Why that song sticks in your head

If you've ever gotten a song stuck in your head, you know how annoying it can be. Researchers at Dartmouth University can't stop the aggravation, but they do have a good idea what parts of the brain keep replaying the music.

Using brain imaging techniques and a good CD collection, they found that the auditory cortex, the same part of the brain that passes information from the ears to the brain, also holds on to musical memories.

If people are listening to familiar music, the researchers say, they automatically call on those auditory memories to fill in gaps when the music stops.

Using functional magnetic resonance imaging, the researchers watched as subjects tried to mentally fill in the blanks to songs both familiar and unfamiliar that were missing short snippets.

All participants reported hearing a continuation of the familiar, but not the unfamiliar, tunes during the gaps. And the imaging tests showed that gaps in the familiar songs induced more activity in the brain's auditory association area.

"We played music in the scanner and then we hit a virtual 'mute' button," explained David Kraemer, a graduate student in Dartmouth's Psychological and Brain Sciences Department and author of the study, published today in the journal Nature.

With familiar songs, "we found that people couldn't help continuing the song in their heads, and when they did this, the auditory cortex remained active even though the music had stopped," Kraemer added.

The researchers said the findings extend previous work on auditory imagery and parallel work on visual memory, which both show that sensory-specific memories are stored in the brain regions that first experienced those events.

"It's fascinating that although the ear isn't actually hearing the song, the brain is perceptually hearing it," said co-author William Kelley, assistant professor of psychological and brain sciences.

The playback also differed somewhat depending on whether a song had words.

If the music gapped during an instrumental song, say the theme from the "Pink Panther," the subjects activated different parts of the auditory cortex, apparently going further back in the memory-processing stream to fill in the blanks.

But when remembering songs with words, people relied only on the more advanced structures for auditory processing.