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PubMed1981

Afferent sources of a lateral midbrain tegmental zone associated with the pinnae in the cat as mapped by retrograde transport of horseradish peroxidase.

A paralemniscal zone in the lateral midbrain tegmentum of the cat has been identified in a possible pathway from the superior colliculus to the facial nucleus that may control pinna movements (Henkel and Edward, '78). Other brainstem afferent projections to this paralemniscal zone have been mapped in the present study using the retrograde horseradish peroxidase tracing method and are discussed in three groups. 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. Labeled cells in other superior olivary regions and the dorsal cochlear nucleus were apparently related to uptake of horseradish peroxidase from the axons of the lateral lemniscus. Second, afferents from several premotor regions involved in aspects of gaze control were identified. These were mainly from the nucleus prepositus hypoglossi and adjacent pontine reticular formation, but also included projections from the medial vestibular an abducens nuclei and possibly subthalamic regions such as the zona incerta and fields of Forel. Third, a relatively large group of midbrain afferents was closely related to the origin of the collicular projection to the paralemniscal zone. This group consisted of labeled cells in the periaqueductal gray matter, nucleus cuneiformis, and pretectum. The relatively sparse labeling in auditory regions that projected to the paralemniscal zone seems to indicate that the sensorimotor integration necessary to guide pinna movements does not take place primarily in the lateral midbrain tegmentum. The interaction of gaze-related sources with the pinna-related pathway is also discussed.

Afferent Pathways↗
PubMed1982

Cytoarchitecture of auditory system in lower brainstem of the mustache bat, Pteronotus parnellii.

To begin an investigation of the auditory pathways in the brainstem of the mustache bat, we examined the cytoarchitecture of the cochlear nuclei, superior olivary complex, nuclei of the lateral lemniscus, and inferior colliculus. Although all of these auditory centers are hypertrophied in this echolocating bat, only some areas have unusual cytoarchitectural features: 1) In the anterior part of the anteroventral cochlear nucleus we do not find the large spherical cells seen in other mammals; instead, very small spherical cells are found in this area. 2) In the posterior part of the anteroventral cochlear nucleus there is a region containing a homogeneous population of very large multipolar cells. 3) The medial superior olive is unusually large for an animal with a small head. 4) The most striking observations are seen in the lateral lemniscus. The ventral nucleus of the lateral lemniscus has a distinct columnar organization. The intermediate area of the lateral lemniscus contains a large and very distinct nucleus. Each of these cytoarchitectural features distinguishes the auditory system of this bat from that of other mammals. The results raise questions about whether or not there are unique subdivisions in the auditory pathways of echolocating bats. The results also identify these unusual nuclei as candidates to play a role in the special auditory functions related to echolocation.

Animals↗
PubMed1982

Origin of ascending projections to inferior colliculus in the mustache bat, Pteronotus parnellii.

The origins of pathways to the inferior colliculus of the mustache bat were identified by retrograde transport of horseradish peroxidase (HRP). A specific goal of this study was to obtain evidence that would help determine whether the nuclei, shown in the previous paper to have unusual cytoarchitectural features, are unique to bats, or whether they are homologous to areas that are not well differentiated in other mammals. The auditory pathways in the lower brain stem of Pteronotus appear to conform to the same basic organization as in other mammals: After injection of HRP into one inferior colliculus, labeled cells are located contralaterally in the cochlear nucleus, ipsilaterally in the medical superior olive, bilaterally in the lateral superior olive, ipsilaterally in the ventral and intermediate nuclei of the lateral lemniscus, and bilaterally in the dorsal nucleus of the lateral lemniscus. These patterns of labeling provide a basis for understanding how the specialized auditory areas of the bat may be organized within a basic plan of mammalian auditory systems. In the anteroventral cochlear nucleus the unusually small spherical cells seem to be homologous to stellate cells in the anteroventral cochlear nucleus of the cat. In the superior olive, differences in patterns of labeled cells distinguish the medial from the lateral superior olive. In the lateral lemniscus the pattern of labeled cells shows clear differences between the two special parts, intermediate and ventral nuclei, as well as between these and the dorsal nucleus of the lateral lemniscus. The results are consistent with the hypothesis that the unusual auditory nuclei of the bat have homologues in mammals whose auditory systems are not specialized for echolocation.

Animals↗
PubMed1982

Tonotopic organization in the central auditory pathway of the Mongolian gerbil: a 2-deoxyglucose study.

