The influence of phase inversion on the auditory evoked response

The amplitude of the auditory evoked response (N₁P₂) was measured over repeated tests on 24 normal hearing listeners. 200 and 2 000 Hz were presented in-phase (S₀) and out-of-phase (S_π) at moderate intensity levels. Response amplitude for S_π was significantly larger (p < 0.025) than that for S₀ when the tonal stimulus was 200 Hz. The results of psychophysical tests ruled out the possibility that this finding could be attributed to differences in loudness between S_π and S₀. No statistically significant difference in response amplitude was found between S_π and S₀ when 2 000 Hz was employed. These data are discussed with reference to the research on masking level differences.     

The auditory steady-state response: comparisons with the auditory brainstem response

Two studies are reported in which the threshold estimates from auditory steady-state response (ASSR) tests are compared to those of click- or toneburst-evoked auditory brainstem responses (ABRs). The first, a retrospective review of 51 cases, demonstrated that both the click-evoked ABR and the ASSR threshold estimates in infants and children could be used to predict the pure-tone threshold. The second, a prospective study of normal-hearing adults, provided evidence that the toneburst-evoked ABR and the modulated tone-evoked ASSR thresholds were similar when both were detected with an automatic detection algorithm and that threshold estimates varied with frequency, stimulus rate, and detection method. The lowest thresholds were obtained with visual detection of the ABR. The studies illustrate that ASSRs can be used to estimate pure-tone threshold in infants and children at risk for hearing loss and also in normal-hearing adults.     

Brain stem auditory evoked response correlates in patients with spinocerebellar lesions

Brain stem auditory evoked responses were obtained in three patients with spinocerebellar dysfunction for assessment of brain stem involvement and lateralization. Computed tomography scan in the three cases showed negative findings for the brain stem. The evoked potentials demonstrated involvement of the pontine tegmentum. Correlation was found for lateralization to the site of greater neurologic deficit. Brain stem auditory evoked response abnormalities reflect disturbance of neural function rather than the underlying anatomic change of that disturbance. It therefore appears to be a more sensitive type of testing than the computed tomography scan in detecting lesions that alter electrophysiology but do not produce alterations of morphology and radiodensity.     

Brainstem auditory evoked response sensitivity: comparison with other neurologic tests in the detection of retrocochlear lesions

Brainstem auditory evoked response (BAER) tests were obtained in 3 patients with suspected retrocochlear lesions. Subsequently, CT scans and the surgical procedure demonstrated tumors of about the same size (2 cm) in the cerebellopontine angle. One was an VIIIth-nerve schwannoma, one a meningioma, and one a VIIth-nerve neuroma. BAER recordings were analyzed with results of other tests: conventional audiometry, stapedius reflex measurements and electronystagmography (ENG). A striking finding was a normal BAER in the patient with the VIIIth-nerve schwannoma. ENG recordings in this case showed ipsilateral impairment of optokinetic nystagmus. The BAER was abnormal in the other 2 patients. A consistent abnormality for the 3 patients was absence of stapedius reflex in the ear in question. This study disclosed the advantage of utilizing a battery of tests in the investigation of retrocochlear lesions. The ENG recordings should include evaluation of the vestibulo-oculomotor pathways.     

Effects of neocortical lesions on the P300 component of the auditory evoked response

P300 event-related potentials were recorded in 10 subjects with neocortical lesions, and 10 control subjects, using a basic oddball paradigm. In separate tests, subjects discriminated rare and frequent tones that differed with respect to frequency, or discriminated the tones in a noise background. Subjects were required to count the number of rare stimuli that occurred during test runs. Recordings were obtained from vertex (Cz) sites referenced to linked earlobe electrodes. Control subjects exhibited P300s on all test runs. Decreasing stimulus differences relative to frequency, or adding background noise, produced significant increases in P300 latency plus decreases in amplitude. In contrast, two of the 10 lesion subjects failed to demonstrate P300 responses, although both subjects accurately counted the rare stimuli. With the remaining lesion subjects, absent or significantly delayed P300 responses occurred in 53 percent of the test runs, while accurate counts of the rare stimuli were maintained in all test runs. Absent or delayed P300s in the lesion group was not correlated with location or extent of the lesions. These results indicate that, while the P300 is susceptible to neocortical damage, it reflects cognitive processing other than simply discriminating differences between rare and frequent stimuli.     

