Diffusion parameter changes in white matter induced by direct intracortical stimulation in rats

Introduction: While existing MR techniques can reliably detect stimuli-induced activation in gray matter (GM), very little is known about the impact of the stimuli on connective white matter (WM) regions. A recent study has looked into this aspect using functional DTI (fDTI) and reported subtle increases in fractional anisotropy (FA) in specific WM pathways in response to motor or visual stimulation in human subjects. In the current study, we aimed to validate these findings with a direct cortical stimulation paradigm in rats. Our fDTI study based on this very effective stimulation paradigm enabled us to perform voxeland ROI-based analysis, which allowed specific assessment of changes in diffusion parameters (FA, mean diffusivity (MD) and T2 signal without diffusion weighting (S0)) in selective WM and GM regions. There are strong indications suggesting that diffusion related changes do take place in WM due to stimulation. There are also indications that the vascular origins of these changes cannot be neglected, as reported by other researchers.