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.
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.