Research Shows Where Brain Interprets 'Pitch'

Given the similarities between monkeys and man, humans may have asimilar pitch-processing region in the brain too, which might one dayhelp those with hearing and speech problems. The paper appears in theAug. 25 issue of Nature.

By recording the activity of individual brain cells as monkeyslistened to musical notes, the scientists identified single neurons,located in what they've called the brain's "pitch center," thatrecognize a middle-C as a middle-C even when played by two differentinstruments.

"Pitch perception is such a basic function of human and animalauditory systems, yet its source has remained elusive to researchersfor decades," says Xiaoqin Wang, Ph.D., associate professor ofbiomedical engineering and neuroscience at the Johns Hopkins Institutefor Basic Biomedical Sciences. "The discovery of a pitch-processingarea in the brain solves an age-old mystery of auditory research."

According to Wang, pitch's importance to humans is found infacilitating our ability to follow a sequence of sounds we wouldrecognize as "melodic" and combinations of sounds we identify asharmony. As a result, pitch gives meaning to the patterns, tones andemotional content of speech, like how raising our voice at the end of asentence indicates a question, and cues the listener to the speaker'sgender and age.

Although a melody or conversation is not as essential tomonkeys, pitch perception is crucial for nonhuman primates to interpretthe source and meaning of prey and predator calls or other sounds fromthe environment. Such information is crucial for the animal's survival.

Wang's team studied marmoset monkeys using single-neuronrecording, a technique that measures the electrical activity ofindividual neurons in the brain. The researchers viewed each neuron'sreaction as different notes were played by a computer.

The majority of pitch-selective neurons are located in aspecific 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 detectthe complex spectrum contained within a sound; for example, with oneset of neurons responding only to a trumpet and another set to aviolin, even if playing the same note," says Wang. "But the neurons wefound respond to a single musical note, regardless if played by atrumpet or violin."

The research was funded by the National Institutes of Health. Daniel Bendor of Johns Hopkins co-authored the paper.

On the Web:http://www.nature.com/nature