Diversity and evolution of cerebellar folding in mammals

Abstract

The process of brain folding is thought to play an important role in the development and organisation of the cerebrum and the cerebellum. The study of cerebellar folding is challenging due to the small size and abundance of its folia. In consequence, little is known about its anatomical diversity and evolution. We constituted an open collection of histological data from 56 mammalian species and manually segmented the cerebrum and the cerebellum. We developed methods to measure the geometry of cerebellar folia and to estimate the thickness of the molecular layer. We used phylogenetic comparative methods to study the diversity and evolution of cerebellar folding and its relationship with the anatomy of the cerebrum. Our results show that the evolution of cerebellar and cerebral anatomy follows a stabilising selection process. Ancestral estimations indicate that size and folding of the cerebrum and cerebellum increase and decrease concertedly through evolution. Our analyses confirm the strong correlation between cerebral and cerebellar volumes across species, and show that large cerebella are disproportionately more folded than smaller ones. Compared with the extreme variations in cerebellar surface area, folial wavelength and molecular layer thickness varied only slightly, showing a much smaller increase in the larger cerebella. These findings provide new insight into the diversity and evolution of cerebellar folding and its potential influence on brain organisation across species.

Primate Cerebellar Scaling in Connection to the Cerebrum: A 34-Species Phylogenetic Comparative Analysis

“…Our study supports primate isometric cerebello-cerebral 50,51,89,118,126 evolution, tending towards hypo-allometry. A recent study reported similar and significant hypo-allometric cerebello-cerebral scaling across mammals 118 .…”

“…Our study supports primate isometric cerebello-cerebral 50,51,89,118,126 evolution, tending towards hypo-allometry. A recent study reported similar and significant hypo-allometric cerebello-cerebral scaling across mammals 118 . When we reran PGLS in the Stephan sample, we observed the same cerebello-cerebral scaling coefficient as this study did (.92) 118 .…”

“…We report cerebellar volumetric data for 34 species (N=63) and ansiform areas (crura I-II) for 13 species (N=30). Our phylogenetic analyses provide corroborating evidence for isometry between cerebellar and cerebral volumes 50,51,118 and evidence primategeneral ansiform area hyperscaling 13,130 . A combination of constrained 59 and modular 64 evolution may shape the primate cerebello-cerebral system.…”

“…A recent study reported similar and significant hypo-allometric cerebello-cerebral scaling across mammals 118 . When we reran PGLS in the Stephan sample, we observed the same cerebello-cerebral scaling coefficient as this study did (.92) 118 . We found no support for distinct scaling patterns in apes.…”

“…Lemurs and apes displayed the highest cerebellum-to-cerebrum ratios. Corroboratively, lemurs may have large brains for their bodies 118 , a trait shared with hominoids and especially humans. High relative volumes (Figure 4c) and positive deviations above the slope of the primate dataset (Figure 5a and Supplemental Figure S6b) evidence relatively large lemur and hominoid cerebella.…”