What makes the human brain distinct?
Despite more than a century of study, we still don’t understand the root of our myriad mental abilities, such as abstract thought, language acquisition, and complex learning. We also don’t understand most brain diseases, some of which — like Alzheimer’s disease — seem to afflict only us out of all mammals.
Part of the difficulty in addressing these questions comes from the difficulty of studying the human brain at work. Many neuroscientists work with donated postmortem tissue, especially when studying individual brain cells.
An ongoing research program at the Allen Institute for Brain Science, a division of the Allen Institute, has found an unusual workaround to study live human neurons — they use pieces of live human brain removed during brain surgery and willingly donated to research. In the course of surgery for epilepsy or brain tumors, neurosurgeons often need to remove healthy pieces of tissue to access the diseased site. These pieces are transported to the laboratory for study, where neuroscientists are uncovering new information about human neurons while they are still alive.
Today, the Allen Institute research team and their collaborators have published an article in the journal Nature describing the details of those precious living cells donated by 90 patients, uncovering an increased diversity in certain types of human neurons as compared to mouse neurons. The study was part of a large, international collaboration brought together by the National Institutes of Health’s BRAIN Initiative to bring cutting-edge technologies to map the different types of brain cells in the human, monkey and mouse brains.
“The cell is, of course, the basic unit of life. Throughout the history of neuroscience, researchers have been trying to define the types of cells that make up the brain,” said Ed Lein, Ph.D., Senior Investigator at the Allen Institute for Brain Science, who led the study. “A fundamental part of what we’re trying to do is to create a census of cell types, which is similar to a census of people. We want to know what the whole population looks like, how many different types of cells are there are, and what their properties are.”
To build this census of the human brain, the scientists needed to get creative with new technologies. Their brain cell classification depends on a modern technology known as single-cell transcriptomics, which reads the complete set of genes a single cell switches on. Armed with this molecular method, the scientists homed in on cells in two layers of the 6-layered human neocortex, the wrinkled outermost shell of the brain and the seat of our higher cognitive functions.
