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The Mysterious White Matter of the Brain

It’s difficult to study but turns out to be very important

We all talk about “gray matter,” the cerebral cortex of the brain, thought to be the basis for learning, remembering, and reasoning. But what about “white matter”?

Neurologist Christopher Filley has the story as to why we don’t know much about it:

This lack of recognition largely stems from the difficulty in studying white matter. Because it’s located below the surface of the brain, even the most high-tech imaging can’t easily resolve its details. But recent findings, made possible by advancements in brain imaging and autopsy examinations, are beginning to show researchers how critical white matter is.

White matter is comprised of many billions of axons, which are like long cables that carry electrical signals. Think of them as elongated tails that act as extensions of the neurons. The axons connect neurons to each other at junctions called synapses. That is where communication between neurons takes place.

Axons come together in bundles, or tracts, that course throughout the brain. Placed end to end, their combined length in a single human brain is approximately 85,000 miles. Many axons are insulated with myelin, a layer of mostly fat that speeds up electrical signaling, or communication, between neurons by up to 100 times.

Christopher Filley, “You’ve likely heard of the brain’s gray matter – here’s why the white matter is important too” at The Conversation (May 5, 2022)

Apparently, our white matter has increased over many millions of years. Dr. Filley thinks that that is one reason humans have “unique mental capacities” though — given the nature of the capacities — one could argue with that.

For example, a really interesting question is how some humans manage with very little brain:

Some people think and speak with only half a brain. A new study sheds light on
how they do it.


Boy born with 2% of brain does maths, loves science. Noah Wall’s story raises intriguing questions about the relationship between the brain and the mind

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The Mysterious White Matter of the Brain