TEHRAN, Young Journalists Club (YJC) - "We found that a certain region of our brains has a stronger preference for sounds with pitch than macaque monkey brains," neuroscientist Bevil Conway, an investigator at the National Institutes of Health's Intramural Research Program, said in a news release. "The results raise the possibility that these sounds, which are embedded in speech and music, may have shaped the basic organization of the human brain."
The idea for the new study came while Conway was working at MIT. Conway and Sam Norman-Haignere, a post-doctoral fellow at Columbia University's Zuckerman Institute for Mind, Brain, and Behavior, were trying to identify differences in the way monkey and human brains manage vision. They didn't have much success.
Norman-Haignere was also studying hearing in the laboratory of Josh H. McDermott.
"I told Bevil that we had a method for reliably identifying a region in the human brain that selectively responds to sounds with pitch," Norman-Haignere said.
The two researchers decided to compare how human and monkey brains control hearing. For the study, Conway, Norman-Haignere and their colleagues played a series of harmonic sounds for healthy volunteers and monkeys. Functional magnetic resonance imaging allowed the researchers to monitor the participants' brain activity.
Researchers also played toneless sounds that matched the frequencies of the harmonic sounds.
The brains of both monkeys and humans showed similar levels of neural activity in response to non-harmonic sounds. But the neural patterns showed humans were more sensitive to tonal sounds.
"We found that human and monkey brains had very similar responses to sounds in any given frequency range. It's when we added tonal structure to the sounds that some of these same regions of the human brain became more responsive," said Conway. "These results suggest the macaque monkey may experience music and other sounds differently. In contrast, the macaque's experience of the visual world is probably very similar to our own. It makes one wonder what kind of sounds our evolutionary ancestors experienced."
When scientists repeated the experiment using sounds that contained natural harmonies for monkeys, including macaque calls, they got the same results. The researchers published their findings this week in the journal Nature Neuroscience.
"This finding suggests that speech and music may have fundamentally changed the way our brain processes pitch," said Dr. Conway. "It may also help explain why it has been so hard for scientists to train monkeys to perform auditory tasks that humans find relatively effortless."