Binaural interaction of bone-conducted auditory brainstem responses.

Bone-conducted auditory brainstem responses (ABRs) elicited by monoaural stimulation are very useful for evaluating hearing in children with congenital atresia of both ears. In a previous study of sound lateralization in children with congenital atresia of both ears, using bilateral bone-conducted stimuli, we found that most of the children could sufficiently retain binaural hearing ability in terms of both intensity and time differences. In this study we attempted to record bilateral bone-conducted ABRs in normal subjects in order to explore binaural interaction objectively. The study revealed that binaural interaction exists in bone-conducted ABRs. This can be taken as neurophysiological evidence that sound lateralization can be detected by children with bilateral microtia and atresia.

Electrophysiological measures of auditory function in the neurofilament-deficient mutant quail (Quv).

Auditory pathway electrophysiological studies were performed on the mutant quail 'Quv'. This mutation is known to result in neurofilament deficiencies of both the peripheral and central nervous systems. Auditory evoked brainstem responses (ABRs), electrocochleograms (EcochGs) and middle latency responses (MLRs) were evaluated. ABRs in Quv quails demonstrated markedly altered waveforms exhibiting longer latencies, absence of the later peaks and lower amplitudes. The EcochG showed normal cochlear microphonics with no obvious abnormalities in amplitude or latency and normal latencies for peak N1. Quv quails had a mild threshold elevation with a normal latency for the first peak of the ABR (P1). The Quv MLRs showed no significant differences in amplitude but they revealed a latency prolongation for peaks N0, Pa and Na relative to the controls. We have discovered abnormal findings of auditory evoked potentials in the neurofilament-deficient quail (Quv). We suggest that the smaller axonal size and axonal hypotrophy due to altered neurofilament expression underlies these abnormal auditory evoked potential responses.

Long-term changes in middle latency response and evidence of retrograde degeneration in the medial geniculate body after auditory cortical ablation in cats.

Short- and long-term changes in the middle latency response (MLR) after bilateral ablation of the auditory cortices were studied in awake cats. The amplitude of the negative peak with a latency of about 15 ms (NA) decreased to 60% of the original value 1 week after ablation (short-term change). In the long term, i.e. 11-30 months, NA either decreased further (decreased group) or remained unchanged (non-decreased group). A histological study with light microscopy revealed degeneration of neurons in the ventral nucleus of the medial geniculate body (MGv) in the decreased group, whereas the neurons in this region were preserved in the non-decreased group. This study suggests that long-term changes in NA reflect retrograde degeneration in the MGv after auditory cortical ablation.

Girl with accelerated growth, hearing loss, inner ear anomalies, delayed myelination of the brain, and del(22)(q13.1q13.2).

We report on an 18-month-old Japanese girl with 46,XX,del(22)(q13.1q13.2). To our knowledge, this is the first report of a case of interstitial deletion of a 22q13.1-q13.2 segment. Clinical features included hearing loss accompanied by inner ear anomalies, hypotonia and minor anomalies, such as a long philtrum, full eyelids, epicanthus, left transverse palmar crease and psychomotor developmental delay. Despite the chromosomal deletion, her physical growth was accelerated: her height was between the 75th and 90th percentiles for her age. Her brain MRI showed signs of delayed myelination. The three-dimensional MRI of the inner ear showed abnormalities of the cochlea and vestibule in both ears. Clinical features of the patient are similar to those of a patient with a del(22)(q13.1q13.33) karyotype previously reported by Romain et al.

Temporal bone pathology findings due to drowning.

It has been reported that anoxia due to near-drowning or near-suffocation causes brain damage but not inner ear damage. On the other hand, it has been shown that brain death causes both brain damage and inner ear damage. However, studies of temporal bone pathology resulting from sudden death due to drowning are few. We studied temporal bone pathology in six cases of individuals who died of accidents due to drowning. In all temporal bones examined, we found extensive congestion petechiae and haemorrhage in the vessels in the mucosal layers of the middle ear and mastoid air cells, as well as in the vessels around the facial nerve and carotid canal. In the inner ear, there was no abnormality in Corti's organ or the vestibular organs, except in one case who died in the bath. Our findings suggest that petechiae haemorrhage or congestion in the vessels of the mucosal layer and the vessels themselves of the middle ear occurs upon acute death due to drowning.

The long-term effect of bilateral inferior colliculus ablation on auditory brainstem response in awake cats.

