Getting a Feel For It

Your sink breaks on a holiday and you consult YouTube for help. You’re gathered around a TV with a group of friends, intently watching your favorite sports team. You’ve just started a retail job, and you watch intently as your supervisor demonstrates just how the register works.

What links these scenarios? In each—just beneath your conscious awareness—your brain is conducting what neuroscientists call a ‘motor simulation’ of the movements you’re observing [1].

The idea of a ‘motor simulation’ is one we’re going to return to now and then in our articles—so, without getting too deep into-the-weeds, let’s talk definitions! A simulation can be defined a few different ways, but the best definition for our purposes is…

...the representation of the behavior or characteristics of one system through the use of another system.

To fully grasp the idea of motor simulation, it’s important to understand that the ways in which our brain communicates information to and from its various regions—these stable patterns themselves can be considered system [2]. Now this idea is quite the titty-twister of abstraction—considering the brain itself is a system. So think of it this way. All the roads in a city constitute a system, serving the broad function of allowing the movement of people and things around the city. Now the public transit system represents a system that exists on top of (or within) the road system, serving a more-specific function (to transport people who are willing to pay a small fee, from pre-determined locations).

Like the public transportation system within the road system, the pattern of cellular communication allowing you to move is a system that exists on top of the brain’s larger system of connected neurons. [3] This system (the motor system) is made up of distinct patterns of electrical impulses in your brain, with each type of movement you make resulting from slightly different patterns of neural activity. Each different movement you make is the result of this system operating in a slightly different state.

Now a motor simulation occurs when you see a person moving, and it’s an attempt by your brain to reverse engineer (or ‘mirror’) the pattern of brain activation it would have taken to produce the movement you’re seeing. Of course, your brain does this without actually causing you to move, meaning this pattern of brain activity has a different function than the motor system—it’s attempting to represent the brain activity of the motor system, not replicate it. Hence the term simulation.

But why does your brain need to produce a motor simulation at all? The explanation for just why our brains evolved to work this way is a big philosophical one we may tackle in another post. For now I’ll just break down a recent study [4] that will illustrate one of the major benefits of motor simulations: our ability to learn movements from watching others.

The set-up…. Subjects held a robotic arm by a handle, and were instructed to move it to target areas that would pop up periodically. Essentially whack-a-mole, with ‘moving the robotic arm’ in place of ‘whacking’.  The twist is that this setup also included a force field that could push the subjects arm left or right, screwing-up their ability to accurately reach out with the robo-arm and hit the target.

First subjects watched a video of a person performing robot-arm-movements with a force field pushing the arm to the right. Then a few minutes later, these subjects were asked to play robot-arm-whack-a-mole themselves, except now (unbeknownst to them) the force field would be pushing the arm in the opposite direction. The idea (supported by similar studies [5]) is that, if watching the video imparted any motor learning to the individual, the force field switcheroo would hurt the subjects’ performance. Specifically, the trajectory of their reach would be more curved, and this curvature was taken as a measure of motor learning through action observation.

 

The experiment… Previous studies have already shown that motor learning through observation is business-as-usual for the brain. [6] The novelty of this study was that while subjects watched the video of the robot-arm-movements with the force field pushing left, the researchers gave a slight electric shock to the median nerve of either both arms, only the left or only the right arms. They also had a group that received no shock, and a group that watched a similar video, but with randomly varying force fields (that is, a control group, exposed to videos of arm movements, but who wouldn’t be able to learn anything about the task, as the force fields randomly changed direction).

Given that this nerve stimulation has been shown to cause activity in the somatosensory cortex, [7] the researchers figured that if the somatosensory cortex was critical for motor learning by observation, then stimulating the arm being used in the task (right arm) should interfere with the observational learning. The somatosensory cortex is organized by the principle of neural representation—meaning different parts of cellular real estate in the brain are associated with processing sensation on different parts of the body. Meaning—if you stimulate the left arm, given the video and task both involve movement of the right arm, learning should be preserved. But if the right arm is stimulated, no learning should take place.

 

The results indeed showed that only the group that watched the learning video (with the left force fields), who received no stimulation, or stimulation of the left median nerve only, showed more curvature in their reaching trajectory, and thus showed motor learning by observation.

 

What might this mean?...

 

This suggests that the part of your brain responsible for processing touch (the somatosensory cortex) is necessary for your ability to learn a new movement by watching it alone. How might this work?

 

We already know that the somatosensory cortex receives information from the brain’s visual areas about what movement it is seeing [8]. Perhaps this input to the somatosensory cortex causes it to calculate ‘what would this feel like if you were executing it yourself?’

 

The authors seem to conclude that the somatosensory cortex then passes on the answer it comes up with (‘this is what it should feel like’) to adjacent motor areas. And moreover, that in order for motor simulations to contribute to motor learning, they need to include information about what sensations are (probably) associated with that movement.

 

Why we think it’s rad!?… These results offer us a fascinating glimpse into the black-box of the brain’s movement processing. You don’t need a neuroscience degree to understand the idea of taste and smell being joined-at-the-hip in some way in our brains. It’s something you can observe in everyday life. Almost common-sensical. The fact that motion and sensation share such a co-dependence, however, is not quite as apparent to most of us [9].

 

Motor simulations—through observing movement, or imagining movement—have been shown to improve physical rehabilitation, [10] and increase our ability to learn new motor skills [11] (a topic discussed in our maiden post). We humans have nary scratched the surface of our ability to learn/change our capabilities by thinking alone. Studies like this bring us a bit more clarity, and over time, these small gains in understand may translate into huge leaps forward (the likes of which I’m sure we’ll wax poetic on in future posts). While this study alone won’t be pointed to as any sort of game-changer, it’s a nice step towards helping us deconstruct how our brains orchestrate our movements.

 

[1] http://www.sciencedirect.com/science/article/pii/S1053811901908328

[2] Basic though useful definition for this occasion = System – a set of connected things or parts forming a complex whole.

 

[3] Neuron = cell in the brain and spinal cord (ie, the central nervous system)

[4] http://www.sciencedirect.com/science/article/pii/S0960982216300112

[5] http://www.sciencedirect.com/science/article/pii/S089662730500125X; http://jn.physiology.org/content/107/6/1564.short

[6] http://www.sciencedirect.com/science/article/pii/S030439401201508X; http://psycnet.apa.org/psycarticles/2014-05299-001

[7] a part of the brain adjacent the motor cortex important for tactile sensation

[8] http://onlinelibrary.wiley.com/doi/10.1002/1096-9861(20001204)428:1%3C112::AID-CNE8%3E3.0.CO;2-9/full

[9] This idea is not a new one birthed from this article alone—many studies on mice have shown that when you damage the somatosensory cortex, you not only knock-out the mouse’s sense of touch, you impair their movement ability as well (http://www.sciencedirect.com/science/article/pii/S0166432899001308)

[10] http://www.sciencedirect.com/science/article/pii/S1053811907002534

[11] http://www.sciencedirect.com/science/article/pii/S030439401201508X; http://psycnet.apa.org/psycarticles/2014-05299-001