Scientists have created miniature brains from stem cells that developed functional neural networks. Despite being a million times smaller than human brains, these lab-grown brains are the first observed to produce brain waves that resemble those of preterm babies. The study, published August 29 in the journal Cell Stem Cell, could help scientists better understand human brain development. “The level of neural activity we are seeing is unprecedented in vitro,” says Alysson Muotri, a biologist at the University of California, San Diego. “We are one step closer to have a model that can actually generate these early stages of a sophisticated neural network.” The pea-sized brains, called cerebral organoids, are derived from human pluripotent stem cells. By putting them in culture that mimics the environment of brain development, the stem cells differentiate into different types of brain cells and self-organize into a 3D structure resembling the developing human brain. Scientists have successfully grown organoids with cellular structures similar to those of human brains. However, none of the previous models developed human-like functional neural networks. Netwo...