Neurons that are listening specifically to the song

On the trail of amazingly brilliant specialties: The brain’s auditory cortex not only contains a kind of music center – there is also a group of nerve cells that are specially adapted to the perception of singing, the researchers say. These neurons respond to sung versions of human sounds, but rarely to speech or instrumental music. This is the result of functional magnetic resonance imaging combined with the recording of nerve activity with electrodes in the brain of epilepsy patients. How and why “singing neurons” respond in such a special way will be elucidated in further research.

The brain is and remains the most mysterious of all organs. Scientists are still wondering how this structure, made up of countless and complex nerves interconnected with each other, produces our mental faculties. It’s clear that there are specific areas of responsibility – regions and groups of neurons that perform specific tasks. For example, motor sequences are controlled in the motor cortex, while the auditory cortex is responsible for processing auditory sensations. In addition to these approximate classifications, scientists have also been able to identify increasingly refined specializations in certain aspects in various brain centers in recent years. A team led by Nancy Kanwisher of the Massachusetts Institute of Technology in Cambridge is also dedicated to this challenge.

Traces of the neuronal echoes of music

In particular, scientists are studying how music is processed in the auditory cortex. The current publication builds on previous research in which the team was able to identify a population of neurons that respond specifically to music. The study uses functional magnetic resonance imaging (fMRI), which may be active in specific areas of the brain. To do this, the researchers scanned the subjects’ brains while listening to 165 sounds of different categories – including various types of speech and music, as well as auditory sensations such as a dog barking. Using a special method of analyzing fMRI data, scientists were able to identify neuron populations with different response patterns – including one responsive to speech and another responsive to music.

Scientists are now showing that neural specialization can be broken down even further with a new bonding method. To do this, they used data generated by a procedure known as intracranial electroencephalography (EkoG). Here, the patterns of nerve activity are recorded by electrodes placed in the skull. The invasive procedure is usually used to screen patients with epilepsy as part of their treatment. The probes can provide more detailed information than fMRI, which uses brain blood flow as an indicator of neuronal activity. “The data we have collected so far tells us that this is the part of the brain that does something. We wanted to know more about what is processed and where, ”says Kanwisher.

In their research, scientists obtained the support of 15 epilepsy patients. Once their brain activity was captured using EcoG, they were recreated with the same set of 165 audio samples that they had used in the previous fMRI study. Using statistical analyzes, the scientists were able to deduce the populations of neurons that generated the data recorded by each electrode. “This pattern of neural responses emerged that emerged only with singing,” says lead author Sam Norman-Haignere. There seems to be a song-specific neuron population that responds very poorly to speech or instrumental music. “It was a result that we did not expect,” says the researcher.

targeting vocal neurons

To study the discovery in more detail, scientists developed a data processing method to combine information from intracranial recordings with fMRI data from their previous studies. Since fMRI can cover a much larger part of the brain, this has allowed it to more accurately locate the population of neurons that respond to singing. The vocal hotspot was found to be in the upper temporal lobe, close to speech-responsive and music-responsive areas more generally. “This kind of combination of ECoG and fMRI is a significant methodological advance,” emphasizes co-author McDermott.

The location of a song-specific neuron population suggests that they may respond to traits such as perceived pitch or the interaction between words and perceived pitch before passing the information to other parts of the brain for further processing, the researchers said. “The results therefore provide evidence for the multi-layered separation of functions in the auditory cortex in a manner consistent with the intuitive distinction in music,” says Norman-Haignere.

However, according to the researchers, insight into the neural code of music raised a few more questions: What exactly do “singing neurons” react to – are tone and timbre, or are certain structures decisive? How does selectivity develop over the course of a lifetime? Scientists now want to address these questions by conducting more detailed research.

Source: Massachusetts Institute of Technology, article: Current Biology, doi: 10.1016 / j.cub.2022.01.069

Leave a Comment