Figure 1. Circuit schematic diagram of entorhinal/hippocampal synaptic pathways.

Inputs from the entorhinal cortex (EC) to hippocampus include the perforant path, originating from layer II EC neurons, and the temporoammonic pathway, originating from layer III EC neurons. These innervate the dentate gyrus (DG) and area CA1, respectively. Projections from these two structures create long (EC–DG–CA3–CA1–EC) and short (EC–CA1–EC) excitatory synaptic loops.