Medial entorhinal grid cell firing can be modelled as the result of interfering sub-threshold membrane potential oscillations (Burgess, Barry, O’Keefe, Hippocampus, 2007). This model makes two kinds of prediction: temporal and structural. Temporal predictions include that the intrinsic firing frequency of grid cells exceeds the EEG theta frequency by an amount that increases with running speed and decreases with the spatial scale of the grid-like firing pattern. Structural predictions include that the grid-like firing pattern is associated to the environment via connections from place cells, which in turn receive inputs from putative ’boundary vector cells’ tuned to respond when at a specific distance from an environmental boundary along a specific allocentric direction. We investigate these predictions in electrophysiological recordings from freely-moving rats. Our results generally support the model, constrain its future development, and highlight the question of the potentially differential functional roles of the different cell layers in medial entorhinal cortex.