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PubMed1990

Visual projections induced into the auditory pathway of ferrets. I. Novel inputs to primary auditory cortex (AI) from the LP/pulvinar complex and the topography of the MGN-AI projection.

The organization of cortical circuitry responsible for processing sensory information is a subject of intense examination. However, it is not known whether cortical cells in different sensory cortices process information in a way that is specific to the modality of their input, or whether there are commonalities in processing circuitry across different cortices. In our laboratory, this question has been investigated at the level of the geniculocortical pathway by routing information of one sensory modality into the processing circuitry of another modality. Appropriate early lesions cause growth of retinal axons into the auditory thalamus (MGN) (Sur et al., Science 242:1437, '88). Previously, we have established that the MGN carries the resulting visual information on to primary auditory cortex (AI), which thus contains visually responsive neurons and a topographic representation of the retina (Roe et al., Soc. Neurosci. Abstr. 14:460, '88; Sur et al., Science 242:1437, '88). In this paper, we describe anomalous projections from the dorsal part of the thalamus, specifically the lateral posterior/pulvinar complex, into AI. This result demonstrates that thalamic neurons belonging to one modality can be induced to project to cortex that is normally of a different modality. In addition, we have studied in detail the nature of the MGN to AI projection in these animals as compared to the normal projection. The MGN to AI projection appears to be unaltered by the lesions; the location and topography of labelled cells are similar to that in normal animals. Because the MGN to AI projection is still highly divergent along the "isofrequency" dimension when compared to the tonotopic dimension, our data suggest that visual topography in the cortical map is created within the auditory cortex, perhaps by activity-dependent sharpening of the retinal representation during development.

Animals↗
PubMed1991

Calcitonin-gene related peptide is an evolutionarily conserved marker within the amniote thalamo-telencephalic auditory pathway.

The distribution of neurons and fibers containing calcitonin-gene-related peptide (CGRP) was mapped in the thalamo-telencephalic auditory pathways of four amniote species, rats, pigeons (Columba livia), caiman (Caiman crocodilus), and turtles (Pseudemys scripta). In colchicine-treated turtles and pigeons, numerous CGRP+ perikarya were observed in the auditory relay nucleus of the thalamus (n. reuniens of reptiles, and n. ovoidalis of birds). In pigeons, these neurons were most abundant in the outer circumference of the nucleus and were not observed without colchicine pretreatment. In the telencephalon of turtles, caiman, and pigeons, CGRP+ fibers were observed within portions of the dorsal ventricular ridge previously shown to receive projections from the auditory thalamus, thus implying that the thalamic CGRP+ neurons observed here in fact project to these telencephalic areas. In colchicine treated rats, numerous CGRP+ perikarya were observed along the ventral margin of the medial geniculate nucleus extending into the posterior intralaminar and peripeduncular nuclei, as well as occasionally within the ventral subdivision of the medial geniculate nucleus. Injections of fluorogold into the auditory cortex combined with immunofluorescence labeling for CGRP revealed that CGRP+ cells in these areas do, in fact, project to the auditory cortices. The present results are interpreted as providing strong support for the theory, advanced previously, that the medial geniculate nucleus of mammals, nucleus ovoidalis of birds, and nucleus reuniens of reptiles contain at least some homologous cell populations. Although the data are consistent with the theory that the telencephalic projection fields are homologous, other interpretations are also consistent with the data presented here. These include the possibility that auditory thalamic projections to the telencephalon arose independently in the lines of evolution leading to mammals and sauropsids.

Alligators and Crocodiles↗
PubMed2004

Acceleration of visually cued conditioned fear through the auditory pathway.

Defensive responses elicited by sensory experiences are critical for survival. Mice acquire a conditioned fear response rapidly to an auditory cue but slowly to a visual cue, a difference in learned behavior that is likely to be mediated by direct projections to the lateral amygdala from the auditory thalamus but mainly indirect ones from the visual thalamus. Here, we show that acquisition of visually cued conditioned fear is accelerated in 'rewired' mice that have retinal projections routed to the auditory thalamus. Visual stimuli induce expression of the immediate early gene Fos (also known as c-fos) in the auditory thalamus and the lateral amygdala in rewired mice, similar to the way auditory stimuli do in control mice. Thus, the rewired auditory pathway conveys visual information and mediates rapid activity-dependent plasticity in central structures that influence learned behavior.

Amygdala↗
PubMed1994

Functional anatomy of forebrain auditory pathways in the budgerigar (Melopsittacus undulatus).

