A research team led by the Massachusetts Institute of Technology (MIT) has recently identified a population of neurons in the human brain that activates when we hear singing, but not when we hear regular speech or instrumental music. This song-specific hotspot is located in the auditory cortex, at the top of the temporal lobe, close to regions that are selective for language and music.
“The work provides evidence for relatively fine-grained segregation of function within the auditory cortex, in a way that aligns with an intuitive distinction within music,” said study lead author Sam Norman-Haignere, an assistant professor of Neuroscience at the University of Rochester Medical Center and former postdoctoral fellow at MIT.
This work builds on a 2015 study in which Dr. Norman-Haignere and his colleagues used functional magnetic resonance imaging (fMRI) to identify a group of neurons that responded specifically to music. By analyzing the fMRI brain scans of participants as they listened to a collection of 165 different sounds, including various types of speech and music, and everyday sounds such as fingers tapping or a dog barking, the scientists managed to identify six neural populations with different response patterns, including speech- and music-selective groups of neurons.
In the new study, in order to obtain higher-resolution data, the scientists used a technique called electrocorticography (ECoG) that allows electrical activity to be recorded by electrodes placed inside the skull. This offered a much more precise map of the brain than the fMRI method, helping the researchers identify a neural response pattern that only responded to singing.
“There’s one population of neurons that responds to singing, and then very nearby is another population of neurons that responds broadly to lots of music. At the scale of fMRI, they’re so close that you can’t disentangle them, but with intracranial recordings, we get additional resolution, and that’s what we believe allowed us to pick them apart,” explained Dr. Norman-Haignere.
This song-specific neural population had very weak responses to either speech or instrumental music, and is thus different from the music- and speech-selective populations identified in 2015. The fact that these neurons are located at the top of the temporal lobe suggests that they may be responding to features such as the perceived pitch, or the interaction between words and perceived pitch.
The scientists are now investigating whether infants have music-selective brain areas, hoping to learn more about when and how these brain regions emerge and develop.
The study is published in the journal Current Biology.