Brain scans. Coloured magnetic resonance imaging (MRI) scans through a human head showing a healthy brain. These are sagittal (side view) sections. The largest part of the brain is the folded cerebrum, which controls conscious thoughts. At the lower right of each scan is the smaller, highly-folded cerebellum, which controls balance and posture. In some of the scans (at top right, for instance) the brainstem is seen (bottom centre of brain), which links the brain to the rest of the body through the spinal cord. MRI uses radio waves and a powerful magnet to provoke tissues to emit signals depending on their composition. It is particularly useful for studying nervous tissue.