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PubMed1986

Central auditory function in a hearing-impaired white mouse.

The dysfunction of the stria vascularis in the viable dominant spotting mutant mouse results in the reduction or the absence of the endocochlear potential. However, these mutants respond to an intense acoustic stimulus with a Preyer reflex (pinna twitch). This study used 14C autoradiography and electromyography to investigate central auditory responses in this mutant. There were three main findings: autoradiography demonstrated an increase in the metabolic rate within each of the central auditory nuclei during noise exposure compared with silence; electromyographic recordings indicated that there was no tensor tympani muscle reflex; the mutants were found to be susceptible to audiogenic seizures. It was concluded that the central auditory pathway of the viable dominant spotting mutant could be activated despite the abnormal strial function. Absence of the tensor tympani muscle reflex, together with auditory deprivation, might contribute to the susceptibility to audiogenic seizures.

Acoustic Stimulation↗

PubMed2001

Imaging evaluation of sensorineural hearing loss.

The imaging evaluation of patients with sensorineural hearing loss (SNHL) focuses on the acoustic pathways from the cochlea to the auditory cortex. Magnetic resonance imaging (MRI) is the modality of choice for most patients with SNHL, though computed tomography (CT) also plays an important role in the evaluation of bony changes and in patients for whom MRI is contraindicated. Conventional enhanced MRI is the most commonly used technique in this clinical setting. High-resolution fast spin-echo T2 MRI is an adjunctive technique that provides exquisite evaluation of the cerebellopontine angle (CPA), internal auditory canal (IAC), cranial nerves, and membranous labyrinth, and plays a significant role in the diagnosis and surgical evaluation of SNHL. Categories of lesions that cause SNHL include brain lesions involving central auditory pathways; neoplasms of the CPA and IAC, the most common being schwannoma; other neoplastic, congenital, and cystic masses of the CPA and IAC; congenital anomalies of the inner ear; intrinsic cochlear nerve defects, inflammatory processes of the inner ear; and temporal bone trauma.

Cranial Nerve Neoplasms↗

PubMed1999

Latency alterations of the auditory brainstem response in audiogenic seizure-prone Long-Evans rats.

Audiogenic seizure susceptibility in the normally seizure-resistant Long-Evans rat may result from altered processing in the auditory pathway. Representative waveform latencies of the auditory brainstem responses (ABR) were recorded to examine generator alterations at different levels of the auditory neuraxis. Male Long-Evans rats primed for audiogenic seizures (AGS) on PND 14 with a 10 kHz pure tone at 120 dB SPL for 8 min were tested for AGS on PND 28 with 120 dB SPL continuous white noise. Primed subjects displayed wild running culminating in clonic convulsions. Following behavioral testing at 4-6 months, vertex recordings of ABR waves Ia-VI were made in anesthetized subjects using pure tone stimulus bursts. AGS subjects showed marginally elevated ABR thresholds. Shorter ABR wave latencies were elicited in AGS subjects for peripheral and central auditory components with stimulus intensities above 50 dB PeSPL at 8 and 40 kHz. Interpeak intervals were reduced for waves Ia-V and III-V in AGS subjects. These results reveal that intense sound stimulation during a sensitive period of development later reduces processing time at higher intensity levels.

Acoustic Stimulation↗

PubMed2000

The functional anatomy of auditory hallucinations in schizophrenia.

We used continuous whole brain functional magnetic resonance imaging (fMRI) with a 3-T magnet to map the cerebral activation associated with auditory hallucinations in four subjects with schizophrenia. The subjects experienced episodes of hallucination whilst in the scanner so that periods of hallucination could be compared with periods of rest in the same individuals. Group analysis demonstrated shared areas of activation in right and left superior temporal gyri, left inferior parietal cortex and left middle frontal gyrus. When the data were examined on an individual basis, the temporal cortex and prefrontal cortex areas were activated during episodes of hallucination in all four subjects. These findings support the theory that auditory hallucination reflects abnormal activation of normal auditory pathways.

