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The Science of Love

Forget Flowers!...Is Dopamine the main stimulus for Romantic Love? Charles Pasternak explores the claims Helen Fisher makes in her new book "Why We Love: The Nature and Chemistry of Romantic Love".

by Charles Pasternak

We mark the 14th of February as St Valentine's Day - a lovers' festival since the 14th century. Quite what a priest named Valentine, who suffered martyrdom in Rome during the 3rd century, had to do with love is not at all clear; if you look up St Valentine in the New Encyclopaedia Britannica you will find reference only to the massacre, by Al Capone and his cronies, of unarmed members of a bootlegging gang in Chicago on the 14th of February 1929. Never mind. Love is what makes the world go round, according to the 19th century French song, and this is as good a time as any to consider just what the feeling of love really is.

Emotions like love are, according to clinical neurologist Antonio Damasio, 'neither intangible nor elusive. Contrary to traditional scientific opinion, feelings are just as cognitive as other percepts. They are the result of a most curious physiological arrangement that has turned the brain into the body's captive audience ... To discover that a particular feeling depends on activity in a number of specific brain systems interacting with a number of body organs does not diminish the status of that feeling as a human phenomenon. Neither anguish nor the elation that love or art can bring about are devalued by understanding some of the myriad biological processes that make them what they are. So what does Helen Fisher tell us about the science of love in her latest book "Why We Love: The Nature and Chemistry of Romantic Love"?

The crux of her argument is that hormones circulating in the brain are the trigger:

"...this fire in the mind is caused by elevated levels of either dopamine or norepinephrine or both, as well as decreased levels of serotonin."

She supports her hypothesis by mapping the areas of the brain that 'light up' by fMRI (functional magnetic resonance imaging) when subjects who are passionately in love are shown pictures of their adored one. The technique of fMRI is essentially a scientific follow-up to the well-known reaction we all experience when a personal comment gets too close: we blush. The reddening of our face is due to increased blood flow below the skin; fMRI localises areas of increased blood flow in the brain when certain bundles of nerve cells respond to a particular stimulus: raising an arm, being confronted by a frightening situation, concentrating on a difficult mathematical calculation. Dr Fisher's contention is that regions of the brain (the caudate nucleus and ventral tegmental area in particular) in which the main chemical responsible for nerve transmission is dopamine, are the ones that respond to the stimulus of romantic love.

In order to recruit appropriate subjects to place inside an MRI machine, Helen Fisher and her colleagues at the State University of New York (SUNY) on the Stony Brook campus advertised for students who had 'just fallen madly in love'. Once inside the machine, they were shown a series of photographs (through an arrangement with mirrors: the entire head is within the machine). Some photographs were neutral, others were of their adored one. Between each picture the brain was cleared of emotional responses by asking the subject to mentally count backwards in increments of 7 from a large number like 4,673.

The results - a correlation between romantic love and the activity of dopamine-fired neurons deep within the brain - astonished the author. I would like to share her enthusiasm, but am constrained by the fact that no images of caudate nucleus or ventral tegmental area glowing as volunteers gaze in rapture at their William, Barbara or Bjorn are shown. There is a 16 page Appendix detailing the ‘Being in Love’ questionnaire that each volunteer had to complete, but no glimmer of an fMRI scan. We are assured that one of Dr Fisher's colleagues 'did many statistical analyses', but these are not presented either. Instead we are referred merely to her recent publications. Neither the Archives of Sexual Behavior nor Neuroendocronology Letters, however, are likely to be found on the average reader's bookshelf. I did not locate them in the extensive library of Imperial College of Science, Technology and Medicine either.

Image Courtesy Veikko Jousmäki

Semir Zeki

Not that I doubt the author's findings. They appear to be supported by independent work of Semir Zeki and his colleagues at University College, London, that predate the publications of the Fisher group by some two years. What I am concerned about is Helen Fisher's implication that of all the pleasurable emotions one might feel, it is romantic love alone that causes one's dopaminergic neurons to work overtime. I suspect that had she shown an 18 year old Carmelite nun pictures of the Virgin Mary, the same result might have been obtained. Indeed I am ready to jump into her brain scanner and have pictures of caviar blinis flashed before my eyes, or excerpts from Schubert's String Quintet in C relayed to my ears: I'll bet my caudate nucleus would respond as well. In short, I believe that gazing at a picture of your sweetheart is but one of thousands of pleasurable emotions that are transmitted along dopaminergic pathways.

The blobs that light up by fMRI may be no bigger than a pin head, but that still means that each encompasses some million neurons (nerve cells), communicating with as many as a thousand others. To establish the precise details of this network - by methods not yet available - is a Herculean task to which Dr Fisher does not allude. Instead she writes entertainingly about topics such as lust (triggered by the hormone testosterone, that inceases sexual drive in women as well as in men), rejection and despair. Her story is peppered with quotations, from Aristotle to Yeats, with more than twenty from Shakespeare alone. No doubt we should be impressed by her literary erudition. Yet the Oxford Dictionary of Quotations - that does find a place on my bookshelf - contains over five hundred references to love, so Dr Fisher's scholarly contribution is not, perhaps, so remarkable after all.

NIMH Laboratory of Brain and Cognition

An fMRI scan investigating areas of the brain used in working memory - Similar types of scans were carried out by Dr Fisher in her research

On the other hand there is no doubt that Helen Fisher writes with a light, breezy touch and that she presents a comprehensive account of the various emotions that interact with romantic love. So far as the underlying chemistry is concerned, that too is presented in a clear manner. But it is not chemistry that will reveal the working of the mind. No more than fifty different types of molecule have so far been recognised to function as neurotransmitters in the human body. Let me remind you what these chemicals do. The connection between one nerve cell and the next is a salt water-filled fibre that stops just short of the nerve cell it is going to innervate. A tiny electric current, generated in the first cell, passes along the fibre until it reaches the gap between nerve fibre and the recipient cell. At this point a chemical substance, the aptly named neurotransmitter, is released.

Neurotransmitter molecules bind to the membrane of the recipient cell, causing it to respond in a particular manner. Within the brain, the outcome is generally to transmit current to a further nerve cell, and so on. There are over a trillion discrete fibers that connect the hundred billion nerve cells in our brain to each other; many nerve cells are linked to more than a thousand other cells. The result is an immensely complicated neural network. No two brains, not even those of identical twins, have exactly the same cell-to-cell connections. With a trillion fibres and just fifty types of neurotransmitter to choose from, it is clear that the vast majority of fibres use the same neurotransmitter. So it is not chemicals like dopamine or norepinephrine that distinguish one set of fibres from another. The discrimination between thoughts of love and every other emotion must reside in the precise pathways – among a myriad of possibilities – that are followed when a new feeling, a novel thought, arises in the brain.

So it is not chemistry but biophysics - or an innovative discipline yet to be developed - that will elucidate the basis of emotions like love and hate, calm and anger, pleasure and sorrow, joy and despair. In the meantime we can do no more than applaud the author's attempts, and look enviously across the Atlantic: what fun it must be for a love-struck psychology student at Stony Brook to have the opportunity of engaging in Helen Fisher's research projects.

[1] Antonio R Damasio: Descartes' Error. Emotion, Reason and the Human Brain (Picador, London, 1995, p xv). Available to Buy from Amazon.com or Amazon.co.uk

[2] Helen Fisher: Why We Love: The Nature and Chemistry of Romantic Love (Henry Holt and Company, New York, 2004, £12.28/$25.00) Available to Buy from Amazon.com or Amazon.co.uk

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First Science 2014