Postnatal development of the hippocampal formation : the entorhinal cortex

The entorhinal cortex is the main gateway for bi-directional communication between the neocortex and the hippocampal formation. Its superficial layers (II and III) represent the main entryways for much of the sensory information processed by the hippocampal formation, whereas its deep layers (V and VI) provide the main exitways through which processed information is sent back to the neocortex. Following our recent neuroanatomical findings revealing differential maturation of distinct hippocampal circuits and the renewed interest in the contribution of the entorhinal cortex in the elaboration of spatial representations of the environment (2014 Nobel Prize in Medicine/Physiology), it is particularly timely and important to obtain fundamental, quantitative information on the structural development of this brain region in primates. Following our previous findings in the hippocampus propoer, we have hypothesized that distinct layers and subdivisions of the primate entorhinal cortex, which contribute to different hippocampal functional circuits, will also exhibit differential maturation during early postnatal development. We have already obtained preliminary evidence showing that the superficial layers II and III mature earlier than the deep layers V and VI. This suggests that neocortical inputs can reach and be processed within hippocampal circuits relatively early, but that hippocampal outputs might be directed mainly toward subcortical structures at early ages, and only reach neocortical areas at later stages of development.