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Mirror Neurons
Posted on 8 May 2008 by Mario Alemi
In 1992, three Italian researchers from Parma, Italy, were studying the motor cortex of monkeys’ brains – a region that until then was supposed to deal exclusively with movement. Through electrodes implanted in the brain, they could “see” neurons firing when the monkey did a simple action, like grasping for food. The surprise came when the monkey’s neurons fired as one of the researchers reached for his own food.
Further research revealed the true nature of these neurons. If the researcher put his hand in a box containing a banana, the neurons fired. If the box was empty, and the monkey knew it, the neurons did not fire. Putting a hand in a box is the same movement, whether or not there is a banana – but is not the same action. The monkey understands, through these new kind of neurons, that the researcher is going to grab a banana. The monkey can build “a true representation in the brain of the action itself”, as the scientists wrote recently in Science magazine. It was not a mere observation of the movement: it was the understanding of the action that made the neurons fire.
The neurons were then called Mirror Neurons and have been regarded with increasingly more interest by the community of neuroscientists around the world. They have recently been said to be for psychology what DNA is for biology. This year, the three researchers – Giacomo Rizzolatti, Vittorio Gallese and Leonardo Fogassi – received the Grawemeyer award for psycology.
From imitation to language
It was Professor Vilayanur Ramachandran, director of the Center for Brain and Cognition at the University of California San Diego, who in 2000 drew a parallel between DNA and mirror neurons. The title of his essay “Mirror Neurons and imitation learning as the driving force behind the great leap forward in human evolution” is self-explanatory: in Mr Ramachandran’s opinion, “they can provide a unified framework [in psychology] and help explain a host of mental abilities that have hitherto remained mysterious and inaccessible to experiments.”
Mr Ramachandran is only one of the most prominent scholars who looked at mirror neurons as the discovery of the century – why so much excitement? Because mirror neurons, apparently, are responsible for the comprehension of what other people do. When someone else smiles, our cortex runs a simulation of the expression, making other parts of our brain understand the message: “I know what you are doing”, says the brain, “because I do the same in similar conditions”.
It is possible to understand the message behind the smile because the same mirror neurons activated in our brain when we smile are activated when others smile. There is an empathy that allows us to understand others’ mood with expressions alone. And expressions are proto-language – if we do not speak the same language as someone else, we can use expressions to communicate simple concepts.
The mirror neurons provide a neural basis for some simple interpersonal relations, like communicating happiness through a smile, on which more complex ones are built, like language. “The billion dollar question,” says Richard Ivry, director of the Cognition and Action Laboratory at The University of California, Berkeley, “is to understand if it is possible to link comprehension of actions to language. Few scientists care about how we understand actions”, he says, “but we all care about how we developed language. That is why what really drives the research in mirror neurons is [research into the] development of more abstract thoughts”.
The human Big Bang
In little more than 100,000 years, human beings have become one of the most successful animals on earth. One hundred thousand years ago the human population was about one million, concentrated in Africa. Now we are 6,000 times more and we have colonized the whole planet – plus the moon. How was it possible? Prof Ramachandran and others think that mirror neurons are the key factor to understand the passage from a smart primate to a human being.
Archaeological studies show that around 200,000 years ago, Homo sapiens was genetically very similar to us. Nevertheless the Homo remained all but sapiens (wise) for more than 100,000 years. No advanced tools, no painting, no language… then, suddenly, the first signs of wisdom appeared. About 100,000 years ago “multi-part tools, tailored clothes, art, religious belief and perhaps even language emerged, quite rapidly”, writes Prof Ramachandran.
Prof Rizzolatti wrote that “200,000 years ago Homo sapiens can be characterized by a further evolution of the mirror neuron system, which corresponded to an increased capacity for communication.” But that did not correspond to the immediate invention of the language, for which the humans had to wait some more 100,000 years. For Prof Ramachandran, the mirror neurons originally created the opportunity to have a mimicking culture for Homo habilis (about two million years ago) and then the evolution of language for the Homo sapiens.
While we may see a sudden appearance of culture (technology, religion, politics etc) in the archaeological record, the reality may be different. Culture is knowledge based. The more I know the more I invent. The more the society knows, the more the society will advance. Passing, with the same 1500 cc brain, from a society without tools to a society with complex tools, is the same leap forward as moving from a society with complex tools to one with nuclear bombs. Then, wrote Prof Ramachandran, “inventions like tool use, art, math and even aspects of language may have been invented ‘accidentally’ in one place and then spread very quickly, given the human brain’s amazing capacity for imitation learning and mind reading using mirror neurons.”
