Development of auditory neuronal responses in avian embryos.

Neurons in the cochlear nuclei of duck embryos become responsive to tonal stimuli in an orderly spatial and temporal sequence. Cells responding to lower frequencies are recorded before those responding to higher frequencies. Auditory neurons are spatially arranged according to their characteristic frequencies, indicating a point-by-point projection of the basilar membrane. Areas of the nuclei where the apical segment of the basilar membrane projects become responsive to sound before regions representing more basal segments. These progressive changes with age are accompanied by a gradual rise both in neuronal sensitivity and in frequency range of maximum sensitivity. The development of auditory neural responses is timed to prepare the embryo for the onset of prenatal mother-young communication.