Abstract
Aging is accompanied by specific changes in the processing of sound information that result from dysfunction of individual parts of the auditory system. Age-related changes in the function of the inner ear caused by pathologies occurring in the outer and inner hair cells (OHCs and IHCs), stria vascularis, and neurons of the spiral ganglion are transmitted to the central auditory system, where further pathological changes take place. The goal of this chapter is to describe aging-related changes that occur in the structure and function of the cochlear nuclei, nuclei of the superior olivary complex, and inferior colliculus. These changes inevitably influence the processing of acoustical information. Major pathological changes occurring in this part of the auditory system represent age-related losses of some specific types of neurons or their parts, particularly those connected with inhibitory functions. As a result of these losses, the processing of the fine temporal details of the acoustical signals appears to be impaired, particularly in the case of such complex signals as human speech. In addition, the brainstem and midbrain parts of the auditory system play important roles in the processing of space information and in the control of the intensity of the incoming acoustical signal by the olivocochlear bundle; both of these functions may be negatively influenced by aging. The effects of aging are described systematically as they appear in the structure, neurochemistry, and function of the brainstem and midbrain parts of the central auditory system.