Our brains seem only tuned for musical pitch

In the eternal quest to understand what makes us human beings, scientists have discovered that our brains are more sensitive to the pitch, the harmonic sounds we hear when we listen to music, than our evolving parent, the Macaque Monkey. . The study, funded in part by the National Institutes of Health, highlights the promises of Sound Health, a joint NIH / John F. Kennedy Center for the Performing Arts project that aims to understand the role of healthy music.

"We found that a certain region of our brain had a stronger preference for pitch sounds than the macaque monkey's brain," said Bevil Conway, Ph.D., researcher in the Intramural Research Program. NIH and lead author of the study published in Nature Neuroscience. "The results raise the possibility that these sounds, which are embedded in speech and music, may have shaped the fundamental organization of the human brain."

The study began with a friendly bet between Dr. Conway and Sam Norman-Haignere, Ph.D., a postdoctoral fellow at the Zuckerman Institute for the mind, brain and behavior of the 39, Columbia University, and the first author of the article.

At the time, both worked at the Massachusetts Institute of Technology (MIT). Dr. Conway's team was looking for differences between how the human brain and the monkey brain control the vision, to discover that there are very few. Their studies of brain mapping suggested that humans and apes see the world in a very similar way. But then, Dr. Conway heard about some of the hearing studies done by Dr. Norman-Haignere, then a postdoctoral fellow in the lab of Josh H. McDermott, Ph.D., associate professor at MIT.

"I told Bevil that we had a reliable method of identifying a region of the human brain that selectively responds to sounds with pitch," said Dr. Norman-Haignere,

It was then that they had the idea of ​​comparing humans with monkeys. Based on his studies, Dr. Conway bet they would see no difference.

To test this, the researchers played a series of harmonic sounds, or tones, to healthy volunteers and monkeys. At the same time, functional magnetic resonance imaging (fMRI) has been used to monitor brain activity in response to sounds. The researchers also monitored cerebral activity in response to noise-free noises designed to match the frequency levels of each sound played.

At first glance, the scans seemed similar and confirmed previous studies. The auditory cortex maps of the human brain and monkey brain had similar activity hotspots, whether the sounds contained sounds or not.

However, when the researchers took a closer look at the data, they found evidence suggesting that the human brain was very sensitive to tones. The human auditory cortex was much more sensitive than the monkey cortex when it examined the relative activity between sounds and noisy equivalent sounds.

"We found that the brains of humans and monkeys reacted very similarly to sounds in all frequency ranges.It was when we added a tonal structure to the sounds that some of these areas of the human brain became more sensitive, "said Dr. Conway. "These results suggest that the macaque monkey is experimenting with music and other sounds differently, but the macaque experience of the visual world is probably very similar to ours." of sounds our ancestors of evolution have experienced. "

Other experiences have corroborated these results. Slightly increasing the volume of tonal sounds has little effect on the sensitivity of the tone observed in the brain of two monkeys.

Finally, researchers found similar results when they used sounds containing more natural harmonies for monkeys by playing macaque call records. The brain analyzes showed that the human auditory cortex was much more sensitive than the monkey cortex when it compared the relative activity between the calls and the noiseless and noisy versions of the calls.

"This discovery suggests that speech and music may have fundamentally changed the way our brain processes sounds," said Dr. Conway. "It can also help explain why it has been so difficult for scientists to train monkeys to perform auditory tasks that humans find relatively little effort."

Earlier this year, other US scientists applied for the first round of research grants from NIH Sound Health. Some of these grants could eventually help scientists who are exploring how music activates the auditory cortex circuits that make our brain sensitive to musical tone.