Music and lyrics: How the brain splits songs
Your favourite song comes on the
radio. You hum the tune; the lyrics remind you of someone you know. Is
your brain processing the words and music separately or as one? It's a
hotly debated question that may finally have an answer.
People with aphasia,
who can't speak, can still hum a tune, suggesting music and lyrics are
processed separately. Yet brain scans show that music and language
activate the same areas, which might mean the brain treats them as one
signal.
"There's conflicting evidence," says Daniela Sammler of the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany.
Now Sammler and her team have
discovered that both arguments may be partially true. Her team worked
out a way to determine when active regions were processing just music
and when just lyrics, by studying a functional MRI brain scan of someone
listening to songs.
Same tune, different lyrics
The team knew that when neurons
process the same stimulus repeatedly, their response to it decreases
over time. "They become kind of lazy," says Sammler.
She reasoned that if she varied just
the tune and kept the lyrics the same, areas showing a decline in
activity must be processing lyrics. If she varied just the lyrics, areas
showing a decline must be processing the tune, while any regions
declining when both the tune and lyrics are repeated must be processing
both.
The team wrote four different sets of
six songs and played these to 12 volunteers while scanning their brains.
In one set, all songs had different melodies and lyrics (listen to these here). In another, the melodies were different but the lyrics were the same (listen to these here), while in the third set, the opposite was true (listen to these here). The fourth set were identical to each other (listen here).
From the fMRI scans the team worked
out that one particular part of the brain – the superior temporal sulcus
(STS) – was responding to the songs. In the middle of the STS, the
lyrics and tune were being processed as a single signal. But in the
anterior STS, only the lyrics seemed to be processed.
Complex separation
Her team couldn't find an area
specific to processing tunes. This may be because no individual, complex
processing occurs for melody, although it might in professional
musicians, says Sammler.
She concludes that the brain first
deals with music and lyrics together. Then, after passing through the
mid-STS more complex processing kicks in, such as understanding what
lyrics mean, and the two are treated separately. "The more they are
processed, the more they are separated," she says.
Stefan Koelsch at the University of Sussex, UK, says he "likes the paper very much".
But Martin Braun
of Neuroscience of Music, an independent research centre in Karlstad,
Sweden, isn't convinced that the brain is processing both together at
any point. "Activation of a particular brain area by different stimuli
doesn't imply that these different stimuli are integrated," he argues.
"The stimuli might just have a similar effect on the area."
Sammler's team argues that the degree
of the decline in activation in the mid-STS was different from what you
would expect if both were being processed individually and
simultaneously.
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