You know that thing about how you use only ten percent of your brain?

Well, there is a special little ten percent that does, admittedly, do a lot of heavy lifting. On the other hand, the brain has this amazing ability to make do with less than its full complement of bits.

This article reports on a recent case report coming out of China and published in Brain,  in which a married 24-year-old mother presented to the hospital with a long history of dizziness and unsteady gait, and a recent history of nausea and vomiting extending back a couple of months. Turns out she has no cerebellum. Take a look at this:

No cerebellum. Like, at all. She’s only the ninth documented case of someone who hasn’t got one.

The cerebellum is an extremely densely packed bundle of neural tissue that sits underneath the back of the brain, right in that space that, in the above MRI image, looks forlornly empty. It’s a fascinating structure, because its anatomical features suggest that it’s extremely important, and yet no one is a hundred percent sure what it does. It takes up about ten percent of the volume inside the skull, but it contains an incredible half of all the brain’s neurons. Just that fact alone has to mean it’s pretty important, and yet its function is not terribly well understood. It’s clear that it contributes to the fine-tuning of motor output and the maintenance of balance. It has a way of popping up here and there in other research as well, though, in ways that aren’t easy to integrate into a comprehensive theory of how it works.

Interestingly, this young woman has made it to age 24, is married, and has a (neurologically normal) daughter. She apparently always did have motor and balance problems. She was four years old before she could stand on her own, and seven before she could walk unassisted. She also did not speak until age six, and now she has trouble articulating words properly, although her ability to understand language is normal. She is apparently mildly cognitively delayed.

The amazing thing is that her balance and motor control problems are what her neurologists would have considered characteristic of mild damage to the cerebellum, rather than not having a cerebellum at all. It’s another remarkable testament to the brain’s ability to find a way to do what’s asked of it, even if the equipment it’s working with is damaged, compromised, or in this case, entirely absent.

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