For example, it has been estimated that if we were to use sections of about 35 square micrometers (millionths of a meter) at a thickness of 20 nanometers, we would need more than 1.4 billion sections to reconstruct fully just one cubic millimeter of tissue. So, while complete reconstructions of a small region of the mammalian brain are feasible, structures like the cerebral cortex – with a surface area of 0.22 square meters and a thickness of between 1.5-4.5 millimeters – cannot be fully reconstructed.