Fig. 1

Simplified functional anatomy of the hippocampus. Hippocampal circuitry is usually described as a trisynaptic loop, with a C-shaped organization. Perforant Path (PP) carries the major hippocampal input, consisting in polimodal sensory information collected by the Entorhinal Cortex (EC) from higher sensory cortices. PP contacts dendritic spines of granule cells in hippocampal Dentate Gyrus (DG), and a smaller part contacts directly neurons of the CA1 and CA3 hippocampal areas. Axons from DG granule cells are collectively named Mossy Fibres (MF) and project to hippocampal CA3 pyramidal cells. These cells represent an important computational node, since they are connected to contralateral CA3 and CA1 pyramidal cells through associational/commissural fibres. Moreover, they receive recurrent connections from ipsilateral CA3 cells, representing “internal” inputs, and they receive “external” inputs from DG and EC. CA3 pyramidal cells then project to ipsilateral CA1 pyramidal neurons, with connection fibres named Schaffer Collaterals (SC). Synapses between SC and CA1 neurons, and their plastic modulation, seem to be crucial for hippocampal computational ability and memory encoding. Lastly, CA1 axons contact directly and indirectly, through Subiculum, the EC