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The study of mimicry shows a close relationship between scientific psychology and the theatre, says Tiffany Watt-Smith.

"Just relax," is what they say in their cheery voices. But an fMRI scanner is not a relaxing place to spend half an hour. You must lie, still as a corpse, inside a metal tube and allow your body to be subjected to the play of magnetic fields. The machine shudders and clangs. You can speak with the technicians on the outside via an intercom, but for the most part you try to suppress the panicky claustrophobia blossoming in your chest. It's hard to imagine anyone giggling. Yet they do when Professor Sophie Scott of University College London conducts her experiments. She plays laughter tracks over the intercom. Soon, the belly-wobbling guffaws of her research subjects can be heard under the din of the scanner - and the subtle changes in the distribution of blood in their brains can be seen on the computer screens outside.

Among the brain processes which neuroscientists hope to make visible using fMRI scans, the hunt for mirror neurons is probably most controversial. In the 1990s, neuroscientists at the University of Parma identified cells in the brains of monkeys which fired not only when the monkeys performed a given action, but also when they saw other monkeys do so too. The Italian researchers dubbed these cells mirror neurons and in the last 20 years they have become one of the most widely-debated concepts in neuroscience.

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Advocates of mirror neuron theory - for example, the neuroscientist Vilayanur Ramachandran - argue that a mirror response is very likely present in the human brain too, and may explain how we feel vicarious emotions like empathy, learn languages and forge societies. They would certainly explain why so many of us find ourselves giggling or yawning when someone else nearby does so. Some of their colleagues are more cautious, reminding us that there is still no hard evidence that mirror neurons exist in humans at all.

Yet, the concept has proved strangely seductive. Poets and artists have rushed to consider their philosophical implications - am I responsible for my actions if my brain helplessly imitates others around me? Are my emotions really mine? Long-held ideas about individuality and authenticity are being rethought. Whether or not mirror neurons do exist, they have certainly brought artists and scientists together in a moment of shared excitement.

In 1959, the novelist CP Snow spoke of two distinct cultures in intellectual life - sciences and the humanities. This division is very familiar today. Most of us have been encouraged to think of ourselves as more of a science or arts sort of person. But it's easy to forget that in 1959, Snow was describing a relatively new and unwelcome development. Only a few decades earlier, such a picture would have been rather baffling to artists and scientists alike.

CP Snow 1905-1980

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Novelist, scientist and government administrator - made a fellow of Christ's College, Cambridge aged 25, where he worked in molecular physics; became a scientific adviser to the British government at the outbreak of World War Two

Author of 11-volume Strangers and Brothers sequence of novels, and the non-fiction work The Two Cultures And the Scientific Revolution (1959), in which he argued that a gulf had emerged between scientific academics and their counterparts in the humanities, which prevented them from communicating properly with each other

When I first began researching the 19th Century history of the mirror neuron phenomenon, it came as a complete surprise to find references to actors, and theatre trips in scientific journals and laboratory notebooks. There were even descriptions of experiments that to me, sounded more like plays than anything else, with scientists acting out emotions while experimental subjects watched. I had good reason to be intrigued, because before I became a historian of science, I was a theatre director. I found it striking that Victorian scientists were so familiar with what I believed were closely guarded rehearsal room secrets - how actors cry, how to time slapstick for maximum laughs. It got me thinking about the role theatre has played in shaping how we think today about the human mind and body.

The story of mirror neurons does not begin in the 1990s with the work of those Italian neuroscientists, but at the beginning of the 19th Century. This was the first time that human mimicry became a serious scientific topic, the first time people spoke of it as having a biological basis - or in today's terms, being "hard-wired". It was also the first time those difficult philosophical questions about identity and agency were raised. This history is largely hidden today. But what has been completely obscured is the role that theatre played in helping scientists understand why we imitate one another. That is what I want to talk about today.

