Coloured diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) scan showing white matter fibres of the corticospinal tract in the brain. The front of the brain is at right. The corticospinal tract conducts nerve impulses to and from the brain's motor cortex and the spinal cord. It is the main motor network fibre bundle. Diffusion tensor imaging measures the direction of water diffusion, which in the brain reveals the orientation of nerve fibres. Red fibres have a left to right orientation, green a front to back orientation and blue an up and down orientation.