Coloured diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) scan showing primary somatosensory white matter fibres in the brain. The primary somatosensory cortex receives sensory information, such as touch, temperature and pain, from various parts of the body. The green tracts highlighted here receive information from the gastrointestinal (GI) tract. 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.