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 neural film 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.

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 versus 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.