Spectral Edges as Optimal Stimuli for the Dorsal Cochlear Nucleus

The principal neurons of the dorsal cochlear nucleus (DCN) form one of several parallel pathways through the brainstem from the cochlear nucleus to the inferior colliculus (Rouiller 1997). Unlike the neurons of the ventral cochlear nucleus, DCN principal cells give strongly non-linear responses to sound (Nelken et al. 1997; Yu and Young 2000), meaning that models of DCN neurons often do not predict the responses to complex sounds. Such nonlinearity is typical of auditory neurons (e.g. Eggermontet al. 1983; Machenset al. 2004) and poses difficulties for studies of the representation of sound in the brain, because it is not possible to obtain a comprehensive view of the representation of sound by such nonlinear neurons. In the case of the DCN, information about function has been provided by behavioral experiments in which the nucleus or its output tract were lesioned (e.g. May 2000), leading to deficits in sound localization. In addition, the DCN receives inputs from various non-auditory sources, including the somatosensory system (Davis et al. 1996; Shore 2005) and these seem to have specifically to do with the position of the external ear in cats (Kanold and Young 2001). These results are consistent with the finding that DCN neurons in the cat respond sensitively with inhibition to the acoustic notches in the head-related transfer functions of the cat external ear (reviewed in Young and Davis 2001). Together, these data suggest a role in sound localization for the DCN, especially in localization based on spectral cues.