Lamination of primary visual cortex in the macaque: Layer 5 subdivisions.

Area of Science:

• Neuroscience
• Comparative Anatomy
• Developmental Biology

Background:

• The primary visual cortex (V1) in primates exhibits complex lamination, with layer 4 divided into sub-laminae based on visual input.
• Previous classifications detailed layer 4 structure, but layer 5's organization remained less understood.

Purpose of the Study:

• To investigate the lamination pattern of layer 5 in the primary visual cortex (V1) of humans and non-human primates.
• To determine if layer 5 exhibits distinct sub-laminae and how this pattern varies regionally and with age.

Main Methods:

• Histological examination of the primary visual cortex (V1) in human and non-human primates.
• Analysis of layer 5 sub-lamination in different cortical regions (opercular vs. calcarine fissure).
• Investigation of layer 5 structure in bilaterally enucleated macaques during embryonic development.

Main Results:

• Layer 5 was found to possess a trilaminar structure (layers 5Aα, 5Aβ, 5B), most prominent in the occipital operculum.
• This trilaminar pattern transitions to a bilaminar structure (layers 5Aβ, 5B) in V1 near the calcarine fissure and with increasing age.
• The trilaminar structure of layer 5 is present even in the absence of visual input, observed in bilaterally enucleated macaques.

Conclusions:

• The trilaminar organization of layer 5 in the primate V1 is established independently of visual experience, suggesting intrinsic developmental mechanisms.
• Regional variations and age-related changes in layer 5 lamination highlight its complex development.
• The proposed functional role of the trilaminar layer 5 structure may be related to the processing of central vision.