A taxonomy of transcriptomic cell types across the isocortex and hippocampal formation

The isocortex and hippocampal formation (HPF) in the mammalian brain play critical roles in perception, cognition, emotion and learning. We profiled ~1.3 million cells covering the entire adult mouse isocortex and HPF and derived a transcriptomic celltype taxonomy which includes many new glutamatergic and GABAergic neuron types. Contrary to the traditional view of HPF as having a simpler cellular organization, we discover a complete set of glutamatergic types in HPF homologous to all major subclasses found in the six-layered isocortex, suggesting that HPF and isocortex share a common circuit organization. We also identify large-scale continuous and graded variation of cell types along isocortical depth, across isocortical sheet and in multiple dimensions in hippocampus and subiculum. Overall, our study establishes a molecular architecture of mammalian isocortex and hippocampal formation and begins to shed light on its underlying relationship with the development, evolution, connectivity and function of these two brain structures.