In this study auditory brainstem responses (ABRs) were recorded repeatedly in three awake cats before and after bilateral aspiration of the inferior colliculi (ICs). All surgical procedures were performed under anaesthesia with Nembutal. Postoperative recordings were obtained 1 week, 3 months, 8 months and 13 months after bilateral aspiration of the ICs in order to study the long-term changes in ABRs. The P5 amplitude was markedly reduced only at 1 week after aspiration. P1 and P2 amplitudes were affected slightly at 3 months and 1 year, but those of P3 and P4 decreased significantly. After perfusion of these cats, histological examination of the brainstem revealed complete ablation of both ICs, neuronal loss in the nucleus of the lateral lemniscus and the superior olivary complex and preservation of the cochlear nucleus. Our results suggest that retrograde degeneration of neuronal cells of the brainstem, which project to the IC from the nucleus of the lateral lemniscus and superior olivary complex except the cochlear nucleus, affect the peak amplitudes of the ABR over the long-term.

ABR and temporal bone pathology in Hurler's disease.

This is believed to be the first report on estimating hearing loss in Hurler's disease, based on the correlation between ABR and temporal bone pathology. ABR findings revealed hearing loss to be about 70 dB or more as result of peripheral mixed impairment. A histological study of the temporal bones revealed almost all pathological findings in the conductive system, except for the hyperplastic arachnoid in the internal auditory canal. In the middle ear cavity, otitis media, residual mesenchyme and deformity of ossicles were found. We explain the conductive component to be due to otitis media and poor ossicular connection. However, the etiology of the sensorineural component remains speculative. In Hurler's disease, hearing loss with mental retardation is often found at infantile age. Therefore, assessing the extent of hearing loss exactly was difficult, for example, the severity. the etiology and incidence of sensorineural impairment. We emphasize the need for not only well-described pathological studies but also for more objective functional investigations, at least ABR.

Spatial memory and path integration studied by self-driven passive linear displacement. I. Basic properties.

According to path integration, the brain is able to compute the distance of a traveled path. In this research we applied our previously reported method for studying memory of linear distance, a crucial mechanism in path integration; our method is based on the overt reconstruction of a passive transport. Passive transport is a special case of navigation in which no active control is performed. Blindfolded subjects were first asked to travel 2 m forward, in darkness, by driving with a joystick the robot on which they were seated. The results show that all subjects but two undershot this distance, i.e., overestimated their own displacement. Then, subjects were submitted to a passive linear forward displacement along 2, 4, 6, 8, or 10 m, and had to reproduce the same distance, still blindfolded. The results show that the distance of the stimulus was accurately reproduced, as well as stimulus duration, peak velocity, and velocity profile. In this first condition, the imposed velocity profile was triangular and therefore stimulus distance and duration were correlated. In a second condition, it was shown that distance was correctly reproduced also when the information about stimulus duration was kept constant. Here, different velocity profiles were used as stimuli, and most subjects also reproduced the velocity profile. Statistical analyses indicated that distance was not reproduced as a consequence of duration, peak velocity, or velocity profile reproduction, but was uniquely correlated to stimulus distance. The previous hypothesis of a double integration of the otolith signal to provide a distance estimate can explain our results. There was a large discrepancy between the accuracy with which the subjects matched the velocity profiles and that of distance reproduction. It follows that, whereas the dynamics of passive motion are stored and available to further use, distance is independently estimated. It is concluded that vestibular and somatosensory signals excited by passive transport can be used to build a dynamic as well as a static representation of the traveled path. We found a close quantitative similarity between the present findings on distance reproduction and those obtained from active locomotion experiments in which the same paradigm was used. This resemblance suggests that the two types of navigation tasks draw on common physiological processes and extends the relevance of our results to naturally occurring path integration.

Auditory evoked responses under total spinal anesthesia in rats.

In order to investigate the function of the auditory pathway from the cochlea to the brain stem under total spinal anesthesia, the auditory brain stem response (ABR), compound action potential of the cochlear nerve (CAP), and cochlear microphonics (CM) were simultaneously recorded in rats. Total spinal anesthesia was induced by infusion of 2% lidocaine hydrochloride at a constant rate of 0.10 mL/min into the cerebrospinal fluid through the rats' skulls. The ABR completely disappeared within 1.5 to 4 minutes. After cessation of the injection, the ABR reappeared, starting from wave I and progressing through waves II and III to wave IV. The latency change of the CAP throughout the recording period was quite similar to that of wave I of the ABR. A reduction in amplitude of the CM was observed, but the CM did not disappear during the recording period. Disappearance of the ABR was due, not to loss of cochlear function, but to anesthetic effects on the acoustic nerve and the brain stem. Monitoring of the ABR provided information on the level of neural activity in the brain stem under total spinal anesthesia.

