Cerebellar function

The cerebellum does not command movement: it fine-tunes it. It regulates movement and controls balance: it coordinates gait, maintains posture, and controls voluntary muscle activity and muscle tone, the background tension a muscle holds even at rest. But there is one thing it cannot do: it cannot initiate the contraction of a muscle. That command starts somewhere else.

What it does is compare. On one side, it receives information coming from the cerebral hemispheres. On the other, it receives sensory feedback, a report of what the body is actually doing, which travels up from the periphery through the spinal cord. It also receives information from the muscles, the tendons, and the joints.

And if the two versions do not match, it steps in. When gait is not coordinated, the cerebellum sends a corrective command that compensates for the difference between the cortex's original command and what the sensors reported. It is not the part that decides to walk; it is the part that keeps comparing the intention with the result and corrects the difference step by step.