Practical Science on Movement and Pain
Practical Science on Movement and Pain
In a recent post I linked to a TED talk by neuroscientist Daniel Wolpert about how the brain controls movement. As promised, here are some more thoughts on Wolpert’s explanation, and how this relates to the Feldenkrais Method. (If you haven’t watched the video yet, I recommend watching before reading this post, but it’s not necessary. If you watched it and then forgot most of it, that’s OK, read on.)
One major takeaway that I got from Wolpert’s talk was that controlling movement is inherently difficult given the hardware that the brain must work with.
First, there are a staggering number of variables to control. The body has hundreds of joints, many of which are capable of wide ranges of movement at many angles. As Wolpert points out, for even the simplest tasks, there are nearly an infinite number of possible joint configurations to get the job done. And, for any particular set of joint movements, there are nearly an infinite variety of possible muscular contractions. Remember that there are around 400 muscles in the body and thousands of motor units per muscle.
With such an amazing number of variables to calculate and analyze, it’s no wonder that even the most powerful computers are complete overwhelmed with the complexity of performing even the simplest motor tasks with any dexterity.
The second challenge is that sensory signalling from the body to the brain is not transmitted and received with total precision. There is always some degree of “noise” in the signal which prevents the brain from knowing with certainty where the body parts are located. Wolpert uses the example of placing a finger under a table and trying to locate its position with the other finger – chances are you will be off by at least a few centimeters.
The third major problem in controlling movement is that there is also quite a bit of noise in the signals that the brain sends to muscle fibers telling them to contract. Because of this, a given command may result in different patterns of muscular contraction. For example, if I tell my finger to a do a particular thing three times, each time I will get slightly different movement, because of signaling errors.
Given these difficulties, trying to control the movement of your body is a little like trying to play a video game with a couple hundred thousand joy sticks. And a fuzzy TV screen and random errors in the commands you send to Super Mario. So, how does the brain deal with all these uncertainties?
According to Wolpert, the brain deals with uncertainty by using Bayesian reasoning, which involves some complicated math and statistics. This is all unconscious of course. Wolpert doesn’t go into the details of how the math works (although he does here in case you are interested.) But the gist is that Bayesian inferences provide an elegant way for the brain to calculate optimal movement solutions in the absence of any certainty about the accuracy of the data, based on a statistical analysis of various probabilities. According to Wolpert, the right movement command is the one which will “minimize the negative consequences of variability in the outcomes.”
So why do we care about any of this? I think this a great framework to analyze what we need to do to acquire movement skill.
One insight is that movement genius resides in the unconscious brain, not the conscious brain. The unconscious brain has an almost unimaginably staggering capacity of computation and analysis in regard to choosing the most efficient movement patterns. Apparently it knows Bayesian statistics and can calculate probabilities based on a monstrous amount of variables. Almost instantly. For example, my unconscious brain knows what degree of contraction in the soleus is necessary to prevent me from falling forwards when I raise my arm in front of me and thereby shift my center of mass a little forward of my base of support. It’s almost like there is some unconscious movement genius living in my brain solving problems of incredible complexity.
My conscious brain can’t do that. And this is part of the reason I don’t want my conscious brain too involved in selecting the muscle activation patterns that will be used in a particular movement. For example, I don’t try to consciously suck in my gut or activate my core muscles or clench my glutes when doing a movement, because some expert said that is the right way to do the movement. My unconscious brain has a much better chance of finding the perfect form for me.
So what is the job of the conscious brain, and what should it do if this supposed movement genius seems to be moving in a very inefficient way?
In my opinion the role of the conscious mind in refining movement patterns is in providing the unconscious brain with the information it needs to make good predictions and good decisions. That’s it. Good movement decisions are based on good information, therefore all we can do to help is to provide good information. We can’t go back there and start crunching the numbers ourselves. So what information does the unconscious need and how do we provide it?
Wolpert’s talk makes clear exactly what information the brain needs to make good movement decisions. First, sensory data about the position of the relevant body parts, and second, memories which store data from past experience about the results of certain motor commands. Let’s look at these factors in turn.
I have written many articles about the importance of accurate body maps and a good proprioceptive sense for better movement. The basic point is that we can all improve our movement by using various coordination exercises such as the Feldenkrais Method or Z-Health to clarify our body maps. For example in Feldenkrais Awareness Through Movement lessons, before doing any movement at all you will probably spend some time trying to sense the locations of certain body parts. This is not as easy as it sounds, and you are sure to find some surprising gaps in your awareness.
Clarifying smudged body maps should be of great general benefit for all your movements, since this data is always useful. For example, a better sense of the ankle will be probably be helpful for any task in which the ankle is involved.
In regard to the performance of any particular task, it will be helpful to focus conscious attention on the sensory data which is most relevant to that task. This will be a very small part of the whole. The amount of sensory data that we are bombarded with at any one moment is overwhelming. The brain will filter data based on where conscious attention is placed. Therefore, the focus of our attention helps determines the information that the unconscious has available to do it’s Bayesian reasoning thing and make good decisions.
So by paying attention to the sensation associated with a particular movement, you can affect the quality of the movement. In other words, if you really pay attention to how a movement feels as you are doing it, you will necessarily do it differently.
One of the basic techniques in a Feldenkrais Awareness Through Movement class is to encourage students to do the same movement many times, and each time focus on a different sensation – how it feels in the spine, or the pelvis, or the sternum, etc. Students are directed to notice that with each change in attention, the movement changes as well, even without any conscious intention to alter it.
This is why you perform better when you are actually paying attention to what you are doing, and why people crash their cars more often when their attention is on the cell phone.
So those are some conscious steps you can take to maximize the quality of the sense data that the unconscious brain uses to make good movement decisions. In the next post, I’ll discuss ways to maximize the quality of the other key source of information that the unconscious needs – past memories of the outcomes of particular motor programs.