Abstract
Numerous studies have noted the importance of white matter changes in motor learning, but existing literature only focuses on structural and microstructural MRI changes, as there are limited tools available for in vivo investigations of white matter function. One method that has gained recent prominence is the application of blood oxygen level dependent (BOLD) fMRI to white matter, with high-field scanners now being able to better detect the smaller hemodynamic changes present in this tissue type compared to those in the gray matter. However, fMRI techniques have yet to be applied to investigations of neuroplastic change with motor learning in white matter. White matter function represents an unexplored component of neuroplasticity and is essential for gaining a complete understanding of learning-based changes occurring throughout the whole brain. Twelve healthy, right-handed participants completed fine motor and gross motor tasks with both hands, using an MRI compatible computer mouse. Using a crossover design along with a prior analysis approach to establish WM activation, participants received a baseline scan followed by 2 weeks of training, returning for a midpoint and endpoint scan. The motor tasks were designed to be selectively difficult for the left hand, leading to a training effect only in that condition. Analysis targeted the comparison and detection of training-associated right vs left hand changes. A statistically significant improvement in motor task score was only noted for the left-hand motor condition. A corresponding change in the temporal characteristics of the white matter hemodynamic response was shown within only the right corticospinal tract. The hemodynamic response exhibited a reduction in the dispersion characteristics after the training period. To our knowledge, this is the first report of MRI detectable functional neuroplasticity in white matter, suggesting that modifications in temporal characteristics of white matter hemodynamics may underlie functional neuroplasticity in this tissue.
Highlights
White matter (WM) is a critically important tissue for brain function, making up almost 50% of the brain’s volume (Black, 2007), and providing connections between cortical areas in a manner vital for communication throughout neural networks (Bassett et al, 2011)
Though studies using blood oxygen level dependent (BOLD) signal have largely focused on gray matter (GM), improved MRI technology is allowing for the detection of the lower amplitude BOLD signals coming from WM (Gawryluk et al, 2014b)
Predictors were constructed in a manner based on the work of Courtemanche et al (2018), which compared the use of a conventional GLM to a model that included hemodynamic response function (HRF) basis sets generated in FMRIB’s Linear Optimal Basis Sets” (FLOBS)
Summary
White matter (WM) is a critically important tissue for brain function, making up almost 50% of the brain’s volume (Black, 2007), and providing connections between cortical areas in a manner vital for communication throughout neural networks (Bassett et al, 2011). An increase in FA within the right CST, along a tract seeded from areas activated by the tapping task, was found (Reid et al, 2017) This task showed a significantly lateralized difference in motor training across several modalities between participants non-dominant and dominant hands. Building on the established differences in WM hemodynamic properties, we included metrics to assess HRF changes beyond traditional measures of BOLD amplitude and extent. This allowed a more complete investigation into functional WM changes during neuroplasticity. The research employed a repeat measures crossover design that included three longitudinal scan sessions (baseline, midpoint, and endpoint)
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