http://www.biosciencetechnology.com/news/2014/10/myelin-vital-learning-new-practical-skills?
New evidence of myelin’s essential role in learning and retaining new practical skills, such as playing a musical instrument, has been uncovered by UCL research. Myelin is a fatty substance that insulates the brain's wiring and is a major constituent of "white matter." It is produced by the brain and spinal cord into early adulthood as it is needed for many developmental processes, and although earlier studies of human white matter hinted at its involvement in skill learning, this is the first time it has been confirmed experimentally.
The study in mice, published in Science, shows that new
myelin must be made each time a skill is learned later in life and the
structure of the brain’s white matter changes during new practical
activities by increasing the number of myelin-producing cells.
Furthermore, the team say once a new skill has been learnt, it is
retained even after myelin production stops. These discoveries could
prove important in finding ways to stimulate and improve learning, and
in understanding myelin’s involvement in other brain processes, such as
in cognition.
For a child to learn to walk or an adult to master a new skill such
as juggling, new brain circuit activity is needed and new connections
are made across large distances and at high speeds between different
parts of the brain and spinal cord. For this, electrical signals fire
between neurons connected by “axons”– thread-like extensions of their
outer surfaces which can be viewed as the "wire" in the electric
circuit. When new signals fire repeatedly along axons, the connections
between the neurons strengthen, making them easier to fire in the same
pattern in future. Neighboring myelin-producing cells called
oligodendrocytes (OLs) recognize the repeating signal and wrap myelin
around the active circuit wiring. It is this activity-driven insulation
that the team identified as essential for learning.
The team demonstrated that young adult mice need to make myelin to
learn new motor skills but that new myelin does not need to be produced
to recall and perform a pre-learned skill. They tested the ability of
mice to learn to run on a complex wheel with irregularly spaced rungs.
The study looked at thirty-six normal mice and thirty-two mice with a
drug-controlled genetic switch to prevent new OLs and myelin from being
made. They found the mice that were prevented from producing new myelin
could not master the complex wheel, whereas those that could produce
myelin did learn, with differences between the two groups’ abilities
seen after only two hours of practice.
A second experiment looked at mice that were first allowed to learn
to run on the complex wheel before being treated with the drug to
prevent further myelin production. When the mice were later
re-introduced to the complex wheel, they were immediately able to run at
top speed without having to spend time re-learning. This shows that the
inability to make new myelin did not affect the mouse’s running ability
and that new myelin is not required to remember and perform a skill
once learned; it is required only during the initial learning phase.
"From earlier studies of human white matter using advanced MRI
technology, we thought OLs and myelin might be involved in some way in
skill learning, so we decided to attack this idea experimentally. We
were surprised how quickly we saw differences in the ability of mice
from each group to learn how to run on complex wheel, which shows just
how fast the brain can respond to wrap newly-activated circuits in
myelin and how this improves learning. This rapid response suggests that
a number of alternative axon pathways might already exist in the brain
that could be used to drive a particular sequence of movements, but it
quickly works out which of those circuits is most efficient and both
selects and protects its chosen route with myelin," said Lead Researcher
and Professor Bill Richardson, director of the UCL Wolfson Institute
for Biomedical Research.
Richardson added: “We think these findings are really exciting as
they open up opportunities to investigate the role of OLs and myelin in
other brain processes, such as cognitive activities (like navigating
through a maze), to see if the requirement for new myelin is general or
specific to motor activity. I’m keen to find out the precise sequence of
changes to OLs and myelin during learning and whether these changes are
needed more in some parts of the brain than others, which might shed
light on some of the mysteries still surrounding how the brain adapts
and learns throughout life.”
Source: University College London
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