The neuronal representation of pitch in primate auditory cortex

Abstract

Pitch is fundamental to our perception of music. A single musical note is placed higher or lower on a musical scale according to its pitch, which is related to the frequency of its acoustic waveform. But pitch perception can remain constant despite large changes in the acoustical input. This may be important for music appreciation, and, importantly, speech perception. Animals too can recognize pitch and now experiments in marmoset monkeys provide evidence for neurons that respond in similar ways to a variety of different sounds that all have the same fundamental frequency. These neurons, grouped in a specific area in the auditory cortex, may therefore encode the pitch of complex sounds. Pitch perception is critical for identifying and segregating auditory objects1, especially in the context of music and speech. The perception of pitch is not unique to humans and has been experimentally demonstrated in several animal species2,3. Pitch is the subjective attribute of a sound's fundamental frequency (f0) that is determined by both the temporal regularity and average repetition rate of its acoustic waveform. Spectrally dissimilar sounds can have the same pitch if they share a common f0. Even when the acoustic energy at f0 is removed (‘missing fundamental’) the same pitch is still perceived1. Despite its importance for hearing, how pitch is represented in the cerebral cortex is unknown. Here we show the existence of neurons in the auditory cortex of marmoset monkeys that respond to both pure tones and missing fundamental harmonic complex sounds with the same f0, providing a neural correlate for pitch constancy1. These pitch-selective neurons are located in a restricted low-frequency cortical region near the anterolateral border of the primary auditory cortex, and is consistent with the location of a pitch-selective area identified in recent imaging studies in humans4,5.