The left and right brain hemispheres share information through the nerves that join them. In some epilepsy patients these nerves are cut to relieve their symptoms. Studying these 'split-brain' patients has revealed a lot about the hemispheres. For example, patients cannot name an object, say an apple, shown on their left-hand side even though they recognise it. This is because information about the apple is sent to the right side of their brain, but cannot cross to the left side, which usually deals with language.