Developmental Biology - Brain Development|
Human Brains Tuned for Musical Pitch
Studies in primates suggest that speech and music may have shaped the human brain's hearing circuits...
In the eternal search for understanding what makes us human, scientists find that our brains are more sensitive to pitch, those harmonic sounds we hear listening to music, than our evolutionary relative the macaque monkey. The study, funded in part by the National Institutes of Health, highlights 'Sound Health', a joint project between the Natioanl Institutes of Health (NIH) and the John F. Kennedy Center for the Performing Arts, in their aim to understand the role of music in health.
"We found that a certain region of our brains has a stronger preference for sounds with pitch than macaque monkey brains," said Bevil Conway PhD, investigator in the NIH's Intramural Research Program and a senior author of the study published in Nature Neuroscience."These results raise the possibility that sounds embedded in speech and music, may have shaped the basic organization of the human brain."
The study started with a friendly bet between Dr. Conway and Sam Norman-Haignere PhD, a post-doctoral fellow at Columbia University's Zuckerman Institute for Mind, Brain, and Behavior and the first author of the paper.
At the time, both were working at the Massachusetts Institute of Technology (MIT). Dr. Conway's team had been searching for differences between how human and monkey brains control vision — to discover there are very few. The brain mapping studies suggested humans and monkeys see the world in very similar ways. But, then Dr. Conway became aware of studies on hearing being done by Dr. Norman-Haignere, at that time a post-doctoral fellow in the laboratory of Josh H. McDermott PhD, associate professor at Massachusetts Institute of Technology, MIT.
"I told Bevil that we had a method for reliably identifying a region in the human brain that selectively responds to sounds with pitch."
Sam V. Norman-Haignere PhD, Zuckerman Institute for Mind, Brain and Behavior, Columbia University, New York, NY; Department of Brain and Cognitive Sciences, MIT, Cambridge, MA, USA.; HHMI Postdoctoral Fellow of the Life Sciences Research Institute, Chevy Chase, MD, USA
That conversation became a joint study to compare human hearing with that of monkeys. Based on previous work, Conway bet there would be no differences. To test this concept, researchers played a series of harmonic sounds, or tones, to healthy volunteers and monkeys. Meanwhile, functional magnetic resonance imaging (fMRI) was used to monitor brain activity in response to those sounds. Researchers also monitored brain activity in response to sounds of toneless noises that were designed to match the frequency levels of each tone played.
At first glance, the scans looked similar and confirmed previous studies. Maps of the auditory cortex of human and monkey brains had similar hot spots of activity regardless of whether the sounds contained tones.
However, when researchers looked more closely at the data, they found evidence suggesting human brains are highly sensitive to tones. The human auditory cortex is much more responsive than the monkey cortex when looking at the relative activity between tones and equivalent 'noisy' sounds.
"We found 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. 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," explains Conway.
Further experiments supported these results. Slightly raising the volume of the tonal sounds had little effect on the tone sensitivity observed in the brains of two monkeys.
Researchers observed similar results when using sounds containing more natural harmonies for monkeys such as recordings of macaque calls. Brain scans showed the human auditory cortex was much more responsive than the monkey cortex when comparing activity between those calls and toneless, noisy versions of the same calls.
"This finding suggests that speech and music may have fundamentally changed the way our brain processes pitch. 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."
Bevil R. Conway PhD, Laboratory of Sensorimotor Research, NEI, NIH, Bethesda, Maryland (MD); National Institute of Mental Health, NIH, Bethesda, MD; National Institute of Neurological Disease and Stroke, NIH, Bethesda, MD, USA.
Earlier this year, the NIH made first round Sound Health research grant money available. Now, scientists from around the USA may apply for grants to explore how music turns on the auditory cortex circuitry making our brains so sensitive to musical pitch.
Videos on this research:
Mapping Musical Pitch in the Brain
Pitch in the Brain
Interview with Bevil Conway
We report a difference between humans and macaque monkeys in the functional organization of cortical regions implicated in pitch perception. Humans but not macaques showed regions with a strong preference for harmonic sounds compared to noise, measured with both synthetic tones and macaque vocalizations. In contrast, frequency-selective tonotopic maps were similar between the two species. This species difference may be driven by the unique demands of speech and music perception in humans.
Sam V. Norman-Haignere, Nancy Kanwisher, Josh H. McDermott and Bevil R. Conway.
The authors thank G. Gagin and K. Bohon for their help in training and scanning animals M1, M2 and M3. They also thank K. Schmidt, D. Yu, T. Haile, S. Eastman and D. Leopold for help in scanning animals M4 and M5. This work was supported by the National Institutes of Health (grant EY13455 to N.K. and grant EY023322 to B.R.C.), the McDonnell Foundation (Scholar Award to J.H.M.), the National Science Foundation (grant 1353571 to B.R.C. and Graduate Research Fellowship to S.N.-H.), the NSF Science and Technology Center for Brains, Minds, and Machines (CCF-1231216) and the Howard Hughes Medical Institute (LSRF Postdoctoral Fellowship to S.N.-H.). The animal work was performed using resources provided by the Neurophysiology Imaging Facility Core (NIMH/NINDS/NEI), as well as the Center for Functional Neuroimaging Technologies at MGH (grant P41EB015896) and a P41 Biotechnology Resource grant supported by the National Institute of Biomedical Imaging and Bioengineering (MGH). The experiments conducted at MGH also involved the use of instrumentation supported by the NIH Shared Instrumentation Grant Program and/or High-End Instrumentation Grant Program (grant S10RR021110). The work was also supported by the Intramural Research Program at the NEI, NIMH, and NINDS.
This study was supported by the NINDS, NEI, NIMH, and NIA Intramural Research Programs and grants from the NIH (EY13455; EY023322; EB015896; RR021110), the National Science Foundation (Grant 1353571; CCF-1231216), the McDonnell Foundation, the Howard Hughes Medical Institute.
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NIH-funded scientists find that our brains may be uniquely sensitive to pitch, the harmonic
sounds we hear when listening to speech or music. CREDIT Courtesy of Conway lab, NIH.