The uptake of 2-deoxyglucose (2-DG) was employed to map functional activation of the central auditory pathway in the mongolian gerbil, during 85 dB SPL stimulation with pure tonal stimuli at frequencies of 0.75, 3.0, or 12.0 kHz. Pure tones produced foci of very high 2-DG uptake, when compared to adjacent tissue, in the cochlear nucleus, superior olivary complex, and inferior colliculus. Less distinct areas of elevated 2-DG uptake were seen in the dorsal and ventral nuclei of the lateral lemniscus, medial geniculate nucleus, and auditory cortex. Little or no change in the distribution of 2-DG uptake was noted in the nucleus of the trapezoid body. The location of discrete regions of relatively high 2-DG uptake varied systematically with stimulus frequency. The tonotopic organization demonstrated by 2-DG mapping agreed well with the results of previous electrophysiological studies for most structures. However, in the inferior colliculus, stimulus-evoked increases in 2-DG uptake were found to occur in a fixed pattern of three to four bands across the central nucleus, which did not correspond to any previously reported anatomical or physiological organization. Pure tonal stimuli activated discrete portions of this banding pattern. Also, a small area at the ventromedial edge of the colliculus was more broadly tuned than other regions of the nucleus. It is concluded that 2-DG uptake is well suited to the investigation of tonotopic organization. This technique reveals patterns of activation which have not been observed with other methodologies.

Animals↗
PubMed1982

A Golgi study of the medial geniculate body in the tree shrew (Tupaia glis).

The subdivisions of the medial geniculate body in Tupaia recognized in previous connectional and cytoarchitectural studies are identified in Golgi-impregnated material. They may be distinguished by the organization of the neuropil, especially the dendrites, and, in many cases, by differences in the neurons. The ventral nucleus contains tufted cells with disc-shaped dendritic fields which are aligned to form laminae. The caudomarginal and deep dorsal nuclei have less tufted, less precisely arranged cells with longer, thin appendages. Neurons in the suprageniculate and dorsal nuclei are similar except that they apparently are arranged more randomly and tend to have more spherically shaped dendritic fields. The medial division is characterized rostrally by the presence of stellate cells and caudally by large cells which appear to be the neurons, observed in previous studies to have widespread connections. The results of this Golgi study suggest that the subdivisions of the medial geniculate body might be grouped differently than in previous reports. When combined with data from previous studies of connections, the results show that the medial geniculate body of even distantly related species may follow a common plan. The ventral nucleus is the medial geniculate component of the central pathway which extends from the central nucleus of the inferior colliculus to the primary auditory cortex. Most of the other medial geniculate subdivisions participate in either pericentral pathways originating in the cortex and other nuclei which surround the central nucleus of the inferior colliculus or in the pathways of the lateral midbrain tegmentum. Pericentral and lateral tegmental pathways terminate in non-primary auditory cortex. The widespread pathway involves only the caudal nucleus of the medial division. It receives afferents from most, if not all, of the midbrain regions that give rise to the other pathways and distributes to all parts of the auditory cortex where it terminated in layers other than layer III-IV.

Animals↗
PubMed1982

The ascending input to the midbrain periaqueductal gray of the primate.

To obtain a comprehensive map of the brainstem and spinal cord areas that project to the mesencephalic central gray small injections of horseradish peroxidase were made into various regions of the periaqueductal gray in a series of monkeys. Despite the fact that different regions of the central gray were injected in separate animals, the majority of the brainstem areas containing retrogradely filled neurons remained the same. Labeled neurons were observed in the superior colliculus, periaqueductal gray, lateral parabrachial, locus coeruleus, nucleus raphe magnus and pallidus, and a variety of brainstem reticular nuclei. In contrast to labeled brainstem areas, where labeled neurons were present predominantly ipsilateral to the injection site, the spinal trigeminal nucleus pars caudalis and the spinal cord displayed labeled cells chiefly on the side contralateral to the injection. Also in contrast to the labeled brainstem sites, where medial and lateral injection sites produced a similar pattern of labeling, medial injections in the PAG labeled almost exclusively neurons in the deep laminae (V-X) in the spinal trigeminal nucleus pars caudalis and spinal cord while more lateral injections labeled neurons in both the deep (V-X) and superficial (I) laminae. No consistent differences were noted in the location of labeled neurons in either brainstem or spinal sites after dorsal vs. ventral injections or caudal vs. rostral injection sites. The present study has demonstrated that the central gray receives afferent projections from a number of brainstem and spinal areas which are known to be involved in the modulation and/or conduction of nociception, while other inputs are probably involved in the regulation of visceral functions. These data support the hypothesis that the mesencephalic periaqueductal gray functions as a visceral, nociceptive, and cognitive integrator.

