The Inferior Colliculus: A Hub for the Central Auditory System

Abstract

The inferior colliculus (IC) (Fig. 7.1) occupies a strategic position in the central auditory system. Evidence reviewed in this chapter indicates that it is an interface between lower brainstem auditory pathways, the auditory cortex, and motor systems (For abbreviations see Table 7.1). The IC receives ascending input, via separate pathways, from a number of auditory nuclei in the lower brainstem. Moreover, it receives crossed input from the opposite IC and descending input from auditory cortex. These connections suggest that (1) the IC integrates information from various auditory sources and (2) at least some of the integration utilizes cortical feedback. The IC also receives input from ascending somatosensory pathways, suggesting that auditory information is integrated with somatosensory information at the midbrain. Motor-related input to the IC arises from the substantia nigra and globus pallidus. These connections raise the possibility that sensory processing in the IC is modulated by motor action. The major output of the IC is to the auditory thalamocortical system. However, it also transmits information to motor systems such as the deep superior colliculus, and the cerebellum, via the pontine gray. These connections suggest that processing in the IC not only prepares information for transmission to higher auditory centers but also modulates motor action in a direct fashion. In short, the IC is ideally suited to process auditory information based on behavioral context and to direct information for guiding action in response to this information (Aitkin 1986; Casseday and Covey 1996).