Development of the place principle.

Two experiments using embryonic and hatchling chickens examined how the representation of frequency along the basilar membrane changed during hearing development. In experiment 1, chicks were exposed to high intensity pure tones (500, 1,500, or 3,000 Hz) at one of three different ages. Analysis of hair cell degeneration indicated a discrete region of damage which systematically changed as a function of exposure frequency and age. With maturation, each frequency produced damage at progressively more apical locations. In experiment 2, the representation of frequency in the brain stem auditory nuclei was compared in embryonic, hatchling, and adult chickens. Microelectrode recordings indicated a systematic shift in the frequency representation. Neurons, which are activated by high frequencies in the adult, initially respond to only low frequencies. These experiments indicate how the mature pattern of frequency representation along the basilar membrane gradually emerges during the stages of hearing development.