INTRODUCTION The diversity of cell types is a defining feature of the neuronal circuitry that
makes up the areas and layers of the mammalian cortex. At a molecular level, the extent of
this diversity is now better appreciated through recent efforts to census all potential cortical
cell types through single-cell transcriptional profiling. Cortical populations can be
hierarchically subdivided into multiple putative transcriptomic cell classes, subclasses, and
types. This new catalog of neuronal subclasses and subtypes opens up new questions and …