Brain scans. Magnetic resonance imaging (MRI) scans through a human head showing a healthy brain. The bottom row (and one at lower right) are axial sections with the front of the head at top. The others are sagittal sections with the front at left. The largest part of the brain is the folded cerebrum, which controls conscious thoughts. The highly-folded cerebellum, which controls balance and posture, is seen at lower right in the sagittal scans. Eyes (white circles) are seen in some of the scans at lower right. 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.