Three Cheers for the Corpus Callosum!

The what? Those of us with MS, likely already understand how the brain isn’t simply one organ, but an entire collection of different organs with chief jobs. One of the brain’s unsung heroes? The hardworking organ is known as the corpus callosum.

I remember learning about the job the corpus callosum plays in brain function during a presentation from my MS specialist. This was before a group of newly diagnosed patients, myself being one of them. I found myself then - and now - marveling at the importance of this organ in our overall brain function.

What is the corpus callosum?

When we imagine the brain, we envision the cerebrum, the largest part of it. It’s divided into two hemispheres, what we think of as the right and left brains.

These hemispheres need each other and must work together. To do so, they’re connected by a thick, C-shaped bundle of nerve fibers positioned right down the center between them. This organ, the corpus callosum (CC), creates a critical communications network that connects and serves both sides of the brain.

The CC is the cerebrum’s largest white matter organ, composed of around 250 million nerve fibers. Its central strip of white matter measures about 4 inches long. From its embedded center between the hemispheres, the CC’s millions of fibers branch out to wrap around four key parts of the brain to connect both halves like a big net.

Think of the CC as a “neural bridge.” It exists to transfer messages—cognitive, motor, and sensory—at a constant rate between hemispheres.^1,2

When you hear people making comparisons between computer processors and the human brain’s neural network, they’re basically describing our own personal “information superhighways.”

How the corpus callosum functions in a person with MS

Personally, I envision our CC as the brain’s “transportation grid.” For instance, if you find you have a “pothole” (or lesion) somewhere in your central nervous system, the CC works to detour messages around and away from that damaged area.

That’s one of the things I find so amazing about this organ buried deep inside our skulls. It exists to keep everything working even in the face of damage. For people with MS with healthy, undamaged CC tissue, the organ works even harder, continually rerouting information around damaged areas of the brain.

It’s likely we experience slowdowns in some of our own messaging because the CC must find alternative routes around our lesions and that takes energy. A busy CC, running detours around active disease in the brain, uses a lot of glucose—the brain’s sole fuel—to do so.³

This may explain the fatigue we feel as people living with MS. We’re literally “running out of gas” as the CC works to complete its nonstop tasks. But don’t blame the CC! It’s just doing its job!

This also may be why taking a nap—which helps restore blood glucose—gives us more energy afterward. As we sleep, the CC can continue to do its job with fewer demands, and the body can recuperate some spent energy, allowing the CC to also work more efficiently.

Can the corpus callosum become damaged?

Of course, it can. The most common CC damage occurs during the brain’s development following birth. But MS can come along, the autoimmune thief that it is, and indiscriminately lay down damage on the CC as well. In fact, the CC is one of MS’s favorite targets.⁴

What happens then? If our neural bridge isn’t functioning because of MS lesions, what can we expect? One study seems to think that both cognitive and physical impairment are, at least in part, influenced by damage to the CC.⁵

But it appears the biggest concern links to cognitive dysfunction—such as memory problems, reductions in the speed of information processing, attention deficit, and speech issues. Research still needs to work out the details, however, as it’s unclear if lesion load might also shoulder some of the blame.⁵

At least from a clinical standpoint, evidence of atrophy in CC does help neurologists in distinguishing MS from other kinds of demyelinating diseases—chiefly, neuromyelitis optica spectrum disorders (NMOSD) and acute disseminated encephalomyelitis (ADEM).⁶

Also, research has found a “statistically significant correlation of future clinical disability (according to EDSS score) with the brain atrophy and corpus callosum atrophy” in another study.⁷ It turns out that damage to the CC in the first year following onset may be the simplest and most reliable predictor of long-term disability progression.⁷

This is to say that the CC is still working hard to help us out, even when it’s damaged. Three cheers for the corpus callosum!