'Agadoo' by Black Lace had a catchy tune for some

A US team from Dartmouth College, reported in the journal Nature, played volunteers tunes with snippets cut out.

They scanned for brain activity and found it centred in the auditory cortex - which handles information from ears.

When familiar tunes played, the cortex activity continued during the blanks - and the volunteers indeed said they still mentally "heard" the tunes.

Catchy songs

Researchers have previously argued that catchy songs work by causing a "brain itch" that can only be scratched by repeating the tune.

The Dartmouth team asked volunteers to listen to excerpts from familiar and unfamiliar songs with lyrics or instrumentals.

These included the Rolling Stones' Satisfaction and the theme tune from The Pink Panther.

Snippets of the music were removed at different points during the songs and replaced with silent gaps.

The researchers used a brain scan called functional magnetic resonance imaging to see which parts of the brain were active while the volunteers listened to the tracks.

The auditory cortex remained active even though the music had stopped

Lead author David Kraemer

After the experiment, the volunteers reported hearing a continuation of the song during the silent gaps when the tune was familiar, but not when the song was unfamiliar to them.

When the researchers looked at the brain scans they found the individuals had more activity in specific regions of the brain during the silent gaps when the song was familiar, than when it was an unknown tune.

Lyrical focus

These brain areas lie in the auditory cortex, which is the part that handles information from the ears.

David Kraemer, a graduate student in Dartmouth's Psychological and Brain Sciences Department who led the study, said: "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."

The researchers also found whether the music had lyrics or not affected brain activity to different degrees.

If the music went quiet during an instrumental song, like during the theme from the Pink Panther, individuals activated many different parts of the auditory cortex, going farther back in the processing stream, to fill in the blanks.

When remembering songs with words, however, people simply relied on the more advanced parts of the auditory processing stream.

"It makes us think that lyrics might be the focus of the memory," said Mr Kraemer.

Domino effect

Co-researcher Dr Bill Kelley said their findings confirmed that sensory-specific memories, those linked to sight, sound or smell for example, are stored in the brain regions that were involved in processing that information in the first place.

"But what we did not know until now was whether the same rules held true for the more complex imagery we see in everyday life."

He said it was unlikely that memories were stored in only one particular brain region because they often involved more than one sensory pathway.

"When you are recalling a particular song that will activate auditory brain regions but that may, in turn, lead to you having a very vivid visual memory as well.

"For example, you may picture yourself at the high school dance when you first heard the song."

He said greater understanding of how memories are formed and recalled could help researchers investigating conditions that affect memory.