Distributed Activation: the M1 on Fire

This article is about a common misconception that the brain contains a “motor map” of our muscles in the same sense we usually think about maps (one-to-one representation). It further explains the term “distributed activation” in movement research and then compares it with the Baseworks Distributed Activation. It also talks about the practical relevance of being informed about this topic. The title of this article was inspired by the title of the Chinese historical drama “Nirvana in Fire.”

M1 is not like a piano keyboard

From my experience, when someone learns about the Primary motor cortex (M1, for simplicity) for the first time, they tend to form a mental image of the M1 akin to a piano keyboard. Of course, this image is typically not verbalized, but it can be easily reconstructed after talking to enough people. The assumption inferred from the piano-keyboard analogy is that when you “press a key” in M1, it results in a contraction of a particular muscle. If you want to contract two muscles, you need to press two keys, and so on.

The question about who’s playing the piano in this analogy put aside, this one-to-one representation between M1 keys (M1 territories) and muscles is simply not the case. If we tried to compare the M1 to a piano keyboard, it would be more like an automatic piano that plays a whole chord, if not a complete melody, when you press a single key—and you can see the keys moving.

In the academic world, motor research specialists have long acknowledged that M1 is not simply like a reversed (actionable) somatosensory map, no matter how intuitive it may seem.

This is how Dr. Marc H. Schieber, Professor of Neurology, Neuroscience, and Biomedical Engineering at the University of Rochester, describes what even scientists hold as intuitions about somatotopy (from Greek soma and topos, body and place)—the technical term for point-to-point map-like representation between a brain area and the body:

“Somatotopy seems so straightforward that it ought be so. The primary somatosensory cortex (S1) has a well-ordered somatotopic representation, and the primary visual cortex (V1) has a well-ordered retinotopic representation. The evidence reviewed above indicating that within-limb somatotopy in M1 is limited, and that a more complex, widely distributed organization exists instead, therefore is likely to reflect important features of functional organization in M1. I close with speculations as to what these features might be.”

Almost 20 years ago, Dr. Schieber published a great review article about the limitations of the somatotopy principle in M1 organization. It describes several features of M1 organization that contradict the idea of point-to-point representation. In brackets, I illustrate these features with analogies as if they applied to Google Maps.

• convergence of output (you type in two completely different addresses, and Google Maps drops its pin on the very same building both times)
• divergence of output (you type in a single address, and Google Maps hands you routes to five different destinations you never asked for)
• distributed activation (you search for one café, and instead of a single pin the whole city lights up—that very same one café seems to exist in multiple places at once)
• effects of lesions (a construction crew closes a particular road in London, and suddenly traffic is affected in Paris and Brussels)
• ability to reorganize (roads periodically change their direction; a road that used to go to Paris now goes to London).

If Google Maps operated like that, nobody would be using it for navigation because it would be useless as a map. M1, of course, isn’t useless—we’re using it in every movement. But its usefulness comes precisely from the architecture that is not like a conventional map.

From my experience, the only one of these features discussed in a popular movement-education-related context is the “ability to reorganize,” popularly referred to as “neuroplasticity.” Usually, with this almost spiritual reverence but without much reference to actual mechanisms.

Distributed activation, Distributed Activation, and the Smart Piano

If you’ve ever tried Baseworks or have spent any amount of time on our website, you might have noticed that one of the principles that limit somatotopy is called Distributed Activation—the same name as one of the key movement principles in Baseworks.

A coincidence? Yes. But there are interesting parallels between the two.

The “distributed activation” in M1 can be understood based on this paragraph from Dr. Schieber’s paper:

“….the process of moving multiple fingers is not simply the sum of activating multiple separate M1 territories, each controlling a different finger; rather, moving a single finger without the others requires more M1 activity than moving multiple fingers simultaneously. Presumably, such extra activation occurs because, besides controlling the motion of the one finger, M1 actively participates in stabilizing other parts of the upper extremity during the individuated movement of a particular finger.”

Moving a single finger requires more M1 activation than moving all fingers simultaneously because the other fingers in a single-digit movement need to be “fixed” (stabilized) to be still. The grasping motion (moving all five fingers simultaneously) is learned early in life. It is a fundamental movement common to many animals who have limb digits. Single-digit movements are much less common, and no other animal uses fingers independently to the extent humans do when typing or playing piano. So the idea here is that a simple common multiple-digit movement can be done with minimal effort/deliberate control (less M1 activation), while a more specialized movement requires more effort and more M1 activation to “fix” other unwanted movements. So, our M1 piano is a very smart piano—it has evolved to reduce effort and cognitive load.

