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Biology Articles » Neurobiology » Systems Neurobiology » When the music stops, the brain gets going

When the music stops, the brain gets going

 
IN STANFORD STUDY, SILENT PAUSES LEND CLUES ON MENTAL PROCESSES
 
While music may soothe the savage breast, the brain thrills to the sound of silence.

That's a new finding by a team of Stanford and McGill University scientists who watched brain images of 18 volunteers listening to a series of movements within symphonies, each punctuated by frequent pauses.

A one- to two-second break between movements triggers a flurry of mental activity, researchers found. When the music resumes, the action shifts to a different part of the brain, then subsides.

"The pause itself becomes the event," said neuroscientist Vinod Menon of Stanford's School of Medicine, the senior author of a paper published in today's issue of the journal Neuron. "A pause is not a time where nothing happens."

Skillful composers have long used silence to build a sense of anticipation. Some of music's finest moments are spent in transition - waiting, in essence, for the other shoe to drop.

Stanford's snapshots of this pause may have implications beyond concert halls, nightclubs and honky-tonks.

They shine a light into what neuroscientists call "segmentation processes" - the techniques used by the brain to take a stream of sensory information and parcel it up into more easily comprehended pieces.

Similar processes

The same processes are thought to be used in other human senses, such as vision, said Menon, associate professor of psychiatry and behavioral sciences and of neuroscience. Menon's collaborators include former record producer Daniel J. Levitin, associate professor of psychology and music at McGill; Stanford neuroscientist Devarajan Sridharan, trained in Indian percussion; Jonathan Berger, composer and associate professor of music at Stanford; and Chris Chase, Stanford professor of music.
The literary equivalent could be the period at the end of a sentence, the space after a paragraph or the penultimate chapter in an Agatha Christie mystery. Poetry even has a name for this natural pause or break near the middle of the line: a caesura.

Because our environment delivers a firehose-size torrent of information, "the brain needs to segment or chunk the incoming stimulus stream into meaningful units," Menon said. "The brain needs to extract information about beginnings and endings."

It helps us extract nuggets of important information from a sea of noise, solving the age-old mystery of how we can follow a single conversation at a crowded cocktail party.

Volunteers in the Stanford study lay motionless for nine-minute intervals inside a magnetic resonance imaging machine, an enclosed tube surrounded by a powerful magnet. An MRI shows which parts of the brain are working during mental activity.

Wearing headphones, they listened to eight symphonies by William Boyce, an obscure 18th century Baroque composer. Boyce was selected because his movements are brief, with frequent pauses, Menon said. A symphony with long movements, such as Beethoven's Ninth, poses greater risk of mind-wandering.

Oldies-but-goodies - say, the William Tell Overture, "Oh Susanna," or anything by the Beatles - were ineligible, because they were familiar and lacked suspense. Songs with lyrics, which engage language-processing parts of the brain, were ruled out, as were participants who were musically trained.

The MRI's digitial images showed that networks of two different but tightly coupled regions of the brain, both in the right hemisphere, are especially active while people listen to music.

The first region to engage is called the ventral fronto-temporal network, whose job is to detect events that are interesting to the individual - that is, anything odd, different or unexpected.

Silence awakens brain

In all 18 subjects, brain response was most powerful during the periods of silence between the total of 20 movements in Boyce's eight symphonies, the scientists found.

This region also responded, more modestly, to a mismatch between what it expected to hear vs. what they actually heard - for example, if an unrelated chord followed a harmony. Because there are rules in music, the brain registers any unexpected violation, Menon said.

When the music resumed, the action shifted to a second site in the brain, called the dorsal fronto-parietal network. This region is responsible for maintaining attention and updating the memory.

"In a concert setting, different individuals listen to a piece of music with wandering attention," Menon said. But a moment of suspension, creating both closure and anticipation, is riveting.

The power of the pause, for centuries understood by composers but never explained, is finally captured on film.

By Lisa M. Krieger. Mercury News. August 2007.

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