Introduction and Overview of Synaptic Plasticity





One of the most beneficial results of learning to play a musical instrument is the functional and structural brain plasticity that is induced by practice(5, 6). The theory of plasticity most referenced by work in this field of research is the Hebbian principle of use and disuse- or more colloquially, neurons that fire together wire together. As we acquire patterns of behavior and thought, the neurons we use most often continue to become activated through depolarization. When depolarized, the neurons release a cascade of neurotransmitters that ultimately contribute to long-term potentiation and allow us to more easily activate these same synaptic pathways in the future. For musicians, the complicated process of learning to simultaneously read, hear, and produce music results in the repeated and coordinated activation of many brain areas, which respond plastically to the activity(5, 6, 8, 10). In many instances there is an increase in brain volume in these areas.

Sensitive Period

Children respond more quickly and drastically to musical training due to the increased number of synaptic connections being made and pruned each day, in what is referred to as a "sensitive" period of development (4) .This is differs from a critical period, wherein if certain essential connections are not properly made within a window of time, the corresponding behavior/morphological features will never develop; in a sensitive period, the child responds to the stimulus (in this case musical training) more drastically than an adult would upon the same exposure(4). Evidence for sensitive periods in childhood is abundant, and includes studies such as second-language learning(1). In these studies, the resulting correlation was that the earlier a child began learning a second language, the more proficient he was (1). This finding can be logically understood with the knowledge that children's brains have a much greater level of activity, and a denser amount of synapses (see Figure 1), than the adult brain (2). Similar studies involving musical training and children are discussed below.


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Figure 1: Adapted from Gogtay et al.(2004); Illustration of gray matter density in correlation to age

Musical Training in Children

Structural Changes

Through longitudinal imaging studies, it is possible to observe the structural differences between musically trained and non-trained children at various stages of training(3, 5, 6). One such study used deformation-based morphometry (DBM) to image the brain on a large-scale comparative basis and measure brain volume changes in voxels(6). Increased volume was associated with increased branching and synaptic density at that location. Children with only 15 months of musical training exhibited increased voxel size in several brain areas(6):

-Primary auditory area

Increasing synaptic connection in this area (including the region known as Heschl’s gyrus) is logical due to the necessity of auditiory stimulation when listening to and producing music. Repeated and intense auditory exercises increases the plasticity of this region.

Primary motor area

The growth in this area is most likely because it is largely responsible for coordination of bimanual sequential finger movements necessary in instrumental training (6). After only 15 months of training in children, the size of this area is significantly larger(6).

-Corpus callosum

It is postulated that the increase in size and strength of corpus callosum fibers (particularly in the mid-body region), which traverse the center of the brain, are due to their connection with the primary sensorimotor cortex areas, which plays an integral role in communication between the two brain hemispheres, both of which are used to execute bimanual musical sequences(5). This finding was reaffirmed and elaborated in a similar study which specifically studied the effects of practice intensity on the development of the anterior corpus collosum in children. This study noted the particular growth in area 3 fibers, which project mainly to the prefrontal cortex, premotor, and supplementary motor areas. These three cortical regions all participate in motor preparation and planning and have modulating effects on motor execution(5). The researchers predict that the differential effect of instrumental music training on structural development of the CC might be due to growth of myelination and axon size, or number of transcallosal fibers that could result from interference of bimanual activities in the pruning of interhemispheric fibers during development(5). They discovered that the most pronounced changes in the growth of the corpus collosum occured with high intensity practice(5, 6). The discrimination between high and low practice groups, with differential results, provides yet more evidence for the causal relationship between musical training and brain plasticity(3, 5, 6).


Behavioral Changes

Near transfer effects: Children who underwent musical training for 15 months showed greater improvements in motor ability and in auditory and rhythmic discrimination skills such as tapping out a melody given to them or identifying patterns in auditory stimuli(6). As shown in Figure 2, these improvements in motor tasks correlated
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Figure 2: Corpus collosum of musically trained children increases in volume in correlation with dexterity
with the morphological brain changes they exhibited(6). Motor ability in this study was measured by finger dexterity, which was greater in both the left and right hands of musically trained children(6). In most short-term music studying, these effects are shown(3, 4, 6, 7). However, it appears to take longer exposure to musical training before far-transfer effects (behavioral/cognitive benefits outside of immediate application to musicality) become apparent(7, 10).


Far transfer effects: After short training times(15-29 months of training, depending on the study at hand), there were little to no transfer effects that extended farther than musically relevant motor and auditory tasks(7). However, several longitudinal studies have given evidence of cross-modal effects after several years of musical study. A study comparing behavior in 9-11 year old musicians vs non-musicians concluded that after an average of 4 years of musical training in childhood, not only were the previously discussed fine motor abilities and auditory discrimination skills improved, but also the children began to exhibit increased abilities in verbal, spatial, and mathematic tasks, not directly related to musical performance(7). The researcher postulated that music training enhances spatial reasoning because music notation itself is spatial in nature, and that since understanding rhythmic notation actually requires the math-specific skills of pattern recognition and an understanding of proportion, ratio, fractions, and subdivision, mathematical performance is improved by exposure (7). Another study found that children who had studied musical instruments for an average of three years demonstrated superior verbal skills (including standard vocabulary tests) and non-verbal reasoning skills than their non-musical counterparts(7). This effect was also found to be enhance in correlation to how long the child had been practicing music(6,7). Superior verbal abilities can result from musical exposure becuase of the synonomous nature of musical and language processing; for a more complete discussion, refer to Music and Language.



