Inferior colliculus
Encyclopedia
The inferior colliculus (Latin
, lower hill) is the principal midbrain nucleus of the auditory pathway and receives input from several more peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex. The inferior colliculus has three subdivisions: the central nucleus (CIC), a dorsal cortex (DCIC) by which it is surrounded, and an external cortex (ICX) which is located laterally. Its bimodal neurons are implied in auditory-somatosensory interaction, receiving projections from somatosensory nuclei
. This multisensory integration may underlie a filtering of self-effected sounds from vocalisation, chewing, or respiration activities.
The inferior colliculi together with the superior colliculi
form the eminences of the corpora quadrigemina
, and also part of the tectal region of the midbrain. 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
(MGN) and the lateral geniculate nucleus
(LGN).
IC are large auditory nuclei on the right and left sides of the midbrain. It is divided into three parts, the Central Nucleus of IC (CNIC), dorsal cortex and lateral cortex; however, 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
(LL) 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 (MGBm), the posterior limitans (PL), suprapeduncular nucleus (SpN) and subparafascicular (Spf) intralaminar nuclei of the thalamus, the substantia nigra, pars compacta lateralis (SNL), the dorsolateral periaqueductal gray (dlPAG), the nucleus of the brachium of the inferior colliculus (BICN) and deep layers of the superior colliculus (SC).
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 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.
. 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
sensitivity of single neurons in the inferior colliculus, and used these to predict behavioural performance. The predicted just noticeable difference was comparable to that achieved by humans in behavioral tests. This suggested that by the level of the inferior colliculus, integration of information over multiple neurons is unnecessary (see population code).
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
, lower hill) is the principal midbrain nucleus of the auditory pathway and receives input from several more peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex. The inferior colliculus has three subdivisions: the central nucleus (CIC), a dorsal cortex (DCIC) by which it is surrounded, and an external cortex (ICX) which is located laterally. Its bimodal neurons are implied in auditory-somatosensory interaction, receiving projections from somatosensory nuclei
Somatosensory system
The somatosensory system is a diverse sensory system composed of the receptors and processing centres to produce the sensory modalities such as touch, temperature, proprioception , and nociception . The sensory receptors cover the skin and epithelia, skeletal muscles, bones and joints, internal...
. This multisensory integration may underlie a filtering of self-effected sounds from vocalisation, chewing, or respiration activities.
The inferior colliculi together with the superior colliculi
Superior colliculus
The optic tectum or simply tectum is a paired structure that forms a major component of the vertebrate midbrain. In mammals this structure is more commonly called the superior colliculus , but, even in mammals, the adjective tectal is commonly used. The tectum is a layered structure, with a...
form the eminences of the corpora quadrigemina
Corpora quadrigemina
In the brain, the corpora quadrigemina are the four colliculi—two inferior, two superior—located on the tectum of the dorsal aspect of the midbrain.They are respectively named the inferior and superior colliculus....
, and also part of the tectal region of the midbrain. The inferior colliculus lies caudal to its counterpart - the superior colliculus - above the trochlear nerve
Trochlear nerve
The trochlear nerve is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye....
, and at the base of the projection of the medial geniculate nucleus
Medial geniculate nucleus
The Medial Geniculate Nucleus or Medial Geniculate Body is part of the auditory thalamus and represents the thalamic relay between the inferior colliculus and the auditory cortex...
(MGN) and the lateral geniculate nucleus
Lateral geniculate nucleus
The lateral geniculate nucleus is the primary relay center for visual information received from the retina of the eye. The LGN is found inside the thalamus of the brain....
(LGN).
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 can finally synapse with horizontally orienting data. This homecoming of the aural dimensions puts these dual mesencephalic bumps in the position to fully integrate all the sound location data.IC are large auditory nuclei on the right and left sides of the midbrain. It is divided into three parts, the Central Nucleus of IC (CNIC), dorsal cortex and lateral cortex; however, CNIC is the principal way station for ascending auditory information in the IC.
Input and Output Connection 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
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...
(LL) 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 (MGBm), the posterior limitans (PL), suprapeduncular nucleus (SpN) and subparafascicular (Spf) intralaminar nuclei of the thalamus, the substantia nigra, pars compacta lateralis (SNL), the dorsolateral periaqueductal gray (dlPAG), the nucleus of the brachium of the inferior colliculus (BICN) and deep layers of the superior colliculus (SC).
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 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 LL project to IC, which means major ascending auditory pathway 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 reflex and vestibulo-ocular reflexVestibulo-ocular reflex
The vestibulo-ocular reflex is a reflex eye movement that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual field. For example, when the head moves to the right, the...
. 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
Interaural time difference
The interaural time difference when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the localisation of sounds, as it provides a cue to the direction or angle of the sound source from the head. If a signal arrives at the head from one...
sensitivity of single neurons in the inferior colliculus, and used these to predict behavioural performance. The predicted just noticeable difference was comparable to that achieved by humans in behavioral tests. This suggested that by the level of the inferior colliculus, integration of information over multiple neurons is unnecessary (see population code).