The auditory steady state response in individuals with neurological insult of the central auditory nervous system

The auditory steady state response (ASSR) has recently gained attention with respect to estimates of hearing sensitivity and configuration of hearing loss. The present investigation compared behavioral thresholds to estimated ASSR thresholds in subjects with confirmed CANS lesions to determine if this population can be accurately evaluated with ASSR techniques. Comparisons were made between the experimental group and a normal control group matched for age and hearing sensitivity. ASSR thresholds were obtained for the carrier frequencies of 500 and 2000 Hz with a 46 Hz modulation rate and compared to behavioral thresholds. Within and between group comparisons were made. The control group demonstrated strong correlation between their behavioral and estimated ASSR thresholds which significantly contrasted the neurological group. Additionally, individuals with neurological impairment of the CANS exhibited elevated thresholds that were on average 24 dB greater at 2000 Hz than their behavioral thresholds. These results suggest that individuals with neurological insult may appear as hearing impaired or having greater hearing loss than is actually present. As a result, the ASSR may demonstrate the potential to assist in the detection of CANS dysfunction.     

Automated system for screening hearing using the auditory brainstem response

Routine screening of hearing using the auditory brainstem response (ABR) in infants, such as neonates in the special care baby unit, requires a system which is quick, user-friendly and gives a simple outcome. A system which consists of a stimulator/amplifier unit for recording the ABR controlled by a standard Master Series BBC Microcomputer is described which fulfils these requirements. The test procedure is highly automated, and a pass or refer decision for the screen on each ear is given by a machine-scoring algorithm which detects the ABR waveform.     

Sound localization: value in localizing lesions of the auditory pathway

Reports in the literature suggest that patients with otosclerosis, neural lesions such as acoustic neuroma, pontine lesions, and temporal lobe lesions may show abnormal sound localization ability. In the present experiment, 15 normal subjects and 22 patients with various auditory pathway lesions had sound localization testing using special apparatus. The results confirmed that patients with otosclerosis were unable to localize low frequency sounds. Those with temporal lobe lesions made judgments not significantly different from normal subjects. Patients with unilateral sensorineural deafness made errors localizing high frequency sounds. Those with acoustic neuromas made greater errors than those without, but the difference between these two groups just failed to reach statistical significance. The number of cases was however small, and further studies are in progress to attempt to define numerical criteria to assist clinical decisions with regard to the selection of patients for invasive investigations such as oil cisternogram.     

The influence of exercise-induced temperature elevations on the auditory brain-stem response (ABR)

The influence of exercise on the auditory brain-stem response (ABR) was examined in 16 healthy volunteers (8 female and 8 male). Ipsilateral ABR recordings were obtained before and after exercise on a bicycle ergonometer. The rise of body temperature so generated was 0.5-2.1 degrees C (mean, 1.3 degrees C) as measured in the contralateral external auditory meatus. Latencies of waves III and V (but not wave I) were found to be significantly lower immediately post-exercise (P less than 0.01). The temperature relations of the latency of wave V are described by the regression equation: Latency (ms) = 11.06-0.146 x temp. (degrees C). (The effects on amplitude were not significant, nor were male/female differences.) It is suggested that exercise hyperthermia could be an appropriate model for the evaluation of the ABR in fever.     

Comparison of auditory steady-state response and auditory brainstem response thresholds in children

Recently, auditory steady-state responses (ASSRs) have been proposed as an alternative to the auditory brainstem response (ABR) for threshold estimation. The goal of this study was to investigate the degree to which ASSR thresholds correlate with ABR thresholds for a group of sedated children with a range of hearing losses. Thirty-two children from the University of Iowa Hospitals and Clinics ranging in age from 2 months to 3 years and presenting with a range of ABR thresholds participated. Strong correlations were found between the 2000-Hz ASSR thresholds and click ABR thresholds (r = .96), the average of the 2000- and 4000-Hz ASSR thresholds and click ABR thresholds (r = .97), and the 500-Hz ASSR and 500-Hz toneburst ABR thresholds (r = .86). Additionally, it was possible to measure ASSR thresholds for several children with hearing loss that was great enough to result in no ABR at the limits of the equipment. The results of this study indicate that the ASSR may provide a reasonable alternative to the ABR for estimating audiometric thresholds in very young children.     

