Introducing the brain: how many cell types? (Introduction)

by David Turell , Friday, October 08, 2021, 01:01 (1140 days ago) @ David Turell

A new study finds lots:

https://www.science.org/doi/full/10.1126/science.acx9293

"To efficiently gather such information, BICCN collaborators agreed to focus on a single region: a strip of tissue across the top of the brain called the primary motor cortex that orchestrates muscle movements. Some techniques could capture multiple features at once. For example, a method developed in Zhuang’s lab allows researchers to image hundreds or thousands of RNA sequences in a slice of brain tissue, revealing both cells’ transcriptomes and their relative locations. Another method, Patch-seq, records electrical activity from cells, stains them to reveal their shapes, and then sucks out their innards to sequence their RNA.

"In BICCN’s data, cells grouped according to their transcriptomes tend to share other features, such as location, shape, and electrical activity. That finding “provides strong validation to the molecularly defined cell types,” the BICCN authors write in a paper summarizing the work. For the human motor cortex, 127 such types emerged.

"The exact number depends on the criteria used to group cells, says BICCN investigator Hongkui Zeng, director of the Allen Institute for Brain Science. “Is it 127? Is it 130? Is it 100? … It’s not clear cut like that.” What’s more important, she says, is the hierarchy of cell types that emerged, with a few basic cell types at the top and more nuanced divisions in lower branches. Cells in the same top-level class tend to be similar across various types of measurements—and across the three species studied. Further down, Zeng says, distinctions between cell types “become a lot fuzzier.”

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"Having created a partial parts list, researchers still need to study how the cell types behave and interact in a functioning brain. UCL neuroscientist Kenneth Harris is among those imaging genetically labeled cells in living mice to relate gene expression to electrical firing patterns. “We’re going to have to learn what all these cell types are and try to figure out how they all work together,” he says. “It’s going to be difficult.” But with the new cell census, “we’re entering this stage where we know how much we don’t know—and that’s progress.'”

Comment: Splitting the cells down so finely recognizes how complex the brain really is. So many types many many subunits of activity. This is far beyond the fMRI regional studies that are quite rough in the analysis of brain function. Must have been designed