Box 3-1: Through a Glass, Darwinian

Music and the Modern Brain

Our ability to experience music is, of course, a function of nervous system physiology. Although the brain’s right hemisphere does the majority of work associated with processing music, no single group of neurons is devoted to the task. Different networks of neurons are activated, depending on whether or not the music involves lyrics, whether a person is playing an instrument or simply listening passively (Lemonick, 2000). Neurological research has shown has shown that intensive practice of an instrument leads to a discernible enlargement of parts of the cerebral cortex, the layer of gray matter most closely associated with higher brain function. MRI studies show that the corpus callosum is 10 – 15% thicker in musicians who began studying music before age seven, compared to nonmusicians and people who began music study later in life (Pantev, Oostenveld, Engellen, Ross, Roberts, & Hoke, 1998). However, the relationship between music ability and other intellectual functions is far from straightforward.

In many people, musical abilities and general cognitive abilities appear to be largely independent processes (Lemonick, 2000). Autistic people are mentally deficient, yet most are proficient musicians and some are even "musical savants" possessed of extraordinary talent. About one per cent of the human population is incapable of processing music at all. This condition is called amusia [a- = without, -musia = music, Latin]. Functional deficits in the more posterior regions of the temporal lobe are implicated in receptive amusia or true tone deafness (Corballis, 1994) Receptive amusics cannot recognize even simple, familiar tunes such as Frere Jacques. They can identify specific songs from the lyrics but it makes no difference whether the lyrics are sung or spoken. Expressive amusia, the inability to produce music has been linked to functional deficits in the frontal cortex. Amusics appear to have been born without the neural pathways required for processing music. Neurological tests of these people fail to show any overt signs of brain damage or short-term-memory impairment and magnetic-resonance-imaging (MRI) scans of their brains look normal.

            The fact that amusics appear to possess normal cognitive functioning despite their complete inability to process music is highly intriguing from an evolutionary perspective. It suggests that music ability is a specialized adaptation rather than a biological side effect of other evolved abilities (see Through a glass, Darwinian 5). The fact that music ability appears to have been completely deleted from the behavioral repertoire of a few people suggests that it falls under the control of a relatively small number of genes. A capacity for music may have emerged very recently in our evolutionary history (within the last 100,000 years) as a result a few gene mutations and novel combinations. Amusia also provides concrete evidence for the existence of a major behavioral difference that can not be detected physically.

            There has been a long standing debate as to whether or not major changes in human neural organization occurred prior to the Creative Explosion of 40 to 50 thousand years ago. Fossil evidence exists for morphological modern humans dating back to over 120,000 years ago. Genetic studies suggest that our species arose over 150,000 years ago. Yet despite their modern appearance, these humans evidenced no changes in cultural/ technological sophistication for tens of thousands of years. A smattering of artwork and tool innovations begin to appear about 50,000 years ago. From that point on, cultural innovation develops at a rapid pace. The level of sophisticated artwork and technology displayed by the Cro-Magnon peoples of Europe during the last ice age leaves no question that their minds were as fully modern as their brains. The cultural stagnation that prevailed for the 100,000 years or so prior to the Creative Explosion raises a question concerning the last stages of human brain evolution. Did microscopic changes occur in neural organization around 50,000 years ago that marked the emergence of the modern human brain? This has certainly been demonstrated to be a viable hypothesis by the existence of hereditary amusia. The fact that a few genes can produce the behavioral capacity for music, without producing detectable changes in the brain, clearly shows that this is a possibility.