Centrifugal pathways protect hearing sensitivity at the cochlea in noisy environments that exacerbate the damage induced by loud sound

Loud sounds damage the cochlea, the auditory receptor organ, reducing heari ng sensitivity. Previous studies demonstrate that the centrifugal olivococh lear pathways can moderately reduce these temporary threshold shifts (TTSs) , protecting the cochlea. This effect involves only the olivocochlear pathw ay component known as the crossed medial olivocochlear system pathway, orig inating from the contralateral brainstem and terminating on outer hair cell s in the cochlea. Here I demonstrate that even moderate noise backgrounds c an significantly exacerbate the cochlear TTSs induced by loud tones, but th is is prevented because in such conditions there is additional activation o f uncrossed olivocochlear pathways, enhancing protection of cochlear hearin g sensitivity. Activation of the uncrossed pathways differs from that of th e crossed pathway in that it is achieved only in noise backgrounds but can then be obtained under monaural conditions of loud tone and background nois e. In contrast, activation of the crossed pathway is achieved only by binau ral loud tones and is not further enhanced by background noise. Thus, conjo int activation of both crossed and uncrossed efferent pathways can occur in noise backgrounds to powerfully protect the cochlea under conditions simil ar to those encountered naturally by humans.