A striking feature of hippocampal place cells is their ability to maintain place fields after removal of all information from one sensory modality. This abilitiy suggests that hippocampal activity expresses information stored within the hippocampus in addition to the current sensory input. To determine whether the inertness of hippocampal firing emerges internally in the hippocampus or upstream in the neocortex, we measured the stability of spatial firing in neurons in the entorhinal cortex after room lights were switched off. Rats with tetrodes at the dorsocaudal pole of medial entorhinal cortex were trained to run in a square box until cells with stable multipeaked place fields were identified in layer II or III (Fyhn et al., SfN 2003). Room lights were then turned off while the rat was running in the box with lights on, or lights were turned on if the trial started in darkness. Place fields were followed across several sessions, with the rat resting on a pedestal between sessions. Place fields in entorh...