What is Love?
"Love is the drug and I need to score," sang Bryan Ferry in the seventies, earning him a smash hit and a small fortune. But apart from being a catchy song lyric, this line is also looking like a scientifically-accurate fact of life.
That's because, in recent years, researchers have begun to bring the power of modern genetics and neuroscience to bear on the workings of the human psyche, including the "big" question of love and what is it?
Somewhat unromantically, the results of these endeavours are showing is that the simple answer is that love amounts to little more than a chemical addiction. In fact the same brain circuits become active when volunteers in a scanner are shown pictures of their loved ones as when a nicotine-starved smoker lights up their first cigarette of the day! And the molecular clockwork of that lovin' feelin' is a small family of nerve transmitter chemicals called oxytocin, vasopressin and dopamine.
Oxytocin is released in the brain during orgasms, during childbirth and by breast feeding, which has led scientists to suspect that it may be linked to mother-baby bonding and that perhaps this, "love" and partner attachments are all a manifestation of the same process.
Experimentally the evidence is quite compelling. Amongst sheep, a mother can be persuaded to foster a lamb that isn't her own by delivering a brief puff of oxytocin into her nose before introducing the lamb, and unmated female rats become highly maternal around rat pups that they would previously have killed when given a dose of the chemical beforehand.
Humans are affected too. Volunteers given doses of oxytocin develop enhanced sensations of trust for those nearby, become more sensitive to the emotions of others and also spend longer looking at peoples' faces (as opposed to the breast or trouser region). This suggests that, couples who experience orgasms together are effectively programming each others' brains to love and trust one another!
But trust also usually demands monogamy, the mediator of which is vasopressin. Studies on voles have shown that a polygamous vole species known as the meadow vole can be transformed into behaving like its monogamous prairie vole cousin either by adding extra vasopressin to its brain or by increasing the brain's sensitivity to the substance.
The same seems to apply to humans: a study carried out last year in Sweden found that individuals with one variant of a gene used in the brain to detect vasopressin levels were twice as likely to report a recent marital crisis, and only half as likely to be married in the first place, compared with individuals not carrying that form of the gene.
Administering vasopressin to volunteers also produces changes in behaviour. Men adopt a more aggressive posture including looking more menacing and also becoming much more protective of their partners. And when shown photographs of other peoples' faces they tend to rate them as looking less friendly than they did before vasopressin was given.
So what about the addictive part of love? The sensation that you cannot survive without the other person, and the rush of joy when you see them after being away?
This is down to dopamine, the brain's pleasure chemical. When nerve cells squirt small amounts of this into a brain region called the nucleus accumbens it produces sensations of euphoria and satisfaction.
We use this circuitry to reward ourselves when we do something right, whether that's learning a new fact, passing a driving test or making someone happy. It's the way that the brain reinforces learning and good behaviour. It's also the target of drugs like cocaine and heroin, which effectively short-circuit this same brain mechanism to achieve their pleasurable effects.
But this is also where Bryan Ferry's famous lyric comes in, because dopamine lies downstream of the effects of the other two chemical love-drugs, vasopressin and oxytocin. When these chemical signals are active they trigger the release of an addictive surge of dopamine in order to consolidate their effects. So you are, quite literally, getting hooked on your partner.
Being able to distil love down to a series of chemical reactions like this is informative and helpful on the one hand because it will very likely enable scientists and doctors to help patients with conditions like autism, which make it hard for them to form relationships with other people.
But it also opens the door to a much more nefarious future, and in which we will have the pharmacological ability to manipulate love with a drug. For now though, the chat up line "could you just sniff this" should probably serve as a warning...!