The human cerebellum has almost 80% of the surface area of the neocortex

Abstract

The surface of the human cerebellar cortex is much more tightly folded than the cerebral cortex. It was computationally reconstructed for the first time to the level of all individual folia from multicontrast high-resolution postmortem MRI scans. Its total shrinkage-corrected surface area (1,590 cm²) was larger than expected or previously reported, equal to 78% of the total surface area of the human neocortex. The unfolded and flattened surface comprised a narrow strip 10 cm wide but almost 1 m long. By applying the same methods to the neocortex and cerebellum of the macaque monkey, we found that its cerebellum was relatively much smaller, approximately 33% of the total surface area of its neocortex. This suggests a prominent role for the cerebellum in the evolution of distinctively human behaviors and cognition.

Keywords: cerebellum; computational; evolution; surface area; unfolding.

Fig. 1.

Coronal high-resolution MRI images of the human cerebellum. Short- and long-TE 9.4-T scans with 0.19-mm-wide isotropic voxels were combined and filtered to reconstruct the cerebellar gray/white (yellow) and pial (green) surfaces (Lower Right).

Fig. 2.

Cerebellar slices and folded, inflated, flattened cerebellar surfaces, all at same scale. Starting in the Upper Left, slice images are tessellated and the resulting surface was unfolded, cut (Upper Right), and flattened. Each surface is shown twice, first color-coded by FreeSurfer average convexity (“sulc,” which marks lobules) and then by local curvature (“curv,” which marks much smaller folia). At Lower Left, a macaque monkey cerebellum is shown at the same scale.

Fig. 3.

Reconstruction of the pial surface of the human cerebellum in superoposterior view.

Fig. 4.

Detailed geometry of lobules and folia. Lobular crests sometimes turn into fissures across the midline (thick blue/cyan arrows). The axes of folia are often not parallel to lobular axes (small arrows). The dashed line (Lower Middle) outlines a single folium that spirals up from the depths of a fissure over the crest of lobule VI. The vermis is indicated by thin dotted lines. In the Lower scan (contrast-reversed long-TE, T2*-weighted), the granule cell (light gray) and molecular layers dark gray) can be distinguished from white matter (white).