Afferent Pathways↗
PubMed1983

Ascending auditory projections to the inferior colliculus in the adult gerbil, Meriones unguiculatus.

Ascending auditory projections to the inferior colliculus (IC) of the adult gerbil were studied using the retrograde transport of horseradish peroxidase. Our results indicate that in gerbils, the IC receives afferent projections from most brainstem auditory nuclei. A strong contralateral projection originates in the cochlear nuclear complex (CN). A smaller but consistent projection from all three divisions of ipsilateral CN is also present. The medial superior olive (MSO), superior parolivary nucleus, and ventral nucleus of the lateral lemniscus all maintain ipsilateral projections to the IC. Bilateral projections arise from the lateral superior olive, lateral nucleus of the trapezoid body, and dorsal nucleus of the lateral lemniscus. Previous investigations in other mammalian species provide conflicting data concerning the magnitude of a direct ipsilateral projection from CN to the IC. Our quantitative data indicate that the ipsilateral projection from CN in the gerbil is nearly one third as large as the projection from ipsilateral MSO. The projection from contralateral CN is six times larger than the MSO projection. The distribution of labeled cells across the rostrocaudal extent of MSO and the three divisions of the cochlear nuclear complex are presented.

Animals↗
PubMed1983

Cytology of periolivary cells and the organization of their projections in the cat.

Projections of cells located near principal nuclei of the superior olive, periolivary cells, were studied by injecting horseradish peroxidase or fluorescent tracers into the cochlea, cochlear nucleus, and inferior colliculus. At least two distinct cytological classes of periolivary cells were found to project to each of these structures. "Large" and "small" olivocochlear cells were labelled. Their cytology and locations were found to be as had been previously described. Some olivocochlear cells also project to the cochlear nucleus. Other major periolivary cell classes that project to the cochlear nucleus include a lateral group of multipolar cells whose members are located around the ipsilateral lateral superior olive and have coarse, darkly staining Nissl substance. The other major periolivary cell class that projects to the cochlear nucleus is the small cell of the ventral nucleus of the trapezoid body. This cell is characterized by its size and by only one or two intensely staining clumps of Nissl substance. Projections of these cells to the cochlear nucleus is from both sides. Periolivary cells that project to the inferior colliculus include medial and lateral groups. Cells of the lateral group project from both sides. These cells are multipolar in shape and contain lightly staining, flocculent Nissl substance. They are predominantly located immediately ventral to the lateral superior olive. Projections from the medial group are predominantly ipsilateral and arise from the region medial to the medial superior olive. The cells are multipolar and contain clumped Nissl substance. They often lie near "large" olivocochlear cells, which they resemble in Nissl material, but are distinguished from the latter in Protargol material by having ring-type axosomatic endings. The appearance and locations of these six classes of periolivary cells make it possible to recognize them in nonexperimental material and to infer with confidence what their projections are. These results show considerable organization of these previously little understood structures.

Animals↗
PubMed1983

Neocortical projections of the suprageniculate and posterior thalamic nuclei in the marsupial brush-tailed possum, Trichosurus vulpecula (Phalangeridae), with a comparative commentary on the organization of the posterior thalamus in marsupial and placental mammals.

Axonal transport methods were used to determine the extent and organisation of neocortical projections from the suprageniculate (SG) and posterior (PO) thalamic nuclei in the brush-tailed possum. Our findings show that SG projects extensively to the auditory cortex, overlapping the cortical projection field of the medial geniculate nucleus, and to the immediately neighbouring association cortex. Though the input relationships of SG appear similar to those reported for other mammals, placental and marsupial, a strong SG projection to auditory cortex has not been reported previously. Neocortical relationships of PO are characterised by an orderly point-to-point projection to all but the most rostral parts of the motor-somaesthetic cortex. There is also a substantial projection to the entire posterior parietal association cortex. The PO-neocortex projection is reciprocally organised. The PO-neocortical projection in the possum is similar to that reported in the Virginia opossum, rat, and several other mammals. There is a major difference in organisation in comparison with certain monkeys where the PO projection is much more restricted and does not involve the motor and somaesthetic cortex. We conclude that PO is similarly organised in many, though not all, mammals, including the marsupials, rodents, insectivores, and prosimian primates. The possum SG, on the other hand, is clearly distinct from other mammals in its extensive projection to auditory cortex, though we cannot say at present whether this a general property of marsupial mammals or a peculiarity restricted to this species and possibly its close relatives.

