Scientists have unexpectedly discovered that the function of brain glial cells (not neurons) to produce new myelin is critical for learning motor skills. A study published in the October 16 issue of Science suggests that changes in myelin, the insulating layer on the axons of neurons, play an important role in learning motor skills. Genetically engineered mice that were unable to produce myelin sheaths were much worse at learning new motor skills than controls. ”This article clearly shows that the ability to generate new myelin is necessary for adult mice to learn complex motor skills,” said Gabriel Corfas of the University of Michigan, who wrote a review article about the study in the current issue of Science. Learning has long been thought to be simply the result of changes in neuronal anatomy or function. This study challenges that view because myelin is generated by oligodendrocytes. “This article is striking in that it tells us that glial cells actually do the more important work,” said Professor Robin Franklin of the University of Cambridge. “There is now a growing body of evidence that glial cells have a fundamental and important role in the brain.” The study reveals changes in the way the brain accesses information, changing the understanding of the mechanisms by which the brain works. Magnetic resonance imaging experiments in humans and rats have correlated the learning of motor skills with changes in the brain’s white matter, which consists of axons encased in myelin sheaths. However, it has been unclear how these changes occur. William Richardson of University College London led a team of researchers who selectively inactivated the Myrf gene, which encodes a myelin regulatory factor, in oligodendrocyte precursor cells from mice. Myrf is not normally expressed in oligodendrocyte precursor cells, although the factor is required for differentiation of new oligodendrocytes. “Myrf is only expressed when precursor cells begin to differentiate, and if Myrf is absent precursor cells are stuck at this stage,” Richardson said. In other words, a lack of Myrf prevents the formation of new oligodendrocytes and the production of new myelin sheaths. But this doesn’t affect the oligodendrocytes that are already there. Compared to mice in which one copy of Myrf is inactivated, both copies have fewer new oligodendrocytes and myelin in the corpus callosum, the area connecting the two hemispheres of the brain that is highly encapsulated in myelin and is associated with learning motor skills. Mice lacking Myrf have difficulty learning to run on a complex wheel. Normal mice, on the other hand, learned this skill quickly and improved every day. The researchers exposed the mice to the complex wheel before removing Myrf. The study showed that for mice that had already learned this skill, Myrf loss did not affect how fast they could run, suggesting that myelin affects learning rather than recall or motor coordination. ”We know that synapses between neurons are reinforced when neural circuits are activated, which is thought to be the basis for neuronal learning. This synaptic reinforcement is known as long-duration enhancement,” Richardson said. “Our study shows that in addition to this mechanism during learning, active circuits need to be covered by myelin.” Next, Richardson et al. will investigate the role of oligodendrocytes in other types of learning. “Finding new mechanisms involved in the learning process can provide people with new targets for interference and improve our ability to learn,” Richardson said. Understanding the role myelin plays in the learning process could also provide help for demyelinating diseases, such as multiple sclerosis. ”This study is a milestone in the field of myelin research and neurology,” Franklin said.