Adult↗

PubMed2002

Contralateral inhibition as a sensory bias: the neural basis for a female preference in a synchronously calling bushcricket, Mecopoda elongata.

Imperfect synchrony between male calls occurs widely in acoustically courting crickets and bushcrickets. Males which are able to establish the temporal leadership usually attract more females in choice experiments but the proximate mechanism for this precedence effect is unknown. Here we show that contralateral inhibition, the neural basis for lateral contrast enhancement in the auditory pathways of insects and vertebrates, is also the probable proximate neural mechanism for this female preference. We recorded simultaneously from a pair of identified auditory interneurons in the synchronizing bushcricket Mecopoda elongata. When two identical acoustic stimuli are presented from opposite directions, one preceding the other by 120 ms, the neural representation within the receiver is far stronger for the leader signal. This results from a suppression of the neural response to the follower chirp by reciprocal contralateral inhibition. The advantage of the representation of the leader is 2-3-fold with time delays between 70 and 130 ms; the most clear-cut female preferences have also been found with such delays in previous behavioural experiments. In time-intensity trading experiments, a lead by 120 ms could only be compensated for by increasing the amplitude of the follower signal by 7-11 dB. We discuss contralateral inhibition in auditory systems as a sensory bias that results in female preference for leading signals, with important evolutionary consequences for male calling strategies.

Acoustic Stimulation↗

PubMed2006

Development of tinnitus-related neuronal hyperactivity through homeostatic plasticity after hearing loss: a computational model.

Tinnitus, the perception of a sound in the absence of acoustic stimulation, is often associated with hearing loss. Animal studies indicate that hearing loss through cochlear damage can lead to behavioral signs of tinnitus that are correlated with pathologically increased spontaneous firing rates, or hyperactivity, of neurons in the auditory pathway. Mechanisms that lead to the development of this hyperactivity, however, have remained unclear. We address this question by using a computational model of auditory nerve fibers and downstream auditory neurons. The key idea is that mean firing rates of these neurons are stabilized through a homeostatic plasticity mechanism. This homeostatic compensation can give rise to hyperactivity in the model neurons if the healthy ratio between mean and spontaneous firing rate of the auditory nerve is decreased, for example through a loss of outer hair cells or damage to hair cell stereocilia. Homeostasis can also amplify non-auditory inputs, which then contribute to hyperactivity. Our computational model predicts how appropriate additional acoustic stimulation can reverse the development of such hyperactivity, which could provide a new basis for treatment strategies.

Acoustic Stimulation↗

PubMed1991

Changes in brainstem auditory evoked potentials during insulin-induced hypoglycaemia in type 1 diabetic patients.

To determine whether the central and peripheral auditory pathways are disturbed during hypoglycaemia, brainstem auditory evoked potentials were measured in 16 Type 1 diabetic patients aged 17-55 years during intravenous insulin infusion. Within 60 min mean blood glucose declined from 5.0 mmol l-1 to a nadir at 1.7 mmol l-1 followed by an increase to 2.8 mmol l-1 30 min after the insulin infusion had been discontinued. The latency of wave I of brainstem auditory evoked potentials remained unchanged during hypoglycaemia. However, latencies of waves III and V and interpeak latencies I-III, III-V, and I-V were significantly prolonged at average blood glucose levels of 1.7 or 2.1 mmol l-1 when compared with baseline: III 3.96 +/- 0.03 (+/- SE) vs 4.01 +/- 0.04 ms; V 5.69 +/- 0.07 vs 5.81 +/- 0.07 ms; I-III 2.30 +/- 0.05 vs 2.37 +/- 0.05 ms; III-V 1.73 +/- 0.06 vs 1.83 +/- 0.07 ms; and I-V 4.01 +/- 0.05 vs 4.14 +/- 0.06 ms (all p less than 0.05). When blood glucose was allowed to increase to 2.8 mmol l-1, these conduction delays were no longer demonstrable. The depression of the brainstem was approximately paralleled by the activation of counter-regulatory hormones and development of hypoglycaemic symptoms. We conclude that hypoglycaemia results in a rapidly reversible delay of the transmission time in the brainstem but not in the auditory nerve. The dysfunction in the brainstem suggests that not only cortical centres are involved in response to hypoglycaemia in Type 1 diabetic patients.

