In-vivo parcellation of human subcortex by multi-modal MRI

Human subcortical grey matter (SGM) structures are crucial hubs for processing, transmitting and modulating brain-wide signals. However, in-vivo characterisation of subnuclei within the SGM structures remains limited, restricting our knowledge of their roles in brain function and in disorders. To address this gap, we introduce the Sydney Subcortical Gray Matter (SydSGM) parcellation— based on a novel data-driven approach using multiple MRI contrasts to assess myelination, directionality of white matter fibres, and diffusion micro-environment. Fifty-four distinct parcels were identified across caudate, putamen, globus pallidus, nucleus accumbens, and thalamus based on the coherent representation of these attributes, which demonstrated remarkable concordance with histology-based delineations. The SydSGM parcellation now facilitates detailed structural connectivity analysis at the subnuclei scale. It can be adopted as a standalone atlas or incorporated into existing brain atlases. We demonstrate SydSGM parcellation’s advantage by revealing declined structural connectivity of highly resolved SGM subnuclei in patients with early Parkinson’s disease.