Johns Hopkins researchers have discovered a discrete
region of the monkey brain that processes pitch, the
relative high and low points of sound, by recognizing a
single musical note played by different instruments.
Given the similarities between monkeys and man, humans
may have a similar pitch-processing region in the brain,
too, which might one day help those with hearing and speech
problems. The paper appeared in the Aug. 25 issue of
Nature.
By recording the activity of individual brain cells as
monkeys listened to musical notes, the scientists
identified single neurons, located in what they've called
the brain's "pitch center," that recognize a middle-C as a
middle-C even when played by two different instruments.
"Pitch perception is such a basic function of human
and animal auditory systems, yet its source has remained
elusive to researchers for decades," said Xiaoqin Wang,
associate professor of
biomedical engineering and
neuroscience at the Johns Hopkins Institute for Basic
Biomedical Sciences. "The discovery of a pitch-processing
area in the brain solves an age-old mystery of auditory
research."
According to Wang, pitch's importance to humans is
found in facilitating our ability to follow a sequence of
sounds we would recognize as "melodic" and combinations of
sounds we identify as harmony. As a result, pitch gives
meaning to the patterns, tones and emotional content of
speech, like how raising our voice at the end of a sentence
indicates a question, and cues the listener to the
speaker's gender and age.
Although a melody or conversation is not as essential
to monkeys, pitch perception is crucial for nonhuman
primates to interpret the source and meaning of prey and
predator calls or other sounds from the environment. Such
information is crucial for the animal's survival.
Wang's team studied marmoset monkeys using
single-neuron recording, a technique that measures the
electrical activity of individual neurons in the brain. The
researchers viewed each neuron's reaction as different
notes were played by a computer.
The majority of pitch-selective neurons are located in
a specific region of the monkey's brain near the primary
auditory cortex, a region already known to interpret
sounds.
"The auditory cortex has traditionally been thought to
detect the complex spectrum contained within a sound; for
example, with one set of neurons responding only to a
trumpet and another set to a violin, even if playing the
same note," Wang said. "But the neurons we found respond to
a single musical note, regardless if played by a trumpet or
violin."
The research was funded by the National Institutes of
Health. Daniel Bendor of Johns Hopkins co-authored the
paper.