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We can't all put ourselves into an fMRI scanner in the hope of seeing our mirror neurons dance. But we can re-create an examination that would have been performed in drawing rooms up and down the country in the first decades of the 1800s. At this time, there was a craze for reading personality traits by examining the lumps and bumps on a person's head. The new science was called phrenology. Its founder, the German physician Franz Joseph Gall, argued that distinct organs in the brain controlled qualities like intelligence and acquisitiveness - the larger the organ, the more it pushed out into the skull to form a lump. Gall believed in an Organ of Imitation, and if you're ready for a little experiment you can try to locate yours now. Run your fingers from the middle of your forehead to the highest point of your skull. And then move them about an inch to the left. If you feel a lump or a ridge, you're the owner of an enlarged Organ of Imitation. It's not good news, I'm afraid - at least, that's what Gall believed. He had turned to actors for proof of the organ's existence - palpating the skulls of the leading thespians of his day, poring over portraits of Shakespeare and Garrick. But he'd also found it on the heads of conmen in prison, and naughty children who mimicked their teachers. A talent for imitation might make you popular, but it could land you in trouble. Mimics, after all, are shape-shifters. And Gall, and his fellow Victorians, believed they were not to be trusted.

Find out more The Human Copying Machine will be recorded at BBC Radio 3's Free Thinking Festival at Sage Gateshead on 1 November, broadcast on BBC Radio 3 on Monday 3 November at 22.45 GMT and will be available for 30 days afterwards on BBC iPlayer. Tiffany Watt-Smith is a BBC Radio 3 and Arts & Humanities Research Council New Generation Thinker.

By the middle of the 19th Century, phrenology was largely discredited. But the copying instinct continued to intrigue scientists who were beginning to see human behaviour in the terms of an emerging evolutionary theory. In the 1830s, as he sailed along the coast of Tierra del Fuego, Charles Darwin had observed that the native people were skilled impersonators. He and the crew carried out ad hoc experiments - coughing and yawning (and in some cases, gurning and squinting) and watching gleefully as the natives on shore copied them. If Gall had studied actors to confirm his organ of imitation, Darwin and his crew became performers themselves - striking poses to elicit an imitative response. Darwin's description of the experiment betrayed a hierarchy between two sorts of theatricality. While the Europeans were shown to be in control of their impersonations, the "savages" as Darwin called them, were framed as mechanical imitators, ludicrous in their helpless repetitions. Such depictions suggested to Victorian men of science that imitation was an atavistic impulse, and confirmed their widely-held belief that some people lacked the will-power to discipline their unruly, primitive bodies. Among hysterical women in asylums, and the so-called "lower races", who were exhibited in travelling human zoos, compulsive imitation was seen as a striking peculiarity.

In the 1880s, the sciences of mind entered a more modern phase. Describing themselves as psychologists, a new generation argued their discipline demanded the same empirical rigour as chemistry or physics. They set up laboratories, the first one being at UCL in 1898. But theatre did linger, both as an experimental technique and a source of anxiety. Because it was at this moment that psychologists started to notice that involuntary imitation might not be confined to the irrational and weak after all.

Theatres were again the scene of their discoveries. Psychologists visited music halls, and sensed that their own eyeballs leapt when the acrobats sprang from their boards, that their bodies leaned along with that of a tightrope walker. Such self-experiments spawned a theory that mimicry was the basis of aesthetic pleasure. German physiologists dubbed the phenomenon Einfuehlung, and English psychologists translated it as "empathy" - a coinage which originally meant the body's mimetic responses to artworks, and only later a kind of emotional resonance between people.

Image copyright Getty Images Image caption Actress Sarah Bernhardt (1844 - 1923) cries during a performance

Alongside this new science of aesthetics, imitation was also seen as the foundation of communities, national identity, and even altruism. This was a dramatic about-turn. By 1895, the American psychologist William Baldwin - foreshadowing the hyperbole of today's claims about mirror neurons - could declare the human brain to be a "repeating organ", and the body a "veritable copying machine".