Adult↗

PubMed1975

Verbal tests of central audition.

The use of sensitized verbal tests in the diagnosis of central deafness is critically reviewed. The concept of intrinsic (neural) redundancy is the main point in the operational model; different modalities of coupling between intrinsic and extrinsic redundancy bring forth different patterns of intelligibility. The age of the subject thus becomes critical; on the contrary, the influence of the IQ can be minimized by carefully selecting the tests. These can be divided into monaural and dichotic; among the latter, only the tests involving competing information are of value, whilst the so-called summation tests should now be disregarded. The clinical results are only briefly quoted, since they are well-known. The contribution to the advances in neurophysiology seems to be more interesting. The influence of reticular formation on auditory stimulation, the crossing of the auditory pathways, the existence of a secondary auditory area have been psychoacoustically confirmed by the use of the monaural tests. In their turn, the dichotic competing message tests have enabled a beautiful model of language perception to be drawn, and have definitely demonstrated the so-called hemispheric specialization (or dominance) for verbal and nonverbal messages.

Acoustic Stimulation↗

PubMed2001

Auditory development and hearing evaluation in children.

This chapter provides an overview of (1) developmental timetables relevant to hearing, and (2) current pediatric audiological techniques and practices. Structural and functional development of the auditory pathway and the development of primary auditory processing are summarized. These developmental sequences appear to follow similar paths in humans and animals. Speech and music perception involve more complex processing and are strongly influenced by experience. Hearing disorders affect the perception of complex sounds in a variety of ways, depending on the sites of lesions. Early-onset hearing impairment, including conductive loss from chronic otitis media, can seriously impede language development. Language cannot develop normally without adequate speech stimulation, and deafness is more prevalent than any other handicapping condition for which mandated neonatal screening programs exist. Sensitive and inexpensive techniques are available for performing neonatal hearing screening, and early intervention has a documented positive effect on development of language skills in hearing-impaired children. Thus, the National Institutes of Health has recommended nationwide universal neonatal hearing screening. The rationale for and the methodology of universal screening programs are summarized. Advances in the genetics of hearing impairment are reviewed. Data from these studies have influenced testing and rehabilitative protocols and have implications for future prevention and treatment of hearing impairment.

Acoustic Impedance Tests↗

PubMed2005

[Audiometric and dynamometric parameters of functional brain asymmetry].

We examined influence of intensive noise on auditory and musculoskeletal system in series of audiometric and dynamometric tests. We considered Karhart's tooth asymmetry and asymmetry of muscular strength of the upper extremities. We demonstrate the significance of these parameters in diagnosis of functional cortical asymmetry and central hearing pathology; provide audiometric and dynamometric evidence of the structure of cortical auditory pathways, the integral function of the auditory cortex, pathophysiological nature of functional asymmetry and their correlation.

Audiometry↗

PubMed2005

Traditional and emerging indications in cochlear and auditory brainstem implants.

Electrical stimulation of the auditory pathway via a cochlear or an auditory brainstem implant has been proved to an effective and safe procedure in the treatment of many patients suffering from a profound sensorineural hearing loss of cochlear and retrocochlear origin. In this paper we will present the impact of experience, technical advances in the design of auditory implants, and improvements in stimulation strategies in traditional criteria for implantation. Besides current indications for cochlear and auditory brainstem implants, we will review a continuously expanding group of potential candidates, namely emerging indications. This review will be exemplified with data from the University of Navarra Cochlear Implant Program, currently accounting for more than 500 patients implanted.

