The 'little brain' at the back of the head holds most of the brain's neurons and fine-tunes movement, balance and timing — and turns out to help with thinking and emotion too.
Brain Anatomy
Intermediate
The Cerebellum
The Editors
January 4, 2026
2 min read
In plain English
The cerebellum sits at the back of the brain, under the cerebrum. It makes movements smooth and accurate, keeps you balanced, and helps you learn physical skills by correcting errors. Surprisingly, it contains about four out of five of the brain's neurons.
Intermediate level: Builds on the basics. Introduces the real vocabulary and the mechanisms behind it.
Concepts to know first
The cerebellum ("little brain") is tucked under the back of the cerebrum, behind the brainstem. It accounts for only about 10% of the brain's volume but contains around 80% of its neurons — some 69 billion — mostly tiny granule cells. Its cortex is folded into very fine leaf-like folds (folia); unfolded, its surface area is a large fraction of that of the cerebral cortex.
A remarkably regular circuit
Unlike the cerebral cortex, the cerebellar cortex has a strikingly uniform, crystal-like wiring. Inputs arrive through mossy fibres (via granule cells, whose axons form the parallel fibres) and climbing fibres from the inferior olive in the brainstem. Both converge on the large Purkinje cells, the only output of the cerebellar cortex, whose flat, fan-shaped dendrites receive up to around 200,000 parallel-fibre inputs. Each Purkinje cell gets just one climbing fibre, which is thought to deliver an error signal.
Coordination and learning
The cerebellum compares what you intended to do with what actually happened, and adjusts. It is essential for smooth, accurate, well-timed movement, for balance and posture, and for motor learning — adapting a reach after putting on prism glasses, keeping your gaze steady while your head moves, or learning to ride a bike. It works partly by building internal predictive models of the body.
Signs of cerebellar damage
Damage causes ataxia: clumsy, poorly coordinated movement, a wide unsteady gait, tremor that worsens as the hand approaches a target, slurred speech, and abnormal eye movements. Alcohol temporarily affects the cerebellum, which is why roadside sobriety tests check balance and finger-to-nose accuracy.
More than movement
Brain imaging and studies of patients have shown that parts of the cerebellum connect to prefrontal and association cortex and contribute to language, working memory, timing and emotion. Damage can cause a cerebellar cognitive affective syndrome with subtle problems in planning, language and mood.
Everyday examples & things to try
Try it
Why you can't tickle yourself
Try tickling your own palm, then have someone else do it. Your own touch feels weaker. The cerebellum predicts the sensory consequences of your own movements and dampens them — so a self-tickle isn't surprising enough.
Analogy
An autopilot that learns
The cerebellum is like an autopilot that constantly compares the planned flight path with the real one and makes tiny corrections — and gets better at it every flight.
Key takeaways
- The cerebellum holds about 80% of the brain's neurons in a highly regular circuit.
- It coordinates and times movement, maintains balance and drives motor learning via error signals.
- Damage causes ataxia; it also contributes to cognition and emotion.
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