Fibro-osseous lesions of the external auditory canal

OBJECTIVES: To differentiate a novel type of benign circumscribed bone lesion of the external auditory canal from those described previously, such as exostoses and osteomas. STUDY DESIGN: Information was obtained from computed tomography (CT) images, surgical findings, and pathologic study. METHODS: Five patients (26 to 82 years old) who presented a hard, round, unilateral, skin-covered mass occluding the external auditory canal to varying degrees were studied. A CT study carried out before resection of the lesions by curettage disclosed the absence of a bony connection to the underlying structures. All the tissue specimens underwent pathologic study. RESULTS: CT and surgical findings demonstrated the absence of a connective pedicle. The pathologic findings showed lesions consisting of an osteoma-like bone formation with sparse osteoblastic areas; mature lamellar bone was observed in three cases, bone marrow containing adipose tissue and hematopoietic remnants in two, and a dense, collagenous stroma in another. They all showed irregular trabeculae, bordered by osteoid osteoblasts. In no case was there evidence of a relationship to the cartilaginous tissue or to the bony structures of the external auditory canal. CONCLUSIONS: The data obtained from the clinical, CT, surgical, and pathologic findings suggest the existence of a lesion unlike those previously known, possibly related to ossifying reactions in other parts of the organism.     

A central auditory evaluation protocol: a guide for training and diagnosis of lesions of the central system

The current paper is a tutorial regarding central auditory evaluation (CAE). Evaluation of lesions of the central auditory nervous system is an area of growing interest and activity. A variety of behavioral and electrophysiological methods has been described to detect lesions affecting auditory structures and tracts of the brain stem and cortical levels. In order to foster an organized and rational approach to CAE, the following topics are discussed: prerequisite knowledge needed to perform CAE; the role of history and the basic evaluation; hypothesis formulation; a two-stage CAE protocol, presented in a coded, diagrammatic fashion; and several caveats regarding factors which may complicate test interpretation. Subject variables and additional criteria to be considered in test selection and data interpretation are described. The tutorial is presented in an effort to promote development and refinement of the CAE battery through its systematic application.     

正常豚鼠听性脑干反应与听性稳态反应的对比

目的 比较正常豚鼠听性脑干反应(ABR)和听性稳态反应(ASSR)阈值的差异,为利用豚鼠进行听力学研究提供理论依据.方法 选正常听力豚鼠12只(24耳),在戊巴比妥钠镇静状态下,分别行ABR和ASSR测试.ABR为click刺激声,刺激率为11.1次/s,记录ABR的Ⅱ渡反应阈值.ASSR载波频率(CF)为0.5、1、2、3、4、6 kHz,调制频率(MF)为154 Hz,记录各载频的反应阅值.结果 正常豚鼠ASSR反应阈值高于ABR反应阈值,CF:0.5.4 kHz时.ABR与ASSR阈值间有统计学差异(P<0.01);CF=6 kHz时,两阈值间无统计学差异(P>0.05).结论 正常豚鼠ABR与ASSR阈值间存在较大差值,但ABR与6 kHz的ASSR阈值间无显著差异.故对豚鼠进行听阈评估时,要注意两者间由于ASSR载波频率不同所引起的差异.     

Neuroplasticity in the auditory system

An increasing interest on neuroplasticity and nerve regeneration within the auditory receptor and pathway has developed in recent years. The receptor and the auditory pathway are controlled by highly complex circuits that appear during embryonic development. During this early maturation process of the auditory sensory elements, we observe the development of two types of nerve fibers: permanent fibers that will remain to reach full-term maturity and other transient fibers that will ultimately disappear. Both stable and transitory fibers however, as well as developing sensory cells, express, and probably release, their respective neuro-transmitters that could be involved in neuroplasticity. Cell culture experiments have added significant information; the in vitro administration of glutamate or GABA to isolated spiral ganglion neurons clearly modified neural development. Neuroplasticity has been also found in the adult. Nerve regeneration and neuroplasticity have been demonstrated in the adult auditory receptors as well as throughout the auditory pathway. Neuroplasticity studies could prove interesting in the elaboration of current or future therapy strategies (e.g.: cochlear implants or stem cells), but also to really understand the pathogenesis of auditory or language diseases (e.g.: deafness, tinnitus, dyslexia, etc.).     