Auditory Brain Stem Implantation↗

PubMed1983

Early auditory evoked potentials (EAEPs) in the rabbit. Normative data and effects of lesions in the cerebello-pontine angle.

Early auditory evoked potentials (EAEPs) were measured in rabbits. After establishing normative data an operative method was developed to expose the cerebello-pontine angle. Compression of the VIIIth nerve and a reduction of blood supply to the cochlea via the labyrinthine artery altered the EAEP systematically. In all cases of an VIIIth nerve lesion wave 1 continued to be elicited whereas waves 2-5 disappeared. Circulatory disturbances had an effect upon wave 1. The results indicate that the generator of wave 1 is the unit cochlea/acoustic nerve and of waves 2-5 the auditory pathway within the brain stem. The resultant data help to understand wave alterations in patients with acoustic neuromas.

Animals↗

PubMed1984

[Brain stem auditory evoked potentials in "alcoholic epilepsy"].

BAEPs were studied in a group of subjects suffering from 'alcoholic epilepsy.' Results were then compared with data from normal subjects and chronic alcoholics without epilepsy. The latency for peak V and the inter-peak latencies (I-III, III-V, I-V) were significantly longer in the 'alcoholic epilepsy' group than in the control group. This increase of neural transmission time in the brain-stem auditory pathways was less important in the 'chronic alcoholics without epilepsy' group than in the alcoholic epilepsy group.

Adult↗

PubMed1985

The influence of raised body temperature on auditory evoked brainstem responses.

The influence of raised body temperature on the auditory evoked brainstem responses (BSER) has been investigated in 9 healthy volunteers. Ipsi- and contralateral BSER recordings were obtained before and after raising body temperature by at least 1 degree C by means of a specially constructed heat cradle. In two of the subjects further BSER recordings were obtained after their body temperature had been allowed to fall again to its preheated level. The results for wave V have been analysed in detail: the latency in the 5 men shortened from a mean of 5.84 ms (s.d. 0.193) to a mean of 5.62 ms (s.d. 0.185). For the 4 women the figures were 5.87 ms (s.d. 0.105) and 5.68 ms (s.d. 0.105). Using paired t-tests this change is highly significant (P less than 0.001). Similar changes were observed in the other waves although they were less consistent. In the 2 subjects who were allowed to cool again after heating, the BSER wave latencies returned to their preheated values. It is concluded that nerve conduction rates in the auditory pathway are influenced by body temperature and that this may have to be taken into account when interpreting BSER recordings.

Adult↗

PubMed1997

Axogenesis in the human fetal auditory system, demonstrated by neurofilament immunohistochemistry.

Morphological, electrophysiological and behavioral evidence indicates that the onset of rapid, synchronized conduction of auditory impulses occurs in the human brainstem during the 28th-29th fetal weeks. This implies that axonal connections in the brainstem auditory pathway are generated prior to this time. In order to investigate the sequence of axogenic events in the human brainstem pathway, we employed immunohistochemical techniques and an antibody to neurofilament protein. Immunostaining for axonal neurofilaments in an age-graded series of fetal brains demonstrates that a small number of cochlear nerve axons have invaded the ventral cochlear nucleus by the 16th fetal week. By this same time point, a limited number of trapezoid body-lateral lemniscus axons have reached the superior olivary complex and inferior colliculus. Between gestational weeks 16 and 26, there is marked expansion and collateralization of the ascending pathway from cochlear nerve to inferior colliculus. By week 26, ascending axons have begun to form plexuses of terminal neuropil within all of the brainstem auditory nuclei. Beginning in week 22, there is development of commissural axons (dorsal commissure of the lateral lemniscus and commissure of the inferior colliculus) and descending projections (descending collicular axons and olivocochlear bundle). This early establishment of a mature pattern of axonal connections presumably forms the basis for the appearance of myelin, acousticomotor reflexes and recordable brainstem responses by fetal week 29.

Auditory Pathways↗

PubMed1977

Development of auditory function in newborn infants revealed by auditory brainstem potentials.

