Week 6: The Brain of Musicians (G. Schlaug)

IMAGE: HUMAN MOTOR CORTEX TOPOGRAPHY (http://upload.wikimedia.org/wikipedia/commons/0/0b/Human_motor_cortex_topography.png_

Disclaimer: This has been one of my favorite articles so far! Very informative…

Schlaug introduces the chapter by discussing brain plasticity, in terms of structure and function, and indicates that music is an ideal area to study this phenomenon.

STRUCTURAL BRAIN DIFFERENCES BETWEEN MUSICIANS AND NONMUSICIANS

Several cross-sectional studies are described here to illustrate finding regarding the structural differences in musicians’ brains. Understanding such neural substrates allow us to understand the effect of music on the brain and potentially other areas for interdisciplinary research. Handedness was controlled for, as this variable can correlate with altered hemispheric brain structures and functions. Using fMRI (with fascinating methodologies that are clearly and succulently described, the following results were attained:

1) The anterior half of the corpus callosum is significantly larger in musicians, particularly those who started musical study when younger than 7 years old. This may be due to the necessity of increased inter-hemispheric communication for completing musical performance tasks.

2) The motor cortex size was measured (indirectly, though measurement of the correlating intrasulcal length of the posterior bank of the precentral gyrus). Results showed a greater symmetry in the left and right hemispheres in the dorsal subregion of the motor cortex. In addition to the greater symmetry, the measures of the motor cortex were larger in both hemispheres than in nonmusicians. This may be due to the right hemisphere controlling the non-dominant left hand, requiring a level of left hand motor refinement unnecessary for nonmusicians.

3) The cerebellum was also examined (in part due to the role of the cerebellum in movement coordination, timing of sequential movements, etc.); as an interesting methodological note, the researcher controlled for the large inter-subject variance in cerebellum size by measuring the cerebellum as a percentage of overall brain matter. There was a gender effect, with male musicians’ brains having a larger cerebellum than nonmusicians. There was no difference in females; of several possible causes, either a ceiling effect (considering the normally smaller size of the female brain) or the fact that most females reach maximum cerebellum size earlier in life than males (and hence not allowing as much time for musical activity to effect its size) are the most likely causes for this gender difference.

4) Regional differences in gray matter (important in processing sensory perceptual data) were examined. Musicians showed greater gray matter in the following regions: the perirolandic region, the premotor region, the posterior superior parietal region, the posterior mesial perisylvian region bilaterally, and the cerebellum.

FUNCTIONAL BRAIN DIFFERENCES BETWEEN MUSICIANS AND NONMUSICIANS

Basic points include:

• While some aspects of music may pertain mostly to one hemisphere (e.g. the right hemisphere in melodic contour tasks and the left hemisphere in rhythmic tasks), extensive usage of both sides of the brain are essential for the musician.
• In a study looking for whether or not musicians have a different degree of hemispheric dominance, the researchers found that in only those musicians with absolute pitch, there is an increased left-sided asymmetry of the planum temporale. Presumably, based on this research, this area of the brain in the neural substrate of absolute pitch. It is uncommon for someone to have absolute pitch if they have not commenced musical study by the age of 7. The planum temprale is part of Wernicke’s area, which is important for the processing of language. This could mean that absolute pitch is based, at least in part, on the categorization that the planum temporale provides in language: absolute pitch means giving language to a particular tone without a reference.

The authors discuss the nature/nurture debate. The cross-sectional design of this study of course does not fully allow one to imply causality, as longitudinal studies (which would be nearly impossible for this field) would be required for that; however, the growing body of evidence relating musical tasks and musicians’ brains with specific neural substrates indeed points in the direction of causality (especially during early, formative years before 7 years of age).