mechanisms for further segregation of representations? How many representations can be generated, and what mechanisms determine their independence? Is the hippocampal output important for generating and maintaining grid formation in the entorhinal cortex and subicular complex, and if so, how do hippocampal activity patterns contribute to properties of grid cells and grid maps?The hippocampal-entorhinal cortex system has a bidirectional, topographically arranged communication with the cortical mantle. Do the different septotemporal segments of this system map onto the neocortex similarly in animals with more complex brains and with a growing share of higher-order cortical areas? Does the region corresponding to the ventral quadrant of the rodent hippocampus grow disproportionally relative to the dorsal part in primates, and what are the consequences of any such shifts in cortical-hippocampal communication?An interesting problem is the dominant direction of flow of neuronal activity in the entorhinal cortex–subiculum–hippocampus system. During memory encoding, the entorhinal cortex is believed to drive the hippocampal circuits, as it does in navigation, in a manner that, at least partly, must rely on external cues32. During spontaneous recall, the direction of flow is from the hippocampus to the entorhinal cortex43,100 but it is not known how this reversed flow is used during
