Scientists build largest maps to date of cells in human brain

An international network of researchers created the most complete cell atlases yet of the human brain. vitstudio / Shutterstock

The human brain is made up of about 86 billion nerve cells, along with many other types of cells. They interact and link together in unique ways, creating distinct brain regions with specific functions. Uncovering the complex makeup and interactions of these many cells could lead to a new understanding of how the brain functions in health and disease, and new tools to study the complex activities and functions of these cells.

To better understand the identities and roles of brain cells, NIH’s Brain Research Through Advancing Innovative Neurotechnologies® (BRAIN) Initiative launched an international network of collaborating researchers called the BRAIN Initiative Cell Census Network. Its aim is to create a comprehensive inventory of all the cells in the human, nonhuman primate, and mouse brains, including cell locations, interconnections, and activities. The study of brain cells across species can pinpoint features that are uniquely human and give insights into which animals to study for different scientific questions. The latest findings were reported in a series of more than 20 papers published in Science, Science Advances, and Science Translational Medicine on October 13, 2023.

One paper examined three human brains to find over 3,000 types of brain cells—more than previously known. The team identified specific types of cells in distinct clusters in different brain regions. These findings could help shed light on conditions that are known to affect specific brain areas, such as cancer or neurodegenerative diseases.

The researchers have created the most detailed cell atlas yet of the adult human brain. The atlas reveals information about each cell’s gene activity and epigenome—the changes to a cell’s DNA and chromosomes that alter genetic activity. The findings also show that, besides variation among brain regions, there is variation between individuals. More people will need to be studied to fully understand the patterns of healthy and diseased brains.

Another paper compared the cellular and molecular properties of the brains of humans and several nonhuman primates: the chimpanzee, gorilla, macaque, and marmoset. The scientists found that a few hundred genes had activity patterns in nerve cells that were unique to humans. These changes might help to explain humans’ remarkable ability to adapt, learn, and change.

The other papers covered various aspects of the brain. One, for example, explored the role that inflammation might play during early brain development. Severe inflammation in childhood has been linked to developmental disorders like autism and schizophrenia. Researchers analyzed gene activity in the brains of children who died when they were 1 to 5 years old. They compared the brains of children who died with inflammatory conditions, such as asthma or infections, to those who died from accidents. The scientists focused on the brain’s cerebellum, which controls muscle movement and cognitive functions like language and social skills. They found evidence that inflammation can block development of specific types of nerve cells in the cerebellum. The finding could lead to better understanding and treatment of developmental disorders that are linked to inflammation.

“This suite of studies represents a landmark achievement in illuminating the complexity of the human brain at the cellular level,” says Dr. John Ngai, director of the NIH BRAIN Initiative.

“These new detailed cell atlases of the human brain and the nonhuman primate brain offer a foundation for designing new therapies that can target the specific brain cells and circuits involved in brain disorders,” adds Dr. Joshua A. Gordon, director of NIH’s National Institute of Mental Health.