The Mirror Neuron Revolution: Explaining What Makes Humans Social

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Neuroscientist Marco Iacoboni discusses mirror neurons, autism and the potentially damaging effects of violent movies.

Marco Iacoboni, a neuroscientist at the University of California at Los Angeles, is best known for his work on mirror neurons, a small circuit of cells in the premotor cortex and inferior parietal cortex. What makes these cells so interesting is that they are activated both when we perform a certain action—such as smiling or reaching for a cup—and when we observe someone else performing that same action. In other words, they collapse the distinction between seeing and doing. In recent years, Iacoboni has shown that mirror neurons may be an important element of social cognition and that defects in the mirror neuron system may underlie a variety of mental disorders, such as autism. His new book, Mirroring People: The Science of How We Connect to Others, explores these possibilities at length. Mind Matters editor Jonah Lehrer chats with Iacoboni about his research.

LEHRER: What first got you interested in mirror neurons? Did you immediately grasp their explanatory potential?

IACOBONI: I actually became interested in mirror neurons gradually. [Neuroscientist] Giacomo Rizzolatti and his group [at the University of Parma in Italy] approached us at the UCLA Brain Mapping Center because they wanted to expand the research on mirror neurons using brain imaging in humans. I thought that mirror neurons were interesting, but I have to confess I was also a bit incredulous. We were at the beginnings of the science on mirror neurons. The properties of these neurons are so amazing that I seriously considered the possibility that they were experimental artifacts. In 1998 I visited Rizzolatti's lab in Parma, I observed their experiments and findings, talked to the anatomists that were studying the anatomy of the system and I realized that the empirical findings were really solid. At that point I had the intuition that the discovery of mirror neurons was going to revolutionize the way we think about the brain and ourselves. However, it took me some years of experimentation to fully grasp the explanatory potential of mirror neurons in imitation, empathy, language, and so on—in other words in our social life.

LEHRER: Take us inside a social interaction. How might mirror neurons help us understand what someone else is thinking or feeling?

IACOBONI: What do we do when we interact? We use our body to communicate our intentions and our feelings. The gestures, facial expressions, body postures we make are social signals, ways of communicating with one another. Mirror neurons are the only brain cells we know of that seem specialized to code the actions of other people and also our own actions. They are obviously essential brain cells for social interactions. Without them, we would likely be blind to the actions, intentions and emotions of other people. The way mirror neurons likely let us understand others is by providing some kind of inner imitation of the actions of other people, which in turn leads us to "simulate" the intentions and emotions associated with those actions. When I see you smiling, my mirror neurons for smiling fire up, too, initiating a cascade of neural activity that evokes the feeling we typically associate with a smile. I don't need to make any inference on what you are feeling, I experience immediately and effortlessly (in a milder form, of course) what you are experiencing.

LEHRER: In 2006 your lab published a paper in Nature Neuroscience linking a mirror neuron dysfunction to autism. How might reduced mirror neuron activity explain the symptoms of autism? And has there been any progress on this front since 2006?

IACOBONI: Patients with autism have hard time understanding the mental states of other people; this is why social interactions are not easy for these patients. Reduced mirror neuron activity obviously weakens the ability of these patients to experience immediately and effortlessly what other people are experiencing, thus making social interactions particularly difficult for these patients. Patients with autism have also often motor problems and language problems. It turns out that a deficit in mirror neurons can in principle explain also these other major symptoms. The motor deficits in autism can be easily explained because mirror neurons are just special types of premotor neurons, brain cells essential for planning and selecting actions. It has been also hypothesized that mirror neurons may be important in language evolution and language acquisition. Indeed, a human brain area that likely contains mirror neurons overlaps with a major language area, the so-called Broca's area. Thus, a deficit in mirror neurons can in principle account for three major symptoms of autism, the social, motor and language problems.

LEHRER: If we're wired to automatically internalize the movements and mental states of others, then what does this suggest about violent movies, television programs, video games, etcetera? Should we be more careful about what we watch?

IACOBONI: I believe we should be more careful about what we watch. This is a tricky argument, of course, because it forces us to reconsider our long cherished ideas about free will and may potentially have repercussions on free speech. There is convincing behavioral evidence linking media violence with imitative violence. Mirror neurons provide a plausible neurobiological mechanism that explains why being exposed to media violence leads to imitative violence. What should we do about it? Although it is obviously hard to have a clear and definitive answer, it is important to openly discuss this issue and hopefully reach some kind of "societal agreement" on how to limit media violence without limiting (too much) free speech.

LEHRER: Are you worried about mirror neurons getting over-sold or over-hyped?

IACOBONI: I am a bit concerned about that. The good news is, the excitement about mirror neurons reveals that people have an intuitive understanding of how neural mechanism for mirroring work. When told about this research, they can finally articulate what they already "knew" at some sort of pre-reflective level. However, the hype can backfire and mirror neurons may lose their specificity. I think there are two key points to keep in mind. The first one is the one we started with: mirror neurons are brain cells specialized for actions. They are obviously critical cells for social interactions but they can't explain non-social cognition. The second point to keep in mind is that every brain cell and every neural system does not operate in a vacuum. Everything in the brain is interconnected, so that the activity of each cell reflects the dynamic interactions with other brain cells and other neural systems.

Mind Matters is edited by Jonah Lehrer, the science writer behind the blog The Frontal Cortex and the book Proust was a Neuroscientist.

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