(A) Classification of established cell types in the cerebral cortex. These cells are broadly divided into neurons and glia. Neurons can be classified into glutamatergic projection neurons and GABAergic interneurons, each of which is highly heterogeneous and can be subdivided into many different subtypes, according to morphological, molecular and functional features. Glia can be divided into astrocytes, oligodendrocytes and microglia, which can also be categorized into several subtypes. (B) Developmental origin of the various cortical cell types. (C) Selected cell type markers of projection neurons21, 24, 25, 136, interneurons40, 41, 137, 138 and glia139-142. * indicates markers labeling a subset of the respective cell type. Abbreviations: CFuPN, corticofugal projection neuron; CThPN, corticothalamic projection neuron; SCPN, subcerebral projection neuron; CPN, callosal projection neuron; DVZ, dorsal ventricular zone; GE, ganglionic eminences.