Mirror Neurons

Mirror neurons are human-kinds success story. About 50,000 years ago in Homo sapiens (a.k.a. humans) there apparently was a mutation in the gene or genes that control the number and location of a special type of neurons in the brain, called mirror neurons.

Found in a wide range of organism from fruit flies to humans, in us these motor neurons played critical, key roles in social skills, recognizing emotions in others, learning, and language. What resulted was a giant leap in social skills and organization, tool making, and language capabilities. Empathy was born. (Well, it was greatly enhanced.)

Of course this 50,000 year scenario is speculation, but supported by research in anthropology and genetics. The human brain's gross anatomy and size has been essentially unchanged for the last 200,000 years. The type of changes we are talking about here are internal changes that would not be picked up in the fossil record.

Where do we find mirror neurons?

They have been identified in many parts of the brain that have to do with movement, language, pain, and empathy. They are referred to as pre-motor neurons, which is more technically correct.

"Pre-motor" means they come before or in front of the motor neurons in the brain. Mirror neurons are located in pre-motor cortex areas of the brain. Motor neurons are located in many areas of the brain that have to do with sending nerve impulses to muscles, organs, and glands to have them take some action.

What do mirror neurons do?

Pre-motor neurons fire when we do something (action) or watch someone else do it. Their function is mental imitation. We observe someone yawn, our premotor neurons fire, and we want to yawn too. We see someone in sadness, our premotor neurons asssociated with that body language fire, and we 'feel' (empathize) with their sadness. Same with miles, anger, dancing, playing tennis, etc.

As it turns out when we see someone that is sad, the muscles involved in showing sadness actually respond in us, that is they contract. Mirror neurons help us make sense of others around us.

They even fire off when we hear something that we have experienced. (I suspect they fire similarly with touch and smell stimuli too.)

Pre-motor neurons fire not only when watching someone do something but when we hear something that we have experienced.

Mirror neurons enable us to read facial expressions in others.

Deficits in the motor neuron system

So what happens when someone has a deficit in their motor neurons? Maybe they were born with fewer motor neurons. Or the ones they do have don't work quite right.

Research indicates that a defective mirror-neuron system may explain the troubles with language, learning and empathy in autism. My suspicion is they also play a critical role in non-verbal learning disabilities too.

One research study found that with autistic teens there was a deficit in mirror neuron activity compared to the non-autistic control group when they were shown pictures of various facial expressions. They could identify the expressions cognitively and even tell what emotions were being expressed. However, they felt no empathy.

References

Arbib, Michael. 2005. From Monkey-Like Action Recognition to Human Language: An Evolutionary Framework for Neurolinguistics. Behavioral and Brain Sciences 28: 105–167.

Azar, Beth. 2005. How Mimicry Begat Culture. Monitor on Psychology, Vol. 36,No. 9, pages 54–57. (Available at www.apa.org/monitor/oct05/mimicry.html)

Dobbs, D. 2006. A Revealing Reflection. Scientific American Mind April/May: 22-27.

Gallese, L., et al. 1996. Action Recognition in the Premotor Cortex. Brain 119, No. 2: 593–609; 1996. (Available at http://brain.oxfordjournals.org/cgi/content/abstract/119/2/593)
 
Iacoboni M, Dapretto M. 2005. The mirror neuron system and the consequences of its dysfunction. Nat Rev Neurosci. 7(12):942-51.

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