Magic Myelin

March 3, 2013 at 9:01 AM
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Magic Myelin

Lauren Blachorsky QC ’15 and Jim Stellar

Lauren and I share a large interdisciplinary class that investigates how the brain mechanisms of pleasure and pain might work in a larger society. She also works in a professor’s laboratory who studies neurogenesis and from where another student came who wrote a blog post with me on the birth of new neurons in the brain and their potential integration into motor skill learning circuits in adults. Another powerful potential form of neuroplasticity is to change the connections between the existing neurons to somehow make them better. In a 2009 book, Talent Code, Daniel Coyle proposes just such a brain mechanism that underlies skill learning in highly talented athletes. For instance, how did Roger Federer get to be so good at his famous backhand swing, or how did Michael Phelps develop his awesome butterfly stroke. This is highly relevant to experiential education when you consider another famous book, Outliers, by Malcolm Gladwell, which proposes that education, experience, training, really can change us to make us something that we were not before – so good that we are an outlier in this area of skill (athletics or violin playing or expert knowledge in the field of accounting). We decided to investigate this idea here.

Laruen, what is myelin and what is the basic idea that it changes when one learn?

Myelin is a substance produced in the brain that wraps around the axons of neurons and axons are the long connections between the nerve cells themselves that make up the brain circuits that underlie our functioning. Because of this wrapping, myelin speeds up conduction of the axon in the nervous system. In English, this means that myelin allows us to send messages from one neuron to another neuron much quicker than if the myelin was not there. Myelin develops as we grow, having its peak effect in childhood and may underlie some of the fundamental changes through which children go when it appears that they have suddenly developed a new ability. The good news is we may be able to grow myelin as adults to better wrap around our neurons. With enough of a certain type of practice, I may be able to trigger myelination and develop the motor skills to snowboard, do backflips, or even more beyond motor skills to understand physics.

Cool. So what evidence is there that myelin changes are associated with skill development in humans?

This blog often cites brain activity scans, most often fMRI, but here we need to look at a different brain scanning device. Using a technique called Diffusion Tensor Imaging (DTI), researchers were able to measure that professional piano players had more myelinated axons in a certain area of the brain, and that the myelination correlated to the amount of time spent practicing.1 A second study taught participants how to juggle, and then using DTI, found that the participants who practiced juggling, had more white matter (cells that have myelinated axons)2. These studies suggest that the level of myelination changed with practice. If so, that practice changes the timing (speeds it up) between neural circuits in various brain areas, these changes in timing could change the way these circuits compute. There is also a general notion in Coyle’s book that because the axons now conduct faster the skill is better. It does seem obvious going back to the athletes you mentioned in the beginning, that they do act faster, as well as with more precision, than do amateurs. That is why we watch them.

OK. Let me play the role of the skeptic. I know the brain scan shows a difference between more vs. less practiced individuals in those brain connections. But I am a neuroscientist. By what mechanism does an axon firing as part of that circuit produce more myelin on that axon?

To understand why myelin forms during training, we need to go a little bit deeper in the process of how neurons send messages to each other. A neuron fires a special signal called an action potential in its axon. This signal is an electrical impulse that relays information from one neuron to another. In most instances, the more a neuron fires action potentials, the more that neuron is being used in the nervous system, perhaps for learning. Bringing this point back to myelin, myelin wraps around the axon of the neuron and does two things. First, it helps conserve energy in the axon, which is important as the brain already uses a disproportionate amount of the body’s energy. Second, myelin makes the action potential go down the axon faster and speeds up neuronal processing. Myelin itself is made by another brain cell called an oligodendrocyte that “grabs” a hold of the axon and wraps around it, much like a person would roll up a rug around a cardboard tube. Interestingly, not all neurons are myelinated, and those that are, do not all have the same amount of myelination.

So what determines the amount of myelination an axon receives? It seems there are many factors, but research3 shows that one factor is a substance called adenosine. It comes from the basic “fuel” molecule of the cell, Adenosine TriPhosphate and a small amount of adenosine is released by the axon each time its sends an action potential. The myelin-making oligodendrocyte cells have adenosine receptors on their surfaces, and when they detect adenosine they start wrapping axons in myelin. This mechanism is activity-dependent. In order to release adenosine, the neuron has to fire action potentials. In order to fire action potentials, a person needs to be using the brain circuitry for something. This means that if I ever want to be able to do backflips, I should go start practicing now, to release adenosine in those skill-producing brain circuits that need refinement so I can do a good backflip.

Whether you are learning to do a backflip or learn accounting or practice the violin, the brain seems to change when you learn. We always knew that, but the old idea in neuroscience was that these changes only occurred where the neurons interacted with each other in their existing (synaptic) connections which could be strengthened or weakened. The old idea was that the fundamental structure of the brain did not change such as the number of neurons in the brain or the basic timing of the communication between them. It now seems that both of these assertions are wrong. The brain can change in remarkable ways as you learn. The good news is that you are not so stuck with the system you have now, even in adulthood, if you practice in such a way that you really engage the relevant brain circuits, you will change your brain. Then you will be what Malcolm Gladwell called an “outlier” in a book by the same name, mentioned above. That is a tremendously exciting concept to both of us and one we intend to pursue. Of course, our thesis is that experiential education coupled to a strong classical education is an excellent way to learn and change your brain.

1 Bengtsson and others 2005

2 Scholz1, Miriam C Klein1,2, Timothy E J Behrens1,2 & Heidi Johansen-Berg1

3 Adenosine: A Neuron-Glial Transmitter Promoting Myelination in the CNS in Response to Action Potentials”)

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