LOVE, LOVE ME DO

Love and the varied emotions it evokes in us are the brain’s child, shows modern science

T THOSE OF US WHO GREW UP watching Bollywood movies were fed a generous dose of colourful scenes of the hero and heroine expressing their love for each other in the most acrobatic ways that often defied the laws of physics—running around trees, rolling down hillsides—all the while singing and dancing away with boundless energy! These memorable scenes may lead you to believe that a supple spinal cord, supported by a strong vocal cord, is all that is needed to express and respond to love. Modern brain science suggests otherwise.

‘Love’ is probably one of the most intriguing and poorly understood behaviours. What goes on inside the human brain when its owner is madly in love? Path-breaking research by Dr Helen Fisher provided the first glimpses, using MRI scans, of the brain of individuals intensely ‘in love’. These studies showed that feelings of romantic love, evoked by images of the beloved, activate dopamine-rich areas of the brain associated with reward and motivation, such as the ventral tegmental area and the caudate nucleus. Dopamine is a ‘neurotransmitter’ or a chemical that conveys feel-good signals between brain cells and activates the brain reward circuit, thereby making love a pleasurable experience. Interestingly, dopamine in these brain areas also plays a pivotal role in addiction to drugs and alcohol. In fact, the same dopamine-rich brain reward system gets hijacked by addiction. Perhaps Robert Palmer had it right when he sang

Addicted to Love. But Tina Turner may ask—What’s Love Got To Do With It? A lot, if you ask the flies—yes, flies—in a 2012 study. Male fruit flies that had suffered sexual rejection drank a lot more alcohol compared to the lucky flies that mated with

female flies. Why blame ‘Devdas’ when even failed lovers amongst fruit flies drown their sorrows in alcohol?

Passionate, romantic love is a splendid thing. But doesn’t time take its toll? In 2011, another study using MRI scans on couples who had been married for an average of 21 years, reported the same intensity and pattern of brain activity in dopamine-rich areas as observed in new lovers. In other words, old love never dies, neither does it fade away. Actually, it gets better. The early stages of romantic love, filled with uncertainty, can be stressful. This ramps up the levels of the stress hormone cortisol and produces strong emotional and physical responses. Just ask a teenager infatuated with his or her lover, overwhelmed by intense feelings of anxiety and passion—pounding hearts, sleepless nights and all! If these early stages of romantic love eventually stabilise into a lasting relationship, the elevated levels of cortisol come down to normal. And this paves the way for a calm and compassionate love that still activates regions of the brain associated with reward and pleasure.

Dopamine is not the only arrow in Cupid’s chemical arsenal. Consider the examples of vasopressin and oxytocin, which play an important role in behaviour that gives rise to long-term, monogamous relationships. Fascinating discoveries by Larry Young and colleagues have shown how oxytocin and vasopressin control social behaviours and pair-bonding in voles that live on the prairies of the United States. After mating, these prairie voles form monogamous pairs that stick together for life. Talk about a one-night stand going strong for a lifetime! Unlike these prairie voles, the closely related montane voles are promiscuous. The difference between these two groups lies in vasopressin and oxytocin and their respective receptors in the brain. This is like a lock-and-key system—vasopressin or oxytocin is the key, but it can only open the door when it fits into the matching slot of the right lock, a specific type of receptor. Brain cells get activated as soon as the key fits into its lock. It turns out that differences in the mating behaviours of these two types of voles depends on how much of the oxytocin and vasopressin receptors can be found in various brain areas. For instance, compared to the polygamous montane voles, monogamous prairie voles have higher densities of oxytocin receptors in the prelimbic cortex and the nucleus accumbens, parts of the dopamine reward system mentioned earlier. Prairie voles also have more of these receptors in the amygdala, a brain structure that forms emotional memories.

In contrast, montane voles, have higher levels of the same receptors in a different part of the brain called the lateral septum. Oxytocin and vasopressin are released into the brain when prairie voles mate. This creates a preference for the mating partner that solidifies long-term pair-bonding in these monogamous voles. If the release of oxytocin and vasopressin is prevented in prairie voles, the same animals become promiscuous, and they lose their partner preference. And here’s the kicker—if a particular kind of vasopressin receptor from the prairie vole is artificially expressed, using genetic engineering techniques, in the montane voles, the latter become monogamous and form long-lasting attachments with their mates just like the prairie voles! Similar patterns of brain activity are also seen in long-term, pair-bonded humans. Just imagine all the exciting possibilities for the troubled love lives of Page 3 celebrities!

Finally, a word on the magical powers of oxytocin that extend beyond romantic love. Oxytocin is also a major player in motherinfant attachment, and helps reduce stress and anxiety. Interestingly, both romantic love and maternal attachment activate overlapping areas of the brain reward circuits—and these same areas happen to be rich in oxytocin receptors. And just in case you think love is the exclusive domain of us humans, how about man’s best friend? As any dog lover will tell you, humans and their companion dogs can form strong bonds. Remember the story of Greyfriars Bobby, a Skye Terrier in 19th century Edinburgh? When Bobby’s owner John Gray died, the dog spent the rest of his life guarding his master’s grave. In a series of elegant studies, Nagasawa and colleagues showed that

interactions with dogs, especially those initiated by the dog’s gaze, can increase oxytocin levels in their owners, which is indicative of attachment behaviour. This, in turn, increased oxytocin levels in the dogs as well. And get this—a canine nasal spray of oxytocin enhanced gazing behaviour in dogs, and this increased the concentration of urinary oxytocin in the owners too. A positive loop of love! Thus, from fruit flies and voles to dogs and humans, the chemistry of love is universal, and immensely powerful. At a time of widespread fear, anger and violence, perhaps this is our only source of hope that, sooner or later, love will trump hate.