Introduction: White matter changes in response to rehabilitation of chronic motor deficits after stroke has not been well understood. Our hypothesis is that there is a relationship between gains in motor function and changes in structure of white matter tracts.
Methods: Fugl-Meyer upper limb (FM) score and Diffusion Tensor Imaging (DTI) were collected before and after a 12-week upper limb motor learning therapy. DTI data was processed using the longitudinal Freesurfer Tracula stream where white matter tracts are reconstructed using global probabilistic tractography. The average fractional anisotropy (FA), as well as axial diffusivity (Da) and radial diffusivity (Dr) were computed for 14 major white matter tracts. General linear models were fit where pre-to-post change in FA for a given tract were dependent variables and pre-to-post change in FM was a predictor. The relationship was adjusted for baseline FM score. Spearman correlations were determined between FA, Da and Dr. Wilcoxon test was used for pre-to-post comparisons.
Results: We evaluated and treated 21 stroke survivors; they were 1.9±1.2 (mean±std.dev) years post stroke, 55.1±12.9 yrs old and 42% female. FM improved from 23±8.75 to 34.1±10.5 (p<0.001). There was a significant association between gain in motor function and the decrease in FA for the following tracts: ipsilesional inferior longitudinal fasciculus (iplsi-ILF), contralesional ILF (contra-ILF) and transcallosal forceps major tract, controlling for baseline FM scores, (for ipsi-ILF: R2=0.4, p=0.006; for contra-ILF: R2=0.38, p=0.004; for forceps major: R2=0.31,p=0.02). According to the correlation analysis, decrease in FA could be explained by increase in Dr, but not by change in Da. Correlation between FA and Dr for ipsi-ILF was r=.75,p<0.001, for contra-ILF - r=.72,p<0.001 and for forceps major - r=.88, p<0.001.
Conclusion: Improvement in function of chronic motor deficits in the upper extremity is related to structural changes in temporal-occipital and transcallosal occipital tracts that connect visual-spatial processing regions. Furthermore, our results suggest that changes in neuronal activity of the identified tracts may be associated with microstructural changes that increase radial diffusivity.