of people who report being "madly in love" when shown a picture of their beloved show activation of an area of the brain known to be part of the brains reward-system. This area is associated with feelings of pleasure, arousal and focused attention and is also responsible for the hormone and neurotransmitter dopamine. At the same time another area of the brain associated with motivation, goals and winning rewards is activated. This area contains about 80% of the brains receptors for dopamine. In laymen's terms, the pleasure and reward-motivation areas of the brain light up like a pinball machine.
These two areas of the brain are responsible for many of the "symptoms" we associate with being in love : Hyperactivity, intense concentration, feelings of ecstasy and despair, reduced sleep, improved memory and even symptoms of addiction (the pain of withdrawal from our loved one, the heightened expectancy of being with them).
In addition to dopamine, the levels of another hormone called serotonin are reduced while the levels of norepinephrine are increased. Reduced levels of serotonin are associated with Obsessive Compulsive Disorder (OCD) and increased levels of norepinephrine are known to increase memory may also be responsible for the racing heart experienced by people first in love.
The Sex drive
While passionate love is often associated with sex, the sex drive has its own regulation system within the body. The sex drive is a powerful urge for sexual gratification and without it the human race would not have got very far. The sex drive is primarily controlled by the hormone testosterone which is present in both women and men. Testosterone is sometimes considered to be the "male hormone" and men do possess it in about 10x the quantity of it that women do but in both sexes it is the primary controller of the libido.
Both women and men who take testosterone supplements (e.g. anabolic steroid users) report increased sexual desire, more erotic dreams and an increase in sexual activity.
But testosterone isn't the only story. Our sex drives are tempered by our genes, our upbringing and culture - informing us when, where and how to indulge our need for gratification.
In women the sex drive has a correlation to the monthly menstrual cycle, with women's sex drives being heightened two or three days before ovulation.
Research carried out in 2006 suggests that the contraceptive pill can have a subduing effect on women's sex drive and some anti-depression drugs are also known to have a negative effect on women's libido.
Under MRI men and women in a state of sexual arousal show activity in many parts of the brain including, as one might expect, many of the deep structures related to our basic drives. There is some overlap with the structures associated with Romantic, passionate love hinting that although these systems are separate, they do interact and it may be the release of dopamine in romantic love that causes an increase in testosterone production leading to activation of the sex drive.
Over time the passionate elements of romantic love subside. The intense feelings of ecstasy and the roller-coaster of emotions are slowly replaced by warm feelings of contentment, security and belonging. Psychologists call this kind of love companionate love to distinguish it from passionate or romantic love. Companionate love is present in the relationship from the beginning but over time it becomes more important. Companionate love is practical. It often endures even through times when the relationship is under stress and the partners do not necessarily get along. The phrase "I don't like you, but I love you" resonates strongly with people experiencing companionate love at certain times of their relationship.
Evolutionary biologists believe that companionate love has its basis in the love of a parent for a child and is especially active when parents work together to raise children. It is a form of reward that is bestowed on us for sticking around to raise children once the initial flush of romantic love has faded.
That isn't to say that passionate love ever disappears from the picture but it's has a tendency to rise and fall over the years of a relationship due to the stresses of everyday living.
In the brain, companionate love is associated with the hormones oxytocin and vasopressin. In animals oxytocin is associated with pair bonding and vasopressin is associated with the behaviours of defending a territory and a mate. These two hormones could be thought of as the chemical basis of monogamy since without them our desire to stay with our current partner wanes.
Oxytocin and vasopressin have a complicated relationship with testosterone and with dopamine. Dopamine makes us attracted to our partner. Testosterone provides the drive to engage in sex and scientists believe that sexual activity releases oxytocin and vasopressin into our systems - making us bond with our partner.
But it's a delicate dance. The levels of testosterone and vasopressin interact with each other in complex ways. The presence of testosterone can elevate the levels of vasopressin resulting in greater bonding but too much testosterone can depress levels of vasopressin resulting in less bonding. This might explain why people with high levels of testosterone have tumultuous relationships, are more likely to stray and have high divorce rates.