The CA3 and CA1 fields of the mammalian hippocampus are strikingly different in their network architecture: massively recurrent the former, essentially feed-forward the latter. The functional significance of this structural differentiation is not clear, in that neural activity is qualitatively similar in the two fields, and computational models generally succeed in mimicking hippocampal functions even when equipped with the architecture of CA3 alone. To assess the functional advantage of the differentiation, a simulation approach has been proposed that quantitatively compares the performance of a differentiated with a uniform network model, each comprised of the same number of units and connections (AT, Hippocampus, 2004). Recent experiments have discovered a striking functional difference between CA3 and CA1 activity patterns: multiple environments with overlapping features are represented by distinct ensembles in CA3, whereas ensembles in CA1 show a correspondingly graded overlap (SL et al, SfN abs, 2003...