Interconnections of forebrain auditory and vocal control nuclei were mapped in the budgerigar using pathway tracing techniques. The anatomical results indicate four circuits by which auditory information may influence the vocal motor system: (1) direct auditory thalamic projections from nucleus dorsomedialis posterior (DMP) to both the neostriatal higher vocal center (HVC) and robust archistriatal nucleus (RA); (2) direct projections from a neostriatal projection field of DMP (i.e., MAN, the magnocellular nucleus of the neostriatum) to HVC and RA; (3) projections from DMP and other 'accessory' auditory thalamic nuclei to the ventral paleostriatum (VP), which in turn projects to MAN and RA; (4) projections to HVC from the lateral hyperstriatum ventrale (HV), which receives input from nucleus basalis (Bas) as well as from the oval nucleus of the HV (HVo), which receives direct input from RA. Lesion methods were used to evaluate the roles of auditory pathways in call learning and production. The results show that pathways associated with Bas are essential for call production in both adult and unfledged budgerigars, while VP efferents influence vocalization only in young, unfledged budgerigars. Lesions centered in either the primary auditory neostriatum (Field L2a) or the neostriatal area in receipt of Field L input (the ventrolateral neostriatum intermedium or NIVL) did not affect vocalization in juvenile or adult budgerigars.

Animals↗
PubMed1994

[Effect of aminoglycoside on ascending auditory pathway evaluated by evoked potentials].

Permanent ototoxic injuries frequently occur after long term administration of aminoglycosides (AGs). An attempt was made to evaluate the effects of AGs on both peripheral and central auditory systems in rats by brainstem auditory evoked potentials (BAEPs). A total of 43 Wistar rats were divided into 4 groups, and 4 kinds of AGs (gentamicin, tobramycin, amikacin and streptomycin) were applied respectively to rats in each group with IM injection daily for 9 weeks. BAEPs were recorded pre- and post-injection weekly. Rats with gentamicin administration had no apparent changes in peak latencies until 7 weeks when prolongations occurred. Tobramycin administration in rats caused peak latencies to prolong progressively. Prolongations of peak latencies initially followed by no more evident changes were present in rats with amikacin or streptomycin. However, few consistent changes in interpeak latencies were shown in all rats. These results indicate that ototoxicity occurs at the peripheral auditory system, and the involvement of central auditory pathway was uncertain.

Aminoglycosides↗
PubMed1997

Protein kinase C in central auditory pathways of the rat.

Protein kinase C is an important intracellular signaling molecule. Many of its ten isoforms are highly expressed in brain, and protein kinase C has been implicated in the regulation of the activity of receptors of several major neurotransmitters, including glutamate, acetylcholine, glycine, and gamma-aminobutyric acid. These neurotransmitters and their receptors are present in central auditory pathways, suggesting their role in auditory signal processing. Although they may be important modulators of the function of these neurotransmitter receptors, the distribution of protein kinase C isoforms in central auditory systems has not been well characterized. By using immunocytochemistry with specific antibodies, we studied the distribution of immunoreactivity of four isoforms of protein kinase C, betaI, betaII, gamma, and gamma, in central auditory systems of rat brain. Each of these protein kinase C isoforms was found to have a unique distribution in the auditory brainstem and cortex, supporting a role for these isoforms of protein kinase C in different aspects of auditory sensory processing.

Animals↗
PubMed1999

c-Fos expression in the auditory pathways related to the significance of acoustic signals in rats performing a sensory-motor task.

Neuronal activity was established in the auditory pathways in relation to behavioural response and cognitive information processing during a sensory-motor acoustic learning. Rats were trained in three consecutive phases. The first phase was an association between an auditory stimulus and a food reward; the second phase a simple discrimination between two sounds of different frequency components, and the third phase a more complex discrimination involving both spectral and spatial sound dimensions. Auditory stimuli were bursts of complex sounds lasting 500 ms. Neuronal activity related to the behaviourally relevant stimuli was established in 20 "learning" rats undergoing this protocol, which were progressively sacrificed at the beginning, middle and end of each phase. For comparison, activity was also established in four "control" rats exposed to the same stimuli delivered pseudo-randomly, thus carrying no behavioural meaning. Neuronal activity was assessed immunocytochemically using the functional marker Fos. To establish a baseline, two rats were unexposed to controlled acoustic stimulation ("unstimulated" rats). In the superior olivary complex (SOC), inferior colliculus (IC) and medial geniculate body (MGB), the number of Fos-like immunopositive cells was comparable in "learning" and "control" animals, but higher than in the "unstimulated" rats. In the auditory cortex (AC), most prominently in the secondary area Te2, the number of Fos-like positive cells differed between "learning" and "control" rats, suggesting that the auditory cortical areas may be involved in the encoding of the behavioural significance of the acoustic stimuli.

