Homology, neocortex, and the evolution of developmental mechanisms.

Area of Science:

• Neuroscience
• Evolutionary Biology
• Comparative Anatomy

Background:

• The mammalian neocortex, a six-layered structure, lacks direct homologs in birds and reptiles.
• Extant amniotes exhibit diverse pallial (brain covering) structures.
• Despite structural differences, conserved neuronal cell types and circuits are observed in amniote pallia.

Purpose of the Study:

• To review similarities in pallial neuronal cell types across amniotes.
• To identify candidate gene regulatory networks underlying cellular identities.
• To propose a model for the developmental evolution of amniote pallial structures.

Main Methods:

• Comparative analysis of neuronal cell types in amniote brains.
• Bioinformatic approaches to delineate gene regulatory networks.
• Developmental modeling to explain structural divergence.

Main Results:

• Conserved neuronal cell types and circuitries exist in divergent amniote pallial structures.
• Natural selection appears to prioritize information processing pathways over specific brain architectures.
• Candidate gene networks for neuronal identity have been proposed.

Conclusions:

• Brain evolution favors the preservation of functional information processing pathways.
• Divergence in brain structures may arise from less constrained developmental processes.
• Understanding conserved cell types provides insights into the evolution of cognitive functions.