The ability to track neural activity as the brain develops in embryos is key to understanding how neurons self-assemble to form the vertebrate brain. In this week’s issue, Jia Liu and colleagues present a bioelectronic solution to this problem in the shape of a soft, stretchable, mesh microelectrode array that can be implanted at the embryonic stage to map the electrical activity of neurons as the embryo grows. Working with frog and axolotl embryos, the researchers implanted their mesh array in the 2D structure called the neural plate, which goes on to become

 the brain. The array integrates with the plate, stretching and deforming as the brain develops, and providing feedback on how single-neuron activity and population dynamics emerge and evolve. The process is captured on the cover in an artist’s impression of the mesh array in place during the four main stages of frog embryo development.