They discover ‘singing’ neurons that are only activated in our brain with singing

For the first time, neuroscientists at the Massachusetts Institute of Technology in the USA (MIT) identified a population of neurons in the human brain that lights up when we hear singing, but not other types of music.

These neurons, found in the auditory cortexseem to respond to the specific combination of voice and music (or melodious singing voice), but not for normal speech or instrumental music. The researchers say exactly what they do is unknown and that more work will have to be done to find out.

“This study reveals some of the dominant response dimensions that organize the human auditory cortex, which is very important for understanding and modeling the neural mechanisms of auditory processing,” the study’s first signatory told SINC. Samuel Norman-Haignereformer MIT postdoc and now assistant professor of neuroscience at University of Rochester Medical Center (USA).

The work also suggests that musical representations are partitioned into distinct neuronal populations that selectively respond to different types of music.

Samuel Norman-Haignere, lead author

“The work also suggests that musical representations are partitioned into distinct neuronal populations that selectively respond to different types of music. Understanding how and why this organization develops is an important question for future research”, adds the expert.

The study, published today in the journal Current Biologyis based on a 2015 job in which the same research team used images of fMRI (fMRI) to identify a population of neurons in the auditory cortex of the brain that specifically responds to music. In the new research, the scientists used measurements of electrical activity taken at the surface of the brain, which gave them much more accurate information than fMRI.

“There is a population of neurons that respond to singing, and very close by is another that responds extensively to a lot of music. At the fMRI scale, they are so close together that they cannot be separated, but with intracranial measurements we get extra resolution, and that’s what we think allowed us to differentiate them,” says Norman-Haignere.

combination of techniques

In the 2015 study, neuroscientists used fMRI to scan the brains of participants as they listened to a collection of 165 sounds, including different types of speech and music, as well as everyday sounds like a finger tapping or a dog barking. Thanks to this research, scientists have identified six neuronal populations with different response patterns, including a music-selective population and a population that selectively responds to speech.

Now, in their new work, the researchers have used a technique known as electrocorticography (ECoG) in order to obtain higher resolution data. This technique allows electrical activity to be recorded using electrodes placed directly on the surface of the brain, providing a much more accurate picture of electrical activity in the brain compared to fMRI, which measures blood flow in the brain as an indicator of neural activity.

“With most human cognitive neuroscience methods, you can’t see the neural representations,” he explains. Nancy Kanwisherprofessor of cognitive neuroscience and member of the McGovern Institute for Brain Research and the Center for Brains, Minds and Machines (CBMM) from MIT. “Most of the data we can collect tells us that there’s a piece of brain here that does something, but that’s pretty limited. We want to know what is represented there.”

Electrocorticography cannot normally be performed in humans because it is a Invasive procedurebut is often used to monitor patients with epilepsy who are about to have surgery to treat their seizures. People are monitored for several days so doctors can determine where the attacks are coming from before operating. During that time, if patients agree, they can participate in studies that measure their brain activity while performing certain tasks. For this work, the MIT team was able to collect data from 15 participants over several years.

“ECoG provides a measure much more accurate of the neural response, but the opportunities for recording responses are scarce and the coverage is much worse than fMRI, as the electrodes are implanted for clinical reasons (mainly to locate the foci of epileptic seizures)”, explains Norman-Haignere to the SINC.“One of the methodological innovations of the study was to develop a technique to combine the precision of the ECoG with the dense spatial coverage of the fMRI responses”, he adds.

Discovery of a new neuronal population

For these participants, the researchers played the same set of 165 sounds they used in the previous study. The placement of each patient’s electrodes was determined by their surgeons, so some did not pick up any response to auditory input, but many did. Through a new statistical analysis they developed, the experts were able to infer the types of neuronal populations that produced the data recorded by each electrode.

“When we applied this method to the dataset, this neural response pattern emerged that just answered singing. It was a discovery we really didn’t expect, so it justifies the purpose of the method, which is to reveal potentially new things,” says Norman-Haignere.

This population of neurons had very weak responses to speech or instrumental music and is therefore different of selective music and speech populations identified in the 2015 survey.

“In our previous study, we found six different response patterns, two of which responded selectively to speech and music, and four of which had responses correlated with standard acoustic measures (eg, sound frequency). Here, in addition, we discovered a neural response that selectively responded to singing”, highlights the expert.

music in the brain

In the second part of their study, the researchers created a mathematical method to combine the intracranial imaging data with the fMRI data from their 2015 study. Because MRI can cover a much larger portion of the brain, this allowed them to determine with more accurately the locations of neuronal populations that respond to singing.

“This way of combining ECoG and fMRI is an important methodological advance,” he says. Josh McDermottassociate professor of Department of Cognitive and Brain Sciences from MIT. “A lot of people have been doing ECoG in the last 10 or 15 years, but it’s always been limited by this recording shortage problem. Samuel Norman-Haignere he is truly the first person to discover how to combine the improved resolution of electrode recordings with fMRI data to better localize global responses.”

This population of music-selective neurons is found at the top of the brain. temporal lobeclose to selective regions for the Tongue and the song. Their location suggests that these neurons may respond to features such as perceived pitch, or the interaction between words and perceived pitch, before sending the information to other parts of the brain for further processing, the scientists explain.

The researchers hope to learn more about which aspects of singing drive the responses of these neurons. Furthermore, together with the MIT professor’s laboratory, Rebecca Saxon, They aim to study whether babies have selective areas for music, in hopes of learning more about when and how these brain regions develop.