It is not surprising therefore that the first studies to investigate the neural correlates of romantic love in the human should have used a visual input. These studies showed that, when we look at the face of someone we are deeply, passionately and hopelessly in love with, a limited number of areas in the brain are especially engaged. This is true regardless of gender.
Romantic love is triggered by a visual input, which is not to say that other factors, such as the voice, intellect, charm or social and financial status does not come into play. Romantic love is of course a complex emotion that includes, and cannot be easily separated from, other impulses such as physical desire and lust, although the latter can be loveless and therefore distinguishable from the sentiment of romantic love.
That love is an affair of the heart is true. But the real secret of true love may be more in the chemistry of the brain. The central neurochemical players responsible for making a person fall in and out of love are:
• Nerve growth factors
The passion of love creates feelings of exhilaration and euphoria, of a happiness that is often unbearable and certainly indescribable. And the areas that are activated in response to romantic feelings are largely coextensive with those brain regions that contain high concentrations of a neuro-modulator that is associated with reward, desire, addiction and euphoric states, namely dopamine. Like two other modulators that are linked to romantic love, oxytocin and vasopressin, dopamine is released by the hypothalamus, a structure located deep in the brain and functioning as a link between the nervous and endocrine systems.
These same regions become active when exogenous opioid drugs such as cocaine, which themselves induce states of euphoria, are ingested. Release of dopamine puts one in a ‘‘feel good’’ state, and dopamine seems to be intimately linked not only to the formation of relationships but also to sex, which consequently comes to be regarded as a rewarding and ‘‘feel-good’’ exercise. An increase in dopamine is coupled to a decrease in another neuro-modulator, serotonin, which is linked to appetite and mood.
Studies have shown a depletion of serotonin in early stages of romantic love to levels that are common in patients with obsessive-compulsive disorders. Love, after all, is a kind of obsession and in its early stages commonly immobilizes thought and channels it in the direction of a single individual. The early stages of romantic love seem to correlate as well with another substance, nerve growth factor, which has been found to be elevated in those who have recently fallen in love compared to those who are not in love or who have stable, longlasting, relationships. Moreover, the concentration of nerve growth factor appears to correlate significantly with the intensity of romantic feelings.
Hormones of Love:
Another factor in the process of love is lust. Lust exposes people to others and is the initial passionate sexual desire that promotes mating. It involves the increased release of chemicals such as testosterone and oestrogen. However, these effects rarely last more than a few weeks or months. According to a conventional biological view there are three major facets of love; attachment, sexual attraction and lust. Each facet is fuelled by the action of various hormones.
• Adrenalin – This neurochemical sparks attraction between two people.
• Phenyl ethylamine – Serotonin, dopamine, norepinephrine and nerve growth factors. Remember the heady feeling of euphoria that you get in the throes of first love? These hormones are responsible for that experience.
• Endorphins – This is the hormone of true love. Once the initial stage of love is over and adrenalin, phenyl ethylamine, dopamine and norepinephrine stop flooding the brain, either the relationship dies down or, for the lucky ones, endorphins take over. Endorphins produce the feeling of calm, warmth, intimacy and dependability that come from being in a committed relationship. In fact, the longer two people are in love, stronger the endorphin becomes.
• Oxytocin – This is the love chemical with a very important and wonderful role in the process. Oxytocin is also called the ‘cuddling hormone’. It calms down men and women and males them more sensitive to the feeling of others. In women it signals orgasm by stimulation uterine contraction. In males, moderate concentration of oxytocin facilitates both erection and ejaculation.
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Oxytocin and another chemically linked neuro-modulator, vasopressin, seem to be particularly linked to attachment and bonding. Both are produced by the hypothalamus and released and stored in the pituitary gland, to be discharged into the blood, especially during orgasm in both sexes and during child-birth and breast-feeding in females. In males, vasopressin has also been linked to social behaviour, in particular to aggression towards other males. The concentration of both neuro-modulators increases during the phase of intense romantic attachment and pairing. The receptors for both are distributed in many parts of the brain stem which are activated during both romantic and maternal love.
Judged by the world literature of love, romantic love has at its basis a concept – that of unity, a state in which, at the height of passion, the desire of lovers is to be united to one another and to dissolve all distance between them. Sexual union is as close as humans can get to achieving that unity. It is perhaps not surprising to find, therefore, that the areas engaged during these two separate but highly linked states are juxtaposed. Indeed the desire for unity through sexual union may be a consequence of it.
In matters of love and attachment, we can go a little further and sketch in outline form the chemistry that underlies the concept of the loved one that the brain forms. Perhaps the first step in this enquiry is to look at the chemistry of the human brain areas that are activated during romantic love, and in particular oxytocin, vasopressin and dopamine. Most brain regions, including subcortical regions, that have been determined to contain receptors for oxytocin and vasopressin are activated by both romantic and maternal love. To better understand the role of these chemicals in bonding, we have to rely on recent experiments on prairie voles.