Human brains are sensitive to musical pitch, unlike those of monkeys: Shots


An MRI of a person listening to music shows the areas of the brain that respond. (This analysis was not part of the research comparing humans and monkeys.)

KUL BHATIA / Kul Bhatia / Science Source

For us, what sounds like music can be just a noise for a macaque monkey.

This is because the brain of a monkey seems to lack critical circuits very sensitive to the tone of a sound, reported Monday a team in the newspaper Nature Neuroscience.

The discovery suggests that humans may have developed pitch-and-pitch-sensitive brain areas to process sounds associated with speech and music.

"The macaque monkey does not have the material," says Bevil Conway, an investigator at the National Institutes of Health. "The question I ask myself is this: what do monkeys hear when they listen to Tchaikovsky's Fifth Symphony?"

The study began with a bet between Conway and Sam Norman-Haignere, who was a graduate student at the time.

Norman-Haignere, who is now a postdoctoral fellow at Columbia University, was part of a team that found evidence that the human brain responds to the sound of a sound.

"I was like, well, if you see that and that's a solid discovery you see in humans, we'll see it in apes," Conway says.

But Norman-Haignere thought that the brain of the monkeys might be different.

"Honestly, I was not sure," Norman-Haignere said. "I mean it's usually a sign of a good experience, you know, when you do not know what's the result."

The two scientists and several colleagues used a special type of MRI to monitor the brains of six people and five macaque monkeys while listening to a range of sounds through headphones.

Some of the sounds looked more like music, where pitch changes are obvious.

Other sounds sounded more like noise.

And Conway says that it did not take long to realize that he had lost his bet.

"In humans, you see this beautiful organization, its bias, and it's clear like the day," Conway said. In monkeys, he says, "we do not see anything".

This surprised Conway because his own research had shown that both species were almost identical when it came to processing visual information.

"When I look at something, I'm pretty sure the monkey sees the same thing as me," he says. "But here, in the auditory field, it seems fundamentally different."

The study did not attempt to explain why the sounds would be treated differently in the human brain. But one possibility involves our exposure to speech and music.

"Speech and music are extremely complex structured sounds," explains Norman-Haignere, "and it is quite plausible that the brain has developed regions highly tuned to these structures."

This setting could be the result of "something in our genetic code that causes these regions to grow as they are and to be localized where they are," says Norman-Haignere.

Or, he says, it is possible that these areas of the brain develop when children listen to music and talk.

Whatever the case may be, the subtle changes in tone and tone seem to be critical when people want to convey emotions, "said Conway.

"You can tell if I'm angry or sad, if I ask questions, or if I'm confused, and you can get almost everything it means simply by tone," he says.


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