Acoustic Stimulation↗
PubMed2002

Effects of Occupational Exposure to Mercury or Chlorinated Hydrocarbons on the Auditory Pathway.

The purpose of this study was to examine the effects of industrial exposure to mercury and chlorinated hydrocarbons (CH) on the auditory pathway. To this effect, auditory brainstem responses (ABR) were recorded from 40 workers exposed to mercury, 37 workers exposed to CH and from a control group of 36 subjects that were never exposed to neurotoxic substances. The interpeak latency (IPL) of waves I-III, III-V and I-V were measured. The mean duration of exposure to mercury and CH was 15.5 (+6.4) and 15.8 (+7.2) years respectively. The air sample monitoring of mercury was 0.008 mg/m(3) (0.32 of the Threshold Limit Value - TLV(R) as published by ACGIH 2000). The mean average air sample monitoring was found to be 98 ppm for TCE, 12.7 ppm for PCE and 14.4 ppm for TCA which is respectively between 0.28 - 0.51 of the TLV(R) of CH. The mean blood mercury (B-Hg) levels were found to be 0.5mgr% (+0.3mgr%), which is 0.13 of the upper range of the permitted biologic exposure index (BEI) published by the ACGIH 2000. The mean urine samples levels of trichloroacetic acid were between 0.11-0.2 of the permitted BEI for the CH workers. The percent of workers exposed to mercury and CH workers with abnormal prolongation of IPL I-III was higher than the control group (42.5% and 33.8% vs. 18.0% respectively p<0.02). These results are consistent with other studies and show that ABR may provide a sensitive tool for detecting subclinical central neurotoxicity caused by CH and mercury

Journal Article↗
PubMed1990

Demonstration of prosthetic activation of central auditory pathways using [14C]-2-deoxyglucose.

The cochlear prosthesis is not applicable to patients who lack an implantable cochlea or an intact vestibulocochlear nerve. Direct electrical stimulation of the cochlear nucleus (CN) of the brain stem might provide a method for auditory rehabilitation of these patients. A penetrating CN electrode has been developed and tissue tolerance to this device demonstrated. This study was undertaken to evaluate metabolic activation of central nervous system (CNS) auditory tracts produced by such implants. Regional cerebral glucose use resulting from CN stimulation was estimated in a series of chronically implanted guinea pigs with the use of [14C]-2-deoxyglucose (2-DG). Enhanced 2-DG uptake was observed in structures of the auditory tract. The activation of central auditory structures achieved with CN stimulation was similar to that produced by acoustic stimulation and by electrical stimulation of the modiolar portion of the auditory nerve in control groups. An interesting banding pattern was observed in the inferior colliculus following CN stimulation, as previously described with acoustic stimulation. This study demonstrates that functional metabolic activation of central auditory pathways can be achieved with a penetrating CNS auditory prosthesis.

Animals↗
PubMed2002

Immunolocalization of PICK1 in the ascending auditory pathways of the adult rat.

Protein that interacts with C-kinase alpha (PICK1) is a PDZ domain protein that interacts with many binding partners in the central nervous system (CNS), including activated protein kinase Calpha and subunits of the AMPA subtype of glutamate receptor. Almost nothing is known about the anatomic distribution of PICK1 in the intact adult CNS. By using PICK1 antisera and peroxidase immunocytochemistry, we report on the distribution of PICK1 in the ascending pathways of the central auditory system of the adult rat. PICK1-immunoreactivity (ir) was observed in many component nuclei of the central auditory system, including the dorsal cochlear nucleus, anteroventral cochlear nucleus, posteroventral cochlear nucleus, some divisions of the superior olivary complex, inferior colliculus, medial geniculate body, and primary auditory cortex. The general staining pattern for PICK1-immunoreactivity was somatodendritic with scattered puncta in neuropil and somatodendritic regions. The distribution of PICK1 partially overlaps with PKCalpha and glutamate receptor subunits such as GluR2. These data suggest that PICK1 may function in the regulation of PKCalpha and GluR2 localization in components of the rat auditory system, which may be a fundamental mechanism of synaptic transmission and/or plasticity. J. Comp. Neurol.

Animals↗
PubMed1986

Auditory pathways to the hypothalamus in ranid frogs.

