Scientists have solved the mystery of the absence of brain convolutions in some monkeys
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- Scientists have solved the mystery of the absence of brain convolutions in some monkeys
The primate brain differs not only in size, but also in shape: in humans, its surface is covered with numerous folds, and in some small monkeys it remains almost smooth. Scientists have found that the differences are related to how the cells from which neurons are formed develop. It turned out that these cells divide more slowly, have a simpler structure, and spend less time in the period of active reproduction. About why the brain of some primates is covered with folds, while others remain almost smooth — in the material of Izvestia.
Why is the brain of gamblers almost smooth
Researchers at the German Primate Center in Göttingen studied the development of the brain of the common marmoset (Callithrix jacchus), a small South American monkey, and compared it with the development of the human brain. Scientists have found that the features of the brain structure of these monkeys are associated with several differences in the work of progenitor cells, from which nerve cells are formed. The results are published in the journal Science Advances.
In humans, the surface of the brain is covered with folds and furrows. This structure significantly increases the area of the cortex, allowing you to place more neurons. In ordinary gamblers, the surface of the brain is almost smooth, and the folds are poorly expressed.
At the same time, at the beginning of development, the brain of gamebirds has a typical structure characteristic of primates with a larger and folded brain. This means that differences arise with further development: the production of nerve cells slows down, and the cortex does not grow as intensively.
Lydia Tynyanskaya, one of the first authors of the study and a graduate student at the German Primate Center
At the beginning of development, the brain of the common marigold exhibits the typical structure and composition characteristic of the large, folded primate brain. Therefore, as it develops, processes must occur that actually slow down the production of nerve cells.
How cells affect brain growth
To understand the reasons for the differences, the researchers compared human and igroon brain organoids, small three—dimensional structures grown from cells and reproducing some features of early brain development. The scientists paid special attention to progenitor cells, which produce neurons and thereby influence the future size and shape of the cortex.
The study showed that some types of progenitor cells divide much more slowly than in humans. Others have a simpler structure and have fewer appendages. Such cells have a lower ability to reproduce, so fewer nerve cells are formed during development.
Cesar Mateo Bastidas-Betancourt, one of the first authors of the work
Our research has shown that some progenitor cells in the common marigold divide much more slowly than in humans. Other progenitor cells have a simpler structure than their human counterparts — they have fewer appendages, and therefore they multiply less actively.
According to him, both of these factors ultimately lead to the formation of fewer nerve cells, which contributes to the smaller size of the cortex of the brain and fewer folds. Thus, differences in brain structure cannot be explained by just one factor. Its growth is simultaneously influenced by the rate of cell division and the features of their structure. Collectively, these processes limit the number of neurons that are formed during development.
Why is brain development slowing down
Scientists have identified another difference: the period during which progenitor cells are able to multiply rapidly is shorter. Compared to humans, their cells exit this active growth phase earlier. Combined with slower division and a less complex structure, this leads to fewer neurons forming in the cortex.
To test the results obtained on organoids, the researchers repeated some key experiments on fetal igrunka brain tissue. This approach made it possible to compare observations of structures grown in the laboratory with the development of a real brain.
Michael Heide, Head of the Brain Development and Evolution Research Group
The study combines the advantages of in vivo and in vitro methods. Organoids are well suited for obtaining statistically reliable results, since such sample sizes cannot be provided in primate studies. Then we repeated some key experiments on fetal brain tissue to confirm the results obtained on organoids.
The scientists also established a correspondence between the development of the laboratory model and the animal's brain. The organoid of the igrunka brain on the 50th day of development corresponded to the stage of development of the real monkey brain on about the 90th day. This comparison helped to interpret the results more accurately: the animal's organoids and brain do not necessarily develop at the same rate.
What does this explain about the evolution of the brain?
The results of the study show how several relatively small differences in cell behavior can lead to noticeable changes in the size and shape of the brain. If progenitor cells produce fewer neurons and stop actively multiplying earlier, the cortex grows weaker and forms fewer folds.
This helps explain the diversity of brain structure in primates. In different species, not only the size of the brain may vary, but also the rate of development, the duration of reproduction of progenitor cells, and the features of their structure. The combination of these factors affects how many nerve cells are formed and how strongly the cortex becomes folded.
The study does not reduce the evolutionary differences to a single mechanism: scientists have discovered several interrelated cellular processes that together explain the features of the brain of gamblers. The data obtained helps to better understand how changes at the cellular level could have been involved in the formation of various sizes and shapes of the brain in primates.
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