Note: See the bottom of the page for an explanation of this hierarchy
 What does this mean?
This is a "classification hierarchy" that is intended to be used by ontology engineers rather than neuroscientists. In this hierarchy each subcategory in the tree is a narrower term than its parent category. A common confusion concerns several categories here that begin with "Regional part of". New users are frequently unclear how it is possible to have a brain region like "Cerebral Cortex" on the same level as "Regional part of cerebral cortex". In this case, the children of "Regional part of cerebral cortex" are intended to capture those brain regions that are sub-parts of the cerebral cortex. In this hierarchy, it would be inappropriate to put sub-parts of the cerebral cortex under the category "Cerebral cortex" because those sub parts are not narrower terms for Cerebral cortex. For example, the Motor cortex is a Regional part of cortex, but the Motor cortex is not a Cerebral cortex.
If this seems too complicated, you might find an easier time looking at the part-wise hierarchy of brain regions that we have assembled.