Animals↗
PubMed1983

Subdivisions of the inferior colliculus in the barn owl (Tyto alba).

The inferior colliculus in the barn owl contains three subdivisions: the central (ICC), external (ICX), and superficial (ICS) nuclei. The nuclei are distinguished on the basis of their cyto- and myeloarchitecture, connectivity, and physiological properties. The ICC may be further divided into dorsal (ICCd) and ventral (ICCv) parts. Auditory fibers ascending in the lateral lemniscus enter the ICCd and ICCv, but not the ICX or ICS. The ICX receives its auditory input from the ICC. The ICC and ICX in owls are similar in position, anatomy, connectivity, and physiology to the ICC and ICX in mammals, suggesting that these structures are homologous. Units in the ICC are organized tonotopically, whereas units in the ICX are organized according to the locations of their spatial receptive fields. This implies that a transformation from a tonotopic to a spatiotopic organization takes place in the ICX of the owl.

Animals↗
PubMed1983

Space-mapped auditory projections from the inferior colliculus to the optic tectum in the barn owl (Tyto alba).

The optic tectum of the owl contains a topographic representation of auditory space. We have investigated the source of this space-mapped auditory activity by using retrograde tracing with horseradish peroxidase. 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. Additional minor projections originate in the superficial nucleus of the inferior colliculus and the nucleus isthmi parvocellularis. There is no apparent projection to the optic tectum from the contralateral ICX or any other brainstem auditory nucleus. The projection from the ICX to the optic tectum is point-to-point: rostral ICX projects to rostral tectum, caudal ICX to caudal tectum, dorsal ICX to dorsomedial tectum, and ventral ICX to ventral tectum. Thus, the space-mapped organization that exists in the ICX is passed on by topographic projections to the optic tectum.

Animals↗
PubMed1983

The inferior colliculopontine neurons of the cat in relation to other collicular descending neurons.

Cells of origin of the pontine afferents from the inferior colliculus (IC) of cats have been identified by means of retrograde axonal transport of horseradish peroxidase (HRP). Following injections of HRP in the pontine nuclei, many labeled neurons were found ipsilaterally in the caudal parts of the external and pericentral nuclei, while a few cells were found in the central nucleus. Additional neurons occurred in the nuclei of the middle and rostral parts. This organization contrasts with that of other collicular descending systems. Thus, neurons projecting to the superior olivary complex and cochlear nuclei were found predominantly in the central nucleus bilaterally. 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. Since the locations of IC-pontine neurons are found to be different from those of other IC descending neurons, it may be assumed that the IC-pontine system does not share common functional properties with the other collicular descending neurons. Functional aspects of the IC-pontine neurons are discussed, with a comment on a pathway for the transmission of auditory impulses to the midvermal area of the cerebellum.

Afferent Pathways↗
PubMed1983

Organization of the efferent projections of the medial superior olivary nucleus in the cat as revealed by HRP and autoradiographic tracing methods.

Features of the organization of the efferent axonal projections from the medial superior olivary nucleus (MSO) in the cat were studied. In order to determine the origin and distribution of projections from MSO, the retrograde horseradish peroxidase (HRP) and autoradiographic tracing methods were used. The results showed that (1) in both HRP and autoradiographic studies the projection to the inferior colliculus was largely ipsilateral, although a contralateral component was present; (2) the projection field of MSO was confined to the ventral division of the central nucleus of the inferior colliculus, and within this field the labeling was heavier in the rostral and dorsolateral parts of the ventral division; (3) the projection to the inferior colliculus was topographic with ventral parts of MSO projecting ventrally and dorsal parts of MSO projecting dorsolaterally; (4) the projection field in the central nucleus formed successive laminae oriented from ventrolateral to dorsomedial; (5) the axonal course was via the medial or internal segment of the lateral lemniscus; and (6) some fibers in this course ended additionally within the dorsal nucleus of the lateral lemniscus. This latter projection was also topographically organized. These observations supported previously described features of lamination and tonotopic order for afferents of the inferior colliculus, as well as recent suggestions that functional segregation of afferent connections exists within the laminated portion of the central nucleus of the inferior colliculus.

