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To Keysers, this makes sense. The somatosensory cortex, after all, is the region of the brain that responds to sensations registered by the skin--among them tickling, itching, tingling and burning. It's why, says Keysers, our skin seems to crawl when we watch James Bond in Dr. No and see the tarantula creeping up Sean Connery's chest. Likewise, our emotional reactions to such scenes may well be crafted by mirror responses in still other brain regions. Among these, one of the most interesting is the insula, a complex structure that integrates sensory with visceral information. For example, as Keysers and his colleagues recently demonstrated, exposure to nauseating smells--rancid butter, rotten eggs--activates the same area of the insula as watching a video of an actor who sniffs a glass, then reacts with a grimace that conveys his disgust.
Static images found in photographs, paintings and sculptures can also evoke mirror responses, says the University of Parma's Vittorio Gallese, one of the researchers who participated in the original macaque experiments. Gallese is now collaborating with Columbia University art historian David Freedberg on a project that will explore the link between mirror activity and aesthetic experience. "Go to the Borghese Gallery and look at Bernini's Rape of Proserpina," Gallese suggests. "Even though the statue is made of marble, one of the coldest materials on earth, it conveys a vivid impression of carnality. Or look at Goya's Disasters of War, with its excruciating images of lacerated bodies. The powerful emotional resonance we get is due, in part, to our empathetic reaction to pain."
That mirroring of pain does occur seems clear. A study undertaken by researchers at University College London recently showed that the mere thought that a loved one's hand is receiving an electric shock lights up many of the same brain areas as shocks that are directly experienced.
It may even be, as Gallese and others have proposed, that mirroring is a general mechanism for grasping the feelings of others and sharing their moods. "It's why, even though we are trapped in ourselves, we can have a good understanding of other people," says Iacoboni. Once again, it appears that the cues can be auditory as well as visual. For example, prosody, the melodic component of human speech, is one of the ways people convey information about their continuously shifting emotional states. Aziz-Zadeh's da-da-da-da-da experiment, in fact, is designed to pinpoint the brain areas that house the prosody mirror circuitry.
THE ROOTS OF EMPATHY
NEURONS WITH MIRROR PROPERTIES ARE NOT SPECIAL IN ANY obvious sense. Under a microscope, they look like other neurons. What makes them special is the web of connections that link neurons in the motor and sensory systems to the limbic centers that process visceral and emotional reactions. And while some of these connections may well be in place at birth, they are, neuroscientists think, vastly expanded through experience. A baby smiles. Her mother smiles back. Click. The brain sets up a circuit linking the motor system that turns up the corners of the baby's mouth to the visual image of the smiling mother to the emotional state we call happiness.