The inferior colliculus (IC) (

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for ''lower hill'') is the principal

midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', " ...

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 auditory cortex is the part of the temporal lobe that processes auditory information in humans and many other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations to ...

. 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 In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), and pain. It i ...

interaction, receiving projections from somatosensory nuclei. This

multisensory integration Multisensory integration, also known as multimodal integration, is the study of how information from the different sensory modalities (such as sight, sound, touch, smell, self-motion, and taste) may be integrated by the nervous system. A coherent r ...

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 Corpus is Latin for "body". It may refer to: Linguistics * Text corpus, in linguistics, a large and structured set of texts * Speech corpus, in linguistics, a large set of speech audio files * Corpus linguistics, a branch of linguistics Music * ...

, and also part of the tectal region of the

. The inferior colliculus lies caudal to its counterpart – the superior colliculus – above the

trochlear nerve The trochlear nerve (), ( lit. ''pulley-like'' nerve) also known as the fourth cranial nerve, cranial nerve IV, or CN IV, is a cranial nerve that innervates just one muscle: the superior oblique muscle of the eye, which operates through the pu ...

, and at the base of the projection of the

medial geniculate nucleus The medial geniculate nucleus (MGN) or medial geniculate body (MGB) is part of the auditory thalamus and represents the thalamic relay between the inferior colliculus (IC) and the auditory cortex (AC). It is made up of a number of sub-nuclei that ...

and the

lateral geniculate nucleus In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projec ...

Subdivisions

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.

Relationship to auditory system

The inferior colliculi of the midbrain are located just below the visual processing centers known as the superior colliculi. The inferior colliculus is the first place where vertically orienting data from the fusiform cells in the

dorsal cochlear nucleus The dorsal cochlear nucleus (DCN, also known as the "tuberculum acusticum"), is a cortex-like structure on the dorso-lateral surface of the brainstem. Along with the ventral cochlear nucleus (VCN), it forms the cochlear nucleus (CN), where all a ...

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.

Input and output connections of 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 The lateral lemniscus is a tract of axons in the brainstem that carries information about sound from the cochlear nucleus to various brainstem nuclei and ultimately the contralateral inferior colliculus of the midbrain. Three distinct, primarily ...

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 Afferent nerve fibers are the axons (nerve fibers) carried by a sensory nerve that relay sensory information from sensory receptors to regions of the brain. Afferent projections ''arrive'' at a particular brain region. Efferent nerve fibers ...

from the inferior colliculus of the

mesencephalon The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', "m ...

to the

. The inferior colliculus receives input from both the ipsilateral and contralateral cochlear nucleus and respectively the corresponding ears. There is some

lateralization The lateralization of brain function is the tendency for some neural functions or cognitive processes to be specialized to one side of the brain or the other. The median longitudinal fissure separates the human brain into two distinct cerebra ...

, 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

and auditory

thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...

(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.

Function of IC

The majority of the ascending fibers from the lateral lemniscus project to IC, which means major ascending auditory pathways converge here. IC appears as an integrative station and switchboard as well. It is involved in the integration and routing of multi-modal sensory perception, mainly the startle response and vestibulo-ocular reflex. It is also responsive to specific amplitude modulation frequencies and this might be responsible for detection of pitch. In addition, spatial localization by binaural hearing is a related function of IC as well. The inferior colliculus has a relatively high metabolism in the brain. The Conrad Simon Memorial Research Initiative measured the blood flow of the IC and put a number at 1.80 cc/g/min in the cat brain. For reference, the runner up in the included measurements was the somatosensory cortex at 1.53. This indicates that the inferior colliculus is metabolically more active than many other parts of the brain. The hippocampus, normally considered to use up a disproportionate amount of energy, was not measured or compared. Skottun ''et al.'' measured the

interaural time difference The interaural time difference (or ITD) when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the localization of sounds, as it provides a cue to the direction or angle of the sound s ...

sensitivity of single neurons in the inferior colliculus, and used these to predict behavioural performance. The predicted

just noticeable difference In the branch of experimental psychology focused on sense, sensation, and perception, which is called psychophysics, a just-noticeable difference or JND is the amount something must be changed in order for a difference to be noticeable, detectable ...

was comparable to that achieved by humans in behavioral tests.Skottun, Bernt C. ''et al.'': ''The ability of inferior colliculus neurons to signal differences in interaural delay.'' PNAS November 20, 2001 vol. 98, no. 24, pp. 14050-14054. This suggested that by the level of the inferior colliculus, integration of information over multiple neurons is unnecessary (see population code). Axiomatically determined functional models of spectro-temporal receptive fields in inferior colliculus have been determined by Lindeberg and Friberg T. Lindeberg and A. Friberg "Idealized computational models of auditory receptive fields", PLOS ONE, 10(3): e0119032, pages 1-58, 2015
/ref> in terms of derivatives of Gaussian functions over the log-spectral domain and either Gaussian kernels over time in the case of non-causal time or first-order integrators (truncated exponential kernels) coupled in cascade in the case of truly time-causal operations, optionally in combination with local glissando transformations to account for variations in frequencies over time. The shapes of the receptive field functions in these models can be determined by necessity from structural properties of the environment combined with requirements about the internal structure of the auditory system to enable theoretically well-founded processing of sound signals at different temporal and log-spectral scales. Thereby, the receptive fields in inferior colliculus can be seen as well adapted to handling natural sound transformations.

Additional images

File:Inferior_colliculus_of_the_human_midbrain.svg, Inferior colliculus (K) from a cerebellar perspective. Sagittal view. File:Gray682.png, Superficial dissection of brain-stem. Lateral view. File:Gray685.png, Deep dissection of brain-stem. Lateral view. File:Gray691.png, Dissection of brain-stem. Dorsal view. File:Gray719.png, Hind- and mid-brains; postero-lateral view. File:Human brainstem-thalamus posterior view description.JPG, Posterior dissection of brainstem with colliculi visible. File:Slide2PITER.JPG, Fourth ventricle. Posterior view. Deep dissection. File:Slide2BRA.JPG, Brainstem. Posterior view.

References

External links

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NIF Search - Brachium of inferior colliculus
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{{DEFAULTSORT:Inferior Colliculus Auditory system Midbrain Tectum Corpora quadrigemina