Every AREA of the Neocortex has 6 main cell layers,  but each AREA is
characterized by its unique variation from the  general pattern:  For example
Visual Cortex  shows a very thickened Layer IV; similarly Motor Cortex shows a
prominent Layer VI; and the Frontal Cortex has almost no Layer IV.  These
differences in layers are due to the cells those layers contain (or don't).