The cerebellum is an intriguing component of the brain. In humans it occupies only 1% of the brain volume, yet has approximately 69 billion neurons; that is 8% of the nerve cells in the brain. The cerebellum first arose in jawed vertebrates such as sharks, and early vertebrates also have an additional cerebellum-like structure in the hindbrain. Shark cerebellum-like structures function as adaptive filters to discriminate 'self' from 'other' in sensory...