Differential adaptation of descending motor tracts in musicians

Abstract

Between-group comparisons of musicians and nonmusicians have revealed structural brain differences and also functional differences in motor performance. In this study, we aimed to examine the relation between white matter microstructure and high-level motor skills by contrasting 2 groups of musicians with different instrument-specific motor requirements. We used diffusion tensor imaging to compare diffusivity measures of different corticospinal motor tracts of 10 keyboard players, 10 string players, and 10 nonmusicians. Additionally, the maximal tapping rates of their left and right index fingers were determined. When compared with nonmusicians, fractional anisotropy (FA) values of right-hemispheric motor tracts were significantly higher in both musician groups, whereas left-hemispheric motor tracts showed significantly higher FA values only in the keyboard players. Voxel-wise FA analysis found a group effect in white matter underlying the right motor cortex. Diffusivity measures of fibers originating in the primary motor cortex correlated with the maximal tapping rate of the contralateral index finger across all groups. The observed between-group diffusivity differences might represent an adaptation to the specific motor demands of the respective musical instrument. This is supported further by finding correlations between diffusivity measures and maximal tapping rates.

Keywords: diffusion tensor imaging; finger tapping; motor skill; plasticity; white matter.

Figure 1.

Schematic overview of masks used for tractography as well as of course of reconstructed canonical PT (right side) and aMF (left side) as they descend from the motor cortex to the pons. To generate the canonical images, individual tracts from all subjects were normalized, converted to binary images, and then summed. Cortical contributions from the 3 following cortical areas to PT and aMF are displayed in different colors: red-yellow = contribution from M1 to PT/aMF; blue = contribution from PMd to PT/aMF; green = contribution from SMA to PT/aMF. Color brightness indicates the degree of voxel-by-voxel overlap of the individual normalized tracts. Tractography masks are described in charts on the left side of the figure. “y” and “z” indicate slice position along y- and z-axis in MNI space.

Figure 2.

Tract-specific FA as a function of group × hemisphere × tract. Maximal tapping rate as a function of hand × group. Error bars denote standard error of the mean. Please note: left and right may refer to the hemisphere as well as to the index finger in this figure.

Figure 3.

A voxel-wise 1-way ANOVA of FA. Cluster shows group effect within right ^M1PT as indicated by F-test (P ≤ 0.05, FWE-corrected; size: 6 voxels, p-max in MNI space: x = 13, y = −31, z = 55). R: right hemisphere; x, y, z: coordinates in MNI space.

Figure 4.

Correlations between tract-specific FA/RD of left/right ^M1PT/^M1aMF and maximal tapping rate of contralateral index finger. Pearson's coefficient (r), sample size (n), and level of significance (P) are provided.