Child's brain. Magnetic resonance imaging (MRI) scan of an axial section through the healthy brain of a three and a half year old child at the level of the corpus callosum. The front of the brain is at top. The corpus callosum links the two hemispheres (right and left) of the cerebrum (highly folded area), the largest part of the brain, and co-ordinates its functions. The cerebrum is responsible for conscious thought, emotion and voluntary movement. The black areas at the centre of the brain are the ventricles (cavities), which are filled with cerebrospinal fluid that cushions the brain.