Small but Mighty

Positioned to the rear of the brain, below the large expanse of the cerebrum, the cerebellum (shown coloured white in the brain of a newborn mouse) occupies only about ten percent of the brain’s volume (in humans). Despite its diminutive size, it contains a whopping eighty percent of the brain’s neurons and recent evidence suggests it has greater influence on the brain than once thought. The cerebellum has long been known to coordinate movements and enable motor learning such as walking and riding a bike, but there’s evidence it’s important for cognition too. Moreover, scientists examining how the cerebellum’s wiring is established have found its projections (multicoloured) to the rest of the brain arise remarkably early in embryonic development. The cerebellum had been assumed to integrate with the rest of the brain more gradually, but the new findings suggest it actually shapes brain function from the earliest stages.

Written by Ruth Williams

Ruth Williams

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Ruth is a freelance science journalist based in the US. She's a regular correspondent for The Scientist, and her work has appeared in The Lancet, Nature, Scientific American Mind, BBC Focus and elsewhere. Twitter @rooph

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• Image from work by Raquel Murcia-Ramón et al, Instituto de Neurociencias UMH CSIC
• Instituto de Neurociencias (Universidad Miguel Hernández-Consejo Superior de Investigaciones Científicas), Alicante, Spain
• Image originally published as 'Credit must be given to the creator' equating to a Creative Commons Attribution 4.0 International (CC BY 4.0)
• Research published in Proceedings of the National Academy of Science (PNAS), July 2025