A Multi-Subject Tractography Atlas of Human Cerebellar Connections

The cerebellum is a highly interconnected structure involved in motor coordination and balance as well as cognitive, sensory, autonomic, and emotional functions. Its connectivity relies on complex afferent and efferent white matter pathways linking it with the brainstem, spinal cord, thalamus, cerebral cortex, vestibular system, and limbic-related structures. Recent advances in diffusion MRI (dMRI) and tractography have enabled the in vivo reconstruction of these pathways, offering new opportunities to study cerebellar anatomy and connectivity. However, compared with supratentorial white matter, cerebellar connections remain underexplored owing to their smaller size, anatomical complexity, and the absence of comprehensive tractography atlases. We propose a white matter fiber atlas of human cerebellar connections based on regions of interest (ROIs) derived from 30 young healthy subjects from the Human Connectome Project (HCP). A total of 23 ROIs were segmented to reconstruct, via tractography, 20 cerebellum-associated pathways, including 8 bilateral pathways and 4 interhemispheric connections. These comprise the three cerebellar peduncles and the cerebello-ponto-hypothalamic, parieto-ponto-cerebellar, fronto-ponto-cerebellar, occipito-ponto-cerebellar, contralateral cerebello-thalamo-cortical, dentato-rubro-thalamo-cortical, olivocerebellar, dorsal spinocerebellar, and periaqueductal gray-cerebellar pathways. A neuroanatomical expert evaluated the 20 atlas tracts using four qualitative criteria, finding good anatomical fidelity with an overall mean score of 3.9 out of 5. The same reconstruction procedure was then applied to 25 additional HCP subjects to evaluate the automatic segmentation of these bundles in unseen subjects. The proposed atlas provides a comprehensive framework for studying cerebellar structural connectivity and its relationship with motor and non-motor functions. It enables quantitative tractometry analyses derived from diffusion MRI models and facilitates the integration of multimodal and functional information. This atlas may support future research in neuroscience, neuropsychiatric disorders, and neurosurgical planning by providing a standardized representation of cerebellar white matter pathways.