A new study shows that despite very obvious physical differences between humans and non-human primates, their brains may be very similar. However, the smallest changes can make huge differences in developmental and mental illness.
Understanding the molecular differences that set the human brain apart can help scientists study the disruptions in its development. A new study investigates the differences and similarities between prefrontal cortex cells between human and non-human primates such as chimpanzees, rhesus monkeys, and marmosets, which is the frontmost region of the brain, which plays a central role in advanced cognitive function.
The study was recently published in the journal Science and was conducted by a research team including Andre Sousa, a professor of neuroscience at the University of Wisconsin-Madison.
The cellular differences between these species may shed light on their evolutionary steps and how these differences are associated with diseases such as autism and intellectual disabilities seen in humans. Sousa, who studies brain developmental biology at the University of Washington, Madison, decided to work with the Yale lab where he worked as a postdoctoral researcher to start with studying and classifying cells from the prefrontal cortex.
researchers analyzed genetic material from prefrontal cortex cells (shaded areas in each brain) from four closely related primates to describe subtle differences in cell type and genetics . Image source: University of Wisconsin-Madison
"We are doing analysis of the dorsolateral prefrontal cortex because it is particularly interesting. This cortical area is only present in primates. It is not present in other species," Sousa said. "It is related to several related functions in high cognitive aspects, such as working memory. It is also involved in some neuropsychiatric diseases. Therefore, we decided to do this study to understand the uniqueness of humans in this brain region."
Sousa and his lab collected genetic information from more than 600,000 prefrontal cortical cells from tissue samples from humans, chimpanzees, macaques and marmosets. They analyzed these data, divided cells into different types and identified differences in similar cells among different species. As expected, the vast majority of cells are quite similar, as these species are relatively evolutionarily close.
Andre-Sousa
Sousa and his collaborators have found five cell types in the prefrontal cortex that are not present in all four species. They also found differences in abundance of certain cell types, as well as diversity of in similar cell populations among different species. When comparing chimpanzees and humans, the difference seems to be huge—from their body appearance to their brain abilities. But at the cellular and genetic level, at least in the prefrontal cortex, there are many similarities and few differences.
"Our lab really wants to know what's unique about the human brain. Obviously, from this study and our previous work, most of it is actually the same, at least in primates," Sousa said.
The subtle differences found by researchers may be the beginning of identifying some of these unique factors, and this information may lead to implications for developmental and developmental disorders at the molecular level.
"We want to know what happened after the evolutionary division between humans and other primates," Sousa said. "The idea is that mutations occur in one gene or several genes that now function slightly differently. But if these genes are related to brain development, for example, the number of cells produced in a certain category, or how the cells connect to other cells, how does it affect the neuronal circuitry and their physiological properties? We want to understand how these differences lead to differences in the brain and then lead to differences that we can observe in adults."
The observations of this study were performed in the brain of adults, after most development was completed. This means that these differences may occur during brain development. Therefore, the next step for the researchers is to study developing brain samples and expand their investigation beyond the prefrontal cortex so that it is possible to find the origin and time of these differences.Hopefully this information will lead to a stronger foundation on which developmental disability research is conducted.
Hopefully this information will lead to a stronger foundation on which developmental disability research is conducted.-
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