Direct Projections from Cochlear Nuclear Complex to Auditory Thalamus in the Rat

Abstract

It is known that the dorsal cochlear nucleus and medial geniculate body in the auditory system receive significant inputs from somatosensory and visual-motor sources, but the purpose of such inputs is not totally understood. Moreover, a direct connection of these structures has not been demonstrated, because it is generally accepted that the inferior colliculus is an obligatory relay for all ascending input. In the present study, we have used auditory neurophysiology, double labeling with anterograde tracers, and retrograde tracers to investigate the ascending projections of the cochlear nuclear complex. We demonstrate that the dorsal cochlear nucleus and the small cell cap of the ventral cochlear nucleus have a direct projection to the medial division of the medial geniculate body. These direct projections from the cochlear nucleus complex bypass the inferior colliculus and are widely distributed within the medial division of the medial geniculate, suggesting that the projection is not topographic. As a nonlemniscal auditory pathway that parallels the conventional auditory lemniscal pathway, its functions may be distinct from the perception of sound. Because this pathway links the parts of the auditory system with prominent nonauditory, multimodal inputs, it may form a neural network through which nonauditory sensory and visual-motor systems may modulate auditory information processing.

Subcortical processing in auditory communication

“…Although hypothetical, the notion that the salience of vocal features may be modulated by activity in the CN e hence, very early in the afferent auditory pathway e is compatible with anatomical evidence of direct projections from this nucleus to the medial geniculate body (MGB) of the thalamus, i.e. bypassing the inferior colliculus (Woollard and Harpman, 1940;Strominger and Strominger, 1971;Strominger, 1973;Strominger et al, 1977;Malmierca et al, 2002;Anderson et al, 2006). Future studies might investigate the functional role of these pathways in processing voices and voice sound features.…”

A Discontinuous Tonotopic Organization in the Inferior Colliculus of the Rat

“…Three-dimensional reconstructions of IC laminae were also made after injections of anatomical tracers in physiologically defined regions in the dorsal cochlear nucleus (DCN) in eight additional cases used previously (Oliver et al, 1997;Malmierca et al, 2002). These provided information on the relationship of the thickness of the axonal laminae in the IC to the size of the injection site in the DCN.…”

Immunocytochemical distribution of Met-enkephalin-Arg6-Gly7-Leu8 (Met-8) in the auditory system of the rat

“…In a recent study Malmierca et al (2002) have described a new pathway from the CNC to the MGB, namely to the MGM with a small component to the suprageniculate nucleus. This is a non-lemniscal pathway that has been suggested to transfer multimodal information to the cortex more rapidly than the lemniscal pathway.…”