Play it again: how can we tell a C is a C regardless of the instrument it is played on?© Punchstock

The discovery of a group of pitch-sensitive cells in the brain has sent reverberations through the field of music perception. Researchers think that studying these neurons will reveal how our minds grasp songs and speech.

Most people can hear that two instruments are playing the same note, even if they sound as different as a trumpet and a piano. Our perception of fundamental sound frequency or 'pitch' remains constant despite differences in an instrument's acoustical traits.

This holds true even when the fundamental frequency is actually missing from a complex sound. If several strings are plucked such that they vibrate at their higher harmonics, at 800, 1,000 and 1,200 hertz for example, we will perceive the sound as belonging to the same pitch as the primary harmonic of those strings: 200 hertz. For centuries scholars have puzzled over how the brain does this.

In recent years, researchers have looked at the role played by the primary auditory cortex, the brain region known to digest sounds. Human brain scans have indicated that a peripheral bit of this brain region is active when we try to identify pitch. But no one could find cells that responded to specific frequencies, leaving it a mystery how we interpret them.

A study with marmoset monkeys (Callithrix jacchus) has now shown up specific neurons that do just that. "This is the first evidence that there are individual neurons in the brain that are encoding for pitch," explains Josh McDermott, a music psychologist based in Cambridge at the Massachusetts Institute of Technology.

Striking a nerve

Daniel Bendor and Xiaoqin Wang of the Johns Hopkins University in Baltimore, Maryland, identified the neurons by recording the response of the monkeys' brain cells while the animals heard various notes from a computer. They found that individual cells consistently got excited by sounds at specific frequencies, or multiples of that frequency.

Just as humans can perceive a pitch even if the fundamental is missing, the monkeys' neurons for 200 hertz lit up when presented with a mix of 800-, 1,000- and 1,200-hertz sounds. The findings appear this week in Nature1.

Exactly how a given frequency sets off a single cell remains unclear. But experts say the location of this unique population of neurons is an important first step.

McDermott says the discovery will open doors for investigators to explore how other primates, including humans, appreciate music. "There are about a thousand studies one can think of doing after this," he says.

Already there is speculation that damage to cells in this brain region could explain why some people can't carry a tune. "There are a lot of different possibilities, but this might be an area that could be affected when someone is tone deaf," Bendor says. 

Massachusetts Institute of Technology

• References

  1. Bendor D.& Wang, X., et al. Nature, 436. 1161 - 1165 (2005). | Article | PubMed | ISI | ChemPort |