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Music Lights up your Brain
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The Mystery Of Music: How It Works In the Brain By SANDRA BLAKESLEE A 61-YEAR-OLD Canadian businessman, who asked that his name not be used, recently took his wife to a fancy restaurant to celebrate their wedding anniversary. As they sat down, he asked the musicians to play the couple's favorite song, "La Vie en Rose." When the meal ended, the man turned to his wife and said: "I'm so sorry, darling. They didn't play our song." She looked back sympathetically and said: "But they did play it. Three times." Neither of them was really surprised. Since suffering a stroke 15 years ago, the man has been afflicted with a rare condition called amusia. He cannot recognize any music or songs, however familiar they once were, though his speech and other auditory faculties are mostly normal. He can hear music, tap out the rhythm and dance to it, and even respond to it emotionally. But the music sounds weird and distorted, and he cannot distinguish Beethoven from Chuck Berry. Patients like this man are helping neuroscientists plumb the mysteries of music in the human brain, raising questions whose answers are as deep and intricate as a Bach cantata: How is music perceived by the brain, and which cells and circuits come into play? Has music blossomed in the march of human evolution, becoming a uniquely human trait, or are other animals, such as songbirds, equally musical? What is the relationship between language and music? Why does music tap our emotions? What makes a tune stick in our heads? What makes some people more musically talented than others? Are musicians' brains wired differently from other people's? And, finally, a question asked by many parents: How does music influence a developing child's brain? While many answers are being found with the help of brain imaging machines and experimental techniques, the question of how and why music arose in human evolution remains speculative. The ability to perceive and enjoy music is an inborn human trait, said Dr. Mark Tramo, a neurobiologist at Harvard Medical School. While many animals use intricate sounds to recognize one another, attract mates and signal danger, humans have developed the richest musical repertoires of any species. A crowning achievement of human evolution is the ability to communicate complex ideas and emotional states, Dr. Tramo said. The human brain has evolved specialized circuits, called feature detectors, for this purpose, which can be used to decode aspects of both speech and music. For example, the temporal lobes at both sides of the head contain cells that recognize and process pitch, which is the unitary pattern of frequencies that one hears when a musical instrument or the vocal cords are vibrated. "Pitch is a part of grammar," Dr. Tramo said. "When you ask a question, the pitch rises. When you string individual speech sounds and sequences into sentences to express ideas, you begin to use pitch." Pitch is also an integral part of music. When the brain listens to music, Dr. Tramo said, it uses many of the same pitch detectors that are used in decoding spoken language. The first musical instrument was probably the human voice, Dr. Tramo said. As language flourished, so did music, with cultures inventing different kinds of resonators -- flutes, reeds, simple strings. While language was used to transmit knowledge, he said, music was used to promote social cohesion through shared tribal rituals. Some scientists think that language and music are two sides of the same intellectual coin, a view supported by the anatomical distribution of feature detectors in the human brain. Cellular circuits that recognize language and music are found on both sides of the brain, said Dr. Jamshed Bharucha, a psychologist at Dartmouth College in Hanover, N.H. But the left hemisphere also contains regions that specialize exclusively in language and the right has some regions that exclusively serve musical perception, he said. In the brains of musical idiot savants -- individuals who are talented musicians despite severe mental retardation -- the dichotomy is especially pronounced.
Researchers are beginning to model these special music circuits in computer neural networks and to map them in living brains, Dr. Bharucha said. Some of the biology is known. When sound waves enter the human ear, they stimulate neurons called hair cells that lie on a flat plane. Depending where it is located, each hair cell responds to a characteristic frequency. Those at one end respond to high frequencies, those at the other end to low frequencies. The signals are then passed up through the brain stem, where information from both ears is integrated to help locate the origin of the sounds. From there they enter the primary auditory cortex, which contains cells that specialize in particular frequencies. Simple sounds are again mapped on neural tissue. At these lower levels, language and music have shared pathways, Dr. Bharucha said. The question is, at what point do they diverge? Where are the neural circuits for music and which qualities of music do they specialize in recognizing? "We predict you should find cells that are tuned to familiar chords," Dr. Bharucha said. Some cells may be tuned for octaves, musical fifths and fourths, he said. Others would specialize in detecting patterns of ascending or descending tones. There even may be cells that are wired together to encode familiar songs and melodies, Dr. Bharucha said. The more familiar the song, the fewer the neurons needed for this task. The idea is supported by classical experiments in which doctors inserted tiny electrodes into the brains of awake patients. As the active electrode was moved from one tiny clump of cells to another, patients reported hearing different songs, fragments of symphonies or familiar voices. Studies of brain-damaged patients shed considerable light on these circuits, said Dr. Isabelle Peretz, a psychologist at the University of Montreal. She has studied three patients who suffered damage to both the left and right temporal lobes -- where major auditory circuits reside -- and as a result have lost the ability to recognize familiar songs, the condition called amusia. Only music is affected, Dr. Peretz said. These patients can recognize human voices, animal cries, traffic sounds and all other auditory information with no trouble. The patients say they can still respond emotionally to music, even though the neural