Temporal envelope processing in the human auditory cortex: response and interconnections of auditory cortical areas

Temporal envelope processing in the human auditory cortex has an important role in language analysis. In this paper, depth recordings of local field potentials in response to amplitude modulated white noises were used to design maps of activation in primary, secondary and associative auditory areas and to study the propagation of the cortical activity between them. The comparison of activations between auditory areas was based on a signal-to-noise ratio associated with the response to amplitude modulation (AM). The functional connectivity between cortical areas was quantified by the directed coherence (DCOH) applied to auditory evoked potentials. This study shows the following reproducible results on twenty subjects: (1) the primary auditory cortex (PAC), the secondary cortices (secondary auditory cortex (SAC) and planum temporale (PT)), the insular gyrus, the Brodmann area (BA) 22 and the posterior part of T1 gyrus (T1Post) respond to AM in both hemispheres. (2) A stronger response to AM was observed in SAC and T1Post of the left hemisphere independent of the modulation frequency (MF), and in the left BA22 for MFs 8 and 16Hz, compared to those in the right. (3) The activation and propagation features emphasized at least four different types of temporal processing. (4) A sequential activation of PAC, SAC and BA22 areas was clearly visible at all MFs, while other auditory areas may be more involved in parallel processing upon a stream originating from primary auditory area, which thus acts as a distribution hub. These results suggest that different psychological information is carried by the temporal envelope of sounds relative to the rate of amplitude modulation.     

Threshold prediction using the auditory steady-state response and the tone burst auditory brain stem response: a within-subject comparison

OBJECTIVE: The purpose of this study was to evaluate the accuracy with which auditory steady-state response (ASSR) and tone burst auditory brain stem response (ABR) thresholds predict behavioral thresholds, using a within-subjects design. Because the spectra of the stimuli used to evoke the ABR and the ASSR differ, it was hypothesized that the predictive accuracy also would differ, particularly in subjects with steeply sloping hearing losses. DESIGN: ASSR and ABR thresholds were recorded in a group of 14 adults with normal hearing, 10 adults with flat, sensorineural hearing losses, and 10 adults with steeply sloping, high-frequency, sensorineural hearing losses. Evoked-potential thresholds were recorded at 1, 1.5, and 2 kHz and were compared with behavioral, pure-tone thresholds. The predictive accuracy of two ABR protocols was evaluated: Blackman-gated tone bursts and linear-gated tone bursts presented in a background of notched noise. Two ASSR stimulation protocols also were evaluated: 100% amplitude-modulated (AM) sinusoids and 100% AM plus 25% frequency-modulated (FM) sinusoids. RESULTS: The results suggested there was no difference in the accuracy with which either ABR protocol predicted behavioral threshold, nor was there any difference in the predictive accuracy of the two ASSR protocols. On average, ABR thresholds were recorded 3 dB closer to behavioral threshold than ASSR thresholds. However, in the subjects with the most steeply sloping hearing losses, ABR thresholds were recorded as much as 25 dB below behavioral threshold, whereas ASSR thresholds were never recorded more than 5 dB below behavioral threshold, which may reflect more spread of excitation for the ABR than for the ASSR. In contrast, the ASSR overestimated behavioral threshold in two subjects with normal hearing, where the ABR provided a more accurate prediction of behavioral threshold. CONCLUSIONS: Both the ABR and the ASSR provided reasonably accurate predictions of behavioral threshold across the three subject groups. There was no evidence that the predictive accuracy of the ABR evoked using Blackman-gated tone bursts differed from the predictive accuracy observed when linear-gated tone bursts were presented in conjunction with notched noise. Similarly, there was no evidence that the predictive accuracy of the AM ASSR differed from the AM/FM ASSR. In general, ABR thresholds were recorded at levels closer to behavioral threshold than the ASSR. For certain individuals with steeply sloping hearing losses, the ASSR may be a more accurate predictor of behavioral thresholds; however, the ABR may be a more appropriate choice when predicting behavioral thresholds in a population where the incidence of normal hearing is expected to be high.