Top-down inferior colliculus signals engage unipolar brush cell circuits in the dorsal cochlear nucleus of the mouse auditory system.

Sensory systems comprise ascending pathways that convey information from the sense organs and descending pathways that provide feedback and contextual signals to guide sensory processing. How top-down signals are integrated at early stages to improve sensory function remains poorly understood. The dorsal cochlear nucleus (DCN) is a cerebellum-like circuit proposed to perform adaptive filtering, including suppression of self-generated sounds. A major question is how sound-frequency-specific top-down information is processed by the DCN, since many top-down inputs target granule cells whose axons span the tonotopic axis and are unlikely to maintain frequency-specific signals. Here, we characterize neurons in the inferior colliculus that provide descending input to DCN. We show that among their targets are unipolar brush cells (UBCs) that distribute and transform descending signals directly to principal neurons and inhibitory interneurons in a circuit that bypasses granule cells. In vivo activation of UBCs attenuated auditory responses in awake mice. Together, these findings identify a circuit through which top-down signals from IC could influence early auditory processing and potentially guide adaptive filtering in the DCN.