The cerebellum, or “little brain,” contains over half of the total neurons in the brain and contributes to multiple functions. Primarily, its functions are related to voluntary movements and balance. Movement of a body part requires multiple muscles to move at different times and with different magnitudes of force. The cerebellum sends signals to the muscles in order to coordinate their relaxations and contractions so an overall movement results. Balance is maintained by the cerebellum. As somebody stands, he shifts minutely in order to maintain his posture. If his body is shifting to the right slightly, his body will tell his brain that he needs to shift to the left to maintain balance. The cerebellum takes this signal and sends others to his body to shift to the left.
Motor learning relies on the cerebellum to learn from mistakes in motion. For example, when somebody learns to walk, she falls down and trips often. Over time, she learns how to coordinate her body in such a way that she manages to put one foot in front of the other while maintaining balance. The same trial-and-error methodology is used to learn other motor skills such as using eating utensils, dancing, sports, etc. Not only would one learn how to, say, catch and throw a ball, but would also learn how to predict where the ball will fall so one could catch it. It analyzes the visual signals associated with movement and adjusts the body’s position and movement accordingly.
Even the way one learns how to enunciate words is mediated via the cerebellum. It is responsible for the movement of the vocal chords to make sound, coordination of exhalation and vocal chord motion to generate deliberately manipulated sounds, and learning how to make different sounds.
Vestibuloocular Reflex (VOR)
Experiments have been done showing the relationship between cerebellar learning and our response to visual stimuli. Imagine you are given a ball and are told to throw it to the right of a wall. Sounds simple. Now you are given goggles that shift everything you see to the left. Initially, you will keep throwing the ball at the center of the wall, but over time you will learn to throw accurately to the right. Now the goggles are taken off. Your motor programs have been calibrated to throw to the left of the original spot, and now you are throwing the ball inaccurately. Over time, your motor programs will recalibrate and you will start throwing accurately. Those with cerebellar damage will find that they cannot adapt to the goggles. They will start throwing to the right and then to the left with the goggles on without ever learning to compensate to the right.