Life Without Your Cerebellum

Tucked away at the back of your brain is a phenomenal, but ignored structure. This amalgamation of neurons contains almost 50% of the cells in your brain, but only takes up 10% of the space. Even so, it remains unextolled and little considered. In the words of researcher and neurologist Jeremy Schmahmann, it’s the “Rodney Dangerfield of the brain” because “It don’t get no respect.” It’s the cerebellum.

The cerebellum in lateral and anterior views, from Anatomography maintained by Life Science Databases (LSDB)

Even though the cerebellum has so many neurons and takes up so much space, it is possible to survive without it, and a few people have. There are nine known cases of cerebellar agenesis, a condition where this structure never develops. These people live life a bit differently than the rest of us and have provided a unique view of how the cerebellum works.

Most scientists, and even regular people, know the basic function of the cerebellum. It helps coordinate motion and ensures that you remain balanced and controlled in daily life. When the motor cortex in your cerebrum tells part of your body to move, the cerebellum makes sure that motion happens in the right way.

If I wanted to scratch my head with my right arm, I’d have to do it in a very specific order. From the lift of my arm to the curl of the fingers, the motion has to be organized just right to make sure I’m not scratching the air or slapping myself in the face. That’s what the cerebellum does. It makes sure that everything goes in order.

Sobriety test photo from www.sandiegoduiattorneynow.com

If you’ve ever seen someone pulled over on the side of the road, doing a sobriety test with a police officer, you’ve seen a basic test for cerebellar function.

But people with cerebellar agenesis have let us see a lot more of what the cerebellum does, and it’s not just motor coordination. Before the development of fMRI, and even today when we have that technology, one of the best ways to learn about how a portion of the brain works is to find people who are missing that portion, or in whom it has become damaged. One of the people who lives without a cerebellum is Jonathan Keleher, a 36 year-old man from Boston.

Jonathan was born without a cerebellum, it just never developed. On an X-ray…