Animals↗
PubMed1984

The neuronal architecture of the inferior colliculus in the cat: defining the functional anatomy of the auditory midbrain.

This study defines anatomical subdivisions in Golgi-impregnated material from the inferior colliculus of the cat. The findings demonstrate that the inferior colliculus consists of a mosaic of morphologically distinct parts of neuropil. Each part is also characterized by a unique set of neuronal types. Each part of the inferior colliculus can be defined as tectal or tegmental on the basis of the fundamental pattern of dendritic branching. The main subdivisions of the auditory tectum are the central nucleus, the cortex, and the paracentral nuclei. The central nucleus is distinguished by its laminated neuropil composed of neurons with disc-shaped dendritic fields oriented in parallel arrays with the lemniscal axons. In contrast, the cortex is identified by its broad layers of loosely woven neuropil, which are orthogonal to those in the central nucleus and lack neurons with disc-shaped dendritic fields. The paracentral nuclei, so called because of their scattered arrangement around the central nucleus, are the commissural, dorsomedial, rostral pole, lateral, and ventrolateral nuclei. The main subdivisions of the auditory tegmentum are the pericollicular areas, the nucleus of the brachium of the inferior colliculus, and the sagulum. The pericollicular areas are intercollicular or subcollicular and separate the tectal division from the superior colliculus, central gray, and remaining portions of the tegmentum. The afferent projections to each tectal and tegmental subdivision, as observed in silver-degeneration experiments, distinguish the parcellations based on the Golgi findings. Subdivisions containing tectal cell types receive afferents predominantly from the auditory pathways, in contrast to subdivisions with tegmental cell types, which receive inputs from a wide variety of sources. This suggests a correlation between neuronal types and the nature of their inputs. This analysis of the subdivisions of the inferior colliculus differs from previous studies, especially those relying on Nissl stains. It is likely that subdivisions distinguished by the pattern of the neuropil differ functionally, since the structural components identified in the Golgi-impregnated material are essential parts of the synaptic organization of the auditory midbrain. Future physiological studies should benefit from approaches in which the cell types serve as the focus for the analysis.

Animals↗
PubMed1984

The central nucleus of the inferior colliculus in the cat.

The central nucleus of the inferior colliculus in the cat is distinguished by its unique neuropil. In Golgi-impregnated material, it is composed primarily of neurons with disc-shaped dendritic fields arranged into parallel arrays, or laminae, complemented by the laminar afferent axons from the lateral lemniscus. Large, medium-large, medium, and small varieties of disc-shaped cells are distinguished on the basis of the size of the dendritic field and cell body size, dendritic diameter, and dendritic appendages. A second major class of neurons in the central nucleus are the stellate cells with dichotomously branched, spherical-shaped dendritic trees. Simple, complex, and small stellate cells can be distinguished by their size and by the complexity of the dendritic and axonal branching. Laminar afferent axons are recognized by the nests of collateral side branches and the grapelike clusters of terminal boutons--thick, thin, and intermediate-sized varieties are apparent. Other axon types include local collaterals of central nucleus neurons, some of which are distinguished by their frequent and complex collaterals. In the central nucleus, the configuration of the fibrodendritic laminae, the presence of subdivisions, and the banding of afferent axons suggest levels of organization which are superimposed on the synaptic arrangements of the individual cell and axon types. The laminar pattern, as studied in serial Golgi-impregnated sections, differs from previous reports. The central nucleus contains subdivisions which can be distinguished by their laminar pattern, different proportions of cell types, and the packing density of the cell bodies and axonal plexus. The patterns of degeneration observed in Nauta-stained material after lesions of caudal auditory pathways show that thick and fine afferent fibers form dense bands of degeneration separated by sparse, fine-fiber degeneration. The bands are thicker than individual laminae but smaller than the subdivisions. The intrinsic organization of the neurons and axons, combined with the laminar organization, subdivisions, and banding patterns, each may contribute different aspects to the processing of auditory information in the central nucleus.

Animals↗
PubMed1984

Isofrequency labelling revealed by a combined [14C]-2-deoxyglucose, electrophysiological, and horseradish peroxidase study of the inferior colliculus of the cat.

