WIKIMEDIA COMMONS, GERRYSHAWThe deeper scientists probe into the complexity of the human brain, the more questions seem to arise. One of the most fundamental questions is how many different types of brain cells there are, and how to categorize individual cell types. That dilemma was discussed during a session yesterday (November 11) at the ongoing Society for Neuroscience (SfN) conference in San Diego, California.
As Evan Macosko of the Broad Institute said, the human brain comprises billions of brain cells—about 170 billion, according to one recent estimate—and there is a “tremendous amount of diversity in their function.” Now, new tools are supporting the study of single-cell transcriptomes, and the number of brain cell subtypes is skyrocketing. “We saw even greater degrees of heterogeneity in these cell populations than had been appreciated before,” Macosko said of his own single-cell interrogations of the mouse brain. He and others continue to characterize more brain regions, clustering cell types based on differences in gene expression, and then creating subclusters to look for diversity within each cell population.
Following Macosko’s talk, Bosiljka Tasic of the Allen Institute for Brain Science emphasized that categorizing cell types into subgroups based on gene expression is not enough. Researchers will need to combine such data with traditional metrics, such as morphology and electrophysiology to “ultimately come up with an integrative taxonomy of cell types,” Tasic said. “Multimodal data acquisition—it’s a big deal and I think it’s going to be a big focus of our future endeavors.”