To track the origin of SSA, we analyzed responses of neurons in the external nucleus of the inferior colliculus (ICX; the source of auditory input to the OT) to similar sequences of sound bursts. 
The external nucleus of the inferior colliculus (ICx) receives ascending projections from both auditory and somatosensory nuclei.
The highest transcript and protein levels were found in the external nucleus of the inferior colliculus and paraolivary nucleus.
At birth, the CNTFRalpha immunolabeling was clearly present in somata of the external nucleus of the inferior colliculus but was diffuse throughout brainstem auditory nuclei.
We could discriminate eight structures that belong to the three subnuclei of the inferior colliculus [ the central nucleus (ICC), the superficial nucleus (ICS), the external nucleus (ICX)] and to the optic tectum.
We studied the development of the projection from the external nucleus of the inferior colliculus (ICX) to the optic tectum (OT) in the barn owl.
In barn owls, this process takes place in the external nucleus of the inferior colliculus (ICX).
When barn owls are raised wearing spectacles that horizontally displace the visual field, the auditory space map in the external nucleus of the inferior colliculus (ICX) shifts according to the optical displacement of the prisms.
In the midbrain sound localization pathway of the barn owl, a map of auditory space is synthesized in the external nucleus of the inferior colliculus (ICX) and transmitted to the optic tectum.
We believe this area to be the ventral extent of the external nucleus of the inferior colliculus (ICXv).
In the barn owl (Tyto alba), the external nucleus of the inferior colliculus (ICX) contains a map of auditory space that is calibrated by visual experience.
We analyzed the representation of ITD in normal and device-reared owls in two nuclei in the ascending pathway: the external nucleus of the inferior colliculus (ICX), the primary source of ascending auditory input to the tectum, and the lateral shell of the central nucleus of the inferior colliculus (ICCls), the primary source of input to the ICX.
The external nucleus of the inferior colliculus in the barn owl contains an auditory map of space that is based on the tuning of neurons for interaural differences in the timing of sound. It has been found that, in an external nucleus that is expressing a learned, abnormal map, the circuitry underlying the normal map still exists but is functionally inactivated by inhibition mediated by gamma-aminobutyric acid type A (GABAA) receptors.
The majority of retrogradely labelled neurons were found in the external nucleus of the inferior colliculus and here predominantly in layer 2. Injections focused onto the medial division of the medial geniculate body additionally labelled magnocellular neurons in layer 3 of the external nucleus and a few neurons in the central nucleus. More ventrally located injections, focused onto the posterior intralaminar and peripeduncular nucleus, almost exclusively labelled neurons in layer 1 of the external nucleus and the dorsal part of the dorsal nucleus.
The external nucleus of the inferior colliculus and medial division of the medial geniculate nucleus were associated more strongly with this pattern for group TL-, which was interpreted as representing the change of the associative value of the tone by the light, mediated through extraauditory influences on these two regions.
Input projections were observed contralaterally from: all three divisions of cochlear nucleus; intermediate and dorsal nuclei of the lateral lemniscus (LL); and the central nucleus, external nucleus and dorsal cortex of the IC. Input projections were observed ipsilaterally from: the medial and lateral superior olivary nuclei; the superior paraolivary nucleus; the dorsolateral and anterolateral periolivary nuclei; the dorsal and ventral divisions of the ventral nucleus of LL; the dorsal and intermediate nuclei of LL; the central nucleus, external nucleus and dorsal cortex of the IC outside the injection site; and small projections from central gray and the medial geniculate body.
After multiple injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the SC, the heaviest concentrations of labelled cells were found in the nucleus of the brachium (BIN) and external nucleus of the inferior colliculus, with much weaker labelling in the nucleus sagulum, dorsal, intermediate and ventral nuclei of the lateral lemniscus, paralemniscal regions, and periolivary nuclei.
Efferent projections were observed ipsilaterally in: medial and ventral divisions of the medial geniculate body (MGB); middle layers of the superior colliculus; central gray; and external nucleus (E), dorsal cortex (DC) and central nucleus of IC.
