The entorhinal cortex (EC) (ento = interior, rhino = nose, entorhinal = interior to the rhinal sulcus) is an area of the brain located in the medial temporal lobe and functioning as a hub in a widespread network for memory and navigation. The EC is the main interface between the hippocampus and neocortex. The EC-hippocampus system plays an important role in declarative (autobiographical/episodic/semantic) memories and in particular spatial memories including memory formation, memory consolidation, and memory optimization in sleep. The EC is also responsible for the pre-processing (familiarity) of the input signals in the reflex nictitating membrane response of classical trace conditioning, the association of impulses from the eye and the ear occurs in the entorhinal cortex.
The superficial layers – layers II and III – of EC project to the dentate gyrus and hippocampus: Layer II projects primarily to dentate gyrus and hippocampal region CA3; layer III projects primarily to hippocampal region CA1 and the subiculum. These layers receive input from other cortical areas, especially associational, perirhinal, and parahippocampal cortices, as well as prefrontal cortex. EC as a whole, therefore, receives highly processed input from every sensory modality, as well as input relating to ongoing cognitive processes, though it should be stressed that, within EC, this information remains at least partially segregated.
The deep layers, especially layer V, receive one of the three main outputs of the hippocampus and, in turn, reciprocate connections from other cortical areas that project to superficial EC.
The rodent entorhinal cortex shows a modular organization, with different properties and connections in different areas