While I'm on the topic of mirror neurons...
A Talking Brains reader recently pointed me towards a published cover story and interview with V.S. Ramachandran in the magazine Khabar that included some discussion of mirror neurons. Rama, of course, is famous for many things including his bold prediction that mirror neurons will do for psychology what DNA did for biology and he has written extensively on the topic. It was pointed out in the interview that there are critics who question the significance of mirror neurons in action understanding. Here is the question and his response:
Some critics like Gregory Hickok of UC Irvine have argued that there is little evidence to support the mirror neuron theory of action understanding. How do you respond to that?
There are two issues. In my book, I do address various criticisms—I’m not familiar with that particular one. It seems plausible there is no direct evidence, but we often go by circumstantial evidence. I’d argue with him that there is no definitive proof of action understanding, but given their properties it seems reasonable to argue that it exists. I mean, you can always say about any neuron system that it’s just a correlation, that it’s not really doing the job. I’ll give you an analogy. They found cone cells in the eye which are responsible for seeing color. Now you can say it’s just a correlation, that they are sitting there and not doing anything. I know it’s an extreme example, but it’s the same logic. (quoted from: http://www.khabar.com/magazine/cover-story/Brain_Man)
So Rama admits that the theory is based on circumstantial, rather than more direct evidence. I will agree with him that we often do develop hypotheses based on circumstantial evidence, or even intuition. And there's nothing wrong with that. I've pointed out previously that the initial proposal regarding the function of mirror neurons was reasonable and interesting. However, as more and more data poured in over the next two decades, many empirical problems with the theory have been revealed. To use Rama's example, the fact that cones fire to specific wavelengths of light is highly suggestive of a role in color vision but this is still just a correlation. In the case of cones though, much other research has confirmed the hypothesis more directly such as cases where cones are dysfunctional and color vision is disrupted. The mirror system has been put to a similar test, but unlike the cone theory of color vision, the mirror neuron theory of action understanding has failed miserably: disruption of the mirror system does not cause substantial deficits in action understanding (see this post, for example). So the mirror neuron theory is based on circumstantial evidence and there is direct evidence to the contrary. Open and shut case in any court of law.
Why isn't the cased dismissed in academic circles? The mirror neuron theory of action understanding is so simple and powerful and the correlations between neuronal activity and behavior so compelling at first glance that it apparently blinds many researchers from seeing the broader array of facts. In one comment in the Mirror Neuron Forum I compared the situation to the powerful intuitive pull of the notion that the sun revolves around the Earth. It is a compelling observation that led to a very reasonable geocentric theory. However, upon further observation the theory failed to account for other, less intuitively compelling but equally valid observations such as apparent retrograde motion of planets. While a geocentric model can explain observations about the apparent motion of the sun, only the heliocentric model explains all the facts. It's an extreme example, but the logic is the same. It is time that we all look a bit more closely at ALL the facts when thinking about the function of mirror neurons and the mirror system.