In the present study, we demonstrate regional structural brain plasticity in the developing brain that occurred with only 15 months of instrumental musical training in early childhood. Structural brain changes in motor and auditory areas (of critical importance for instrumental music training) were correlated with behavioral improvements on motor and auditory–musical tests. This study is the first longitudinal investigation to directly correlate brain structure and behavioral changes over time in the developing brain.
The lack of brain and behavioral differences between the instrumental and control children at baseline (before any music training) is consistent with previous findings from a larger sample that included the present subset of children tested here (Norton et al., 2005
). It is not possible from these findings to completely rule out that musicians may be born with preexisting biological predictors of musicality or that some children may have a certain genetically determined trajectory of cerebral development that may lead them to more likely continue to practice music relative to other children without this same predisposition. However, our findings do support the view that brain differences seen in adult musicians relative to nonmusicians are more likely to be the product of intensive music training (Norton et al., 2005
; Schlaug et al., 2005
). Children who played and practiced a musical instrument showed greater improvements in motor ability (as measured by finger dexterity in both left and right hands) and in auditory melodic and rhythmic discrimination skills. Contrary to previous findings, however (Chan et al., 1998
; Vaughn, 2000
; Ho et al., 2003
; Schellenberg, 2004
; Rauscher et al., 1997
, 2000), children who studied an instrument for 15 months did not show superior progress in visual–spatial and verbal transfer domain outcomes than children who did not receive instrumental training. We propose three reasons why 15 months of instrumental music training may not have been sufficient to result in far transfer: (1) 15 months of instrumental lessons may be too short a period of time (duration explanation); (2) children in our instrumental group may have practiced too little (intensity explanation); or (3) a larger sample may be required to demonstrate far transfer (power explanation).
The brain deformations found over 15 months in our controls (see supplemental Fig. 2
, available at www.jneurosci.org
as supplemental material
) are consistent with previous findings in normal development that have included similar age ranges (from 5 to 7 years old) (e.g., Sowell et al., 2004
). The consistency of the brain deformation found here in our controls with other studies of typical brain development in frontal, temporal, and parieto-occipital brain areas strengthens our conclusions that the brain deformations observed here between instrumental and control children are due to musical training. The present findings of structural brain changes in response to 15 months of instrumental music training are consistent with previous findings of training-induced structural brain differences in adults in various contexts (Draganski et al., 2004
; Draganski and May, 2008
). More specifically, the brain deformation differences found in primary motor brain regions are consistent with structural brain differences found between adult musicians and nonmusicians in the precentral gyri (Gaser and Schlaug, 2003b
) and the corpus callosum (Schlaug et al., 1995
; Oztürk et al., 2002
; Schmithorst and Wilke, 2002
; Lee et al., 2003
). Although the right auditory cluster was not significant at a whole-brain level, this result was strongly predicted on the basis of findings of previous structural brain differences in right auditory cortex in adult musicians (Schneider et al., 2002
; Gaser and Schlaug, 2003b
; Bermudez and Zatorre, 2005
). Thus, we report this right primary auditory region at an a priori threshold.
