Researchers at Stanford and McGill universities say they have learned more about how memories are catalogued, by studying brain activity as people listen to unfamiliar symphonies with gaps between movements.

When the music stops, brain scans register a burst of activity, apparently drawing a line between one musical event and another, Daniel Levitin, a co-author of the study, told CBC News Online on Friday.

"Usually you associate brain activity with something going on," he said. "Here it's associated with something going off, essentially."

Levitin, a  McGill psychologist, collaborated with California researchers Devarajan Sridharan, Chris Chafe, Jonathan Berger and Vinod Menon on an article published Thursday in Neuron, a scholarly journal based in Cambridge, Mass.

As he explained it, their work was based on a long-held view of the structure of memory.

"Memory is not like a videotape where you just remember an undifferentiated stream of activity in your life. In fact, memory is more like a DVD with chapter headings," he said.

He offered an everyday example:

"If I were to ask you what you had for lunch yesterday and you had to start with when you crawled out of bed and sort of run through and fast forward, as it were, until you came upon lunch time, that would be a very inefficient way to access memory. But because lunch has a beginning and an ending, you can find it."

Brain activity and music monitored

Marking such episodes "is a crucial process that the brain undertakes without our conscious awareness throughout the day," he said. "It divides the continuous stream of activity and perception into discrete events, and what we were probing was the mechanisms in the brain that accomplish this."

In the study, subjects lay inside functional magnetic resonance imaging (fMRI) scanners as they listened to symphonies by the English composer William Boyce (1711-79), chosen partly because his music is not widely known.

Why music?

"We used music for a couple of reasons," Levitin said. "One is it's fun. I mean, you want to give subjects something to do that's going to hold their attention, of course.

"But the other reason is that music turned out to be a very fruitful window into studying the brain because music activates virtually every region in the brain that we've mapped so far."

The researchers were looking for "that neural circuit that is involved in event segmentation, or in lay terms, noting beginnings and endings," Levitin said.

"So we chose these musical pieces that were unfamiliar to listeners but had very clear transitions between movements."

They found, as they expected, that there was a flareup of brain activity during each brief silence, Levitin said.

It started in a region of the brain called Brodmann Area 47, or BA47, "a tiny little area about the size of your pinkie" found on each side roughly between the eye and the top of the ear, he said.

But it was nothing like the sort of nervousness evoked by the old Hollywood cliche, "'It's quiet out there. Too quiet,'" he said.

"When we put people in the scanner and we have them just exposed to silence, you get something different. These processes that we're studying kicked in because it's a very pregnant silence, as it were — a silence that was between the ending of one movement and the beginning of another."

For a psychologist interested in memory formation, the findings are exciting, he said.

"And to get on the cover of Neuron is a big deal in my field. That's like a Top 10 record."