A novel physiological mechanism for pitch encoding in monkey primary auditory cortex.

Abstract

Pitch is a fundamental perceptual attribute of hearing. While auditory cortex is implicated in pitch perception, how pitch is represented at the cortical level remains unclear. The present study examines a novel hypothesis for how the pitch of pure tones and of harmonic complex tones, with or without the fundamental frequency, is encoded in primary auditory cortex (A1): pitch is represented non‐topographically by the temporal distribution of population activity in A1. Sounds of lower pitch evoke a greater proportion of sustained multiunit activity (MUA), relative to initial onset MUA, than sounds of higher pitch, such that the temporal distribution of MUA systematically varies with pitch. Pure tones and harmonic complexes with the same pitch evoke a similar proportion of sustained MUA. The temporal distribution of MUA is largely invariant to changes in stimulus parameters (e.g., level and relative phase) that leave the perceived pitch unchanged. Timing of AEP components recorded in superficial layers of A1 parallels similar pitch‐related changes in AEPs recorded in humans. Coding of perceptual qualities based on the time course of neural activity has been proposed in other sensory modalities (e.g., olfaction) and offers a novel alternative to topographic representations of pitch at the cortical level.