| Description |
• The neural coding of a signal embedded in noise may improve from mechanisms such as short-term neural adaptation1 and medial olivocochlear (MOC) feedback2. • Adaptation improves neural coding by quickly (1-10 ms)3 reducing the firing rate of auditory nerve fibers to continuous stimuli, such as tonal pedestals, while retaining a constant firing rate to transient stimuli, such as brief increments in the level of a tonal pedestal1. • This increase in the ratio of firing to a transient (i.e., signal) to that of a pedestal (noise) is consistent with short-term adaptation resulting in a rapid improvement in neural SNR1. • A similar improvement in neural SNR is observed in laboratory animals when the MOC reflex is elicited by contralateral acoustic stimulation2. • Unlike adaptation, improvements in SNR from the MOC reflex are due to a rapid decrease in cochlear amplifier gain4. • It is well established that neural adaptation and MOC feedback lead to improved neural SNRs in laboratory animals; however, similar findings in humans are limited. • This study measured temporal changes in neural SNRs in humans by recording the compound action potential (CAP) in response to clicks in bursts of noise, where bursts were preceded by silence or by a broadband noise precursor. • SNRs were hypothesized to improve from burst to burst and improve as a result of the precursor. The following patterns of results for CAPs and cochlear microphonics (CMs) are consistent with neural adaptation, MOC feedback, and middle ear muscle (MEM) activity in terms of the time course and level dependence of improvements in neural SNRs. |