network that recognizes melody and other musical qualities has been destroyed. Clues to what has been lost may be found in connections between the temporal lobes and frontal lobes, where higher-order decisions are made, said Dr. Robert Zatorre, a psychologist at the Montreal Neurological Institute and Hospital. "Music evolves over time and to decode it you need to hold information in working memory," he said. "You need a sophisticated buffer to relate an event happening now to an event 12 seconds ago. We think this is happening in the frontal and temporal lobe interaction. The frontal lobe runs the traffic here, holding the relevant information." Depending on what you are listening for in a particular piece of music, the relevant information may be repeated themes, for instance, or timbres of different instruments. Music can also be imagined, as Dr. Zatorre points out, because people have stored representations of songs, melodies and the sounds of instruments. These representations can be stimulated internally, he said. When a song is "imagined," the cells and networks that are activated are identical to those used when a person actually hears music coming from the external world. But when songs are imagined, Dr. Zatorre said, parts of the visual cortex also light up, suggesting that tonal patterns evoke visual imagery patterns. "We don't know what triggers musical imagery," Dr. Zatorre said, "but it is very common for people to wake up in the morning with songs running through their heads." Brain mapping shows that musical networks also extend into the brain's emotional circuits in the limbic system, Dr. Zatorre said. People report strong emotional sensations when they listen to music, saying, for example, that they feel like their hair is standing on end or that they have a lump in their throat, he said. How these circuits are wired up has yet to be determined. Dr. Fernando Nottebohm, a neuroscientist at Rockefeller University in New York, suggests that bird songs may also have an emotional component. "I believe some birds sing purely for pleasure" he said. "I wouldn't be surprised if a male song bird singing on top of a tree is having a glorious time." Research into how the brain decodes music reveals insight about what makes music so interesting to most people. It is a matter of surprise, researchers say. The brain becomes accustomed to patterns of music based on exposure to various musical traditions, Dr. Bharucha said. Groups of cells may be especially attuned to sounds heard in rock-and-roll, Mozart or riffs on a sitar. When the brain hears, say, 10 notes of a melody, it will predict the 11th note based on these stored connections. When the note is predicted correctly, he said, the cellular connections become even stronger. If a note is slightly off, it can be either jarring or aesthetically pleasing. It is the violation of these brain-based expectations that makes music interesting, Dr. Bharucha said. Composers regularly exploit them. For example, the note-to-note violations in classical music are very subtle. "At the beginning of a Handel violin sonata, the violin plays notes that lead you to expect completion of a chord with a D on the musical scale," he said. "Instead, you hear an E, which is a subtle violation in the same key in the same scale. "If you want more serious violations, you pick notes out of key," Dr. Bharucha continued. "Western music pushed the limit of these violations until, in the early 20th century, the whole thing collapsed." Composers like Schoenberg minimized the degree of expectation completely, but it never caught on with popular audiences. Minimalist music by composers such as Philip Glass is a revenge against excess surprise, he said. It is very predictable, some would say boring. Rock-and-roll, Dr. Bharucha said, is often thought to be a new form of music, but in fact it uses chords and elemental patterns that go back centuries. Ironically, as far as pitches and harmonies go, rock-and-roll is more traditional and has changed less than classical music, he said, which may help explain its popularity. Musical talent is another mystery. As with any kind of intelligence, the neural maps that serve music perception may be stronger or larger or better in some people. Earlier this year researchers reported that people with perfect pitch have in their left hemispheres highly developed structures associated with musical perception. But there is no single musical talent, said Dr. Peter Ostwald, a psychiatrist at the University of California School of Medicine in San Francisco. There may be separate talents for tone recognition, melodic structure, movement, ability to play an instrument well, and the gift for dramatizing oneself and playing in public. Nevertheless, early exposure to music and musical training does make a difference in musical talent. Like language, music follows a course in infant and child development, Dr. Zatorre said. Six-month-old babies are sensitive to musical patterns. A 2-year-old hearing the Barney song will pick it up and start singing it incessantly. Children sing songs to themselves as they play. At the University of California at Irvine, researchers built computer models of how cells in the auditory cortex might fire together during learning. When the computer program was connected to a device that translated its mathematical code into sounds, musical themes appeared. "It got us to thinking," said Dr. Gordon Shaw, a physicist at Irvine's Center for the Neurobiology of Learning and Memory. He said that the way cells are connected throughout the cortex might compose the basic neural language of the brain. "When you hear music, you are exciting inherent brain patterns that derive from this structure and connectivity. "Then we made another big jump," he added. "Musical training at an early age might reinforce these patterns. Music is structured in space and time. Could it enhance or strengthen the circuits that help you think and reason in space and time?" To find out, Frances Rauscher, an Irvine researcher, has been working with preschool children in Los Angeles. One group of 3-year-olds received weekly piano lessons and participated in daily sessions of group singing. Another group did not get the extra training. After a year, she said, the musically trained children scored 80 percent higher on tests of spatial and temporal reasoning, an ability that underlies many kinds of mathematics and engineering. Could this explain why so many physicists and mathematicians are also gifted musicians? |
