Segmentation and morphometric MRI atlas of the chimpanzee cerebellum

Abstract Increased appreciation of the functional heterogeneity of the cerebellum and its contribution to various neuropsychiatric impairments has sparked a resurgence of interest in its comparative anatomy and evolution. Recent evidence suggests that (1) the cerebellar lobules play a prominent role in cognitive, social, and behavioral computations (Desmond et al. 1997; Schmahmann and Sherman 1998; Stoodley and Schmahmann 2009a), and that (2) select portions of the cerebellum may have undergone evolutionary expansion in some lineages of mammals, including humans (Balsters et al. 2010; Smaers et al. 2018), thus creating a need for a higher neuroanatomical resolution of the cerebellum across a broad comparative sample. Here, we provide a detailed magnetic resonance imaging (MRI) atlas of the chimpanzee cerebellum as well as a methodology for the systematic delineation of the vermal and hemispheric lobules. Group averaging across 67 individuals facilitated the characterization of 32 cerebellar masks across the anterior, posterior, and flocculonodular lobes of the cerebellum. A segmentation protocol, including detailed anatomical definitions of each structure, provides the foundation for the construction of future multimodal cerebellar atlases that can deliver insight into cerebellar evolution and pathology.