Microcircuits of the Dorsal Cochlear Nucleus

Abstract

The dorsal cochlear nucleus (DCN) integrates excitatory input from auditory and nonauditory sources. Auditory signals are conveyed to the deep layer by the auditory nerve and by excitatory interneurons in the ventral cochlear nucleus (VCN). Signals from diverse auditory, somatosensory, proprioceptive, and vestibular sources arrive through mossy fibers in the molecular layer. Thus the DCN is a multisensory integrator. Auditory and mossy inputs are processed through separate microcircuits and are then integrated and conveyed to the inferior colliculus by fusiform cells. Signals arriving from the auditory nerve and VCN in the DCN deep layer are refined by inhibitory neurons that give the acoustic responses of the principal cells a striking nonlinearity as a function of sound intensity and inhibitory sidebands in the spectral domain. Mossy inputs are preprocessed by local circuits in a granule cell region and further refined in the molecular layer. Unlike the auditory signals in the deep layer, signals in the molecular layer exhibit diverse forms of long-term synaptic plasticity. The function of the DCN is not fully understood. The sensitivity of the DCN to spectral notches suggests a role in sound localization using monoaural cues. Input associated with pinna muscles and the trigeminal nerve suggests that the DCN relates head orientation to incoming sounds. The anatomical and physiological similarity of the DCN to structures in electric fish that sensitize the fish to novel signals in the environment has led to the idea that the DCN cancels self-generated and expected features of sounds.