What makes the human brain unique?

What makes the human brain different from all other animals, including our closest relatives? In an analysis of four primate prefrontal cortex cell types, Yale researchers identify species specificity -- especially human-specific traits -- they report in the Aug.

They found that the factors that make us human may also predispose us to neuropsychiatric disorders

In this study, the researchers looked specifically at the dorsolateral prefrontal cortex (dlPFC), a brain region unique to primates that is critical for higher-order cognition

"Today, we think the DLPFC is a central component of human identity, but we still don't know what makes humans so unique and sets us apart from other primate species

To answer this question, the researchers first asked whether there were any unique cell types in humans or other non-human primate species analyzed

The researchers found that human-specific microglia cell types are present throughout development and adulthood, suggesting that these cells play a role in maintaining brain function rather than fighting disease

"We humans live in a very different environment and have a unique way of life compared to other primates; and glial cells, including microglia, are very sensitive to these differences and are found in the human brain The microglia cell type may represent an immune response to the environment

Analysis of microglia gene expression revealed another human-specific surprise—the presence of the FOXP2 gene

Sestan and colleagues found that the gene showed primate-specific expression in a subset of excitatory neurons and human-specific expression in microglia

"Forkhead box p2 has attracted many scientists for decades, but we still don't know what makes humans different from other primate species," said Shaojie Ma, a postdoctoral associate in Sestein's lab and one of the first authors

The research was funded by the National Institutes of Health and the National Institutes of Mental Health

Original title:

Molecular and cellular evolution of the primate dorsolateral prefrontal cortex