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. Author manuscript; available in PMC: 2024 Aug 16.
Published in final edited form as: Neuron. 2023 Jun 21;111(16):2557–2569.e4. doi: 10.1016/j.neuron.2023.05.021

Figure 5: Schematics summarizing dNG and iNG contribution to cortical structures, a mosaic of neocortical PN types and subnetworks, and evolutionary implications.

Figure 5:

(A) Along the medial to ventral axis of the mouse embryonic pallium, dNG and iNG generate dPNs (red) and iPNs (green) that populate all cortical structures, with decreasing iNG contributions to lateral and ventral structures.

(B) Within the neocortex, dNG generates CT (dark shade), PT (medium shade), and IT (light shade) class dPNs (red) across layers, whereas iNG differentially amplifies and diversifies genetically defined iPN types (green) within each class. iPNs have a disproportionally large contribution to the IT class.

(C) dNG (red) and iNG (green)-derived PN types are highly intermixed within the neocortex and yet show distinct projection patterns both across and within genetically defined subpopulations. Thus, dNG and iNG construct lineage-based fine mosaics of cortical subnetworks.

(D) A conceptual schema depicting the evolutionary trajectory of dNG (red) and iNG (green) with their derived major PN types in dorsal pallial homologs across vertebrates (modified from Suryanarayana et al., 202150; Briscoe and Ragsdale, 201832). dNG and their derived IT (circle) and PT (square) classes are present in lamprey (cyclostomes) and thus predate the dawn of vertebrates. IPs and iNG may have originated in the last common ancestor of amniotes. Among the Sauropsids, dNG has dominated PN production across different pallial structures, including the three-layered dorsal cortex of extant non-avian reptiles and the pallia of most avian species; iNG has remained rudimentary, only to expand in certain birds (corvids) where it drives increased neuron numbers and density in nuclear structures of their pallium. Among Synapsids including mammals, the expansion of iNG greatly amplifies and diversifies PN types across neocortical layers and PN classes. Abbreviations: M, medial pallium; D, dorsal pallium; L, lateral pallium; V, ventral pallium; Ncx, neocortex; Hippo, hippocampus, Cl, claustrum; Ins, insular cortex; BLA, basolateral amygdala; Pir, piriform cortex; ipsi, ipsilateral; contra, contralateral, BS, brain stem; Spd, spinal cord; LCA, last common amniote, IT, intratelencephalic; PT; pyramidal tract; CT, corticothalamic.