While M1 is nothing like a conventional piano keyboard, let’s revisit our M1-inspired automatic piano analogy. On our M1 piano, we press a single key to play a melody. Then, if we want to play a single note, we need to hold other keys simultaneously to prevent them from playing their sounds. What an inefficient way of playing piano, you’d think. Absolutely. But this way of wiring is quite efficient for muscles. It is not unlike a smart home where you can link together all your 20 mood lights in the living room so that you can turn them on with a single command instead of wasting effort and time doing it one-by-one.

In Baseworks, Distributed Activation (DA) is a technique of muscle co-activation. To create the state of DA, we use various movements, opposing movements, and tractioning movements to activate as many muscles as possible at the same time in low-level isometric contractions. This is usually combined with micromovements. So, DA is a state where we try to perform multiple highly specialized, highly unusual movements simultaneously, creating a field of ever-changing, ever-adjusting alternations between micro-eccentric and micro-concentric contractions in every muscle we can control. This way of engaging muscles is very different from the natural human movement and common approaches to exercise.

Here’s the parallel. Although it takes some time to learn to perform this technique—pressing all the keys simultaneously—once we achieve that, every single co-contraction can be seen as analogous to a single-digit movement; we do these “single-digit movements” with all body parts all at the same time. So each component of DA should use large M1 areas to “fix” other unwanted movements, thus, presumably, covering very large and overlapping areas. By doing DA, we set our M1 piano keyboard ‘on fire’—presumably, at least, since no one has yet put a Baseworks practitioner into an fMRI scanner to check.

How to Outsmart the Smart Piano?

The process of wiring the M1 keys together to play useful movement melodies is called “chunking.” Discrete movements are connected into a well-timed co-activation sequence so that they could be called “as one unit” next time you need to perform this action. This is handled automatically, ‘under the lid,’ in the process of motor development in childhood and then continuing in skill acquisition in adulthood. As a result, you can perform sequences of movements without thinking.

The problem of course is, what are you going to do if you want to unwire/rewire a chunked action?

This process will, in fact, involve deliberately suppressing unwanted actions while your brain is building a new stable chunk. This is often effortful and requires mental resources. It’s much easier to just let your smart piano play pre-wired movement melodies.

Baseworks DA is usually applied during static movements. But once we’ve learned to perform DA statically, we transition from one static movement to another, while holding DA, moving one joint at a time. We call this the principle of “Fixing-Separating-Isolating” (FSI). FSI requires that only one macro movement is performed at a given time. What the DA does is that it is helping to “hold all the keys down” to prevent unwanted melodies. While this is extremely counterintuitive if you don’t spend much time studying motor control, it makes perfect sense once we look under the lid of our M1 piano. DA → FSI is a tool that helps isolate complex movements into separate chunks for independent control—so you can enjoy this control when you go to your dance class or learn a new martial arts move.

The Origin of The Distributed Activation

My first experience with Baseworks many years ago was a light shock. I couldn’t guess why anyone would want to engage muscles in such an unusual way. More understanding came from my own training in the method, observing others as they follow movement instructions, and thousands of hours of study of sources such as the review article linked above.

Patrick Oancia had been using the term “Distributed Activation” long before I joined Baseworks and asked him whether he was familiar with the principle of “distributed activation” in the context of M1 research. First inspired by Patrick’s own experience with sports injuries and receiving physiotherapy, DA originated as a technique to co-activate muscles around joints for stabilization—similar to what a PT may ask you to do to speed up recovery. Then, in the process of iterative refinement, as the method was optimized for communicability, it turned out that the idea that “all the muscles needed to be contracted all the time in any movement” was very easy to remember, both for junior instructors and for students. And once DA spread across all the movements in the syllabus, it turned out that it made learning separate control easier.

While I understand very few people would commit to a specific physical activity just to get an experiential insight into the M1 organization, I believe that the number of people who could benefit from the DA and FSI techniques is virtually limitless.

These unintuitive but simple techniques effectively improve the ability to sense muscles at higher resolution and aid in rebuilding and universalizing the movement vocabulary, which can then be used to learn more complex motor skills.

If you are interested to know more about the neuroscience behind Baseworks, check out this page.