Estimated reading time: 3-4 minutes
WASHINGTON — By examining the human brain at the cellular level in more detail than ever before, scientists have identified an enormous array of cell types — more than 3,300 — populating our most complex organs, creating an atlas that may help determine the cellular basis of neurological diseases. and facilitating new treatments.
The ambition unveiled Thursday also examined similarities and differences between the brains of humans and other primates — chimpanzees, gorillas, rhesus monkeys and apes — highlighting some of the factors that separate us from our evolutionary relatives and make us truly human.
This work was presented in 21 studies published in Science and two other journals, and was supported by the Cell Count Network Consortium of the US government’s BRAIN Initiative.
The human brain is complex in both its utility—sensing, movement, reading, writing, speaking, thinking, and more—and its cellular diversity.
Nerve cells – or nerve cells – are the basic units of the brain, receiving sensory input, relaying commands to muscles and transmitting electrical signals along the way. The brain consists of about 100 billion neurons, in addition to a larger number of non-neuronal cells. All of these are organized into hundreds of distinct brain structures that govern a range of functions.
The research identified 3,313 cell types, nearly 10 times more than previously known, as well as the full set of genes used by each cell type while mapping their regional distribution in the brain.
“The atlas of brain cells as a whole provides the cellular substrate for everything we can do as humans,” said neuroscientist Ed Lin of the Seattle-based Allen Institute for Brain Science, one of the researchers.
Different cell types have distinct characteristics and are likely to be affected differently in disease, Lin said.
One surprise was that cellular diversity was concentrated in the evolutionarily older parts of the brain — the midbrain and hindbrain — rather than the neocortex, which is responsible for higher cognitive functions including learning, decision-making, sensory perception, memory, and language. .
Brain-related diseases, such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis, are among the most incurable diseases.
“Most brain diseases still have no cure or even cures, and this atlas should serve as a baseline for accelerating progress in understanding the detailed cellular basis of disease and targeting future generations of therapies,” Lin said.
Researchers have mapped the genetic switches and brain cell types associated with Alzheimer’s disease – the most common type of dementia – and various neurological and psychiatric disorders including schizophrenia, bipolar disorder and major depression.
They confirmed a link between microglia – a type of immune cell in the brain – and Alzheimer’s disease, and revealed a link between certain types of nerve cells in the brain and schizophrenia, a severe mental illness characterized by a disconnection from reality.
In addition, the researchers looked for human-specific traits by comparing the temporal cortex — an area of the neocortex associated with language comprehension, among other higher cognitive functions — in humans and our closest evolutionary relatives, such as chimpanzees and gorillas.
While the cellular organization was similar, some genes were found to function differently in humans than in the other two species, including several genes involved in neural communication.
“This means that there are accelerated specializations of cortical neurons in humans that may contribute to differences in cortical circuit function and our distinct cognitive abilities,” said Trygve Bakken, a neuroscientist at the Allen Institute.
Lin added that these molecular modifications that occurred in certain cell types in humans compared to chimpanzees and gorillas likely affect how they “connect together — or the flexibility of those connections — and may be an important part of what makes the human brain special.”
Scientists expect a long way to go in brain research.
“We are only beginning to determine the complexity of the human brain,” said one of the other researchers, Ping Ren, director of the University of California, San Diego Center for Epigenetics. “More work is needed to fully understand the diversity, diversity, and function of brain structure and function.”
