How Brain's 'Mirrors' Aid Our Social Understanding
Monday, September 25, 2006
Whenever my editor approaches me, I quickly size up his body language before he has said a word. If he looks genial and relaxed, he probably liked my story. If his face looks set and determined, I know a wrangle over copy is probably ahead.
Human beings are exquisitely attuned to social cues and the behavior of others. Such signals tell us what is ahead and give us time to prepare. They tell us about many things that are never explicitly articulated in everyday life. Much of the time, in fact, we do not appreciate how skilled we are at reading social situations. We only realize how ingrained our ability to read social cues is when we see people with serious deficits in social awareness, such as people with autism or schizophrenia.
One of the most intriguing theories to emerge in recent years about how our brains perform these feats -- far beyond the ability of the most powerful supercomputers -- is that we have neurons in our brains that essentially act as mirrors of people around us. When we see someone scratch his head or furrow her brow, we instantly have a sense of their mental state, because those actions trigger an equivalent pattern of neural activity in our own minds and allow our brains to quickly deduce the other person's mental state.
"These mirror systems give us a fast and intuitive idea of what is going on," said neuroscientist Christian Keysers at the University of Groningen in the Netherlands. "If I hear a rhythmic squeak in the hotel room next door, I quite intuitively get a sense of what is going on in there without having to do much thinking. Much of our social understanding is at this level. If I see you grab a hamburger, I know you are hungry. There are so many things we intuitively understand without much thought."
This is why, Keysers added, a radio commercial can be highly evocative even though all you hear is the sound of a can being opened, a liquid being poured into a glass filled with tinkling ice cubes, followed by a contented "Ahh!" The mirror system allows us to virtually experience that soft drink as if it were in our own hands.
Three new studies published independently last week in the journal Current Biology have yielded new insights into "mirror neurons" and point the way to two intriguing conclusions: The mirror system seems to be involved in the human capacity for language, and people with stronger mirror neuron responses to sounds seem to also have a larger capacity for empathy, suggesting the mirror system is part of the brain mechanisms that produce altruistic behavior.
Keysers and his colleagues placed volunteers in fMRI scanners that monitor the activity of distinct regions of the brain and played sounds related to hand actions, such as the noise made by a piece of paper being torn or a zipper being opened. The experiment, led by Valeria Gazzola at Groningen, found that the systems of mirror neurons activated by the sounds were also active when the volunteers tore a piece of paper themselves.
"The actions of other people stop just being a sound out there in the world and acquire meaning because you associate them with your own actions," Keysers said in a telephone interview.
The experiment leads to a question that would normally seem absurd: If the same brain systems light up when a person performs an action as when she watches someone else do it, how does the person know who actually did it?
In a separate experiment focusing on this rather metaphysical question, researchers led by Simone Schuetz-Bosbach at University College London, found that mirror systems in the brain allowed people to distinguish between the actions of another person and their own. In fact, the mirror systems seem to be activated only in social contexts -- they are designed to pay attention to those around us.
"It is a very important social function," she said. "You have to understand other people in order to predict what they are going to do."
In a third experiment led by Lisa Aziz-Zadeh, who is now at the Brain and Creativity Institute at the University of Southern California, volunteers were placed in an fMRI scanner while watching videos of hand, foot and mouth movements. Researchers observed which mirror systems responded. Next, the volunteers read descriptions of the same actions, and the researchers saw that the same systems were activated.
What this implies, said Aziz-Zadeh, is that human language may depend in part on the activation of mirror systems in the brain.
"The word 'cup' might activate the motor plan for grasping the handle for a cup," said Arthur Glenberg, a cognitive psychologist at the University of Wisconsin at Madison, who has studied mirror neurons and wrote a commentary about the new experiments. "The word 'give' may activate the plan for stretching out the hand with the thumb touching the index finger and then opening the fingers."
This means that at least some aspects of language may be rooted in a very physical understanding of the world, the way we see and touch and feel things. It helps address a long-standing puzzle about language: How do we understand what words mean? If words are defined only by other words, what does the whole deck of cards rest on?
The new research suggests that language may depend at least in part on representations in the brain of the physical world, a much more concrete way to conceptualize language. When we hear words, we essentially act out their meanings in our own minds.
"If we empathize with other human beings because of mirror neurons rather than rules, I know what it is for you to be sad because I know what it is to be sad myself," Glenberg said. "When I see you hurt, my mirror neuron system is responding; it is giving me a sense of pain."
And by removing complex thinking from the ledges of abstraction and rooting it in the physical world, the research also helps show how the physical brain can produce the ephemera of thought. To Glenberg, it suggests that humans are far from alone in being sophisticated thinkers. Research has shown -- in some ways more convincingly than in humans -- the role of mirror neurons in other animals.
"In fact, when I started investigating these things, I became a vegetarian," Glenberg said. "It became clear to me as a consequence of these theories of embodied cognition that virtually all animals are thinking, and it is difficult to draw a line between those who are thinking and those who aren't."