Wednesday, May 9, 2007

Prehending mirror neurons by the throat

When is the last time you used the verb prehend, as opposed to its more common cousins comprehend or apprehend? Has it been a while? I thought so.

I couldn't help wondering about this when thumbing through the May issue of the Journal of Cognitive Neuroscience. I came across the latest article from those über-neurolinguists over at the MPI for Human Cognitive and Brain Science in Leipzig. The article, "Comprehending prehending: Neural correlates of processing verbs with motor stems" by Shirley-Ann Rüschmeyer, Marcel Brass, and Angela Friederici, is the latest chapter in the craze about mirror neurons and their implications for embodied language.

This being a blog about neuroscience, I'm sure that most of you have already read if not blogged about mirror neurons yourselves, and probably have some ideas about various theories of embodied meaning that have stemmed, in part, from their discovery. In short, monkeys have neurons in the premotor cortex (and the posterior parietal lobule) that respond both when the monkeys perform particular hand movements (ones that are typically object oriented) and when they observe someone else doing the same thing. Some have suggested that this premotor area is the homologue of Broca's area in humans, and that the idea of conceptualizing perceptions as actions lays the groundwork for the evolution of communicative gesture, and eventually to spoken languages (albeit spoken language that is grounded in embodied thought). Evidently, this also leads to jumping in front of trains to save people.

Given this, neuroimagers have become interested in whether producing or perceiving language that has more to do with concrete physical actions might implicate motor areas of the brain, like the primary motor cortex or the premotor cortices anterior to it. Not only does this seem to be the case, but there may be some somatotopic correspondences between the two, i.e., when you hear lick, pick, and kick, motor representations for the face, arms, and legs appropriately perk up (Hauk, Johnsride, & Pulvermüller, 2004).

This new study in JOCN takes things in a slightly different direction. The question is first, what is the difference between perceiving motorically grounded words like greifen (to grasp) compared to more abstract words like denken (to think), and more interestingly, what is the difference between perceiving derivations of such words that have distinct meanings, like begreifen (to comprehend) and bedenken (to consider). For you true psycholinguistic geeks, it was a 2 x 2 design (motor-abstract and simple-complex) using visual presentation of single words and a lexical decision task (responding only to nonwords).

Rüschmeyer et al. find that when comparing the simple motor words like greifen to simple abstract words like denken, they observe greater activity in several areas including the primary motor and somatosensory areas in the pre- and postcentral gyri, consistent with the idea that a motor words implicate (sensori)motor representations. No significant effects were observed with the reverse contrast.

Interestingly, the analogous comparison with the morphologically complex words (begreifen words minus bedenken words) did not show differential involvement in motor areas. (They did find effects in the right middle temporal gyrus and left cerebellum, and as before, no significant effects with the reverse contrast.)

I wonder if things would have been different if the morphological derivations were more transparent. Sure, if we think about it we can see that greifen and begreifen are morphologically related, at least from a historical perspective, but would we have reason to expect that all such relationships are psychologically real in today's speaker? I certainly had not ever thought of the word comprehension as a more abstract derivation of the physical word prehension before today, and I suspect that my motor cortex didn't either.

(This may not be the best example to consider in English, since to prehend is archaic whereas greifen is not. So consider another: do you understand the word authority immediately as a derivation of author, in the same way that you understand serenity as a derivation of serene? I think there's a difference psycholinguistically, and I suspect that most of the items used in this study were more like the former example.)

Is this a diachronic versus synchronic issue? I'd be interested in what a historical linguist has to say.

This guy knows what I'm talking about.

References:

Rüschmeyer, S.-A., Brass, M., & Friederici, A.D. (2007). Comprehending prehending: Neural correlates of processing verbs with motor stems. Journal of Cognitive Neuroscience, 19, 855-865.

Hauk, O., Johnsrude, I., & Pulvermüller, F. (2004). Somatotopic representation of action words in human motor and premotor cortex. Neuron, 41, 301-307.

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