The Human Cerebellum Is Far Bigger Than Originally Believed

The cerebellum, which is Latin for “little brain” plays crucial roles in integrating signals, enabling coordination and movement, including in the actions that enable us to speak and see normally. It sits behind the top of the brainstem, where the brain and spinal cord meet. New research has suggested that the cerebellum may not be so little after all.

The cerebellum is like a sheet that has been crinkled up to create hundreds of folds, compacting the structure so it’s about one-eighth of the volume of the cerebral cortex. It had been thought that the cerebellum was, therefore, comparatively small. With a powerful MRI, scientists have found, however, that the surface area of the cerebellum is actually about eighty percent as big as the cerebral cortex.

“The fact that it has such a large surface area speaks to the evolution of distinctively human behaviors and cognition,” said Martin Sereno, psychology professor, cognitive neuroscientist, and director of the SDSU MRI Imaging Center. “It has expanded so much that the folding patterns are very complex.”

In this study, which was reported in the Proceedings of the National Academy of Sciences, the investigators utilized open-source computational tools to reconstruct the cerebellum’s folded surface. Sereno and colleagues learned that when unfolded, the cerebellum looks like a “crepe” that’s about four inches wide and three feet long.

“Until now we only had crude models of what it looked like,” Sereno said. “We now have a complete map or surface representation of the cerebellum, much like cities, counties, and states.”

Previous work has shown that the cortex and cerebellum are similar, except in the cortex, the brain is arranged roughly like the regions of the body it represents, while in the cerebellum, the arrangement is more random. The cerebellum is thus able to easily gather information from different places.

“You get a little chunk of the lip, next to a chunk of the shoulder or face, like jumbled puzzle pieces,” Sereno explained. “When you think of the cognition required to write a scientific paper or explain a concept, you have to pull in information from many different sources. And that’s just how the cerebellum is set up.”

Once thought of as an integrator of basic functions, the cerebellum also now seems to play a role in more advanced processes as well, like mathematics.

“Now that we have the first high-resolution base map of the human cerebellum, there are many possibilities for researchers to start filling in what is certain to be a complex quilt of inputs, from many different parts of the cerebral cortex in more detail than ever before,” Sereno said.

Sources: AAAS/Eurekalert! via San Diego State University, Proceedings of the National Academy of Sciences

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