Simplify the following text for a Grade 15 native English-speaking person.
Original: The phylogenetically most recent part of the cerebral cortex , the neocortex ( also called isocortex ) , is differentiated into six horizontal layers ; the more ancient part of the cerebral cortex , the hippocampus ( also called archicortex ) , has at most three cellular layers , and is divided into subfields .
Simplified: The phylogenetically most recent part of the cerebral cortex , the neocortex , has six horizontal layers ; the more ancient part of the cerebral cortex , the hippocampus , has at most three cellular layers .