This is not to say that the earlier connection between mimicry and deviancy disappeared entirely. If actors continued to play an important role in experiments, they brought with them a nervousness about what being a copying machine might mean. While some psychologists went to the music hall, others followed in Darwin's footsteps, and became actors themselves. James Sully, one of the pioneers of scientific psychology in Britain, saw no contradiction between theatrical performances and empirical experiments. In his book Studies of Childhood, published in 1898, he described a father trying to elicit a mimic response from his year-old son. The father indulges in a bit of amateur dramatics. He pretends to cry, at which the boy becomes similarly distressed. "The experiment was repeated" writes Sully. This language surprises me - to find Sully, a moderniser, calling this obviously theatrical performance an experiment. It's not that he hadn't noticed its similarity to theatre - a few lines later, he describes it as a "curious little play". A "play" and an "experiment". No "two cultures" then, for Sully. It seems he thought a scientist could also be a performer, faking his emotions, and then peeking out from between his fingers, like a bad actor, to check the response of his tiny audience.

James Sully 1842-1923

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English psychologist and professor of philosophy at University College, London

Born near Bristol, Sully studied philosophy at universities in Germany

His most important textbook was titled The Human Mind; his friends included GH Lewes, Mary Anne Evans (George Eliot) and the psychologist William James

Theatre may have been an integral part of late 19th Century scientific practice, but it also shaped the way psychologists thought about mimicry. This is not so unexpected. One of the insights of historians of science in the last few decades is that experimental techniques shape scientific ideas. An obvious example is the way technologies give birth to metaphors which help us conceptualise the body. We only talk of bits of the brain "lighting up" for instance, because of the vividly coloured blobs in computer-generated images of the brain. What is actually detected in fMRI scans is miniscule alterations in the composition of blood at a sub-atomic level - nothing is alight at all. But machine and metaphor collide to reframe the way we imagine our bodies.

In late 19th Century scientific writing about mimicry, theatrical metaphors are certainly hard to miss. But they don't always arrive in uncomplicated forms. Sully, for instance, on one page writes admiringly that children are "little actors", then on the next that impersonation is the root of adult insincerity and deceit. He quotes actors who claim that pretending to cry made them feel sad but then, in a footnote, gets cold feet. Perhaps the emotions actors think they're feeling are simply the efflorescence of their over-active imaginations. To me, these contradictions and hesitations in Sully's text hint at his deeper queasiness about the implications of his theory. If we are compelled to copy, how can we be authentic at all?

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As is the case with today's debate on mirror neurons, these problems were played out in technicolour by the period's novelists. In HG Wells's "The Sad Tale of the Dramatic Critic", a shy young journalist called Cummins is - despite never having set foot in a theatre in his life - appointed his paper's new drama critic. When the curtain rises on his first theatrical outing, he's horrified - the actors are dreadful, with their "melodius snortings" and "agonizing yelps". The following morning in the bathroom mirror, Cummins is astonished to see he's assumed a peculiar pose. His left hand is flung up, fingers extended, his right clutched at his diaphragm. He starts bowing to strangers. His fiancee Delia is disgusted, and breaks off their engagement - but all Cummins can do is clasp his hand to his brow. All that remains of the old Cummins is a dreadful, capering creature, who lacks all depth of feeling.

It's this very predicament which has raised its head again today. But perhaps the furore over mirror neurons will fizzle out - just as the excitement over the human copying machine in the 1890s had lost momentum by the turn of the century. But even if it does, the Victorian engagement with human mimicry will remain important - not just because it foreshadows our own concerns, but also because of the theatrical techniques scientists used to study involuntary imitation. In Britain today, the idea of two cultures still prevails, with clear public policy implications. I worry about hierarchies of knowledge which place science at the top, and drama somewhere near the bottom, for many reasons. Not just because of the intellectual and practical skills developed through studying drama, but also because knowledge is not created in a disciplinary vacuum.

Theatre and science may seem like incompatible fields of endeavour. Yet, the history of mimicry shows that actors and acting helped shape scientific understanding of the human mind, laying the foundations for our own neuroscientific theories. In those early years of scientific psychology, theatre was a vital part of laboratory life.

And if you look close enough, you might find that it still is.

Listen to The Human Copying Machine on BBC Radio 3 on Monday 3 November at 22.45 GMT or catch up afterwards on BBC iPlayer.

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