Brainwaves: The Cerebellum

When we view the brain from the back, the cerebellum is the part that is very wrinkled and looks like a second, smaller, brain (Figure 1). At one time the cerebellum was indeed described as "the lesser brain". When one cerebral hemisphere is flattened out, (the wrinkly "bark" or one half of the brain) its surface area is almost equivalent to the surface of a flattened and folded out cerebellum. However, when the cerebellum is folded up it take up much less space and is about the size of a human fist. Flattening out the cerebellum produces a surface with an average area of 1128 cm² which is around the size of an old-fashioned record album cover (Bowen & Parsons, 2003). The cerebellum contains more neurons (nerve cells) than the rest of the brain combined. While the cerebellum has become bigger during evolution, the way its neurons are wired has remained unchanged for over more than 400 million years. Therefore, the neurons in the cerebellum of a shark are organised in a similar fashion to that of a human (Bower & Parsons, 2003). The cerebellum is larger and more important in those animals that need to aim their movements precisely and take more time to do so. For example, the cerebellum is large in most bird species that require precision when landing. However, the cerebellum can be damaged by lesions in the sloth (an animal renowned for its slowness) and there are no behavioural changes produced (Murphy & O'Leary, 1973).