Healthy brain. Coloured Magnetic Resonance Image (MRI) scan through the human head, showing the brain in coronal section. The brain is seen to consist largely of the two cerebral hemispheres with white matter (coloured blue), rich in nerve fibres, and grey matter (orange) rich in nerve cells. These are linked (at upper centre) by a thick band of nerve cells known as the corpus callosum. At lower centre is the middle part of the brainstem, or pons, which form a connection between the midbrain and the medulla oblongata (below). MRI scanning creates slice" images through the body, useful in the diagnosis of brain tumours and cancer."