Neurons are the best-known cells in the brain, but they are far from the only ones. Another type, called glia, actually makes up a whopping 85 percent of brain cells. For a long time, scientists thought that glia simply held neurons together. (Indeed, “glia” take their name from the Greek word for glue.) But recent research reveals that glial cells also become active during learning.
One type of glial cell wraps around nerve axons. (Note: Not all axons have this wrapping.) These wrapping cells create what’s known as a myelin sheath. Myelin is made of protein and fatty substances. It insulates the axons. Myelin is a bit like the plastic coating that jackets the copper wires in your home. That insulation prevents electrical signals from inappropriately leaking out of one wire/axon and into another.
In axons, the myelin sheath has a second role: It actually speeds the electrical signals along. That’s because glial cells force a signal to jump from one spot on the axon to the next. As it hops between glial cells, the signal moves faster. It’s kind of like flying from one spot to the next, instead of taking the train. As the brain learns, the glial cells grow, change and help increase the efficiency with which axons move signals.
Research has found that when new skills are learned, the amount of myelin insulating an axon increases. This happens as the size of individual glial cells increases. New glial cells also may be added to bare axons. These changes improve the ability of a neuron to signal, and that leads to better learning.
A thicker myelin sheath helps improve all types of brainy tasks. These include reading, creating memories, playing a musical instrument and more. A thicker sheath is also linked with better decision-making because the nerves are firing faster.
Nerve cells continue to add myelin well into adulthood, as our brains continue to grow and develop. The prefrontal cortex, for example — that area where decisions are made — gains myelin well into a person’s 20s. This may explain why teens don’t always make the best decisions. They’re not finished sheathing their nerve cells. But there is hope. And getting enough sleep certainly can help. Glial cells, like neurons, seem to change most during certain stages of sleep.
Exactly what causes the glial cells to change remains a mystery. The research keeps coming to the same conclusions though: the more you exercise your brain, the better and more efficient it functions.