Scientists have determined what happens in our brains when we hear music in our heads, an advance that could help people who have lost the ability to speak.
When we listen to music, different parts of our brain process different information - such as high and low frequencies - so that our auditory perception of the sounds matches what we hear.
It is easy to study the brain activity of someone who is listening to a song, for instance, as we have the technology to record and analyse the neural responses that each sound produces as it is heard.
However, it is much more complicated to try and understand what happens in our brain when we hear music in our heads without any auditory stimulation.
As with analysing real music, the brain's responses have to be linked to a given sound. However, when the music is in our heads, that sound does not actually exist - or at least our ears do not hear it.
Using a novel approach, researchers at Ecole Polytechnique Federale de Lausanne in Switzerland were able to analyse what happens in our brains when we hum in our heads.
The EFPL researchers, in collaboration with a team from the University of California, Berkeley, in the US worked with an epileptic patient who is also an experienced pianist.
Initially, the patient was asked to play a piece of music on an electric piano with the sound turned on. The music and the corresponding brain activity were recorded.
The patient then replayed the same piece, but this time the researchers asked him to imagine hearing the music in his head with the sound on the piano turned off.
Once again, the brain activity and the music were recorded. The difference this second time around was that the music came from the mental representation made by the patient - the notes themselves were inaudible.
By gathering information in these two different ways, the researchers were able to determine the brain activity produced for each sound, and then compare the data.
"The technique used electrocorticography is extremely invasive. It involves implanting electrodes quite deep inside the patient's brain," said Stephanie Martin, lead author of the study published in the journal Cerebral Cortex.
"The technique is normally used to treat people with epilepsy who cannot take medication," said Martin.
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