The grey matter contains the bodies, axon terminals, and dendrites of the brain cells, and it is where all of the higher mental processing occurs. The grey matter is what is typically depicted when you see a picture or icon of a brain, as it is primarily located around the outside. This outermost layer of the brain is also referred to as the cerebral cortex.
The cerebral cortex is subdivided into 4 major lobes: Frontal, Parietal, Occipital and Temporal. These lobes are further subdivided into smaller cortical areas or regions based on function and morphology.
If you click on the Grey Matter button above, you can examine the subdivisions of the cerebral cortex and other subcortical regions of the brain in 3D.
The white matter contains the axons of the brain cells and forms the internal portion of the brain. The axons are what connect the different grey matter regions together. You can think of the grey matter as the 'computers' of the brain, while the white matter is made up of all the 'cables' that connect the computers, allowing them to send data and interact.
The white matter can be subdivided into individual tracts based on the grey matter regions the axons are connecting. These tracts are also grouped by the types of regions they connect. Association tracts connect different regions within the same hemisphere of the brain. Projection tracts extend vertically between superior and inferior brain areas and the spinal cord. These tracts carry information from the brain to the rest of the body. Commissural tracts cross between brain hemispheres, connecting the corresponding lobes of each side.
If you click on the White Matter button above, you can examine 20 of the major white matter tracts of the brain in 3D.
The grey matter 3D visualization is displaying 3D surfaces from Freesurfer's aparc+aseg segmentation. Code for translating the labels from the aparc+aseg.mgz file into individual 3D surfaces can be found here.