Cochlear nucleus small cells use olivocochlear collaterals to encode sounds in noise

Understanding speech, especially in noisy environments, is crucial to social interactions. Yet, as we age, speech processing can be disrupted by cochlear damage and the subsequent auditory nerve fiber degeneration. The most vulnerable-medium and high-threshold-auditory nerve fibers innervate various cell types in the cochlear nucleus, among which, the small cells are unique in receiving this input exclusively. Here, we characterize small cell firing characteristics, demonstrating superior temporal as well as intensity coding. We show that small-cell unique coding properties are facilitated by direct cholinergic input from the medial olivocochlear system. These results highlight the small cell-olivocochlear circuit as a key player in signal processing in noisy environments, which may be selectively degraded in aging or after noise insult.