Mixing Memory tosses a helpful bucket of cold water on the mirror neuron frenzy. The post focuses on the hypothesis that mirror neurons were a crucial ingredient in the development of human language. While I think much of the skepticism is well deserved – mirror neurons remain a mysterious bunch of cells – I think Mixing Memory neglects to mention one important bit of evidence that supports the mirror neuron-language connection. Specifically, Giacomo Rizzolatti (the godfather of mirror neuron research) has shown that mirror neurons can be activated by fragments of language that are about actions. For example,when we say “golf swing” or “kick the ball,” mirror neurons in our motor cortex automatically get excited. Abstract sentences, on the other hand, fail to excite our motor cortex. Of course, this study has little bearing on whether or not mirror neurons are a necessary part of language acquisition. But it does demonstrate that mirror neurons in the motor cortex are uniquely plugged into sentences that are about doing something.
But I think Mixing Memory’s post raises an interesting question. Why are mirror neurons so hyped? Why are journalists (like me) so eager to write about this strange group of cells?
My own theory is that mirror neurons are popular because their activity is directly related to what we actually experience. These cells fire whenever we see someone smile, or swing a golf club, or say they are swinging a golf club. Their activity reflects the ordinary events of real life.
On the other hand, just about every other sensory neuron in the brain seems to respond to abstract bits of information. For example, the cells of the V1 in the visual cortex respond to abstract lines and contrasts of light. (The world they inhabit looks just like a Mondrian canvas, and most of us don’t live in a world that looks like that.) The V2, V3 and V4 aren’t much better. In fact, you have to go to the medial temporal lobe (aka, the V5) before you get cells that respond to complex stimuli, like a smiling face.
This abstract anatomy reflects the workings of the brain. Behind the glossy cinema of consciousness is a neural army of stagehands, assistant directors, cinematographers, editors, writers, etc., all of whom are content to remain behind the scenes of experience. Our reality, in other words, depends upon a wealth of unconscious processing.
This is fascinating stuff, but after awhile one begins to crave a group of cells that map onto the world we actually know. Mirror neurons ably fill this void. Instead of describing some abstract universe, they are activated by the actions, verbs and facial expressions we continually perform. (Of course, it also doesn’t hurt that mirror neurons help to explain sports, porn, autism and movies.) Sure, mirror neurons are overhyped, but it’s not everday that we get neuroscientific insight into everyday life.