The Human Periallocortex: Layer Pattern in Presubiculum, Parasubiculum and Entorhinal Cortex. A Review.

Area of Science:

• Neuroscience
• Comparative Anatomy
• Mammalian Cortical Development

Background:

• The mammalian cortical mantle exhibits significant heterogeneity, leading to classifications of allocortex, periallocortex, and isocortex.
• These distinctions are primarily based on morphological differences, including layering, overall organization, and connectivity, and are conserved across mammalian phylogeny.

Purpose of the Study:

• To delineate the specific morphological and laminar characteristics of the periallocortex, focusing on the presubiculum (PrS), parasubiculum (PaS), and entorhinal cortex (EC).
• To describe the transitional zones between these cortical types, particularly the proisocortex, and its relationship with the isocortex.

Main Methods:

• Comparative morphological analysis of cortical layers across different mammalian species.
• Detailed examination of cytoarchitecture and laminar organization within the PrS, PaS, and EC.
• Histological evaluation of transitional cortical areas, including the proisocortex.

Main Results:

• The allocortex is characterized by three layers, while the periallocortex, including PrS, PaS, and EC, exhibits six layers with distinct patterns.
• The presubiculum features outer (I-III) and inner (V-VI) principal layers separated by a cell-poor layer IV (lamina dissecans).
• The parasubiculum and entorhinal cortex display increasingly defined laminar patterns, with the EC showing variations justifying subfield distinctions, and a less distinct layer IV.

Conclusions:

• The periallocortex, comprising PrS, PaS, and EC, demonstrates a conserved six-layered structure with unique laminar variations.
• The entorhinal cortex exhibits complex layering and borders the proisocortex, an intermediate zone bridging periallocortex and isocortex.
• Understanding these laminar differences is crucial for comprehending cortical organization and evolution in mammals.