Saturday, March 20, 2010

Mirror Neurons/Systems Present Method Problems for Science

Giving empirical explanations for what mirror neurons are supposed to be doing in the brain ain't as easy as one might wish.

Mirror neurons are "a particular class of neurons, originally discovered in the ventral premotor cortex, that code goal-related motor acts such as grasping. Specifically, mirror neurons require action observation for their activation; they become active both when the subject makes a particular action and when it observes another subject making a similar action."[1] For example, implant wires in the appropriate region of a monkey's brain, and you can detect when these kinds of neurons fire. So when a monkey watches a researcher bring an object to his mouth (e.g. an ice cream cone), the same neurons will fire as if the monkey were bringing food to its own mouth.

Mirror neurons fire both when an animal sees or hears an action and when the animal carries out the same action on its own. Follow up studies showed the same kind of results in humans, though humans have a far more subtle and flexible set of such neurons. Further studies would show that mirror neurons are found in several areas of the brain, such as the premotor cortex, the posterior parietal lobe, and the superior temporal sulcus [see map]. But that might be several areas too many, as Greg Hickok of Talking Brains blog points out.

Mirror neurons have been associated with all sorts of social behaviors, such as detecting other minds, learning in children, aesthetic responses to dance and music, and even to why males like pornography. [2] Yet Hickok objected "if the mirror neuron system is really important for action understanding, then damage to action execution should result in action understanding deficits. I have pointed out that this prediction doesn't hold, either in apraxia or with more force in aphasia. "[3] If you're just brushing up on your brain malfunction vocabulary, recall that apraxia is an inability to make purposeful movements, while aphasia is an inability to use or understand language, spoken or written, because of a brain lesion.

Hickok also points out the common reply--namely, that of lots of areas with their own mirror neurons are working together--is not a good answer the problem, since this makes an alleged mirror system too powerful of an explanation. The matter was noted by a well-known philosopher of mind during discussions of the issue:
"At this point in the talk, Pat Churchland, who was my host, jumped in and said (and I paraphrase here), 'Now wait a minute. If mirror neurons are all over the brain then don't they lose their explanatory power? Aren't we now just back to our old friend, the How Does the Brain Work Problem?' "[3]
Hickok found this charge convincing, and now worries if mirror neurons' function can be empirically outlined at all, at least as distinct from other subsystems in the brain. Hickok's blog entry[3] and some of the comments therein are definitely worth a read.



[image] "Auditory Mirror Neurons" Mixing Memory Blog Oct. 2, 2006 (Accessed March 20, 2010) -- This is also a good article in itself about pianists and nonmusicians responses to watching others press keys on a silenced piano.

[1] Glossary of Terms Nature Vol. 3, No. 6, June 2002 (Accessed March 20, 2010)

[2] As an aside, I don't know who has the weirder job in this experiment, the researchers or the participants: Alison Motluk "Mirror neurons control erection response to porn" NewScientist June 2008 (Accessed March 20, 2010)

[3] Greg Hickok "Mirror Neurons - The Unfalsifiable Theory" March 19, 2010

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