Postnatal shift of tonotopic organization in the chick auditory cortex analogue

The existence of an ontogenetic shift of tonotopic organization throughout the auditory pathway concomitant with cochlea maturation is a matter of controversy. Using the 2-deoxyglucose method we demonstrate here for the first time the shift phenomenon in an auditory forebrain structure, field L, the auditory cortex analogue of the chick. During the first postnatal month isofrequency contours move to positions where, in younger chicks, lower frequencies (up to half an octave) are represented. This developmentally changing place code of sound frequencies at the forebrain level is similar to the one previously reported for brain stem auditory nuclei. It raises the question of constancy of frequency-related pitch perception during development and may be a complication of early auditory learning and memory.