Development and organization of the evolutionary conserved three-layered olfactory cortex

Abstract

The olfactory cortex is part of the mammalian cerebral cortex together with the neocortex and the hippocampus. It receives direct input from the olfactory bulbs and participates in odor discrimination, association and learning (Bekkers and Suzuki, 2013). It is thought to be an evolutionary-conserved paleocortex, which shares common characteristics with the three-layered general cortex of reptiles (Aboitiz et al., 2002). The olfactory cortex has been studied as a “simple model” to address sensory processing, though little is known about its precise cell origin, diversity and identity. While the development and the cellular diversity of the six-layered neocortex are increasingly understood, the olfactory cortex remains poorly documented for these aspects. Here is a review of current knowledge on the development and organization of the olfactory cortex, keeping the analogy with those of the neocortex. The comparison of olfactory cortex and neocortex will allow the opening of evolutionary perspectives on cortical development.

Significance statement The olfactory cortex is an evolutionary-conserved paleocortex implicated in odor processing. While several studies addressed how the olfactory cortex encodes and processes odorant information, little is known about its precise cellular origin, diversity and identity. Unraveling where the cells are born and how they migrate towards and settle the olfactory cortex during development is of main importance to understand its circuit organization and function. In addition, comparing the developments of the olfactory cortex with the neocortex will help identifying common evolutionary conserved developmental mechanisms as well as new mechanisms specific to the neocortex, that appeared later during evolution and participate in building the mammalian cortex.