Everything about The Entorhinal Cortex totally explained
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.
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.
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, 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.
Anatomy
In rodents, the EC is located at the
caudal end of the
temporal lobe and 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
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
Further Information
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