The inferior colliculus (IC) (Latin for lower hill) is the principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex. The inferior colliculus has three subdivisions: the central nucleus, a dorsal cortex by which it is surrounded, and an external cortex which is located laterally. Its bimodal neurons are implicated in auditory-somatosensory interaction, receiving projections from somatosensory nuclei. This multisensory integration may underlie a filtering of self-effected sounds from vocalization, chewing, or respiration activities.

The inferior colliculi together with the superior colliculi form the eminences of the corpora quadrigemina, and also part of the midbrain tectum. The inferior colliculus lies caudal to its counterpart - the superior colliculus - above the trochlear nerve, and at the base of the projection of the medial geniculate nucleus and the lateral geniculate nucleus.

The inferior colliculi of the midbrain are located just below the visual processing centers known as the superior colliculi. The inferior colliculus has three subdivisions – the central nucleus, the dorsal cortex by which it is surrounded, and an external cortex which is located laterally. The inferior colliculus is the first place where vertically orienting data from the fusiform cells in the dorsal cochlear nucleus can finally synapse with horizontally orienting data. Sound location data thus becomes fully integrated by the inferior colliculus.

IC are large auditory nuclei on the right and left sides of the midbrain. Of the three subdivisions the central nucleus of IC (CNIC) is the principal way station for ascending auditory information in the IC.

The input connections to the inferior colliculus are composed of many brainstem nuclei. All nuclei except the contralateral ventral nucleus of the lateral lemniscus send projections to the central nucleus (CNIC) bilaterally. It has been shown that great majority of auditory fibers ascending in the lateral lemniscus terminate in the CNIC. In addition, the IC receives inputs from the auditory cortex, the medial division of the medial geniculate body, the posterior limitans, suprapeduncular nucleus and subparafascicular intralaminar nuclei of the thalamus, the substantia nigra pars compacta lateralis, the dorsolateral periaqueductal gray, the nucleus of the brachium of the inferior colliculus (or inferior brachium) and deep layers of the superior colliculus. The inferior brachium carries auditory afferent fibers from the inferior colliculus of the mesencephalon to the medial geniculate nucleus.

The inferior colliculus receives input from both the ipsilateral and contralateral cochlear nucleus and respectively the corresponding ears. There is some lateralization, the dorsal projections (containing vertical data) only project to the contralateral inferior colliculus. This inferior colliculus contralateral to the ear it is receiving the most information from, then projects to its ipsilateral medial geniculate nucleus.

The inferior colliculus also receives descending inputs from the auditory cortex and auditory thalamus (or medial geniculate nucleus).

The medial geniculate body (MGB) is the output connection from inferior colliculus and the last subcortical way station. The MGB is composed of ventral, dorsal, and medial divisions, which are relatively similar in humans and other mammals. The ventral division receives auditory signals from the central nucleus of the IC.