Stem‑Cell‑Derived Brain Organoids Explain Why Most Primates Exhibit Cortical Folding Whereas Marmosets Remain Smooth

Research employing stem‑cell‑derived brain organoids has uncovered developmental processes that account for why most primates form heavily folded cerebral cortices, while the diminutive common marmoset (Callithrix jacchus) possesses a largely smooth, virtually unfurled brain exterior.

The investigation, featured on Phys.org, contrasted organoids derived from marmoset cells with organoids from species exhibiting prominent gyri and sulci. Monitoring neural tissue development under laboratory conditions, the team detected differing cell‑proliferation and migration patterns that align with the formation of cortical folds in the latter group.

Among primates possessing larger brains, swift growth of the cortical plate generates mechanical stresses that cause the tissue to buckle, yielding the typical ridges and valleys that augment surface area. The organoid data indicated that this enlargement stems from an early surge of neuronal progenitor activity, a phenomenon considerably subdued in organoids derived from marmoset cells.

In contrast, marmoset organoids displayed a steadier growth pattern, missing the localized over‑growth that initiates folding. This points to an evolutionary decrease in cortical progenitor proliferation as a pivotal element underlying the species’ smooth brain shape, which may affect neural wiring and potentially its behavioral repertoire.

Grasping the cellular foundations of cortical folding carries wide‑reaching significance for evolutionary biology and medical science. The extent of gyrification differs markedly among mammals and correlates with cognitive ability; irregular folding also characterizes numerous neurodevelopmental disorders. By pinpointing the precise developmental programs that produce folds, this work provides a framework for probing how genetic or environmental perturbations could cause malformations.

Upcoming research is expected to broaden the organoid model to other primate lineages, creating a comparative map of folding mechanisms throughout the evolutionary tree. Such studies could reveal how minor alterations in early brain development have shaped the varied cognitive capacities seen across primates, and might eventually guide therapeutic approaches for human brain disorders associated with atypical cortical architecture.