Chinese scientists have recently created the most detailed map that has ever been made of the types of cells in the brains of monkeys. The map, which shows how the various cells are distributed, could help scientists better understand how the brain works.

The creation of the map was the result of intensive research by the scientists. It provides a molecular cellular basis for further study of the connections between various types of neurons and may provide insights into research of brain diseases, including Alzheimer's disease and depression, the scientists said.

A paper reporting the results was published on the website of the journal Cell on Wednesday. This milestone study was conducted by scientists from several institutions, including the Center for Excellence in Brain Science and Intelligence Technology of the Chinese Academy of Sciences, the BGI Group, the Lingang Laboratory, the Shanghai Brain Center, the Tencent AI Laboratory and the Karolinska Institute in Sweden.

Primate brains have a large number of neurons, which form a complex, delicate and specific neural circuit that supports high-level cognition and behavior.

Compared with other species, primates have higher cognitive and social abilities as well as a larger cortex and more cell types. For example, the macaque — the genus of which is closely related to humans — has a brain that contains more than 6 billion neurons.

The brain is made up of many different types of cells, which can be categorized based on their molecular, morphological or physiological characteristics. These cells are also distributed in different brain regions.

Analyzing the composition and spatial distribution of these cell subtypes is important for understanding how the brain is organized. This is because different cell types have different functions, and the way that they are distributed in the brain can affect how they communicate with each other.

Scientists have discovered that the distribution of the cells in the cerebral cortex is not random. In fact, it is very specific to different cortical layers and brain regions. This specificity is even more pronounced in primates, where certain types of cells are only found in certain layers.

The scientists also found that there is a correlation between cell type composition and the hierarchical organization of brain regions. This means that brain regions that are at the same hierarchy often have similar cell type compositions.

For example, the scientists found that the fourth layer of the cerebral cortex in primates contains a unique type of excitatory neuron that is highly expressed in genes related to human diseases. This finding could help scientists better understand the causes of these diseases, said Li Chengyu, a corresponding author of the paper and a senior researcher at the Center for Excellence in Brain Science and Intelligence Technology.

The scientists used a new technology called spatial transcriptome sequencing to study the distribution of cells in the cerebral cortex. This technology allows scientists to see the distribution of cells at a very high resolution.

Poo Muming, a CAS scientific director at the Center for Excellence in Brain Science and Intelligence Technology, said that brain science, which is still in its relative infancy, is an important part of China's innovation initiative that was proposed two years ago.

"The research conducted on the map of the neural connections in the whole brain is of great scientific significance, and may work to guide brain disease prevention and treatment, as well as the development of intelligent technology," Poo said.

Li said that the team will conduct further research on brain disease mechanisms — which will help scientists design corresponding medicines — and the evolutions of cells and structure to better understand brain functions.