# Motor learning induces myelin-related white matter changes revealed by MRI-based in vivo histology

## TL;DR

This study shows that motor learning leads to myelin-related changes in white matter pathways, which are linked to improved brain function and behavior.

## Contribution

The study introduces a novel multivariate MRI framework to reveal myelin-related white matter plasticity in humans during motor learning.

## Key findings

- Motor learning induces myelin-related changes in distributed white matter pathways.
- Training-related modulation of the aggregate g-ratio was observed in humans.
- Changes in white matter are linked to neocortical plasticity and behavioral learning.

## Abstract

Motor learning induces widespread brain changes, yet the microstructural mechanisms underlying human white matter (WM) plasticity remain poorly understood. Animal studies have identified roles for neurites, glia, and myelin, but in vivo human evidence has been limited by measurement specificity. Here, we combine multi-contrast quantitative MRI (qMRI), tractometry, and a novel multivariate analysis framework to investigate the microstructural basis of WM plasticity during motor skill learning. In a longitudinal within-subject study, 24 healthy adults completed 4 weeks of balance training following a baseline control period without training. We mapped changes across tractography-defined WM pathways using complementary qMRI markers related to tissue density, myelin, neurite architecture, and iron. Multivariate analysis revealed biologically plausible, behaviorally relevant plasticity in distributed pathways—including the cortico-ponto-cerebello-thalamo-cortical loop, anterior thalamic radiation, and corticospinal tracts—with important contributions from myelin-related metrics. Notably, we observed changes consistent with training-related modulation of the aggregate g-ratio in humans. These spatially distributed effects converged into a single latent dimension predicting neocortical plasticity, suggesting a coordinated, cross-tissue mechanism of brain adaptation. This biologically interpretable framework offers a powerful new approach for investigating WM microstructure in the contexts of plasticity, development, aging, disease, and rehabilitation.

Multicontrast qMRI with multivariate tractometry reveals predominantly myelin-related changes across distributed motor fiber tracts, linked to behavioral learning and neocortical plasticity.