How does the brain build a map of three-dimensional space when a full volumetric representation would be prohibitively expensive? Neuroscientist Kate Jeffery explains why the rat navigation system appears to favor flat maps stitched together into a mosaic , and what this reveals about the evolutionary trade-offs shaping spatial cognition. Subscribe for more from the Convergent Science Network podcast series. Kate Jeffery joins Paul Verschure and Tony Prescott at the BCBT summer school to discuss her research on how place cells, grid cells, and head direction cells handle the vertical dimension. Her laboratory has found that grid cells, which fire in periodic hexagonal patterns on flat surfaces, do not produce the same metric structure in the vertical plane. On a pegboard where rats move horizontally at different heights, grid fields extend into s ...