Back in the 1990s neuroscientists at the University of Parma identified cells in the premotor cortex of monkeys that had an unusual response pattern. They were activated when the monkeys performed a given action and, mirror-like, when they saw another individual perform that same movement. Since then, the precise function and influence of these neurons has become perhaps the most hyped topic in neuroscience.
In 2000, Vilayanur Ramachandran, the charismatic neuroscientist, made a bold prediction: “mirror neurons will do for psychology what DNA did for biology.” He's at the forefront of a frenzy of excitement that has followed these cells ever since their discovery. For many, they have come to represent all that makes us human.
Perhaps, in those early heady years, Ramachandran was just getting a little carried away? Not at all. For his 2011 book, The Tell-Tale Brain, Ramachandran took his claims further. In the chapter “The neurons that shaped civilisation”, he argues that mirror neurons underlie empathy, allow us to imitate other people, that they accelerated the evolution of the brain, that they help explain the origin of language, and most impressively of all, that they prompted the great leap forward in human culture that happened about 60,000 years ago.
“We could say mirror neurons served the same role in early hominin evolution as the Internet, Wikipedia, and blogging do today,” he concludes. “Once the cascade was set in motion, there was no turning back from the path to humanity.”
Ramachandran is not alone. Writing for The Times (London) in 2009 about our interest in the lives of celebrities, the eminent philosopher AC Grayling traced it all back to those mirror neurons. “We have a great gift for empathy,” he wrote. “This is a biologically evolved capacity, as shown by the function of ‘mirror neurons’.” In the same newspaper this year, Eva Simpson wrote on why people were so moved when Tennis champ Andy Murray broke down in tears. “Crying is like yawning,” she said, “blame mirror neurons, brain cells that make us react in the same way as someone we’re watching (emphasis added)”. In a New York Times article in 2007, about one man’s heroic actions to save another, those cells featured again: “people have ‘mirror neurons,’” Cara Buckley wrote, “which make them feel what someone else is experiencing (emphasis added)”.
If mirror neurons grant us the ability to empathise with others, it follows that attention should be drawn to these cells in attempts to explain why certain people struggle to take the perspective of others – such as can happen in autism. Lo and behold the “broken mirror hypothesis” of autism.
The ubiquitous idea that mirror neurons “cause” us to feel other people’s emotions can be traced back to the original context in which they were discovered – the motor cells in the monkey brain that responded to the sight of another person performing an action. This led to the suggestion that mirror neurons play a causal role in allowing us to understand the goals behind other people’s actions. By representing other people’s actions in the movement-pathways of our own brain, so the reasoning goes, these cells provide us with an instant simulation of their intentions – a highly effective foundation for empathy.
It’s a simple and seductive idea. What the newspaper reporters (and over-enthusiastic neuroscientists) don’t tell you is just how controversial it is. The biggest and most obvious problem for anyone advocating the idea that mirror neurons play a central role in our ability to understand other people’s actions, is that we are quite clearly capable of understanding actions that we are unable to perform.
A non-player tennis fan who’s never held a racket doesn’t sit baffled as Roger Federer swings his way to another victory. They understand fully what his aims are, even though they can’t simulate his actions with their own racket-swinging motor cells. Similarly, we understand flying, slithering, coiling and any number of other creaturely movements, even if we don’t have the necessary motor cells to simulate them. From the medical literature there are also numerous examples of comprehension surviving after damage to motor networks – people who can understand speech, though they can’t produce it; others who recognise facial expressions, though their own facial movements are compromised. Perhaps most awkward of all, there’s evidence that mirror neuron activity is greater when we view actions that are less familiar – such as a meaningless gesture – as compared with gestures that are imbued with cultural meaning, such as the victory sign.
Mirror neuron fans generally accept that action understanding is possible without corresponding mirror neuron activity, but they say mirror neurons bring an extra depth to understanding. In a journal debate published this year in Perspectives in Psychological Science, Marco Iacoboni insists mirror neurons are important for action understanding, and he quotes others saying how they allow “an understanding from within”. Critics in the field believe otherwise. Gregory Hickok at the University of California Irvine thinks the function of mirror neurons is not about understanding others’ actions per se, but about using others actions’ in the process of making our own choice of how to act. Seen this way, mirror neuron activity is just as likely a consequence of action understanding, as a cause.
What about the grand claims that mirror neurons played a central role in accelerating human social and cultural evolution by making us empathise with each other? Troublesome findings here include the fact that mirror neurons appear to acquire their properties through experience. Research by Cecelia Heyes and others has shown that learning experiences can reverse, nullify or exaggerate mirror-like properties in motor cells. It can’t reasonably be claimed that mirror neurons made us imitate and empathise with each other, if the way we choose to behave instead dictates the way our mirror neurons work. On their role in cultural evolution, Heyes says mirror neurons are affected by cultural practices, such as dancing and music, just as much they influenced them.
Finally, what about the suggestion that mirror neurons play a role in autism? It’s here that the hype is probably the least justified. There are numerous findings showing that people with autism have no problem understanding other people’s actions (contrary to the broken mirror hypothesis) and that they show normal imitation abilities and reflexes. For a new review paper, Antonia Hamilton assessed the results from 25 relevant studies, concluding: “there is little evidence for a global dysfunction of the mirror system in autism.”
Motor cells that respond to the sight of other people moving are intriguing, there’s no doubt. It’s likely they play a role in important social cognitions. But to claim that they make us empathic, and to raise them up as neuroscience’s holy grail, as the ultimate brain-based root of humanity, is ridiculous. The evidence I’ve mentioned is admittedly somewhat biased, designed to counteract the hype and show just how much debate and doubt persists. In fact, the very existence of mirror neurons in the human brain is still disputed by some. That’s where we’re at with the study of these cells. We’re still trying to find out whether they exist in humans, where they are, and what exactly it is they do. Mirror neurons are fascinating but they aren’t the answer to what makes us human.
Update December 2013: A new review paper has provided a sober assessment of what we currently know about mirror neurons.