Gliogenesis in the outer subventricular zone promotes enlargement and gyrification of the primate cerebrum

Significance The formation of cortical convolutions of primates, including humans, is one of the most important subjects in developmental neuroscience, but the underlying mechanisms—considered mostly solved toward the end of the 20th century—have become controversial in the last decade. Recent studies suggest that a stem cell zone called the outer subventricular zone (oSVZ) induces gyri to form directly through neurogenesis. Here, we provide evidence in macaque monkey demonstrating that oSVZ neurogenesis is actually complete before gyrification begins and that a major function of the oSVZ is to produce the glial cells associated with the rapid expansion and folding of the cortical surface.