Development and Evolution of Cerebral and Cerebellar Cortex

Abstract

Cerebral cortex and cerebellar cortex both vary enormously across species in their size and complexity of convolutions. We discuss the development and evolution of cortical structures in terms of anatomy and functional organization. We propose that the distinctive shapes of cerebral and cerebellar cortex can be explained by relatively few developmental processes, notably including mechanical tension along axons and dendrites. Regarding functional organization, we show how maps of myelin content in cerebral cortex are evolutionarily conserved across primates but differ in the proportion of cortex devoted to sensory, cognitive, and other functions. We summarize recent progress and challenges in (i) parcellating cerebral cortex into a mosaic of distinct areas, (ii) distinguishing cortical areas that correspond across species from those that are present in one species but not another, and (iii) using this information along with surface-based interspecies registration to gain deeper insights into cortical evolution. We also comment on the methodological challenges imposed by the differences in anatomical and functional organization of cerebellar cortex relative to cerebral cortex.

Keywords: Cerebellum; Cerebral cortex; Development; Evolution; Human; Neuroanatomy; Nonhuman primate; Parcellation.

Figure 1

Adapted, with permission, from Herculano-Houzel (2009). Approximate ratios are based on weight differences; ratios for neuronal number differ modestly.

Figure 2

Schematic drawings of the hypothesized complementary roles of intraventricular pressure and axonal tension in early stages of cortical expansion and gyrification. Reproduced, with permission, from Van Essen (1997).

Figure 3

Group average cortical myelin maps from human, chimpanzee, and macaque. Black bars indicate relative size of the group average inflated surfaces for each species. The “MT+” complex refers to heavily myelinated area MT plus the heavily myelinated portions of the neighboring MST complex, also implicated in motion processing. Data available at https://balsa.wustl.edu/XPNr

Figure 4

A, B. Marmoset parcellations (A: reproduced with permission from Majka et al., 2016; B: reproduced with permission from Hashikawa et al., 2015). C, D. Macaque parcellations (C: Paxinos et al., 2000; D: Van Essen et al., 2012). E. Human HCP_MMP1.0 parcellation (Glasser et al., 2016a). Data for panels C, D available at https://balsa.wustl.edu/8Zqq and for panel E at https://balsa.wustl.edu/