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One such approach, probabilistic cell typing by in situ sequencing (pciSeq), leverages single-cell RNA-sequencing data to guide cell type assignment 8, 9. Various analytical approaches can assign detected transcripts to segmented cells and subsequently, cells to cell types. Hybridization-based in situ sequencing (HybISS) is an image-based multi-targeted gene expression profiling technique that allows the precise mapping of individual cells in human brain tissues 7. However, the precise laminar locations and abundances of many of these cell types have not yet been described, and beyond coarse layers most of these types are at low proportions and intermingled with one another. Hodge and colleagues characterized 15,928 cell nuclei from the human middle temporal gyrus (MTG, Brodmann area 21, a part of the temporal lobe) by single-nucleus RNA-sequencing (snRNA-seq) 4.
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Evolving single-cell technologies have recently allowed scientists to start to comprehend the cellular composition of the human cortex 3, 4, 5, enabling quantitative descriptions of cellular diversity and definitions 6. The human cortex contains roughly 80 billion cells 1, 2 and understanding the identity of all the cells is challenging.