Wall Street Journal 3/4/05
by Sharon Begley
As the argument at the bar grows more heated, you notice that you're right in the flight path should the ranting man decide to turn glassware into missiles. You watch tensely as he clasps and unclasps the tumbler in front of him, and then suddenly his grip changes. Is he about to take a gulp...or fire the glass in your direction?
If you duck just as it sails over your head, you can thank a cluster of neurons whose existence scientists didn't even know about a few years ago: mirror neurons.
Their modest name reflects their most obvious function but hardly does justice to their talents, which neuroscientists seem to uncover mnore [sic] of every time they look - from intuiting[doesn't exist] other people's intentions to feeling their pain. Literally.
"Mirror neurons promise to do for neuroscience what DNA did for biology," neurobiologist V.S. Ramachandran of the University of California, San Diego, has written, explaining "a host of mental abilities that have remained mysterious."
In 1992, biologists at the University of Parma, Italy, were probing the brains of macaque monkeys when they made a curious discovery. It had been known for years that brain cells in the premotor cortex, the area that plans movements, fire right before the monkey grasps, manipulates or reaches for something such as fruit. But it turns out that these specialized neurons also fire when the monkey sees someone else (monkey or human) do so. Whether planning a movement or seeing one, mirror neurons fire the same way: The firing pattern that precedes, say, the monkey's lifting a raisin to its mouth is identical to the pattern when it sees someone else doing that.
The human brain has mirror neurons, too, and recently neuroscientists have been behaving like Egyptologists after the discovery of the Rosetta Stone: using mirror neurons to explain a backlog of enigmas.
For one thing, mirror neurons may be how we understand the intentions of other people, a crucial social skill whether or not you frequent fight-prone bars. In a new study, neuroscientists scanned the brains of volunteers while they watched videos of a hand reaching for a mug. In one clip, the mug sat in a neat arrangement of teapot, mug, pitcher of milk, and plate of cookies; in another, it sat amid a knocked-over pitcher, used napkin and cookie crumbs; in a third the mug sat alone.
If the only thing mirror neurons do is fire when they see someone perform a movement, the volunteers' brains should have shown the same activity whether the hand was reaching for the mug as if to drink, in the first scene, to clean up in the messy scene or with no context. But that's not what happened. As Marco Iacoboni of UCLA and colleagues report in the March issue of PLoS Biology, mirror neurons were only a little active when the hand grasped the lone mug. But they perked up when the hand reached for the cup as if to drink from it (in preparty mode) or to wash it (post party).
"This suggests that mirror neurons do not simply recognize actions but are also involved in decoding people's intentions," says Prof. Iacoboni. "People seem to have specific neurons that code the 'why' of some action, predicting the behavior of others."
And that makes social interactions possible. At the annual meeting of the American Association for the Advancement of Science [ 1 ] (AAAS) last month, researchers said that because these neurons fire both when we see someone move as when we move ourselves, they make equivalent "what others do and feel and what we do and feel." We do not just see an action; we also experience what it feels like to someone else.
Mirror neurons "re-create the experience of others within ourselves," as UCLA's Mark Thompson put it in his AAAS remarks. They "allow us to put ourselves in the shoes of another." That makes them the neural basis of empathy.
"To function well with other people, we need to understand where they're coming form so as not to misread their intentions," says Regina Pally, a psychotherapist in Los Angeles and a clinical professor at UCLA. "Mirror neurons are what let us understand others' emotions." In fact, mirror neurons in people are connected to the brain's emotion region, the limbic system: When your mirror neurons fire in a reflection of someone else's, it triggers empathic emotions.
Mirror neurons also let us feel another person's pain. The same cortical neurons that process the sense of touch also fire when you see someone else touched. And a region that registers disgust that you feel directly also fires when you see expressions of disgust on others (hence the vesceral wallop of "Fear Factor").
Instead of merely seeing what other people do and feel, said Christian Keysers of the University of Groningen, the Netherlands, "we start to feel their actions and sensations in our own cortex as if we would be doing these actions and having those sensations."
Except when we don't. In children with autism, "there may be a deficit in the mirror-neuron system," says Prof. Iacoboni, which may explain why they are unable to infer the mental state and intentions of others. Without mirror neurons to serve as bridges between minds, everyone seems like a cipher.