The brain has more than 3,000 different types of neurons and glial cells, a monumental scientific project involving hundreds of neuroscientists in the United States and Europe has revealed since 2017. The results offer the most detailed atlas of the human brain to date. , which lays the foundation to advance research into neurological and psychiatric diseases and to better understand how the brain works.
Researchers have applied the latest cellular analysis techniques to study the nervous system at the scale of individual cells, something that until now had been technically impossible. This has allowed them to map the different regions of the brain, evaluate the differences between the brains of different people, study how the brain evolves from the prenatal stage to adulthood and compare the human brain with that of other species.
“It is the beginning of a new era in brain science,” said Joseph Ecker, of the Salk Institute in California, one of the three institutions that coordinated the project, in a statement. This project, called BICCN (Brain Initiative Cellular Census Network), is funded primarily by the US government through its National Institutes of Health (NIH). It is part of the BRAIN initiative, launched in 2013 by the NIH to “revolutionize our understanding of the human brain.”
The results of the BICCN project are presented today in 21 scientific articles that are published simultaneously, most of them in the journal Science.
“I see this as a moment of historic change in neuroscience, in which new technologies are allowing us to understand the very detailed organization of the human brain and other primate brains,” Ed Lein, of the Allen Institute of Science, said in another statement. Cerebro in Seattle (USA), and one of the principal investigators of the project.
A team from the Allen Institute, in collaboration with the Karolinska Institute in Stockholm, has sequenced the RNA of single cells in one hundred different brain regions of three people. RNA indicates which genes are active and which proteins are made in each neuron and each glial cell, which are cells of the nervous system complementary to neurons. According to the researchers, RNA informs about the identity of each cell, as it is related to its shape, function and connectivity.
In the one hundred regions analyzed, more than 2,400 types of neurons and more than 600 different types of glial cells have been identified. The greatest diversity has been found in regions such as the hypothalamus, brainstem and cerebellum, which is consistent with the diversity of functions of these regions. On the contrary, cellular diversity is lower in the cerebral cortex, the most studied region of the nervous system and the one that most distinguishes humans from other animals, as it is the seat of abilities such as language, planning, moral judgment or decision making.
“We have done a kind of census of brain cells,” said Sten Linnarsson, researcher at the Karolinska Institute in Stockholm and co-director of this part of the project, in which the Catalan neuroscientist Ernest Arenas, also at the Karolinska Institute, has played a prominent role. .
Another team at the Allen Institute has analyzed the differences between the brains of 75 people by comparing the DNA and RNA of all types of cells in the cortex. The results show that, although the general architecture of the brain is consistent between people, the fine detail of the different cell types in each region, and the genes that are expressed in each cell, vary according to each individual.
“There is no single prototypical human,” neuroscientists Alyssa Weninger and Paola Arlotta write in an analysis article in Science. “There is a spectrum of differences (...) both in healthy individuals and in disease states.”
The potential of the brain atlas to investigate neuropsychiatric disorders is demonstrated in a part of the project that has identified relationships between different types of cells and diseases such as - among others - schizophrenia, bipolar disorder, depression and Alzheimer's. Another team of researchers has studied the relationship between autism and brain development in early life.
“Since Ramón y Cajal's beautiful images offered the first insight into the immense diversity and complexity of brain cell types, neuroscience has been challenged to understand how these diverse cells produce the brain's capabilities,” conclude Alyssa Weninger and Paola Arlotta in Science. The BICCN results “lay the foundation for understanding how the human brain is made and how it works, and reinforce a new era of research into the causes of neurological diseases.”
