Brain scans. 3D-magnetic resonance imaging (MRI) scans of a healthy brain. Axial (horizontal) sections through the brain from the top of the brain towards the cerebellum. The largest part of the brain is the cerebrum, which is divided into two cerebral hemispheres. It is responsible for conscious thought, emotion and voluntary movement. Below this is the cerebellum, which controls voluntary muscular movement and maintains posture and balance.