You might be surprised how little 3D they are. Look at the top line model: the human cortex is only about 3 mm thick, and comprised of only six layers of neuron

You might be surprised how little 3D they are. Look at the top line model: the human cortex is only about 3 mm thick, and comprised of only six layers of neurons. It may look like a big lump of meat, but that's because it's folded to fit more area into the limited volume available in the skull. If you unfold it, you get this very thin sheet with a whopping area of 2500 cm^2.