Hippocampal place cells are selectively active when a rat occupies restricted locations in an environment. Head direction (HD) cells fire selectively when the rat's head is pointed in a particular direction in allocentric space. Both place cells and HD cells have been modeled as attractor neural networks. If the intrinsic connections of an attractor network are strong compared to the external inputs, the network should tend to maintain internal coherency of its representation when the input patterns are altered. Previous studies have shown that the CA3 network is more coherent than the CA1 network when the distal landmarks in a familiar environment are rotated relative to the salient local cues on the behavioral track (Lee et al., SFN Abstracts, 2003). To test whether the HD cell system remained coherent under these conditions, ensembles of 1-33 hippocampal CA1 place cells & 2-9 HD cells from the anterior dorsal nucleus of the thalamus were recorded simultaneously in 6 rats during standard (familiar) and c...