Connectional heterogeneity in the mouse auditory corticocollicular system

The auditory (cochlear) nerve and a set of intricately connected brainstem nuclei, auditory thalamus and neocortical regions, all comprise the central auditory system. This system can be further described in terms of its ascending and descending components, or pathways. The ascending pathway starts with the cochlea at the periphery; it processes and then propagates the information about sound towards the auditory cortex. The descending component consists of neural pathways that originate at the top of the central auditory system’s hierarchy and may exert focal and wide-spread influences at various lower levels of the ascending auditory pathway, determining or modifying how the ascending auditory information is processed. This dissertation is focused on understanding of neuroanatomical and functional organization of the corticocollicular system – one of the largest descending projections within the central auditory system. The first chapter of this work lays out a detailed background about the auditory corticocollicular system. The focus of this chapter is on the mouse brain, however, some information is also drawn from neuroscience research on other mammalian species, when appropriate. In the second chapter, I describe the results of my first neuroanatomical study, which postulate that layer 5 and layer 6 corticocollicular neurons arise from distinct neocortical regions, with cellular distributions that only partially overlap. This organization suggests that layer 5 and layer 6 corticocollicular neurons have different functions in terms of modulating auditory processing in the midbrain. In the third chapter, a wide-field in vivo imaging approach is combined with neuroanatomical tracing of the corticocollicular pathway to examine the specificity of origin of layer 5 and layer 6 corticocollicular neurons in the mouse auditory cortex. A key finding of this chapter shows that layer 6 corticocollicular neurons are likely to be more involved in carrying non-auditory or multisensory information signals to the inferior colliculus. Retrograde and viral anterograde tracing were used in the final study and are described in the fourth chapter. These experiments provided further support for differential roles of layer 5 and layer 6 corticocollicular neurons in sound processing, and plausible multisensory nature of layer 6 corticocollicular neurons. An important finding from this chapter is the dichotomy of layer 5 and layer 6 synaptic innervation of different target regions within the inferior colliculus. Together, the results of this work add to the foundation upon which the differences between layer 5 and layer 6 corticocollicular neurons can be understood. The new organization principles of the system described in this dissertation are important for understanding the functions of the corticocollicular system, as well as how the limbic, memory and other sensory systems may affect and integrate with early-stage auditory processing.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste