Normal human brain. Coloured magnetic resonance imaging (MRI) scan of a human head. The sagittal (side view) scan has revealed the head in cross section, passing through the left ear. The front of the head is at left. The largest part of the brain (orange) is the cerebrum, which is made up of two hemispheres and fills most of the head. It is responsible for conscious thoughts and actions, memory and personality. The arrangement of the muscles is shown in purple.