Connections in the brain of a healthy 29 year old female human viewed from the front, face on (anterior view). The top of the brain is at the top of the image. Brain cells communicate with each other through these nerve fibres, which have been visualised using diffusion imaging tractography. Diffusion weighted imaging is a specialised type of magnetic resonance imaging (MRI) scan which measures water diffusion in many directions in order to reconstruct the orientation of bundles of axons. Tractography is used to indirectly model these bundles of axons (nerve fibres), which transmit information between cortical regions at the brain's surface. For example, the bundles of fibres (tracts) closest to the viewer are travelling to the frontal lobe of the brain. Connections travelling from the corticospinal tract to the motor cortex are visible in blue/purple. The brain measures approximately 18 cm from front to back.