Thread by @hipposubfields

Hello subfield-fans! Last week's #SubfieldWednesday topic was the layered composition of the hippocampal subfields. We learned that the subfields contain three major cellular layers which makes them a part of the allocortex.

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@thomcat992 replied that the hippocampus is archicortex, which is also correct! Archicortex is a type of allocortex.

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Now what about the entorhinal cortex (ERC)? The ERC has six layers, so does that make it neocortex (also known as the isocortex)?

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@DrNeuroChic correctly replied that the ERC is mesocortex, which refers to a transitional cortex that does not have the same layer features as neocortex!

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Insausti describes ERC (as well as the pre- and parasubiculum) as being a part of a specific transitional cortex called periallocortex.

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A common feature of all components of the periallocortex is the presence of a cell free zone, parallel to the pial surface, which receives the name of lamina dissecans.

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Insausti further describes perirhinal (PRC) and parahippocamal cortex (PHC) as being a part of a different transitional cortex called proisocortex.

According to Insausti, the proisocortex does not fulfill all the layering features of neocortex.

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"The proisocortex shows six layers, ...., but retain some of the periallocortical features such as prominent layers II and V, the lack or a thin layer IV, and an overall lesser columnarity than the isocortex." (Insausti et al., Front Neuroanatomy, 2017)

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@madeopyj ventured a guess that medial and lateral ERC might be composed of different kinds of cortex. Indeed, Insausti describes medial-lateral gradients within the ERC, such that lateral ERC is more similar to the proisocortex of the PRC.

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That's all for this week! Thanks to all who participated in the "quiz"! See you next week!

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I should clarify that *some* of the subfields have three layers:

The dentate gyrus, cornu ammonis, and subiculum proper

See thread below regarding which subfields have more than three layers!

@threadreaderapp unroll