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

The cerebellum has long been recognized as a partner of the cerebral cortex, and both have expanded greatly in human evolution. The thin cerebellar cortex is even more tightly folded than the cerebral cortex. By scanning a human cerebellum specimen at ultra-high magnetic fields, we were able to computationally reconstruct its surface down to the level of the smallest folds, revealing that the cerebellar cortex has almost 80% of the surface area of the cerebral cortex. By performing the same procedure on a monkey brain, we found that the surface area of the human cerebellum has expanded even more than that of the human cerebral cortex, suggesting a role in characteristically human behaviors, such as toolmaking and language. 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. Datasets including (i) original high-resolution isotropic 3D MRI data of the human cerebellum with two different contrasts; (ii) computationally combined, normalized, filtered, and edited versions of that 3D data; and (iii) FreeSurfer-compatible subject surfaces and vertexwise measurements reconstructed from the data can be downloaded from . Software for performing the analyses presented in this paper is available at or [http://www.cogsci.ucsd.edu/∼sereno/.tmp/dist/csurf][1]. We also used some of the utilities from the standard FreeSurfer 5.3 distribution (available at [https://surfer.nmr.mgh.harvard.edu][2]/) and from the AFNI distribution (available at [https://afni.nimh.nih.gov][3]/). [1]: http://www.cogsci.ucsd.edu/%7Esereno/.tmp/dist/csurf [2]: https://surfer.nmr.mgh.harvard.edu/ [3]: https://afni.nimh.nih.gov/