“A person growing up, alone, in a cave does not develop any language capacity” said Prof Ramachandran. Mirror neurons are necessary, but not sufficient, to develop language. It is thanks to mirror neurons and to “our species’ remarkable propensity for miming, that any major invention would tend to spread very quickly through the population.”
“Mirror neurons, said Prof Gallese, are physiologically equal to other neurons (a neuron is characterized by its connections with other neurons), and it is not yet clear why 20-25% of the neurons become mirror neurons. It is the revenge of the environment on DNA: we are not what we are, but we are our history,” he said. Developing a brain suitable for language it is not simply a matter of DNA: we must grow up in a society with language. And our society could have developed language through small leaps forward. As said, one person, growing up alone in a cave, would not develop language capability — but nor would ten people. Language appears to be something humanity has built on an increasingly more efficient ability to use the brain to communicate, thanks to mirror neurons.
Communication, the real asset
Spinoza said the human being is a social animal, and we are indeed social, in a very profound way. Human society is built on communication. Without the capacity to exchange information and retain information through generations thanks to language and memory, the human being would be nothing more than a hairless monkey, as Huxley said, with a very low probability of survival. The fact that we are “immersed in a culture that can take advantage of the learnability” makes human society what it is.
Isaac Newton said, quite modestly, that he only “worked on the shoulder of the giants” . Giants like Galileo, who could use the so called “Arabic” numerals, invented by some Indian sapiens and brought to Europe by the Arabs. What Newton meant was that, provided you are smart enough, it is all about exchanging information. Today, huge software applications like the GNU/Linux operating system have been developed thanks to the possibility of exchanging information and knowledge through the Internet.
All this would have not been possible if our progenitors 200,000 years ago had not begun to develop a mirror neuron system capable of giving humanity empathy and language. Prof Gallese, during a conversation from Italy, called the mirror neurons “the collaborative neurons”. Prof Ramachandran, some hours later from India, said that mirror neurons are “the first Internet, built by our brain”. The two academics speak a common language and, just like everybody else, have different media to exchange easily information from any part of the world. Whatever the origin, communication has always played the central role in our society. The Latin words “socius”, friend, and “communem”, obliged to participate, gave rise to the words “society” and “community”. Indeed, the essence of our society was clear to our ancestors, much before any theory of the brain was formulated.
PS1 Prof Ramachandran’s essay was written before mirror neurons could be studied on human beings. But he successfully explained some brain disorders in terms of mirror neuron deficiencies. One disorder was autism. Autistic people have both language disorder and problems in understanding others’ feeling in a social environment. Prof Ramachandran’s group predicted successfully that autism could be related with mirror neuron system, a theory that was finally confirmed in November 2006. Autistic children have a problem in activating their mirror neuron system when observing someone else performing an action. In autistic people, for some reason (either genetic or due to problems of neural development), fewer neurons become mirror neurons.
PS2 The best known theory of how human beings can use language, probably, is Noam Chomsky’s language organ, situated in the brain, which mediates language. According to Prof Chomsky, arguably the most influential linguist of the twentieth century, language is innate. This would explain the ease with which children can learn languages, how different languages have a common “universal grammar” and how it is possible that Creole languages can build a high level grammar after a single generation. The problem with Chomsky’s innateness of language is that, as Prof Ramachandran put it, the language organ “comes out of the blue.” On the other hand, mirror neurons offer a less ad hoc explanation.
PS3 Charles Darwin analyzed the capacity to pass information through expressions. He took as an example the expression of disgust. In The expression of the emotions in man and animals, 1872, Darwin wrote: “Extreme disgust is expressed by movements round the mouth identical with those preparatory to the act of vomiting “. Expression of disgust is a form of language, although a rudimentary language. Our ancestors, Darwin said, would surely have the “power of voluntarily rejecting food”, and understanding the expression of disgust could have saved the life of early primates: a child seeing an adult contracting the muscles that draw the corners of the mouth downwards after lunch would immediately understand that the food was not… that good, and eventually reject it if eaten.
What is amazing is the simplicity with which Darwin goes from the communication through expressions to the communication through language: “We can see that a man is able to communicate by language to his children and others the knowledge of the kinds of food to be avoided…” That means: at a certain point in history, our progenitors began speaking, and a mother could simply tell the child not to eat the food, without expressing particular disgust with her face.
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