How the hippocampus and entorhinal cortex encode spatial position — the brain's GPS (Nobel Prize 2014)
Place cells (O'Keefe 1971, hippocampus CA1/CA3): each neuron fires only when the animal is in a specific "place field" — a roughly Gaussian region of the environment. Together, overlapping place cells form a population code for position. Grid cells (Moser & Moser 2005, medial entorhinal cortex): fire in a periodic triangular lattice tiling the entire environment, parameterized by spacing λ, orientation θ, and phase offset. Multiple grid modules with different spacings create a combinatorial code — like an odometer. The Nobel Prize in Physiology 2014 was awarded for this discovery.