Investigating female versus male differences in white matter neuroplasticity associated with complex visuo-motor learning

Abstract

Magnetic resonance imaging (MRI) has increasingly been used to characterize structure-function relationships during white matter neuroplasticity. Biological sex differences may be an important factor that affects patterns of neuroplasticity, and therefore impacts learning and rehabilitation. The current study examined a participant cohort before and after visuo-motor training to characterize sex differences in microstructural measures. The participants (N = 27) completed a 10-session (4 week) complex visuo-motor training task with their non-dominant hand. All participants significantly improved movement speed and their movement speed variability over the training period. White matter neuroplasticity in females and males was examined using fractional anisotropy (FA) and myelin water fraction (MWF) along the cortico-spinal tract (CST) and the corpus callosum (CC). FA values showed significant differences in the middle portion of the CST tract (nodes 38-51) across the training period. MWF showed a similar cluster in the inferior portion of the tract (nodes 18-29) but did not reach significance. Additionally, at baseline, males showed significantly higher levels of MWF measures in the middle body of the CC. Combining data from females and males would have resulted in reduced sensitivity, making it harder to detect differences in neuroplasticity. These findings offer initial insights into possible female versus male differences in white matter neuroplasticity during motor learning. This warrants investigations into specific patterns of white matter neuroplasticity for females versus males across the lifespan. Understanding biological sex-specific differences in white matter neuroplasticity may have significant implications for the interpretation of change associated with learning or rehabilitation.

Figure 1

Cortico-spinal tract tractography results of representative female and male subjects and group mean tract profiles separated by sex (with standard error shading). Nodes used for repeated measures analysis of variance highlighted in dotted box and plotted. Additionally, color intensity mapping of F-values from cluster-based permutation method are portrayed on the model cortico-spinal tract at approximate node locations (A). Change in average speed and standard deviation of speed for all participant movements from the first 200 movements to last 200 movements (B).

Figure 2

Change in mean movement speed and in mean movement speed variability in seconds from the first 200 movements to the last 200 movements. Results are colour coded by female (blue) and male (brown). Both dependent variables showed a significant main effect of time (p < 0.001).

Figure 3

Cortico-spinal tract fractional anisotropy (FA) and myelin water fraction (MWF) profiles at baseline and endpoint for both the tract pertaining to the trained arm and untrained arm. Standard error shading is included. Grey shaded region covers the nodes that were then used in the mixed repeated measures analysis of variance (Female: A; Male: C). Mean FA and MWF changes in grey shaded nodes (FA: 38–51; MWF: 18–29) for females and males (B).

Figure 4

Baseline and endpoint myelin water fraction (MWF) and fractional anisotropy (FA) tract profiles of tracts traversing from left medial cortex to right medial cortex through the body of the corpus callosum (CC) for female and male brains. Shading represents standard error (A). A representative’s CCMid tractography result with faded whole brain tractography background (B).