Mirror, mirror, in the brain
In the mid-1990s, researchers at the University of Parma in Italy were investigating motor neuron activity in the brains of macaque monkeys. They placed electrodes on the premotor cortex, a region of the brain which controls movement. Then they recorded activity in the brain when the monkey grabbed a peanut, noting how its neurons reacted when it carried out this particular action. During the experiment, the researchers, led by Prof Giacomo Rizzolatti and Prof Vittorio Gallese, noticed something surprising. Some of the neurons they were monitoring responded not only when the monkey performed a certain action, but also when the monkey watched that action being performed. So, for example, the same neurons that responded when the monkey grasped a peanut, also responded when the monkey watched one of the researchers grasp a peanut.
The researchers dubbed these newly-discovered neurons mirror neurons because of the way they apparently mirrored an observed action in the monkey's brain. When subsequent research found corresponding results in humans, these tiny cells were hailed as "one of the most important findings in neuroscience in the last decade". Indeed, mirror neurons are an amazing discovery, important not just for neuroscientists but for us all. They are the first neurological findings that help us start to unravel how humans interact socially.
"It is the discovery of the most basic building block that allows us to understand vicariously or empathically the actions of other people", says Dr Mary Helen Immordino-Yang, assistant professor of psychology at the Brain and Creativity Institute in Los Angeles. Thanks in part to their evocative name, mirror neurons have been posited as the answer to long-standing questions on subjects as wide ranging as art appreciation, empathy, language, imitation, mind-reading and autism.
Yet mirror neurons themselves are not special neurons. Their distinctiveness comes from their location in the brain, between mechanisms for perception and mechanisms for action. "What they do," says Dr Immordino-Yang, "is enable a convergence between the motor planning that your brain would do to produce the actions that you see another person doing and the perception mechanisms that allow you to actually perceive what the other person is doing."
Since mirror neuron activity is believed to create a simulation of the activity being observed in the observer's brain, the observer seems to gain a deeper understanding of a particular movement through simulation rather than through inference. Looked at in this way, the mirror neuron system emerges as the most basic, low-level system in the brain by which humans impute a goal to the actions of another human being and then understand the actions as if they were their own.
Significantly however, these neurons do not, as their name suggests, mirror the observed world. "The word 'mirror' is actually misleading," says Dr Immordino-Yang. "Mirror neurons are not mirrors. It's not that they just automatically reflect what is going on in front of you." The triggers, it turns out, are in the neurons of the beholder. For your mirror neurons to function, you have to know something about the action you are observing and its meaning.
Dr Daniel Glaser, a cognitive neuroscientist at University College London, conducted a ground-breaking study on this subject using contrasting dance styles. Dancers from the Royal Ballet in London and dancers of capoeira, a martial art form from Brazil, watched videos of ballet dancers and capoeira dancers performing. The mirror neuron systems of the ballet dancers showed more activity when watching ballet dancers, while the mirror neuron systems of the capoeira dancers showed more activity when watching capoeira dancers. In other words, the mirror neuron system functions differently depending on your particular physical expertise.
"We think that this is a form of resonance," said Dr Glaser in an interview about the study. "That your own motor control cortex is more excited when you see other people doing moves that you can do." Exactly how these mirror neuron systems work and what happens in the brain when they are triggered is still being investigated. "Nobody really knows," says Dr Immordino-Yang. "The activation of these neurons is only the very first, low-level step in being able to understand somebody else's actions. You then call up all kinds of experiences that you've had in similar contexts, what they mean, how you evaluated them emotionally, how you remembered them and what happened next. You use all that information to extrapolate beyond."
In all likelihood, this process happens very quickly and involves not just mirror neurons but many parts of the brain. "You have to understand the action of these mirror neuron systems as falling into a bigger paradigm about the role of action and mental action in understanding the world in general," says Dr Immordino-Yang. As Antonio Damasio and Kaspar Meyer wrote in an article in Nature in July 2008: "The neurons at the heart of this process ... are not so much like mirrors, after all. They are more like puppet masters, pulling the strings of various memories."
Whatever their name and however these neurons function, the research underway has far-reaching implications for our understanding of, among other things, the way we appreciate art and engage with films, theatre and television. After all, mirror neuron activity may be most pronounced when people are face to face, but it does occur when we observe actions, in any format, about which we understand the implicit goal.
However, science has yet to reach this complex level of understanding about how mirror neuron systems work. "We are still working on very basic questions," says Dr Immordino-Yang. "For example, people who are subjectively more empathetic, more in tune with the people around them, do they have more mirror-neuron activity compared with people who aren't when they are just watching a certain action, such as somebody lifting a tea cup?"
One thing is certain, unravelling how mirror neuron systems work and their connections with other parts of the brain is a key to understanding the relationship between what we see and what we do. firstname.lastname@example.org
Updated: November 5, 2008 04:00 AM