Tonotopic sequences of single units were recorded in the central nucleus (ICC) of the inferior colliculus of cats. The sites of units with a particular characteristic frequency (CF) were marked histologically. After injection with [14C]-2-deoxyglucose (2-DG), each animal was stimulated with tone bursts, which corresponded to the CFs of the selected units. The position of a selected unit was found to correspond with the position of a band of discrete 2-DG labelling. In some animals, multiple penetrations revealed that more than one unit with the same CF was located on the same band, indicating that the 2-DG bands represent isofrequency contours. Single units were recorded in the pars lateralis (LV) of the medial geniculate body of cats and areas of consistent CF were found, which contained the same frequencies as some of those employed with 2-DG. Horseradish peroxidase (HRP) was ejected into these selected areas and labelled cells were identified in ICC after retrograde transport. The labelled cells were found to lie in a band which had a similar orientation to the 2-DG bands produced by the same frequencies. Both sets of data indicate that ICC is organized into three-dimensional isofrequency sheets, the orientation of which do not match the concentric model of frequency organization inferred from some Golgi studies. The isofrequency sheets slope from medial to lateral throughout ICC with high-frequency contours found more medially and caudally and low-frequency contours more laterally and rostrally. The organization of the isofrequency contours is largely in agreement with a recent Golgi model of the laminations in ICC put forward by Oliver and Morest ('84). The 2-DG contours do not agree with the orientation of laminae in the lateral part of ICC as described by this model. The 2-DG contours also extend further into the dorsal cortex than previous degeneration evidence would suggest. The functional isofrequency contours are often quite narrow and could represent two or three overlapping cellular laminae. The results show clearly that there is only one tonotopic organization extending throughout ICC and the dorsal cortex.

Animals↗
PubMed1984

Topographical organization of the inferior collicular projection and other connections of the ventral nucleus of the lateral lemniscus in the cat.

The topographic distribution of projections from the ventral nucleus of the lateral lemniscus (VNLL) in the cat was investigated with the autoradiographic tracing method. The origin of minor projections was verified by retrograde tracing methods. Small injections of tritiated leucine were placed in restricted zones of VNLL. A major afferent fiber system to the inferior colliculus was labeled in all cases. From the injection site labeled fibers coursed through and around the nuclei of the lateral lemniscus to enter the ipsilateral inferior colliculus. Regardless of the position or small size of the injection, labeled fibers distributed widely in the inferior colliculus. Fibers ended in the central nucleus and deeper layers of the dorsal cortex in most cases. There was also labeling in the ventrolateral nucleus, but very few fibers ended as lateral as the lateral nucleus. A small number of labeled fibers passed from the inferior colliculus into the nucleus of the brachium of the inferior colliculus and adjacent tegmental areas. Some labeled fibers entered the commissure of the inferior colliculus where they were traced into the dorsal cortex and rostral pole of the inferior colliculus on the side contralateral to the injection site. Though the projections labeled in individual cases were similar in their divergent pattern within the central nucleus of the inferior colliculus, specific variations in the pattern were found. The dorsal zone of VNLL projected more heavily to the deeper layers of the dorsal cortex and an adjacent field in the central nucleus than the other zones. Dorsal injections in the middle zone of VNLL, on the other hand, labeled the medial part of the central nucleus more heavily, whereas ventral injections in the middle zone resulted in heavier lateral labeling. The ventral zone of VNLL projected heavily to a central field in the central nucleus. In addition to this major afferent system of VNLL to the inferior colliculus, a smaller descending projection was found. The descending projection ended mainly in the dorsomedial periolivary region and ventral nucleus of the trapezoid body. However, in some cases a few fibers were traced to the cochlear nuclei. Finally, we observed projections to the medial geniculate body from the dorsal and ventral zones of VNLL that ended diffusely in the medial division of the medial geniculate body. Possibly some fibers from the dorsal zone contribute to a broader projection of the lateral tegmentum to the dorsal division of the medial geniculate body.

Animals↗
PubMed1984

Hearing loss in dogs after lesions of the brachium of the inferior colliculus and medial geniculate.

Seven dogs were tested for their sensitivity to pure tones following lesions of the brachium of the inferior colliculus and medial geniculate body. Bilateral section of the brachium of the inferior colliculus consistently resulted in an average hearing loss of as much as 37 dB in the midrange of the animals' audiograms. Lesions of the medial geniculate appear to produce a similar hearing loss if the ventral division of the medial geniculate is completely destroyed.

Animals↗