Three multisynaptic pathways from the midbrain auditory center (torus semicircularis) of the bullfrog, Rana catesbeiana, to the infundibular hypothalamus were found using the axonal tracer wheat germ agglutinin-horseradish peroxidase. Toral neurons project to the secondary visceral nucleus of the isthmus and to the central and anterior thalamic nuclei of the dorsal thalamus. All 3 of these nuclei project to the infundibular hypothalamus. These findings indicate multiple connections between two centers presumed important for reproductive behavior in frogs, a midbrain sensory region processing acoustic communication signals and a hypothalamic endocrine control area regulating gonadotropin and gonadal steroid secretion.

Animals↗
PubMed2004

[Delay in the development of the auditory pathways. A differential diagnosis in hearing impairment in young infants].

BACKGROUND: Due to the increased frequency of screening tests in new-born infants, the number of subsequent examinations of very young children has increased in the Departments of Phoniatrics and Pediatric Audiology. To exclude hearing loss in young children, click stimulated brainstem evoked response audiometry (BERA) and otoacoustic emission tests are, in general, considered to be reliable methods. However, pathologic BERA thresholds and pathologic hearing reactions have been observed occasionally in young infants who show improved and even normal hearing reactions in subjective and objective hearing tests after some months. PATIENTS AND RESULTS: Our group of 14 children (ten female, four male) was initially examined by BERA at the ages of 1-7 months. Twelve children had an elevated risk of hearing loss due to complications in the pre-, peri- and postnatal period. In the BERA, no deafness was diagnosed, but in all children at least monaural pathologic BERA thresholds were observed. Subjective hearing tests confirmed hearing loss. Objective and even subjective hearing reactions improved and normalised within a few months at least monaurally. CONCLUSION: In very young infants, the possibility of a delayed maturation of the auditory pathways must be considered when a hearing loss is diagnosed. Our examples prove that young children with sensorineural hearing loss need more than one objective hearing examination during the first year of life.

Auditory Pathways↗
PubMed1996

Auditory pathways of caudal telencephalon and their relation to the song system of adult male zebra finches.

Auditory information is critical for vocal imitation and other elements of social life in song birds. In zebra finches, neural centers that are necessary for the acquisition and production of learned vocalizations are known, and they all respond to acoustic stimulation. However, the circuits by which conspecific auditory signals are perceived, processed, and stored in long-term memory have not been well documented. In particular, no evidence exists of direct connections between auditory and vocal motor pathways, and two newly identified centers for auditory processing, caudomedial neostriatum (Ncm) and caudomedial hyperstriatum ventrale (cmHV), have no documented place among known auditory circuits. Our goal was to describe anatomically the auditory pathways in adult zebra finch males and, specifically, to show the projections by which Ncm and vocal motor centers may receive auditory input. By using injections of different kinds of neuroanatomical tracers (biotinylated dextran amines, rhodamine-linked dextran amines, biocytin, fluorogold, and rhodamine-linked latex beads), we have shown that, as in other avian groups, the neostriatal field L complex in caudal telencephalon is the primary forebrain relay for pathways originating in the auditory thalamus, i.e., the nucleus ovoidalis complex (Ov). In addition, Ncm and cmHV also receive input from the Ov complex. Ov has been broken down into two parts, the Ov "core" and "shell," which project in parallel to different targets in the caudal telencephalon. Parts of the field L complex are connected among themselves and to Ncm, cmHV, and caudolateral Hv (clHV) through a complex web of largely reciprocal pathways. In addition, clHV and parts of the field L complex project strongly to the "shelf" of neostriatum underneath the song control nucleus high vocal center (HVC) and to the "cup" of archistriatum rostrodorsal to another song-control nucleus, the robust nucleus of the archistriatum (RA). We have documented two points at which the vocal motor pathway may pick up auditory signals: the HVC-shelf interface and a projection from clHV to the nucleus interfacialis (NIf), which projects to HVC. These data represent the most complete survey to date of auditory pathways in the adult male zebra finch brain, and of their projections to motor stations of the song system.

Acoustic Stimulation↗
PubMed1995

Auditory pathway plasticity in adult humans after unilateral idiopathic sudden sensorineural hearing loss.

We recorded auditory evoked magnetic fields from 8 patients with unilateral, idiopathic, sudden, sensorineural hearing loss and from 8 healthy controls, using a 122-channel whole-scalp neuromagnetometer. The stimuli were 50-ms l-kHz tone bursts, delivered to the healthy ear at interstimulus intervals (ISIs) of 1, 2, 4, 8, and 16 s. On average, as in normal-hearing controls, the dipole moments and the latencies of N100m, the 100-ms response, increased as a function of ISI over both hemispheres to left- and right-ear stimulation. Four patients had shorter response latencies and 4 had stronger dipole moments over the hemisphere ipsilateral to the stimulation. In 3 patients, one additional source was observed over the anterolateral right hemisphere and another near head midline. These findings suggest that unilateral sensorineural hearing loss may modify information processing in the central auditory pathways.

