Time course of structural neuroplasticity induced by procedural motor learning: DTI vs SANDI

Motivation: Performance gains during motor sequence learning (MSL) are linked to increased hippocampal activity and fast changes in mean diffusivity. Yet, DTI is not biologically specific. Goal(s): To identify the biological compartment(s) driving changes in gray-matter microstructure during MSL. Approach: We applied SANDI to multi-shell-DWI acquired in 28 subjects on the Connectome scanner before, 30 min, and 24h post MSL training. Results: MSL-induced transient changes in DTI were associated with a temporary increase in soma fraction at 30 min, compatible with a fast homeostatic response (e.g. astrocytic swelling). Long-lasting DTI changes were associated with an increment in neurite fraction compatible with structural remodelling. Impact: Our work may broaden the scope of understanding of human hippocampal memory and help pinpoint the biological substrates of plasticity. Moreover, it may set the basis for developing a biologically meaningful biomarker of neuroplasticity to detect early signs of neuropathology.