Orientation Preference Maps in Microcebus murinus Reveal Size-Invariant Design Principles in Primate Visual Cortex.

Area of Science:

• Neuroscience
• Comparative Anatomy
• Visual System Research

Background:

• Orientation preference maps (OPMs) characterize primate primary visual cortex (V1), unlike the "salt and pepper" organization in rodents.
• It remains debated whether a minimum size limit exists for orientation columns (OCs) below which they cannot scale down with decreasing V1 size.

Purpose of the Study:

• To investigate the existence and characteristics of OCs in one of the smallest living primates, the mouse lemur (Microcebus murinus).
• To determine if primate-type visual cortical organization has a minimum size constraint.

Main Methods:

• Chronic intrinsic signal imaging was employed to examine the V1 of the mouse lemur.
• Analysis focused on the presence, size, and spatial arrangement of OCs and pinwheels.

Main Results:

• Robust OCs, arranged in a pinwheel-like fashion, were identified in the mouse lemur V1.
• OC size in mouse lemurs was comparable to macaques, indicating near incompressibility.
• Mouse lemur V1 occupies a large cortical area (one-fifth of the cortex), a high V1-to-cortex ratio, to accommodate OPMs.

Conclusions:

• Primate-type visual cortical organization is constrained by a fundamental size limitation.
• The emergence of OPMs may have resulted from disruptive innovation rather than gradual evolutionary changes.