by Guillermina Griffa, Marco Palombo, Abraham Yeffal, Hong-Hsi Lee, Agustin Solano, Susie Y. Huang, Valeria Della-Maggiore Structural neuroplasticity supports learning, development, and shapes vulnerability to brain disorders, making it a central priority in neuroscience research. However, progress in humans has remained limited by the inability to probe cellular processes in vivo, leaving mechanistic insight largely dependent on animal models. To address this gap, here we combined the sub-voxel sensitivity of ultra–high-gradient diffusion MRI with the cell-compartment specificity of the Soma and Neurite Density Imaging (SANDI) model to probe structural plasticity directly in the living human brain. By tracking how learning modulates the temporal dynamics of cell bodies and cell processes, we aimed to distinguish plastic from nonplastic biological processes driving changes in microstructure. We found that learning a motor skill triggered two distinct temporal responses: a transient exp