Researchers from the Massachusetts Institute of Technology have discovered that a specific set of neurons located in the auditory cortex in the brain respond to singing but not other sounds like speaking or instrumental music.
“This work suggests there’s a distinction in the brain between instrumental music and vocal music,” says study co-author Sam Norman-Haignere, who was formerly an MIT researcher and is now a professor of neuroscience at the University of Rochester Medical Center, to New Scientist’s Jason Arunn Murugesu.
The research team measured neural responses to sounds using a technique known as electrocorticography (ECoG), a process of recording brain activity by placing electrodes directly on the brain’s surface. Electrocorticography is not typically performed in humans because of its invasiveness, but it is used to monitor epilepsy patients who are about to have surgery to treat seizures, per a statement from MIT. Patients can opt in to participate in studies while they are already being monitored.
They tested 15 participants’ responses to 165 different noises, including toilet flushing, road traffic, instrumental music, speaking and singing. Some neurons responded almost exclusively to singing, though they also had a small response to instrumental music and speaking, per New Scientist. The study was published this week in Current Biology.
"The singing voice is the only musical instrument that almost everyone is born with, so one might expect us to have a rather different relationship with human song, relative to other kinds of music,” says Sophie Scott, a professor of cognitive neuroscience at University College London who was not involved in the research, to the Guardian’s Nicola Davis
The researchers developed a new statistical method that allowed them to infer the types of neural populations that produced the data each electrode recorded, per the statement.
“When we applied this method to this data set, this neural response pattern popped out that only responded to singing,” says Norman-Haignere, the lead author on the study, in a statement. “This was a finding we really didn’t expect, so it very much justifies the whole point of the approach, which is to reveal potentially novel things you might not think to look for.”
The study built on previous research from the MIT team, which collected functional magnetic resonance imaging (fMRI) data from patients who were played the same set of 165 sounds, the study states. An fMRI measures brain activity by looking at blood flow in the brain, whereas ECoG gives more precise data about electrical activity. The scientists combined fMRI and ECoG data in their new study.
“This way of combining ECoG and fMRI is a significant methodological advance,” study co-author Josh McDermott, an associate professor of brain and cognitive sciences, says in the MIT statement. “A lot of people have been doing ECoG over the past 10 or 15 years, but it’s always been limited by this issue of the sparsity of the recordings. Sam is really the first person who figured out how to combine the improved resolution of the electrode recordings with fMRI data to get better localization of the overall responses.”
The scientists don’t know why some neural populations respond only to singing, but it may have to do with our survival.
“To be able to distinguish the musical properties of sounds is fundamental for survival,” Jörg Fachner, co-director of the Cambridge Institute for Music Therapy Research in the United Kingdom, tells New Scientist. “It makes sense that this dispositional ability is wired into our auditory cortex.”