Cells That Read Minds (January 10, 2006)
The cells in question are "mirror neurons". They were discovered around 1990 in the laboratory of Giacomo Rizzolatti, a neuroscientist at the University of Parma, Italy. Researchers in the laboratory had been studying brain activity in macaque monkeys.
The monkey brain contains a special class of cells, called mirror neurons, that fire when the animal sees or hears an action and when the animal carries out the same action on its own.
But if the findings, published in 1996, surprised most scientists, recent research has left them flabbergasted. Humans, it turns out, have mirror neurons that are far smarter, more flexible and more highly evolved than any of those found in monkeys, a fact that scientists say reflects the evolution of humans' sophisticated social abilities.
The human brain has multiple mirror neuron systems that specialize in carrying out and understanding not just the actions of others but their intentions, the social meaning of their behavior and their emotions.
"We are exquisitely social creatures," Dr. Rizzolatti said. "Our survival depends on understanding the actions, intentions and emotions of others."
He continued, "Mirror neurons allow us to grasp the minds of others not through conceptual reasoning but through direct simulation. By feeling, not by thinking."
The discovery is shaking up numerous scientific disciplines, shifting the understanding of culture, empathy, philosophy, language, imitation, autism and psychotherapy.
Everyday experiences are also being viewed in a new light. Mirror neurons reveal how children learn, why people respond to certain types of sports, dance, music and art, why watching media violence may be harmful and why many men like pornography.
I highly recommend you go read the whole article yourself at the link given above. It's well worth your time.
I'd like to write a whole book on this set of interrelated issues connected with mirror neurons -- but that would be an investment of a lot more time than I have available at the moment, so I'll just set down a few notes about some of the topics touched upon in Blakeslee's article.
If you'd like a little more background on mirror neurons to begin with, you might try this Wikipedia article. Unfortunately it's rather sketchy and lacks references for most assertions.
However, it does refer to a longer article at Edge by V. S. Ramachandran that was written in early 2000. You might also want to look at the introductory material and especially a discussion of the article by several experts in related fields. You may find the critiques in this discussion to be a bit confusing, as they assume some acquaintance with fields like neuroscience, linguistics, anthropology, and so forth. But if that doesn't scare you off, the discussion is worth reading. You may even wish you could jump in yourself to reply to some of the arguments, especially with an individual like Rafael Nuñez (a rather ideological anti-reductionist).
Also, keep in mind that many of the remarks in the Ramachandran paper are conjectural or speculative. There are many hypotheses about the role that mirror neurons may play in the workings of the human brain. A great deal of work remains for scientific research to confirm or disprove many of these speculations -- probably enough to keep researchers busy for decades. Ramachandran himself has recently been working on some of these questions, as we will see.
Anyhow, let's get back to Blakeslee's article. She summarizes the key property of mirror neurons as follows:
Studies show that some mirror neurons fire when a person reaches for a glass or watches someone else reach for a glass; others fire when the person puts the glass down and still others fire when the person reaches for a toothbrush and so on. They respond when someone kicks a ball, sees a ball being kicked, hears a ball being kicked and says or hears the word "kick."
So mirror neurons are associated with a wide variety of fairly complex actions, where many muscles have to be activated in order to accomplish some intended goal. This idea of "intention" is very important. Blakeslee quotes neuroscientist Marco Iacoboni:
"When you see me pull my arm back, as if to throw the ball, you also have in your brain a copy of what I am doing and it helps you understand my goal. Because of mirror neurons, you can read my intentions. You know what I am going to do next."
This is the sense in which mirror neurons can "read minds" -- some of your mirror neurons respond to seeing another person do something in the same way as the neurons would if you were doing the action yourself. And you are able to detect this neural activity and correlate it with the particular action.
For example, in February 2005 Iacoboni and colleagues published a paper that described research demonstrating that the firing patterns of mirror neurons discriminated between moving a teacup to drink from it or to remove it from the table. See UCLA Neuroscientists Pinpoint New Function For Mirror Neurons. (Here's an earlier study from the same laboratory: UCLA Imaging Study Reveals How Active Empathy Charges Emotions; Physical Mimicry Of Others Jump-starts Key Brain Activity (4/8/03).)
Being able to infer the intentions of other people is an extremely important ability for humans in their social interactions with others. It's a large part of what makes humans such a social species. Think of the importance of being able to tell from the way someone else handles a rock whether he is just studying it or getting ready to throw it at you.
Psychologists describe this ability as being part of a "theory of mind". This is the idea that humans (and possibly a few other animals) recognize that others have minds like their own and that people can make accurate hypotheses about beliefs, desires, intentions, and mental states of others. As a scientific notion, the idea seems to have originated in the 1970s. It seems to have been suggested by various people. The discussion of Ramachandran's article exposes some of the controversy about who gets the credit. Some of the names offered are Nicholas Humphrey, Simon Baron-Cohen, David Premack, and Daniel Dennett. Ramachandran was onto the idea himself at an early stage.
Dennett is also known for extending the idea to his notion of the "intentional stance". As the Wikipedia article says, "To use the intentional stance in explanation one looks at a particular bit of behaviour and ask what beliefs and desires could give rise to that behaviour. One then assumes that those beliefs and desires are actually held by the creature." Clearly, mirror neurons could well be a basis for inferring beliefs and desires from observed behavior of others. Dennett's theorizing goes on to incorporate this intentional stance into his ideas about consciousness, as described in his book Consciousness Explained.
This is hardly the time to launch into an extended discussion of consciousness. But we can't help noting a slightly different way in which mirror neurons may play a part. Blakeslee has a further quote from Iacoboni:
"[I]f you see me choke up, in emotional distress from striking out at home plate, mirror neurons in your brain simulate my distress. You automatically have empathy for me. You know how I feel because you literally feel what I am feeling."
