The Effect of Sound Stimulation on Hearing Ability

In the late 1990s, researchers discovered that acoustic stimuli slow progressive sensorineural hearing loss and exposure to a moderately augmented acoustic environment can delay the loss of auditory function. In addition, prolonged exposure to an augmented acoustic environment could improve age-related auditory changes. These ameliorative effects were shown in several types of mouse strains, as long as the acoustic environment was provided prior to the occurrence of severe hearing loss. In addition to delaying progressive hearing loss, acoustic stimuli could also protect hearing ability against damage by traumatic noise. In particular, a method called forward sound conditioning (i.e., prior exposure to moderate levels of sound) has been shown to reduce noise-induced hearing impairment in a number of mammalian species, including humans. Interestingly, recent report has suggested that low-level sound conditioning also reduces free radical-induced damage to hair cells, increases antioxidant enzyme activity, and reduces Cox-2 expression in cochlea, and can enhance cochlear sensitivity. Specifically, increased cochlear sensitivity was observed when distortion product otoacoustic emissions (DPOAEs) and compound action potentials (CAPs) were measured. In addition to forward sound conditioning, backward sound conditioning (i.e., the use of acoustic stimuli after exposure to a traumatic noise) has been shown to protect hearing ability against acoustic trauma and to prevent the cortical map reorganization induced by traumatic noise. In this study, the investigators examine the effect of sound stimulation on hearing ability in human subjects.