Mirror, mirror, in the brain / You are tricky to explain

So I’m finally getting my first post up now. It’s amazing how good intentions dissipate when work creeps up on you.

I was going to try to do some real “science journalism” on this blog, but for the sake of trying to write regularly, that’s going to be on hold, at least until the summer. That being said, I still want to talk about science here. It will just be more from an angle of personal interest. My research interests include medical technology and neural control of movement, but I won’t be limiting posts to those topics.

About a month and a half ago (January 27, 2014), Prof. Roger Lemon of UCL came to USC to give a talk he titled “Mirror neurons, motor commands. and movement: new insights into corticospinal function”. 

The concept of “mirror neurons” in the sensorimotor system dates back to research from the early 1990s (for example, [1]). When researchers were studying cortical activation in macaque monkeys, they also observed that some neurons were firing in response to observing the researcher doing the task. This phenomenon was also later identified for humans in cortical area F5 (i.e., ventral premotor cortex), which is adjacent to primary motor cortex (M1).

M1 is one of the structures whose functional neuroanatomy seems to be more well understood. The neurons of the spinal cord that cause contraction of muscle fibers are called “alpha-motoneurons”, and the neurons of M1 have monosynaptic connections to alpha-motoneurons. So it’s assumed that M1 activity should (in general) correlate with muscle activation (i.e., EMG).

But now, Prof. Lemon’s group has observed mirror activity in M1 as well! M1 displays activity both during execution and observation! Although, as one might expect, the activity is much less during observation than execution, which may allow the CNS to prevent that from translating into EMG. But the question remains: for what reason (or purpose) does M1 activity correlate with observation alone?! Prof. Lemon cited a recent paper [2] that proposed a framework in which neural information is not a sequential process, but a distributed one. He suggested that if information processing is really more distributed, then we can hypothesize that our perceptual systems will be more tightly linked with our motor systems, and perhaps that could explain the existence of neural activity in the motor system when it’s not being used.

I remember that in a recent conference (I believe it was one of the “Neural Control of Movement” conferences), there was a panel of speakers that spoke on the topic of “what have we learned after decades of studying M1”. I think that studies like Prof. Lemon’s underscore that while we may have learned quite a bit, the brain is incredibly complex and there is a lot that we don’t understand about how it works.

In our lab (since my advisor is a crazy math genius) we have always tended to think about the brain as a distributed controller/processor, so the suggestion that Prof. Lemon makes resonates with me. My advisor is very into using his mathematical know-how to write theory papers where he describes his theories about motor control using the language of math, and he recently published a paper describing how a distributed controller should work mathematically [3]. It usually takes me a number of readings to understand his papers, but if I can finally understand it and tie it into this topic at a later time, there will be a new post about it!

Happy Daylight Savings! It will be nice to go home in sunlight again! =D

References:

[1] Di Pellegrino, G., Fadiga, L., Fogassi, L., Gallese, V., & Rizzolatti, G (1992). Understanding motor events: a neurophysiological study. Experimental Brain Research, 91, 176-180.

[2] Cisek P., Kalaska J.F. (2010). Neural mechanisms for interacting with a world full of action choices. Annual Review of Neuroscience, 33, 269–298

[3] Sanger, T.D. (2011). Distributed Control of Uncertain Systems using Superposition of Linear Operators. Neural Computation, 23, 1911-1934.

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