Auditory nerve disease of both ears revealed by auditory brainstem responses, electrocochleography and otoacoustic emissions.

We report on two patients who showed absence of auditory brainstem response (ABR) but broad compound action potentials on electrocochleograms and almost normal otoacoustic emissions, together with absence of caloric response and preservation of per rotatory nystagmus for both ears. Patient 1, a 53-year-old woman, had noted auditory and vestibular problems since the age of 15 years, and Patient 2, a 68-year-old woman, had noted problems of the same age of 30 years. They could hear words and understand sentences if spoken slowly, but they could not discriminate monosyllables very well. Their auditory examinations disclosed mild threshold elevation in pure-tone audiometry and markedly poor scores in speech audiometry and good scores in auditory comprehension test. They were diagnosed as having auditory nerve disease of unknown cause.

Spatial memory of body linear displacement: what is being stored?

The ability to evaluate traveled distance is common to most animal species. Head trajectory in space is measured on the basis of the converging signals of the visual, vestibular, and somatosensory systems, together with efferent copies of motor commands. Recent evidence from human studies has shown that head trajectory in space can be stored in spatial memory. A fundamental question, however, remains unanswered: How is movement stored? In this study, humans who were asked to reproduce passive linear whole-body displacement distances while blindfolded were also able to reproduce velocity profiles. This finding suggests that a spatiotemporal dynamic pattern of motion is stored and can be retrieved with the use of vestibular and somesthetic cues.

[Clinical use of EVAR and OVAR by the dumped rotation test--comparison of normal volunteers and patients with unilateral vestibular nerve section].

Horizontal eye movements in response to either earth vertical axis rotation (EVAR) or off vertical axis rotation (OVAR) by a 10 degree tilted axis were recorded in six normal subjects and three patients with unilateral vestibular nerve section. Both trials consisted of acceleration at approximately 400 deg/sec2 until an angular velocity of 180 deg/sec was reached followed by deceleration at -4 deg/sec2 until rotation ceased. This is the so-called dumped rotation procedure. Total numbers of nystagmic beats and the duration of perrotatory nystagmus in these two different trials were compared. The results were as follows: 1) Total numbers of nystagmic beats in OVAR were significantly larger than in EVAR. 2) The duration of perrotatory nystagmus in OVAR was significantly longer than in EVAR. Only the horizontal semicircular canals were stimulated by angular acceleration in EVAR, whereas both otolith organs and semicircular canals were stimulated on changing the position of the head around the direction of the gravity in OVAR.

Modification of parameters in vertical optokinetic nystagmus after repeated vertical optokinetic stimulation in patients with vestibular lesions.

Eye movements were recorded in patients with unilateral and bilateral vestibular lesions after upward and downward optokinetic (OK) stimulation before and following 6 weeks' repeated exposure to OK stimulation. In control subjects there was no asymmetry between upward and downward slow-phase velocity (SPV). Before training, less subjects showed that upward and downward SPV was significantly lower than that of controls. There was no asymmetry between upward and downward SPV. After training, in unilateral cases, the values of both upward and downward SPV recovered to the control range. In bilateral cases, the downward SPV values returned to the control range, whereas the values of upward SPV exceeded the control range. The frequencies of both upward and downward OKN in controls were about 3.0 Hz. In unilateral and bilateral cases, before and after training, the OKN frequencies approximated 3.0 Hz, showing no significant differences. The recovery of the SPV in unilateral and bilateral cases after training suggests that OK stimulation acts to stabilize the body and consequently to provoke pronounced OKN, due to eye-head-body co-ordination. The asymmetry of SPV after training in bilateral cases might be a result of the lack of otolith function.

Analysis of auditory brain stem response with lidocaine injection into the cerebrospinal fluid in rats.

Auditory brain stem response (ABR) was recorded in 10 rats with total spinal anesthesia induced by injection of 2% lidocaine hydrochloride into the subarachnoid space through the skull. The ABR disappeared immediately (within 4 minutes) after the injection of 13.3 to 40.0 mg/kg lidocaine. The disappearance started with the later waves of the ABR. After cessation of the injection, the ABR reappeared and recovered progressively from wave I to wave IV. The effect of lidocaine on the ABR was reversible and extended in the acoustic nerve to the midbrain.