Adult Musicians vs. Non-Musicians

Many studies offer comparative analyses of adult musician brains to the brains of non-musicians. The unique conditions under which profession musicians function (constant practice of novel musical sequences employing auditory and sensorimotor coordination) leads to the functioanl and anatomical brain differences, and lends convincing evidence to the theory of activity-induced plasticity(8, 9, 10). Several aspects of the adult brain are morphologically different in musicians vs. non-musicians. Magnetic resonance (MR) imaging studies have highlighted an increase in gray matter volume in the sensorimotor cortex, and other studies have indicated that musicians exhibit a larger anterior corpus callosum region (similar to the structural changes seen in children training on a musical instrument).
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Figure 3: Regional grey matter differences (from left, precentral gyrus, Heschl's gyrus, right superior parietal cortex) between musician groups. Adapted from Gaser et al. (2003).



Additionally, differences in brain regions within musician groups has given further proof of activity-based plasticity; violin players specifically have larger, elaborated right precentral gyrus regions, while piano players exhibit bilateral precentral gyrus elaborations(13).Thus, plasticity in the brain regions affected by musical training has been shown in adult musicians, leading to the theory that the functional plasticity seen in young children during the sensitive period continues into adulthood if practice of the musical instrument continues(10). In one such study, it was found that musicians have a greater cortical response to TMS (trans-cranial magnetic stimulation) as opposed to non-musicians. This finding implies that adult musicians respond more plastically to sensory cues than non-musicians, possibly as a result of intensive practice involving responses to auditory cues and intensive bimanual executions(8).


The Mozart Effect

Since the early 90s, interest in a “Mozart effect,” the popularized version of which asserts that merely listening to classical music as a child or in utero, could improve intelligence and other aspects of mental development. There has been some evidence to indicate that listening to such music does improve results on cognitive tests for a short period of time extending no longer than 15 minutes, but little to no conclusive research has proven that listening to music induces long-term brain changes(11). The original 1993 study published in Nature, which explored the effects of listening to Mozart, other music, or silence before taking a portion of an IQ test, indicated increased scores for the Mozart group. Though this study was by no means generalizing its results to indicate that the music had a long-lasting effect on mental capacity, it generated widespread interest in the topic. Results from a similar study in which participants listened to Mozart before taking a test claimed that they scored better than their control counterparts on IQ subtests, but the improvement was only shown if there was also a change in mood and arousal after listening to the music(11). This correlation suggests that cognitive performance can be enhanced by increasing arousal, which is possible when listening to music (not necessarily Mozart or classical music). For a description of research on this topic, refer to the exerpt of Dr. Glenn WIlson's lecture on the subject:

As of 2012, an overwhelming amount of research seems to show that as far as mental capability is concerned, certain aspects may be improved through music, but only by extensive musical study of an instrument and through years of practice, not just exposure via listening. Much is known about the relationship between music and emotional state; for a more comprehensive discussion, refer to Music and Emotion.

References
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2. Gogtay, N., Giedd, J., Lusk, L. (2004) Dynamic mapping of human cortical development during childhood through early adulthood. PNAS May 25, 2004 vol. 101 no. 21 8174-8179.

3. Bailey J and Penhune V.(2010) Rhythm synchronization performance and auditory working memory in early- and late-trained musicians. Experimental Brain Research, 204: 91e101.
4. Wan CY, Schlaug G. (2010) Music Making as a Tool for Promoting Brain Plasticity across the Life Span. The Neuroscientist. 16(5):566-577.
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(2009) Training-induced Neuroplasticity in Young Children. Ann NY Acad Sci. ;1169:205-208

6. Hyde KL, Lerch J, Norton A, Forgeard M, Winner E, Evans AC, Schlaug G.(2009) Musical training shapes structural brain development. J Neurosci. 29:3019-3025
7. Forgeard M, Winner E, Norton A, Schlaug G (2008) Practicing a Musical Instrument in Childhood is Associated with Enhanced Verbal Ability and Nonverbal Reasoning. PLoS ONE 3(10): e3566. doi:10.1371/
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9. Schmithorst VJ, Wilke M. (2002). Differences in white matter architecture between musicians and non-musicians: a diffusion tensor imaging study. Neurosci Lett. 321:57–60
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11. Schellenberg, E, Nakata,T, Hunter, G, and Sachiko Tamoto. Exposure to music and cognitive performance: tests of children and adults.Psychology of Music January 2007 35: 5-19,
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13. Bangert, M., & Schlaug, G. (2006) Specialization of the specialized in features of external human brain morphology. Eur. J. Neurosci., 24(6), 1832-1834