A Brain of two Halves

‘Your left hand doesn’t know what your right hand is doing’ is a saying used to convey the idea of disorganisation. Strangely, some people experience exactly that feeling because the part of their brain that knows what one hand is doing really does not know what the other hand is doing. How could this be? The brain is divided into two relatively symmetrical halves; they are only relatively symmetrical because although they look the same they have very different functions. The split occurs from nose to back so the two halves are known as the right hemisphere and the left hemisphere. They are joined at the base of the hemispheres by commissural fibres which are bundled into structures called ‘commissures’ (the corpus callosum, the massa intermedia, and the anterior commissure are the most important of these structures). If these fibres are cut, the two hemispheres of the brain become disconnected and have no internal means of communicating with each other.