Brain cells responsible for distinguishing between sounds have been found

Researchers at the Hebrew University discovered that although the range of sounds that humans hear is smaller, they know how to better differentiate between sounds and thanks to this, among other things, they can enjoy music

Do humans hear better than animals? It is known that cats, rats and mice, for example, can distinguish higher and lower frequencies compared to humans. Now researchers from the Hebrew University and other universities have found the nerve cells in the human brain responsible for detecting the subtle differences between sounds. It turns out that in the auditory cortex there are cells that are responsible for the hearing cells that exist in the ear. It is these cells that allow humans to distinguish between musical sounds.

The work of Prof. Israel Nelkan from the Institute of Life Sciences and the Interdisciplinary Center for Neural Computation at the Hebrew University, Prof. Yitzhak Fried from the University of California and Tel Aviv University, and Prof. Rafi Malach from the Weizmann Institute, together with research students Roy Mokamel and Yael Bitterman, was recently published in the journal Nature .

Knowledge about the auditory cortex is largely based on previous studies that tracked brain activity in animals while they were exposed to sounds. These studies provided very valuable information regarding the processing of sounds in the auditory system, but not regarding the unique characteristics of the auditory system in humans. In the present study, the sensitivity of cells in the cerebral cortex of humans was examined for the first time. For the purpose of the study, the researchers used a unique technique for the treatment of epileptic patients. As part of their medical treatment, the patients were connected to electrodes that record the activity of individual nerve cells in the cerebral cortex. With their consent, sounds were played to them and they were asked to press a key each time they detected a difference in the sound.

In tests that measured the subjects' response to artificial sounds, the researchers found that nerve cells in the human auditory cortex responded to changes in certain sounds with surprising precision. It turns out that a change in pitch by a quarter-tone interval (a 'tone' is the basic unit for measuring musical interval) can be accurately detected by the unit responses of individual neurons. In comparison, the sensitivity of individual nerve cells in the same area in the cat is much lower.

However, when the subjects in the study were exposed to the sounds of the "real world" - such as dialogues and music (from the movie "The Good, the Bad and the Ugly") and background sounds - the nerve cells showed complex patterns of action that cannot be explained solely on the basis of the frequency sensitivity of the nerve cells in the cerebral cortex. This phenomenon was seen in the past only in animals but never in humans and there is room to continue further research. Unlike artificial sounds, sounds related to behavior, such as speech and music, involve additional context-dependent processing processes in the auditory cortex of humans.

"The sensitivity of the cells in the cerebral cortex to sound is higher than we expected," claims Prof. Nelkan. "The findings showed that the sound processing processes take place at a fairly early stage in the brain. In addition, the experiment showed that the cell's sharp discrimination ability matches the behavior of the participants in the study." The meaning of the findings is that the cells responsible for distinguishing between sounds in the human brain, despite their similarity to similar cells in other animals, also have unique characteristics.