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Brain: Entorhinal cortex
Gray-Brodman-Entorhinal Cortex EC .png
Medial surface. (Entorhinal cortex approximately maps to areas 28 and 34, at lower left.)
Medial surface of cerebral cortex - entorhinal cortex.png
Medial surface of right hemisphere. Entorhinal cortex visible at near bottom.
Part of Temporal lobe
Artery Posterior cerebral
Choroid
Vein Inferior striate
NeuroNames hier-150
MeSH Entorhinal+Cortex
NeuroLex ID birnlex_1508

The entorhinal cortex (EC) is an important memory center in the brain. The EC forms the main input to the hippocampus and is 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 EC-hippocampus system plays an important role in memory consolidation and memory optimization in sleep.

The entorhinal cortex is one of the first areas to be affected in Alzheimer's Disease, and one of the first symptoms is impaired sense of direction. In 2005, it was discovered that entorhinal cortex contains a neural map of the spatial environment in rats.[1]

The rodent entorhinal cortex shows a modular organization, with different properties and connections in different areas. Neurons in the lateral entorhinal cortex exhibit little spatial selectivity[2], whereas neurons of the medial entorhinal cortex (MEA), exhibit multiple "place fields" that are arranged in an hexagonal pattern, and are therefore called "grid cells." These fields and spacing between fields increase from the dorso-lateral MEA to the ventro-medial MEA.[1][3]

Contents

Anatomy

In rodents, the EC is located at the caudal end of the temporal lobe. In primates it is located at the rostral end of the temporal lobe and stretches dorsolaterally. It is usually divided into medial and lateral regions with three bands with distinct properties and connectivity running perpendicular across the whole area. A distinguishing characteristic of the EC is the lack of cell bodies where layer IV should be; this layer is called the lamina dissecans.

Inputs and outputs

View of left entorhinal cortex (red) from beneath the brain, with front of brain at top. Artist’s rendering.

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.

Brodmann's areas

References

  1. ^ a b Hafting T, Fyhn M, Molden S, Moser M, Moser E (2005). "Microstructure of a spatial map in the entorhinal cortex". Nature 436 (7052): 801–6. doi:10.1038/nature03721. PMID 15965463. 
  2. ^ Hargreaves E, Rao G, Lee I, Knierim J (2005). "Major dissociation between medial and lateral entorhinal input to dorsal hippocampus". Science 308 (5729): 1792–4. doi:10.1126/science.1110449. PMID 15961670. 
  3. ^ Fyhn M, Molden S, Witter M, Moser E, Moser M (2004). "Spatial representation in the entorhinal cortex". Science 305 (5688): 1258–64. doi:10.1126/science.1099901. PMID 15333832. 

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