Differences Between the Brains of Musicians and Non-Musicians
...as to best comprehend complex brain mechanisms involved in musical perception. These complex systems often are more definable when they malfunction due to brain injury than when they are functioning normally ( Peretz, Champed, Hyde 2003 ). Specifically, pitch, melody, harmony, rhythm, tempo, meter, and duration are all separate components that are processed differently (Parsons 2001). Parsons and his colleagues chose to advance upon their previous work of measuring cerebral blood flow (CBF) while a musician sight read and played a musical piece with their right hand by letting the musician play a memorized piece with both hands. A stronger activation in the right auditory cortex for the performance of the memorized piece is consistent with previous results indicating that areas in right auditory association cortex are involved in the reception and expression of melody. These findings suggest that some of the important areas specifically representing the higher-order representations of musical meaning, particular in performance, lie in these regions of temporal cortex. There was also correlated activation during the performance between right anterior temporal areas and left posterior lateral cerebellum. Parsons and his researchers hypothesize because the left cerebellum has its primary connectivity with right cerebral cortex, that during performance, activation in right auditory cortex is related to that in left cerebellum. There was a smaller correlation between left temporal areas, and the right posterior cerebellum. This contra-lateral activation of the auditory temporal cortex and lateral cerebellum suggests that they form a neural circuit for performance cognition, because the cerebellar activity appears to be effectively dissociated from motor components. Unfortunately, Parsons did not include non-musicians in this study, he possibly could have had them play an improvised piece as they were scanned. If he had he might have found that there was a difference between the non-musicians who merely improvised. Parsons did decide to further investigate melody, harmony, and rhythm in another study. Each condition showed a distinct pattern of brain activity compared to passive listening, activating different sub-areas of a particular major brain area. Globally, sight reading and comprehension of melodic, rhythmic, and harmonic features of a piece were supported by processes in both cerebral hemispheres. Melodic comprehension activated each hemisphere uniformly, while harmonic and rhythmic comprehension activated more of the left hemisphere than the right one. Interestingly, the rhythm component activated comparatively few brain areas outside the cerebellum. On an unrelated note, to me activation in the “old” brain may show that the perception of rhythm has been with us for a while. In a further study, Parsons, along with Michael Thaut, found both non-musicians and musicians, showed distinct patterns of brain activity for the discrimination of pitch and rhythm (Parsons 2001). For pitch, superior temporal areas were activated on the right in non-musicians and on the left in musicians. However, in both groups middle and inferior temporal areas were activated on the right. These finding support their previous research. One interesting finding showed activity within the right inferior frontal cortex in control but not in AP subjects during an interval-judgment task, suggesting that AP possessors need not access working memory in this task. This also implies a learned conditional association because the activation was located in the left posterior dorsolateral frontal cortex (Zatorre, Perry, Beckett, Westbury, Evans 1998). So in regards to the functional differences of musical perception between musicians and non-musicians one can see from the literature that neural circuits are highly complex and individualistic, it was best stated in an article by Eckart O Altenmuller, “ We demonstrated that cortical activation during musical processing reflects the auditory ‘learning biography,’ the personal experiences accumulated over time. Listening to music, learning to play an instrument, formal instruction, and professional training result in multiple, in many instances multi-sensory, representations of music, which seem to be partly interchangeable and rapidly adaptive.” With relation to AP, musicians who possess it may in fact respond to tones in a “verbal-tonal association” (Zatorre, Perry, Beckett, Westbury, Evans 1998). Other researchers have found through magnetoencephalography (MEG), that 19-30 ms after a sinusoidal tone (pure sine wave) was presented, musicians showed a 102% greater evocation of events in areas of the primary auditory cortex than non-musicians. The size, of cortical representation was positively related to a tested musical aptitude ( Schneider, Scherg, Dosch, Specht, Gutschalk, Rupp 2002). Not touched upon yet are the adaptations of the motor and sensory-motor cortex in response to bimanual