In other words, mirror neurons help us understand not only the intentions of other people, but their feelings and emotions as well. They enable us to empathize with others.
For instance, most people can easily read the emotions of others from facial expression, tone of voice, and other body language. It seems rather likely this is because our mirror neurons simulate the muscular activity that underlies these kinds of emotion-expressing behaviors. Further, if one tries to imitate facial expressions associated with emotional states (like fear, sadness, joy, etc.), one actually feels at least a little bit of the emotion itself.
Some neuroscientists have suggested that emotions originate, at least in part, from our perceptions of how our own bodies react when in situations that naturally evoke fear, pleasure, and so forth. This idea is propounded, for instance, in Antonio Damasio's book Descartes' Error. Damasio then goes on, in The Feeling of What Happens to construct from these ideas a more general theory of consciousness. So it's not too much of a stretch to think of mirror neurons as important parts of the neural basis for the phenomenon of consciousness.
But we're still not done. As if enabling consciousness were not enough, mirror neurons may also play a big role in the development of human culture, by enabling humans, from a very early age, to acquire complex behaviors (such as using tools, learning language, participating in group social activities, etc.) by a process of imitation. Blakeslee quotes psychologist Patricia Greenfield:
Until now, scholars have treated culture as fundamentally separate from biology, she said. "But now we see that mirror neurons absorb culture directly, with each generation teaching the next by social sharing, imitation and observation."
Other animals - monkeys, probably apes and possibly elephants, dolphins and dogs - have rudimentary mirror neurons, several mirror neuron experts said. But humans, with their huge working memory, carry out far more sophisticated imitations.
This isn't just speculation. There's already research that has implicated the mirror neuron system in imitation. For example, this from January 2005: Human See, Human Do: Ballet Dancers' Brains Reveal The Art Of Imitation
While previous studies have found that the system contains mirror neurons or brain cells which fire up both when we perform an action and when we observe it, the new study shows that this system is fine tuned to each person's 'motor repertoire' or range of physical skills. The mirror system was first discovered in animals and has now been identified in humans. It is thought to play a key role in helping us to understand other people's actions, and may also help in learning how to imitate them.
It's hard to overestimate the importance of learning by imitation in the transmission of human culture. Most things humans really need to learn how to do can only be learned by carefully observing someone who already has the skill. For early humans it was things like making stone tools, building a fire, or throwing a spear. For more modern humans it's painting a landscape scene, playing a violin, or making wooden furniture.
What else might mirror neurons be involved in? Well, how about learning language? Blakeslee mentions neuroscientist Michael Arbib's work. Some of this goes back to 1998. For instance, this: Monkey Do, Monkey See ... Pre-Human Say?
"This mechanism provides the neural prerequisite for development of inter-individual communication, and finally of speech," Dr. Arbib says.
"For communication to succeed, both the individual sending a message and the individual receiving it must recognize the significance of the sender's signal. Mirror neurons are thus the missing link in the evolution of language. They provide a mechanism for the sharing of meaning."
And the language involved need not be just literal statements of facts. It could extend to figurative language such as simile and metaphor. When we talk about "reaching for an understanding" we are using the physical act of reaching in a metaphor. Or Shakespeare's "Tomorrow, and tomorrow, and tomorrow, Creeps in this petty pace from day to day..." Ramachandran's Center for Brain and Cognition at the University of California, San Diego is investigating metaphors and slyly using them in their press releases (May 2005): Grasping Metaphors: UC San Diego Research Ties Brain Area To Figures Of Speech
Ramachandran's lab is continuing work on linking other brain areas, the supramarginal gyrus and human homologues of mirror neurons, for example, to other types of metaphoric abilities.
Recall that it's not only the act of observing another person doing something that activates mirror neurons. Just thinking about an action or hearing about one or (especially) reading about one can also cause activation. This may well account for a large amount of the pleasure we obtain from viewing photographs or reading literature depicting people engaged in all kinds of activities -- running a marathon race, climbing Mt. Everest, or having sex. (Reading or viewing pornography was bound to come up, no?) It's called vicarious experience. (I wrote here about a related, though different, way that literature seems to arise out of characteristic ways that human brains work.)
So there's plenty of evidence now about the great things that mirror neurons do. But what happens if there's a problem in the mirror neuron system? The answer appears to be simple: autism. Mirror neurons enable humans to understand the intentions of other people and have a "theory of mind", to have empathy with the emotions of others, and to learn cultural skills by imitation from watching others. A person who is lacking in those abilities, especially a child, is autistic. Actually, some autistic children can mimic facial expressions other actions of others, but they don't understand the corresponding emotions or intentions of others.
Research is accumulating that impairment of the mirror neuron system is implicated in autism. Here are reports of some of the studies: UCLA Imaging Study Of Children With Autism Finds Broken Mirror Neuron System (12/6/05), Abnormal Brain Activity During The Observation Of Others' Actions (2/18/05), Autism's Fogged-up Mirror (1/3/05).
Undoubtedly, there's still much more to learn about mirror neurons and other brain systems that may also be involved in such things as imitation and perceiving the emotions and intentions of others. But what we've figured out so far is pretty interesting.
Here are reports of some other studies in the same general area --
Brain Patterns The Same Whether Doing Or Just Watching, Queen's Researcher Discovers (8/14/03)
Brain Senses The Pain Of Someone Else's 'Ouch!' (2/24/04)
Discovering That Denial of Paralysis Is Not Just a Problem of the Mind (8/2/05)
The First Laugh: New Study Posits Evolutionary Origins Of Two Distinct Types Of Laughter (11/22/05)
Tags: mirror neurons, neuroscience, autism, empathy, imitation, theory of mind
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