Neurons, Connections, and Microcircuits of the Inferior Colliculus

Abstract

In this chapter, the neural circuitry of the inferior colliculus (IC) is described at a cellular level. The IC is subdivided into the central nucleus (ICC) and surrounding cortices that receive specific combinations of inputs and generate diverse outputs. Neuronal types in the IC can be distinguished by their dendritic arborization patterns, neurochemical profiles, and physiological properties. Based on these properties, neuronal types organizing the ICC appear to be different from those organizing the IC cortex. The IC receives ascending inputs from the cochlear nuclei, superior olivary complex, and nuclei of the lateral lemniscus, and the IC receives descending inputs from the auditory cortex and nonauditory inputs from various nuclei. Each input source forms terminal fields in particular zones of the IC. Massive commissural and local inputs are also present. One well-characterized cell type, the large GABAergic IC neuron, receives convergent input from all of these sources. The IC neurons project to the auditory thalamus as well as to lower brain stem nuclei. Anatomical and physiological features suggest that ICC acts as an auditory integration center, and IC cortex acts as a multimodal integration center and novelty detector. These data support the view that the lemniscal and nonlemniscal pathways emerge at the midbrain level.