Science | [...] Imagine my renewed excitement when, as a budding neuroscientist at university, I learned that there was crystal-like neural activity in the brain. There is a group of neurons in the parahippocampal formation named “grid cells” that fire in hexagonal symmetry (3) (see the figure, panel A, left). Grid neurons themselves are not necessarily arranged in a crystal-like pattern in the brain [although some argue this could be the case (4)]. Rather, each cell acts as a crystal “generator,” where the fundamental blocks are fields of neural activity.
Grid cell firing appears to be invariant to properties of the enclosure (e.g., size, shape), as well as an animal's behavior (e.g., running speed, grooming), which prompts the suggestion that they represent an internally generated path integration system for navigation (3). The universal metric of space had been found (3, 5, 6)!