Neurophysiological correlates of auditory maturation.

Abstract

At the time of its birth, the auditory system of the cat is not completely developed. Anatomic maturity of the peripheral auditory system, ie, the cochlea, auditory nerve and cochlear nucleus, is attained at about two or three weeks of age. Physiological response properties of neural elements of the peripheral auditory system change radically during the first few weeks of life, with most measures of responsiveness to acoustic stimuli reaching adult status by the end of the third of fourth postnatal week. The physiological maturation of neural responses correlates well with the anatomic maturation of the auditory structures. At least one physiological response property, namely the ability of cochlear nucleus neurons to time their discharges in response to low-frequency tones, is not fully achieved until the sixth postnatal week or later. Although considerably less is known about the development of the central auditory system, it appears that it is in part dependent upon the maturation of more peripheral elements. Auditory evoked responses, for example, follow roughly the same developmental time course as do the majority of response properties of peripheral neurons. This implies that the central system is ready to function at birth, but that it must await the maturation of more peripheral elements before it can function properly. In contrast to that of the cat and other mammals, the auditory system of the human is relatively well advanced at birth. Certain aspects of brain development, such as dendritic aborization and axonal myelination, undergo considerable change postnatally. How these factors influence hearing is not known.