White grey sign

White grey sign is useful for identifying the central sulcus on MRI images. It reflects that fact that primary motor and sensory cortex has more myelin in it than other cortices. This results in a whitening of the cortex on T1-weighted imaging, especially noticeable at higher field strengths. One can quickly assess the grey-white junction, and confirm that the central sulcus exhibits reduced contrast on both sides. This sign is synergistic with a differential in cortical thickness across the pre and postcentral gyri in the central sulcus (pre=thicker and post=thinner). This sign is also present in other primary cortices: primary visual and primary auditory.