The brain–behavioral correlations found here in motor and auditory brain regions for performance on motor and auditory (melodic/rhythmic) tests show that different motor and auditory behavioral functions (both musically relevant) appear to be driving the group differences in separate predicted brain regions. These results are important from a functional perspective since these brain regions are known to be of critical importance in instrumental music performance and auditory processing. For example, the primary motor area plays a critical role in motor planning, execution, and control of bimanual sequential finger movements as well as motor learning (Karni et al., 1995
; Grodd et al., 2001
). The correlation found between the brain deformation measures and the motor test at the corpus callosum is consistent with the fact that the peak voxel lies in the fourth and fifth segments of the corpus callosum (Witelson, 1989
) (also called mid-body), which contains fibers connecting primary sensorimotor cortex (Wahl et al., 2007
). Moreover, it has been suggested that intense bimanual motor training of musicians could play an important role in the determination of callosal fiber composition and size (Schlaug et al., 1995
). Last, the correlation found between the brain deformation measures and the melody/rhythmic test battery in the right primary auditory region is consistent with functional brain mapping studies that have found activity changes using auditory–musical tests in similar auditory regions (Zatorre et al., 2002
While structural brain differences were expected in motor and auditory brain areas, unexpected significant brain deformation differences were also found in various frontal areas, the left posterior pericingulate, and a left middle occipital region. However, none of these unexpected deformation changes were correlated with motor or auditory test performance changes. While we do not currently have an interpretation for some of these unexpected brain findings since they did not correlate with the auditory and motor behaviors, the left posterior pericingulate region warrants additional discussion since it showed a highly significant deformation difference. This region lies in the vicinity of Brodmann area 31 in the transition between posterior cingulate and occipital cortex and is involved in the integration of sensory (mostly visual) information and the limbic system. Such integration is involved in learning to read musical notation and relating music to its emotional content. The relative voxel size increases in frontomesial regions also stand out, although no obvious relationship with changes in motor and auditory performance was seen in these regions. Overall, these findings indicate that plasticity can occur in brain regions that control primary functions important for playing a musical instrument, and also in brain regions that might be responsible for the kind of multimodal sensorimotor integration likely to underlie the instrumental learning. None of the unexpected brain deformation differences mentioned above were correlated with behavioral performance changes in any of the far-transfer domains. This may indicate that brain structural changes in association areas and multimodal integration regions may develop before the emergence of significant behavioral/cognitive changes in far-transfer domains.
While we have discussed the functional significance of the brain–behavioral structural changes, the underlying structural properties of the results are not trivial to explain. The brain deformation techniques used here are key to localize brain size/shape changes over time, but are not able to inform us on the microstructural nature of these changes. Overall, instrumental children showed greater relative voxel size expansion than controls over the 15 months, and only one area of voxel size contraction. A voxel expansion or contraction may reflect increased or decreased gray or white matter due to neural reorganization/pruning or increased/decreased brain connectivity. Evidence from animal models investigating the effects of long-term learning and practice of complex motor skills (Anderson et al., 2002
) on brain structure may shed light on the structural neural basis of the brain structural changes seen here. Several groups have demonstrated microstructural brain changes as a function of long-term motor learning, including an increased number of synapses and glial cells, increased density of capillaries in primary motor cortex and cerebellum, and new brain cells in the hippocampus after long-term motor training in adult rats (Black et al., 1990
; Isaacs et al., 1992
; Anderson et al., 1994
; Kleim et al., 1996
; Kempermann et al., 1997
; Anderson et al., 2002
). The sum of these microstructural changes could amount to structural differences that are detectable on a macrostructural level, such as those observed in the present study (Anderson et al., 2002
; Bangert and Schlaug, 2006
). It is possible that the specific and continuous engagement of a unimodal and multimodal sensorimotor network, and the induced changes in this network across a musician’s career, may provide the neural basis for some of the sensorimotor and cognitive enhancements attributed to musical training. Future, even higher-resolution morphometric investigations with more direct measures of gray and white matter will be key to developing a better understanding of the underlying nature of the brain deformation differences found here. We also did not find any differences in MR intensities between groups, though using T1-weighted sequences is clearly a limitation in this regard. Future studies should examine quantitative sequences, such as diffusion tensor imaging, magnetization transfer, etc., in more detail to see whether microstructural changes can be captured separately from the volumetric differences described herein. Last, we wish to point out that one of the potential confounds of deformation-based morphometry is that the deformation procedure can sometimes result in changes being propagated to regions distant from their actual origin. Given that the present results were predicted based on the functional literature, we feel it is unlikely that such propagation accounts for the results presented in this manuscript. In the future, converging results from additional structural and functional analyses metrics will serve to strengthen our conclusions.
In summary, our findings show for the first time that musical training over only 15 months in early childhood leads to structural brain changes that diverge from typical brain development. Regional training-induced structural brain changes were found in musically relevant regions that were driven by musically relevant behavioral tests. The fact there were no structural brain differences found between groups before the onset of musical training indicates that the differential development of these brain regions is induced by instrumental practice rather by than preexisting biological predictors of musicality. These results provide new evidence for training-induced structural brain plasticity in early childhood. These findings of structural plasticity in the young brain suggest that long-term intervention programs can facilitate neuroplasticity in children. Such an intervention could be of particular relevance to children with developmental disorders and to adults with neurological diseases.