- Entorhinal cortex
Name = Entorhinal cortex
Caption = Medial surface. (Entorhinal cortex approximately maps to areas 28 and 34, at lower left.)
Width = 300
Artery = Posterior cerebral Choroid
Vein = Inferior striate
BrainInfoType = hier
BrainInfoNumber = 150
MeshName = Entorhinal+Cortex
MeshNumber = A08.186.211.577.710.225
The entorhinal cortex (EC) is an important
memorycenter in the brain. The EC forms the main input to the hippocampusand is responsible for the pre-processing (familiarity) of the input signals. In the reflex nictitating membraneresponse of classical trace conditioning, the association of impulses from the eyeand the earoccurs in the entorhinal cortex. The EC-hippocampus systemplays an important role in memory consolidationand memory optimizationin sleep.
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.cite journal |author=Hafting T, Fyhn M, Molden S, Moser M, Moser E |title=Microstructure of a spatial map in the entorhinal cortex |journal=Nature |volume=436 |issue=7052 |pages=801–6 |year=2005 |pmid=15965463 | doi = 10.1038/nature03721 ]
The entorhinal cortex shows a modular organization, with different properties and connections in different areas.Neurons in the lateral entorhinal cortex exhibit little spatial selectivity [cite journal |author=Hargreaves E, Rao G, Lee I, Knierim J |title=Major dissociation between medial and lateral entorhinal input to dorsal hippocampus |journal=Science |volume=308 |issue=5729 |pages=1792–4 |year=2005 |pmid=15961670 |doi=10.1126/science.1110449] , whereas neurons of the medial entorhinal (MEA) cortex 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. [cite journal |author=Fyhn M, Molden S, Witter M, Moser E, Moser M |title=Spatial representation in the entorhinal cortex |journal=Science |volume=305 |issue=5688 |pages=1258–64 |year=2004 |pmid=15333832 |doi=10.1126/science.1099901] ]
In rodents, the EC is located at the
caudalend of the temporal lobe. In primates it is located at the rostralend of the temporal lobe and stretches dorsolaterally. It is usually divided into medialand 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
The superficial layers - layers II and III - of EC project to the
dentate gyrusand hippocampus: Layer II projects primarily to dentate gyrusand 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
hippocampusand, in turn, reciprocate connections from other cortical areas that project to superficial EC.
Brodmann area 28is known as the "area entorhinalis"
Brodmann area 34is known as the "area entorhinalis dorsalis"
* [http://www.ramsoy.dk/images/Brodmann_templobe.jpgDiagram at ramsoy.dk]
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