Research at Yale University reveals how human brain is different

CONNECTICUT: What distinguishes the human brain from all other animal brains, even those of our closest primate relatives? Researchers from Yale University discovered species-specific characteristics in the prefrontal cortex of four different primate species.

They published their findings in the journal 'Science' on August 25. Additionally, they discovered that part of what makes us human may also predispose us to neuropsychiatric illnesses. The dorsolateral prefrontal cortex (dlPFC), a part of the brain that is particular to primates and necessary for higher-order cognition, was the focus of the study.

They assessed the gene expression levels in millions of cells taken from the dlPFC of adult humans, chimpanzees, macaques, and marmoset primates using a single-cell RNA-sequencing approach.

Although the dorsolateral prefrontal cortex is now thought to be the fundamental element of human identity, it is still unclear what makes humans different from other ape species.

Nenad Sestan, the Harvey and Kate Cushing Professor of Neuroscience at Yale and professor of genetics, psychiatry, and comparative medicine, is the paper's lead senior author. "We now have additional hints."

In order to respond to this, the researchers first questioned whether any cell types are only found in humans or the other non-human primate species under study.

They discovered 109 shared primate cell types after grouping cells with comparable expression profiles, but they also found five that weren't shared by all species.

These included two distinct types of microglia, or immune cells with a specific function in the brain, found only in humans and chimpanzees, respectively.

Researchers discovered that the human-specific microglia type persists throughout development and adulthood, indicating that these cells are more involved in maintaining healthy brain function than fighting disease.

Glia cells, particularly microglia, are extremely sensitive to these variations since we humans lead a very different lifestyle from other primate species, according to Sestan. The type of microglia seen in the human brain may be an indication of an immunological reaction to the surroundings.

Another human-specific surprise was found when the gene FOXP2 was examined for expression in the microglia. Variants of FOXP2 have been related to verbal dyspraxia, a disorder in which sufferers struggle to produce language or speech, thus this discovery sparked a lot of attention.

Additional research has revealed a connection between FOXP2 and other neuropsychiatric disorders, including autism, schizophrenia, and epilepsy. Sestan and colleagues discovered that this gene expresses specifically in microglia from humans and a subset of excitatory neurons from primates.

According to Shaojie Ma, a postdoctoral associate in Sestan's group and co-lead author, "FOXP2 has captivated many scientists for decades, but still, we had no concept of what makes it distinctive in humans versus other primate species."The FOXP2 findings open up new avenues for the study of language and diseases, which makes us very excited.