Brain sections from such rats showed dense labeling in both the dorsal cortex and external nucleus of the inferior colliculus.
The divisions of the inferior colliculus could be distinguished on the basis of GluR1-4 immunoreactivity, with high levels of GluR4 and moderate levels of GluR1 in the external nucleus.
The external nucleus of the inferior colliculus (ICx), an auditory center that projects massively to the tectum, is the main site of plasticity; however, it is unclear by what mechanisms the alignment between the auditory map in the ICx and the visual map in the tectum is established and maintained.
In auditory structures retrograde labeling was found mainly in the external nucleus of the inferior colliculus and in the nucleus of the brachium of the inferior colliculus.
In the guinea-pig two subcortical structures have been shown to contain representations of auditory space, the deep layers of the superior colliculus (SC) and the external nucleus of the inferior colliculus (ICX).
A topographic representation of the auditory azimuth has been described in the external nucleus of the inferior colliculus (ICX) of the guinea-pig [ 3].
Dynamic changes in ITD tuning similar to those recorded in the optic tectum also occurred in the external nucleus of the inferior colliculus (ICX), which provides the major source of ascending auditory input to the tectum.
In the cases with intercollicular lesions, HRP-labeled axons were observed to arise from neurons in both the external nucleus and dorsal cortex of the IC, but not the central nucleus, and they entered the deep layers of the superior colliculus. These results indicate that the projection from the central nucleus to the external nucleus of the IC is important for the propagation of seizure activity in GEPR-9s.
It is known that some neurons in the external nucleus of the inferior colliculus (ICX) receive both auditory and somatosensory input.
The external nucleus of the inferior colliculus was also found to contain significantly greater numbers of GAD67 cRNA labeled neurons whereas in the frontal cortex, a region of the brain that is not required for audiogenic seizure activity in GEPR-9s, there were no significant differences in hybridization between GEPR-9s and SD rats.
The map appears in its final form in the external nucleus of the inferior colliculus (ICx) and is projected from there to the optic tectum (OT).
Labeled cells were more common in the caudal half of the central nucleus, and in the external nucleus and dorsal cortex.
These areas include zona incerta, nucleus of the posterior commissure, anterior and posterior pretectal nuclei, nucleus of the optic tract, superior colliculus, cuneiform nucleus, subcuneiform area, substantia nigra pars reticulata and pars lateralis, periparabigeminal area, external nucleus of the inferior colliculus, the area ventral to the external nucleus of the inferior colliculus, mesencephalic reticular formation, dorsal and ventral nuclei of the lateral lemniscus, and the perihypoglossal nucleus.
The central nucleus of the inferior colliculus contains a larger number of fusiform and stellate GABAergic neurons and a dense plexus of immunoreactive terminals, whereas the external nucleus contains slightly fewer immunoreactive cells and terminals.
The representation of contralateral space in the lateral shell is ultimately conveyed to the external nucleus of the inferior colliculus where it contributes the horizontal axis to a two-dimensional map of space..
Injections of WGA-HRP into the superior colliculus gave terminal label in the cuneiform nucleus and also in surrounding structures which included central grey, the midbrain tegmentum bordering the parabigeminal nucleus, and the external nucleus of the inferior colliculus.
The positions of retrogradely labeled cells in the external nucleus of the inferior colliculus (ICX) were the same as those observed in control birds (Knudsen, E.
In animals with lesions, the lateral part of the deep grey layers of the superior colliculus, the intercollicular area and the rostromedial portion of the external nucleus of the inferior colliculus were destroyed. Injections made in the area of the lateral cervical nucleus and in the cuneate and gracile nuclei labelled fibres and "terminal-like" fields in the external nucleus of the inferior colliculus, the intercollicular area, the deep grey layers of the superior colliculus and in the mesencephalic lateral tegmentum. After injections in the posterior nucleus and ventroposterior complex of the thalamus, retrogradely labelled cells were found in the lateral tegmentum, the intercollicular area and the external nucleus of the inferior colliculus.
