The medial olivocochlear bundle suppresses outer hair cell (OHC) amplification in response to acoustic stimulation, a response known as the medial olivocochlear reflex (MOCR). This gain reduction appears as suppression of otoacoustic emissions (OAEs). By using this technique, MOCR strength under passive conditions has been reported to decline with age. Meanwhile, centrifugal pathways from cortical regions to MOC neurons exist, and OAE suppression is indeed reported to be modulated by auditory attention in young adults. However, the impact of aging on the active control of MOCR remains unclear. In this study, we compared MOCR strength during passive and task conditions in younger and middle-aged adults. The younger group showed a significant increase in MOCR strength during the auditory task compared to the passive condition. In the older group, by contrast, no significant difference was found between the conditions. Additionally, in the older group, speech-in-noise performance was negatively correlated with MOCR strength measured during the task but was not significantly correlated with the one measured during the passive condition. These results suggest that reduced active control of the MOCR is one of the factors contributing to the decline in speech-in-noise perception in middle-aged adults.
Dowaki et al. (Wed,) studied this question.