Figure 1.

Myelinated cortical thickness measurements. The depth of the human cerebral cortex can be roughly subdivided into lightly myelinated and heavily myelinated portions, as seen in representative 40 μm thick histological sections stained for myelin (adapted from Braitenberg, 1962). This leads to intracortical contrast on heavily T₁-weighted MRI, which can be used to segment the cerebrum into lightly myelinated gray matter (GM), heavily myelinated gray matter (mGM), and white matter (WM) tissue classes. Measuring the thickness of the GM and mGM tissue classes yields the thickness of the lightly myelinated (G) and heavily myelinated cortical layers (M). Overall cortical thickness (T) is also measured. The mGM class is thicker in regions known to be highly myelinated, such as the primary motor cortex in the precentral gyrus (PG) and the primary auditory cortex in Heschl's gyri (HG), MFG, middle frontal gyrus.