Entorhinal-hippocampal connections: a speculative view of their function

On the basis of neuroanatomical studies, the entorhinal cortex (EC) has long been regarded as a relay station that provides the major source of afferent input to the hippocampus. The perforant path input to the dentate gyrus from layer II has traditionally been regarded as the major pathway by which information is transferred. However, electrophysiological studies are now indicating that other elements of the perforant path that project directly to CA1 and CA3 are more important than thought previously, and that the properties of different neuronal elements in the EC may determine the way in which information is passed on to and processed by the hippocampus. This article summarizes some of the properties of synaptic transmission in the EC and speculates on how frequency-dependent changes in transmission may be involved in the pre- and post-processing of hippocampal information by the EC.