Stimulation sites within the dorsal mesencephalon effective in antidromically activating M and MD neurons were in the caudal ventrolateral superior colliculus, the intercollicular area, and external nucleus of the inferior colliculus. This input is probably responsible for providing some of the somatosensory input to the deeper layers of the superior colliculus, the external nucleus of the inferior colliculus, and the intercollicular area, regions known to have neurons responding to somatosensory stimuli..
A smaller number of labelled cells was observed in the ipsilateral external nucleus of the inferior colliculus and a few labelled cells were distributed in the dorsomedial part of the inferior colliculus ipsilaterally.
The external nucleus of the inferior colliculus (IX) receives the heaviest projection from both the gracile and cuneate nuclei.
Injections of HRP into the medial division (MGM) produced labeled cells scattered throughout the external nucleus of the inferior colliculus and the ventral part of ICC.
In the external nucleus labeled cells tended to be distributed in the middle to rostral regions, but they were few in number in the caudal part.
The major source of auditory input to the optic tectum is the ipsilateral external nucleus of the inferior colliculus (ICX), which is known to contain a map of auditory space also.
In hamster only two putatively auditory structures showed labeled cells, the external nucleus of inferior colliculus and nucleus of the brachium of the inferior colliculus, whereas in cat additional cells are reported in the dorsal cochlear nucleus, trapezoid and superior olivary nuclei, and nucleus of the lateral lemniscus.
After injections of horseradish peroxidase into the central tegmental field of the midbrain reticular formation and centrum medianum of the thalamus in the cat, labelled neurons were found in the nucleus of solitary tract, cuneate and gracile nuclei, spinal nuclei of trigeminal nerve, external nucleus and brachium nucleus of inferior colliculus, nuclei of the lemniscus lateralis in the area pretectalis, nucleus of the posterior commissure and stratum intermediale of the superior colliculus and in reticular structures of medulla and pons.
First, potential sources of auditory afferents were limited mainly to the external nucleus of the inferior colliculus, the nucleus sagulum, and the dorsomedial periolivary cell group.
Within IC, labeling is dense in the ventrolateral part of the central nucleus (CNv) and moderate in the external nucleus (EN).
Parallel single unit and retrograde tracing experiments were carried out in the anesthetized cat to elucidate the representation of the auditory and somatosensory systems in the external nucleus of the inferior colliculus (ICX).
Other projections replicated in several animals included the zona incerta and nearby sectors of the substantia nigra; three distinct mesencephalic arrangements within the deep layers of the superior colliculus, the external nucleus of the inferior colliculus, and the intercollicular nucleus; the anterior pretectal nucleus; dorsal sectors of the inferior olivary complex and the ipsilateral cerebellar cortex.
It is noteworthy that the external nucleus of IC (EN) projects to the superior colliculus, part of the pretectum, and the anterior extremity of MGB ipsilaterally, in addition to the ventral and medial divisions of MGB.
Other ipsilateral targets of the deep tectal layers are the cuneiform nucleus and the external nucleus of the inferior colliculus.
In addition to its classical connection with VPLm, nucleus cuneatus projected to the following contralateral brainstem or thalamic nuclei: medial and dorsal accessory olives, external nucleus of the inferior colliculus, ventrolateral part of the superior colliculus, nucleus ruber, medial geniculate nucleus pars magnocellularis, suprageniculatus, medial and lateral divisions of the posterior thalamic nuclear group, zona incerta, and Fields of Forel.
The intercollicular terminal zone covers the entirety of the external nucleus of the inferior colliculus and the intercollicular nucleus of Mehler, spilling over into adjacent parts of the central gray and deep layers of the superior colliculus. These materials showed that the dendritic spread of neurons in the external nucleus of the inferior colliculus and the intercollicular nucleus, taken together, covers the entirety of the intercollicular terminal zone.
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