The hippocampus is amongst the most widely studied of mammalian brain regions (see The Hippocampus Book, Eds. P. Andersen, R. Morris, D. Amaral, T. Bliss, J. O’Keefe. Oxford University Press, 2007) and is hypothesized to play a role in the short-term storage of declarative memories. Recent years have witnessed a dramatic accumulation of knowledge about the morphological, physiological and molecular characteristics as well as the connectivity and synaptic properties of the various cell types found in the hippocampus.