This work aims at investigating the histology of hippocampus formation as structural model of information processing. The study addressed the question whether the pattern of cellular type distribution within hippocampal fields could be used as support of information processing in the hippocampus. Method: Pyramidal-shaped neurons presenting both cytoplasm and nucleus outlined clearly were measured systematically on brain slides, using a light microscope connected to a microcomputer equipped with

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... a scanner software for measuring particles. Morphological types of cells were identified following class sizes and their distribution determined through hippocampal fields. Results: A battery of statistical tests: Sturges' classification, class sizes distribution around overall mean, Bartlett's sphericity test, principal components analysis (PCA) followed by correlations matrix analysis and ANOVA allowed two cellular groups to be identified in the hippocampus: large and small pyramidal-shaped cells. Conclusion: The results show that sensory information processing in the hippocampus could be built on two classes of pyramidal neurons that differed anatomically with probably different physiological functions. The study suggests combination ensembles clustering large and small pyramidal cells at different rates, as fundamental signaling units of the hippocampus.