Evolutionary innovations that gave rise to the mammalian six-layered neocortex

Cell-type profiling in salamanders identifies innovations in vertebrate forebrain evolution https://t.co/zKcEFCWpdV

— Bill Benzon, BAM! Bootstrapping Artificial Minds (@bbenzon) February 27, 2023

From the linked article:

Trade-offs in brain development

Salamander brains share some, but not all, structures with the mammalian brain. They also have greater capacity to regenerate in response to damage. Three groups now come together with single-cell transcriptomics analyses that set the salamander brain in evolutionary context (see the Perspective by Faltine-Gonzalez and Kebschull). By comparing salamander brains with those of lizard, turtle, and mouse, Woych et al. track the evolutionary innovations that gave rise to the mammalian six-layered neocortex, which salamanders do not have. Lust et al. take a close look at why the axolotl brain is so much more capable of regeneration than is the mammalian brain. Finally, Wei et al. compare the developmental and regenerative processes in the axolotl brain. —PJH

Abstract

The evolution of advanced cognition in vertebrates is associated with two independent innovations in the forebrain: the six-layered neocortex in mammals and the dorsal ventricular ridge (DVR) in sauropsids (reptiles and birds). How these innovations arose in vertebrate ancestors remains unclear. To reconstruct forebrain evolution in tetrapods, we built a cell-type atlas of the telencephalon of the salamander Pleurodeles waltl. Our molecular, developmental, and connectivity data indicate that parts of the sauropsid DVR trace back to tetrapod ancestors. By contrast, the salamander dorsal pallium is devoid of cellular and molecular characteristics of the mammalian neocortex yet shares similarities with the entorhinal cortex and subiculum. Our findings chart the series of innovations that resulted in the emergence of the mammalian six-layered neocortex and the sauropsid DVR.