skill learning. It has been shown that over the course of as little as 5 days cortical motor areas which represented finger muscles enlarged significantly in response to the learning of a five fingered exercise on a piano ( Amunts, Schlaug, Jancke, Steinmetz, Schleicher, Dabringhaus, Zilles 1997). It is from this data that researchers are investigating if an activity related to long term potentiation causes the over-used cortical areas to be enlarged. Also the instrasulcal length of the precentral gyrus (ILPG) has been found to be deeper and more symmetrical in musicians who had commenced their musical training before the age of 7. The ILPG is found in the sensory-motor cortex of the brain. In fact, an enlargement of the anteromedial portion of Heschl’s gyrus (amHG) was found by Schneider in 2002 that was directly related to the enlargement of the cortical representation of the sinusoidal tones. The enlargement was found to be as much as, 130% +/- 23% in the grey matter of the cortex of musicians when it was averaged over both hemispheres. From table I of the article one can see how drastically the enlargement is compared to adjacent areas of Heschl’s Gyrus (HG). In the left HG the three groups comparatively similar in grey matter estimation. As you move anteromedially we see the drastic change in structure. Also noted in this article is that the normal maturation age for HG and the Planum Temporal (PT) is at or around 7 years of age with the age of 9 being the cut-off point for their measure of musical aptitude. Gottfried Schlaug and Christian Gaser used a voxel-by-voxel technique to measure grey matter volume in 20 professional musicians, 20 matched amateur musicians and 40 matched non-musicians. They found gray matter volume differences in motor, auditory, and visuospatial brain regions in agreement with musical skill level (Schlaug, Gaser 2003). Schlaug attributes these differences to the complex motor movements, and mental processes musicians must repeatedly practice. The main areas where an enlargement was found were the primary sensorymotor region, the premotor cortex, and the cerebellum. Schlaug and Gaser propose that either these differences are due to the intensive training the musicians undergo or these individuals are “drawn” to music because their individual brain structures can readily handle musical cognition and performance (Schlaug, Gaser 2003). The Corpus Callosum (CC) is another brain structure that is associated with adaptation in response to intensive musical training. This is due to the fact that the corpus callosum is the main interhemispheric fiber tract which organizes information cross-hemispherically, evidence suggesting that change in the CC can occur in a child up to 11 years of age, and a correlation between CC size and the number of fiber tracts located in the CC. Significantly larger anterior CC were found in the musicians group who started training early as compared to controls and amateurs. This viewpoint would coincide with research that I mentioned earlier suggesting greater bi-hemispheric activation in musicians during various musical tests as compared to non-musicians who showed an overall asymmetrical musical processing pattern. Also the complex bi-manual motor movements that are required for musicians would necessitate the need for fast cross-hemispheric communication in my own personal estimation. The phenomena of AP, I feel must be discussed all on its own in regards to neurophysiology and neuroanatomy. AP is the ability to name the pitch of a musical tone or to produce a musical tone at a given pitch without the use some sort of reference strategy. Most humans process musical pitch in a relative way. That is to say they process the melodic relations between pitches instead of the absolute pitch of the tones themselves. AP is a rare; it is possessed by less than .01% of the general population (Takeuchi, Hulse 1993). Evidence suggests that the ability of AP is acquired during a critical time of brain development. Although the basis for AP is still unclear, it is thought that early exposure to music during the critical period can influence the structure of the Planum Temporal (PT). The PT has traditionally been associated with language and auditory cognition. Schlaug and his research team (1995) found a leftward asymmetry of the PT in musicians who possessed AP as measured with an AP test. It has been found that a majority of right-handed individuals show a leftward PT asymmetry, whereas the majority of left-handers have either a symmetric PT or show a rightward asymmetry (Schlaug 2001). In an MRI study designed to test the hypothesis that musicians might different hemispheric dominance than non-musicians, Schlaug found that musicians had an increased left-sided asymmetry of the PT. The surprising finding was that musicians who had absolute pitch accounted for the difference between the musician and non-musician group ( Schlaug 2001). Schlaug also states that of the 50+ right and left handed musicians that have been studied ...