The human brain contains billions of cells with a wide variety of functions, and how this intricate network forms during development has intrigued neuroscientists for decades. Researchers have now used lab-grown brain tissue to peer — in real time — into the development of the forebrain, the part of the brain that controls higher mental functions, including cognition and language.

Using human stem cells as a starting material, William Greenleaf and Sergiu Pașca at Stanford University in California and their colleagues grew pea-sized brain organoids that recreate features of some of the regions in the human forebrain. The researchers then set out to identify the molecular signals that guide the fate of specific cells.

The team found several proteins that seem to regulate the development of specific types of brain cell — from star-shaped cells that support and protect neurons to neurons that transmit signals to other neurons. The authors also mapped an elevated genetic risk for autism spectrum disorder to the precursors of non-neuronal cells called glia and to a group of fully developed neurons in the forebrain.