The Biology of Music

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"The Biology of Music", an article from the February 12th - 18th, 2000 issue of The Economist, provides a useful summary of key findings in regard to neuroscience and music.  While language is thought to be an acquisition that is uniquely human, arguably, humans' capacity for music-making, both vocally and instrumentally, is unsurpassed in the animal kingdom.

While some linguistic and musical areas overlap in the brain, evidence suggests that musical and linguistic processing, are to some degree, independent.  People with damaged language-processing centres do not automatically lose their musical abilities. Vissarion Shebalin, a Russian composer who suffered a stroke to the left hemisphere of his brain in 1953, was able neither to understand speech nor speak after his illness—yet retained his ability to compose music until his death ten years later. Conversely, some people's musical abilities have been destroyed without detriment to their speech.

Musical processing encompasses a number of separate tasks, all handled by different parts of the brain. As early as 1905, for example, the neurologist Bonvicini discovered a brain-damaged individual who could recognize the sounds of different musical instruments, and also detect wrong notes, but not identify well-known tunes, such as his own national anthem.

In the late 1990s, Dr Liégeois-Chauvel and Dr Peretz examined 65 patients who had undergone a surgical procedure for epilepsy, involving the removal of part of one temporal lobe. This enabled researchers to investigate whether music, like language, is processed predominantly on only one side of the brain, but also permitted them to investigate which bits of the temporal lobe are doing what.
Liégeois-Chauvel and Dr Peretz asked each of their subjects to listen to a series of short melodies written especially for the project in order to study individual components of melody: pitches, musical intervals between the notes, key, contour (how the melody rises or falls), rhythm and tempo.
 
Liégeois-Chauvel and Peretz's results showed that people with right-temporal-lobe damage had difficulty processing both the key and the contour of a melody, while those with left-temporal-lobe damage suffered problems only with the key. This suggests that, like language, music is processed asymmetrically in the brain (although not to quite the same degree). It also suggests that if one hemisphere of the brain deserves to be called dominant for music, it is the right-hand one—the opposite of the case for language in most people.  The part of the lobe involved in the case of contour is known as the first temporal gyrus, though the site of the key-processor was not identified. In addition, those subjects who had had another part of the lobe, Heschl’s gyrus, removed, had difficulty—regardless of whether it was the left or the right Heschl’s gyrus that was missing—in identifying variations in pitch.

Liégeois-Chauvel’s and Dr Peretz’s second set of experiments looked at the perception of rhythm. This time, the possible distinction between the presentations of a melody was that one might be in “marching” time (2/4, to music aficionados) while the other was in “waltz” time (3/4). Again, subjects were asked whether the two presentations differed. In this case, however, there was no effect on the perception of rhythm in any subject, suggesting that rhythm isn't analyzed in the temporal lobe.

Evers and Dannert (1999) used “functional transcranial Doppler sonography”, a technique measuring blood-flow rate in a particular artery or vein, to study the response of blood-flow to music. Their subjects were a mixture of musicians: people who knew how to play at least two musical instruments, and non-musicians: people who had never played an instrument, and did not listen regularly to music. Subjects listened to a 16th-century madrigal whose lyrics were in Latin, a language chosen because it was not spoken by any of the participants, and so would not activate speech processing.    In non-musicians, blood flow to the right hemisphere increased on exposure to music with a lot of harmonic intervals. In musicians, however, the reverse was true; blood-flow increased to their left hemispheres, suggesting that musical training was affecting the way they perceived harmony.  When the participants were exposed to strongly rhythmical modern rock, rather than harmonic music, responses changed. Rock music produced an equal increase of blood flow in both hemispheres in both groups of subjects, confirming Dr Liégeois-Chauvel’s and Dr Peretez’s observation that pitch and rhythm are processed independently.

Platel, Baron, et al, utilized a non-invasive technique, positron-emission tomography, or PET, to investigate which bits of the brain activate when someone listens to a melody. They studied healthy  musical illiterates: people who cannot read musical notation.  One of their most intriguing results came when they changed the pitch of one or more of the notes in a melody. When they did this, they found that in addition to activity in the temporal lobes, parts of the visual cortex at the back of the brain lit up.  These areas--Brodmann’s area 18 and 19--are the location of the “mind’s eye”—the place where images are conjured up via imagination alone. Using PET technology, researcher Justine Sergent also found Brodmann's area 18 and 19 lit up in pianists playing their instruments. Baron theorizes that when the pitches of a sequence of notes are being analysed, the brain uses some sort of “symbolic” image to assist in deciphering each pitch, in similar manner to an orchestra conductor lifting his arm for “high” pitches and lowering it for “low” pitches.  Baron's theory might help explain how and why people perceive notes as high and low in the first place.

Krumhansl, a psychologist at Cornell University, examined the physiological changes in blood circulation, respiration, skin conductivity and body temperature that occurred in volunteer subjects while listening to different pieces of music. Music with a rapid tempo, and written in a major key, correlated precisely with the induction of happiness. A slow tempo and a minor key induced sadness, and a rapid tempo combined with dissonance--the sort of harsh musical effect favored by composer Arnold Schoenberg--induced fear.

Zatorre and Blood used PET scans to study the emotional effects of music.  When test subjects heard dissonance, areas of their limbic systems known to be responsible for unpleasant emotion lit up and, moreover, volunteers used negative adjectives to describe their feelings. Consonant music, by contrast, stimulated parts of the limbic system associated with pleasure, and the subjects’ feelings were incontestably positive.

Music’s emotional and conscious effects are completely separate. Peretz did a study on Ms. R, who'd sustained damage to both of her temporal lobes as a result of surgery undertaken to repair some of the blood vessels supplying her brain.  While her speech and intellect remained unchanged after the accident, Ms. R's ability to sing and identify once-familiar melodies disappeared. Remarkably, though, she claimed she could still enjoy music. For comparison, subjects with healthy, intact temporal lobes were also tested. While Ms R failed to identify any melodies played to her, no matter many times they were repeated, and couldn't consciously detect pitch changes, she could still feel emotion—a result confirmed by manipulating the pitch, the tempo and the major or minor nature of the key of the various pieces of music being played, and comparing her reactions to the altered tunes with those of the control group.

Finally, Geoffrey Miller, an evolutionary psychologist at University College, examined the linkage between music and love. He postulated that because music demands skill, it is a way of manifesting fitness to be someone’s mate. Singing, or playing a musical instrument, requires fine muscular control. Remembering the notes demands a good memory. Getting those notes right once they'r remembered suggests hearing is in top condition. And the fact that much music is sung as part of courtship, suggests that it is, indeed, a way of showing off.