There is a population of neurons in the human brain that light up when we hear singing, neuroscientists at Massachusetts Institute of Technology (MIT) have found, publishing their results in Current Biology.
Found in the auditory cortex, part of the temporal lobe that processes sound, these neurons appear to respond to the specific combination of voice and music, rather than just ordinary speech, or instrumentals with no vocals.
“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 lead author Dr Samuel Norman-Haignere.
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These findings build on a 2015 study from the same research team, where they investigated the relationship between music and the human brain using functional magnetic resonance imaging (fMRI). In exploring the brain networks in professional composers during music creation, they found that when composing, a specific brain state is formed that enables composers to integrate musical notes with emotion.
During musical creation, the integration of primary visual and motor areas is not necessary in a composer’s brain. Instead, the neurons from these brain areas are put to work elsewhere. They’re used to enhance connectivity between two key brain areas: the anterior cingulate cortex (ACC), largely associated with emotion, and the default mode network (DMN), which is largely active during when we’re daydreaming, recalling memories, or imagining the future.
And now this new study takes the research one step further. Using a method called electrocorticography (ECoG), where electrodes are placed inside a person’s skull, researchers have been able to precisely record the electrical activity that occurs in response to external stimulants. In this case, the same set of 165 sounds that were used in the 2015 fMRI study.
“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,” said Norman-Haignere.
In combining this data with that from the previous fMRI study, researchers were able to more accurately pinpoint the locations of these neurons that respond to singing.
The difficulty, however, comes with obtaining data using ECoG. Although accurate, it is an invasive procedure that involves placing electrodes directly onto the exposed surface of the brain via a craniotomy (a surgical incision into the cranium), and as such, it’s not one that’s typically used.
ECoG is however, used to monitor patients with epilepsy prior to surgery. For several days, ECoG is used to determine where their seizures are originating, and it’s during this window that a patient can opt-in to other studies that measure brain activity, such as this one.
Neuroscientists hope to learn more about what aspects of singing cause these neurons to light up. It is also hoped they can investigate how (and when) these brain regions develop, by looking at responses in infants.
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