The Mouse Hippocampus

The hippocampus is the phylogenetically second oldest part of the telencephalon after the olfactory system (Chap. 14). The rodent hippocampus is a continuous structure that changes its cranial dorsal position to a lateroventral location in the more caudal parts where it eventually reaches the ventral surface of the brain. The human hippocampus has a basal position in the telencephalon but, regarding its fine structure, is very much alike that of the rodent hippocampus. By contrast to the neocortex (Chap. 10), the hippocampus consists mainly of three layers and can roughly be subdivided into the dentate gyrus and the Cornu Ammonis. It is part of a functionally very important circuit for the short-term and long-term memory starting in the neighboring entorhinal cortex via the dentate gyrus and Cornu Ammonis back to the entorhinal cortex (classical trisynaptic pathway). The disruption of this circuit by decline of neurons of the entorhinal cortex is a hallmark of human Alzheimer’s disease which leads to a loss of the short-term and long-term memory. In addition to the memory function, the hippocampus subserves spatiotemporal orientation.