Why do grid cells, the brain's metric system for space, appear last in development, days after place cells and head direction cells are already active? Neuroscientist Francesca Cacucci explains what the developmental sequence of spatial circuits in the rat hippocampus reveals about how the navigation system bootstraps itself, and why the sudden emergence of grid cells around postnatal day 20 may mark a genuine cognitive transition. Subscribe for more from the Convergent Science Network podcast series. Francesca Cacucci joins Paul Verschure and Tony Prescott at the BCBT summer school to discuss her research on the development of spatial representations in the rat hippocampus and entorhinal cortex. Her laboratory has documented a clear developmental timeline: head direction cells appear first, as early as postnatal day 12–13, providing a compass si ...