369(7 years old).^8 The differences in callosal size might be due to more fibres crossing
through the corpus callosum, a larger proportion of thicker myelinated fibres with faster
interhemispheric transfer, or fibres with thicker axons or more axon collaterals. The anterior
part of the corpus callosum contains mainly fibres from frontal motor related regions and
prefrontal regions,^47 and the anterior corpus callosum matures the latest of all callosal sub-
regions. The anatomical difference in the mid-sagittal area of the anterior corpus callosum
has to be seen in the context of a requirement for increased inter-hemispheric communi-
cation subserving complex bimanual motor sequences in musicians. This structural differ-
ence could have been triggered by performing and continuously practicing complicated
and independent bimanual finger movements.
Motor cortex
The exact histological extents of the primary motor cortex cannot be defined on current
MR images. Therefore, we used a gross anatomical marker of the motor cortex, the intra-
sulcal length of the posterior bank of the precentral gyrus (ILPG). This marker corres-
ponds roughly with the histological extent of the primary motor cortex.^48 All brains were
spatially oriented and normalized to the coordinate system of Talairach and Tournoux. The
ILPG was measured in horizontal slices (parallel to the AC–PC plane) from the deepest
point of the central sulcus following the contour line of the posterior bank of the precen-
tral gyrus to a lateral surface tangent which connected the crests of the pre- and postcent-
ral gyrus. Results revealed a greater symmetry of the ILPG in the musician group in a dorsal
subregion of the motor cortex (Talairach coordinates z69 to z55; Figure 24.2).
In addition to the greater symmetry, both left and right hemispheric measures were
larger in musicians in this region. The greater symmetry was due primarily to a much
larger size of the ILPG in the right hemisphere controlling the nondominant left hand. In
addition, we found strong correlations (Figure 24.3) between the age of commencement of
musical training and the mean right as well as left ILPG size.^10
Cerebellum
Several animal studies have provided compelling evidence that the cerebellum shows
microstructural changes (e.g. increased number and density of synapses, glial cells, and
Table 24.1 Midsagittal area of the corpus callosum
Group Size of corpus callosum Anterior part Posterior part
(mm^2 (meanSD))
Musicians (n30) 687 (85) 371 (46)* 314 (43)
7 years (n21) 709 (81) 384 (42) 321 (44)
7 years (n9) 637 (77) 340 (43) 297 (38)
Nonmusicians (n30) 649 (88) 344 (48)* 305 (43)The anterior part of the corpus callosum differs insignificantly between musicians and nonmusicians
(*). This difference was mainly due to musicians who started before 7 years of age with their musical
training ().