Acoustic Stimulation↗
PubMed1972

On the existence in human auditory pathways of channels selectively tuned to the modulation present in frequency-modulated tones.

1. The sensitivity of detecting modulation in a test tone sinusoidally frequency-modulated at a rate varphi(test) is diminished after exposure to a conditioning tone more deeply frequency-modulated at a rate varphi(cond) provided that varphi(cond) is not very different from varphi(test), the sound amplitude being kept constant for each tone at a comfortable hearing level 40-45 dB above threshold.2. When varphi(cond) = varphi(test) the frequency deviation in the modulated test tone must be increased to about three times the unconditioned threshold magnitude to be detectable immediately after exposure to the conditioning tone. Detection sensitivity returns to normal in about one minute.3. At low modulation frequencies the conditioning effects are tuned, being much diminished when varphi(cond) differs from varphi(test) by a few cycles per second.4. Comparing monaural with contra-aural conditioning demonstrates a considerable interaural transfer of about 60-80% of the effect, indicating that the conditioning and its selectivity are predominantly central phenomena.5. The magnitude of the deterioration in detection sensitivity after conditioning is about 3 x at modulation frequencies between about 3/sec and 30/sec. It diminishes at lower and higher modulation frequencies and is effectively absent at 100/sec modulation. The bandwidth of the effect increases from a few cycles per second at the lower end of this range, to some tens of cycles per second at the upper end.6. For the same modulation frequency, the conditioning is relatively insensitive to the mean ;carrier' audiofrequency, f(0). The band width in terms of carrier frequency is at least as wide as ;critical bands'. With a test signal f(0) = 250 Hz, varphi(test) = 8/sec, conditioning is still appreciable for a conditioning tone of varphi(cond) = 8/sec but centred upon f(0) = 150 Hz or = 350 Hz. Conditioning is thus not explicable in terms of coincidences between particular spectral components in the conditioning and test tones.7. Whereas the sensitivity of detecting 8/sec amplitude modulation in a tone is conditioned by prior exposure to either amplitude- or frequency-modulated tones, in contrast the detectability of 8/sec frequency-modulated signals is conditioned only by prior exposure to frequency-modulated tones and not by amplitude-modulated conditioning tones. This underlines the special place of frequency modulation in human audition and emphasizes that the operative stimulus cannot be some aspect common to amplitude modulation and frequency modulation, like identical periodicity or coincident positioning of bands in the integrated spectra of the tones, but points to the instantaneous frequency-modulated wave form as the adequate stimulus.8. These findings strongly suggest that the human auditory pathways contain ;channels' in their organization which determine a final response selectively tuned to particular frequency-modulations. Periodicity coding alone cannot adequately explain this effect which may well only be understood in terms of a ;place' theory of frequency selectivity.9. This organization is well suited to subserve the recognition of frequency-modulation patterns in acoustic signals rather independently of the mean audiofrequency that carries the frequency modulation.

Acoustic Stimulation↗
PubMedDate not supplied

Brainstem auditory pathway degeneration associated with chronic cochlear implants in the monkey.

The form and pattern of first-order and transsynaptic degeneration in the central auditory pathway was studied in monkeys following inner ear stimulation by a cochlear implant. Multielectrode, scala tympani, and modiolar systems were implanted; in some cases, neomycin was perfused into the cochlea to destroy the organ of Corti at the time of implantation. The monkeys were maintained chronically for 5 to 120 weeks, then the cochleas and brainstems were examined histologically. The extent of spiral ganglion cell loss across animals showed variability, reflecting the different procedures and devices used. The degree and distribution of spiral ganglion cell loss was related to the degree and distribution of neural degeneration seen in the cochlear nucleus in all cases. Peripheral damage progressed toward the cochlear apex as survival time increased, and this progression was reflected in the cochlear nucleus by a ventrolateral shift in the locus of degeneration over time. In addition, evidence for transneuronal degeneration was seen at the superior olive, the lateral lemniscus and the inferior colliculus. Our findings indicate that several factors inherent in the use of a cochlear prosthesis, i.e., insertion trauma, host reaction, and/or electrical stimulation, may be associated with a long-term, continuing process of central degeneration visible at several levels of the auditory system.

Animals↗