Can global hexagonal order emerge in 2D but not 3D?

After years spent getting the technology and experimental setup right —which included building a latticelike climbing frame for the rats and setting up wireless recording and three-dimensional tracking systems —[Kate] Jeffery and her colleagues were finally able to take a look at grid cell activity in the animals’ entorhinal cortex during 3D navigation.

To their surprise, the hexagonal patterns that defined the cells’ behavior in 2D were gone entirely: The researchers couldn’t find even traces of that global order. 

Instead, the clumps of grid cell activity seemed to be distributed throughout the three-dimensional space at random. “Some properties were preserved,” Jeffery said, “but the most visually striking property of grid cells was not.”