Middle-latency responses of awake and anesthetized Japanese macaques.

The middle-latency response (MLR) of two Japanese macaques were investigated. In the awake state, the configuration of the MLR components showed two positive peaks: Pa and Pb. The latency and the configuration of Pa were very similar to those of humans. In the topographic recordings, the largest Pa amplitude was found from the vertex, or R1, which is 1 cm lateral to the vertex. In the anesthetic state, Pa and Pb gradually disappeared. This study shows that the MLR in awake Japanese macaques is similar to that in humans, and differs from that in cats. Therefore these awake monkeys are suitable as animal models of human MLR.

Effects of primary auditory cortex lesions on middle latency responses in awake cats.

In order to clarify the role of the primary auditory cortex (AI) on middle latency responses (MLRs), we recorded the auditory evoked potentials (AEPs) from the vertex and the right and left AI areas of the skull simultaneously before and after creating serial lesions of the AIs contralateral and ipsilateral to the stimulated ear in 7 awake cats. The auditory brainstem responses (ABRs) and MLRs recorded from the vertex in normal awake cats revealed the presence of peaks 1-8, NA and PA within the analysis time of 50 msec. After there were serial AI lesions, (1) all the peaks remained at nearly the same latencies, (2) the amplitude of the NA was decreased significantly, that of the PA was slightly decreased and those of peaks 6, 7 and 8 were variable, and (3) the difference between the effects of the first operation (contralateral AI) and the second operation (ipsilateral AI) was not statistically significant. These findings indicated that the main, prominent effect of bilateral AI lesions on MLRs in the awake cat is a significant decrease in the NA amplitude.

40-Hz steady state response in awake cats after bilateral chronic lesions in auditory cortices or inferior colliculi.

To reveal the generators of 40-Hz steady state response, the following investigations in awake cat were performed: (i) analyses of 40-Hz SSR without any lesions, and study of stimulus rate; (ii) effect of chronic lesions in the bilateral auditory cortex; (iii) effect of chronic lesions in the bilateral inferior colliculus. The maximum amplitudes were obtained at stimulus rates of 40-50 Hz. In cat with lesions in the bilateral auditory cortex, the wave configurations and the phase were retained but the amplitude was reduced to 90%. In cat with lesions in the inferior colliculus, the wave configurations and the phase were retained but the amplitude was reduced to 60%. These data suggest the following conclusions: (i) cat was a suitable animal model for human's 40-Hz SSR; (ii) the auditory cortex could be one of the generators of 40-Hz SSR; (iii) the inferior colliculus could be an important generator of 40-Hz SSR; (iv) 40-Hz SSR seems to be generated through not only primary auditory pathways, but also nonspecific auditory pathways, which receive auditory information in parallel from the brainstem, thalamus, and cerebrum.

Temporal bone findings in keratitis, ichthyosis, and deafness syndrome. Case report.

In 1981, the term KID syndrome was suggested for patients with congenital ichthyosis associated with deafness and keratitis. We had a chance to examine the temporal bone of an infant with this syndrome. This patient showed no auditory brain stem response in either ear. Temporal bone studies revealed cochleosaccular abnormality. These findings are offered as a possible explanation for the patient's deafness. The pathologic inner ear findings of congenital deafness syndromes associated with ichthyosis have been heretofore reported in Refsum's syndrome and in a case with universal alopecia. In these cases, the temporal bone pathologic findings were a result of cochleosaccular abnormality. From our case and previous reports, it is suggested that the deafness associated with congenital ichthyosis might be the result of cochleosaccular abnormality.

Delayed motor function and results of vestibular function tests in children with inner ear anomalies.

The relation between the results of vestibular function tests and gross motor development was examined in 4 children with inner ear anomalies. CT scans demonstrated the absence of lateral semicircular canals in both ears in all 4 cases. None responded to caloric stimulation using 40 ml of icewater. In contrast, the damped rotation test elicited per-rotatory nystagmus in all cases. Per-rotatory nystagmus was provoked in only two cases by the Bárány rotation test. Development of gross motor function, especially independent walking, was more delayed in the two children in whom the Bárány rotation test failed to elicit per-rotatory nystagmus.