Just because you're hearing Billie Eilish sing doesn't mean you're hearing her sing the words of her latest hit (without music) or just the melody of the same Billie Eilish song (without vocals). Neuroscientists at the Massachusetts Institute of Technology (MIT) have now revealed that our brains respond differently to each of these events. In contrast to conventional speech or instrumental music, a specific mix of voice and music activates a distinct group of neurons in the brain.

Using functional magnetic resonance imaging (fMRI), the same research team found a group of auditory cortex neurons that respond uniquely to music in 2015. The latest discovery, published in Current Biology, expands on that work.

Participants' brains were scanned as they listened to a collection of 165 sounds, including conversation, music, and ordinary sounds like tapping fingers or a dog's barks. Using a new approach of processing fMRI data, the researchers were able to identify six distinct populations of neurons, each of which had a unique pattern of activity in response to sound and/or music.

Electrocorticography (ECoG) is a technology employed in the current study that allows electrical activity to be monitored using electrodes inserted into the skull. Blood flow is used as an indicator of brain activity in fMRI, however this provides a much more accurate picture.

"One group of neurons responds to singing, while another group of neurons responds more broadly to a wide range of musical styles. We couldn't separate them using fMRI because they're so close together, but we were able to do so using intracranial recordings because the extra resolution allowed us to do so "Professor Sam Norman-Haignere of the Rochester Institute of Technology, an ex-MIT postdoc who is now a faculty member in neuroscience, explains this.

Patients with epilepsy
The intrusive nature of electrocorticography means it cannot be used on people, but it is frequently employed to keep tabs on epileptic patients awaiting surgery. Prior to surgery, patients are kept under observation for several days so doctors can pinpoint the source of their seizures. Participation in research monitoring brain activity while a patient does particular tasks is possible at this stage if the patient agrees. There were fifteen participants in this study, and the MIT researchers had access to their data for several years.

The researchers employed the same 165 sounds that they used in the last fMRI study for those participants. Some patients didn't respond to auditory input since surgeons selected the placement of their electrodes, but others did. The researchers were able to deduce the types of neuronal populations that generated the data captured by each electrode using a new statistical methodology they created.

Singing activated a specific sequence of neuronal responses in the brain, according to Norman-Haignere. "This was a discovery that we really did not expect, so it pretty well confirms the aim of the technique, which is to uncover possibly innovative things you might not think to look for," he says.

Their 2015 study found that a song-specific population of neurons was unique from the music- and speech-selective populations they had previously observed.

the hippocampus
A mathematical method was developed in the second portion of the study to merge the data from intracranial recordings with the fMRI data from the prior investigation. They were able to more precisely locate the locations of the neuronal populations that respond to song because fMRI can cover such a bigger area of the brain.

In the upper part of the temporal lobe, near areas selective for language and music, the researchers discovered a hotspot for song-specific brain activity. A song-specific population may be responding to elements such as perceived pitch or the relationship between words and a song's perceived pitch, the researchers explain.

It is hoped that further research will provide light on the specific features of singing that elicit these neural reactions. They are also trying to find out if babies have sections of the brain that are specifically tuned to music.