Auditory brainstem potentials were recorded from scalp electrodes in 42 infants ranging in gestational age from 25 to 44 weeks. The latencies of the various potential components decreased with maturation. Wave V, evoked by 65-dB sensation level clicks, changed in latency from 9.9 msec at 26 weeks of gestation of 6.9 msec at 40 weeks of gestation. Central conduction times in the auditory pathway also decreased with maturation from 7.2 msec at 26 weeks to 5.2 msec at 40 weeks. The effects of brainstem and cochlear disorders on auditory brainstem potentials were noted in several abnormal infants. The application of all of these techniques could permit an objective definition of both normal and abnormal sensory processes in newborn infants.

Action Potentials↗

PubMed1984

Connections of the auditory midbrain in a teleost fish, Cyprinus carpio.

Central auditory pathways were traced in Japanese carp, Cyprinus carpio, using electrophysiological mapping and HRP tract-tracing methods. Multiunit recordings made from the carp torus semicircularis, the major midbrain area for processing octavolateralis information, revealed a mediolateral segregation of auditory and lateral line sensory modalities. Iontophoretic injections of HRP were made into the medial torus to trace afferent and efferent projections of the carp auditory midbrain. Following unilateral HRP injections into the medial torus, retrogradely labeled neurons were observed within six nuclei of the carp medulla. Two octaval nuclei, the anterior octavus nucleus and descending octavus nucleus, contained HRP-filled neurons. Labeled neurons were also observed within the ipsilateral superior olive, scattered among fibers of both lateral lemnisci, and bilaterally within the medullary reticular formation. In addition, bilateral retrograde cell labeling was found within a group of Purkinje-like cells located adjacent to the IVth ventricle, just rostral to the level of the VIIIth nerve. Few labeled neurons were found within the nucleus medialis, a principal target for lateral line afferents within the medulla. At midbrain levels, retrogradely labeled neurons were observed within the contralateral torus semicircularis and the ipsilateral optic tectum. Three forebrain nuclei project to the carp auditory midbrain. Within the diencephalon, descending projections originate from the anterior tuberal nucleus, bilaterally, and from the ipsilateral central posterior thalamic nucleus. The ipsilateral caudal telencephalon also projects to the carp auditory midbrain via large multipolar neurons within area dorsalis pars centralis. Anterograde labeling of fibers and terminals revealed efferent projections of the carp auditory midbrain to the following targets: the ipsilateral superior olive, the ipsilateral medullary reticular formation, the deep layers of the optic tectum, the contralateral torus semicircularis, the anterior tuberal nucleus, and the central posterior thalamic nucleus. These results, together with recent studies of lateral line pathways in teleosts (Finger, '80, '82a), demonstrate that central auditory and lateral line pathways are anatomically distinct in the carp, at least from medullary to diencephalic levels. Furthermore, there are striking similarities in the organization of the central auditory pathways of the carp and those of amphibians and land vertebrates.

Afferent Pathways↗

PubMed2005

Auditory and electrophysiological patterns of a unilateral lesion of the lateral lemniscus.

Auditory disorders resulting from focal brainstem lesions are rarely symptomatic. Isolated lesions of the inferior colliculus have previously been reported, whereas no detailed description of a localized involvement of the lateral lemniscus is yet available. We report a unilateral lesion of the lateral lemniscus by a bleeding in a cavernoma. Symptoms included strictly contralateral tinnitus and auditory impairment, with normal pure-tone and speech audiometry. Conversely, the dichotic listening test revealed an extinction of contralateral ear input. The brainstem auditory evoked potentials disclosed a reduced and delayed wave V only after contralateral ear stimulation, while the middle latency evoked potentials were normal. This observation shows that a unilateral lesion of the lateral lemniscus can produce auditory symptoms. The dysfunction of auditory pathways is associated with specific electrophysiological abnormalities that can be assessed by evoked potential recording.

Adult↗