Effects of stimulus repetition rate on slow and fast components of auditory brain-stem responses

Effects of stimulus repetition rate on the slow and fast components of the auditory brain-stem response (ABR) were investigated in 10 adult subjects with normal hearing. The ABRs were recorded with click stimuli at repetition rates of 8, 13.3, 23.8, 40 and 90.9/sec and at an intensity level of 55 dB nHL. Power spectral analysis of the averaged responses was performed. Then the responses were divided into a slow component (0-400 Hz) and a fast component (400-1500 Hz) by using digital filtering technique. The magnitude of the slow component was little affected with increasing stimulus rate from 8/sec to 90.9/sec, while successive waves of the fast component, including wave V, decreased in amplitude as stimulus rate was increased. The latency of the slow component and each wave of the fast component was prolonged with increasing click rates. The shift of latency became longer in the later waves than in the earlier waves.     

Cross-correlation and latency compensation analysis of click-evoked and frequency-following brain-stem responses in man.

Cross-correlation (CC) and latency compensation (LC) analysis were applied to the human click-evoked brain-stem auditory evoked response (BAER) and the brain-stem frequency-following response (FFR). FFRs were elicited by pure tone stimuli (230 Hz and 460 Hz) or by complex tones derived from the sum of 3rd (920 Hz), 4th (1150 Hz), and 5th (1380 Hz) harmonics of the missing 230 Hz fundamental. The lower and upper harmonics always began in sine phase, while the middle harmonic varied in starting phase, resulting in harmonically complex stimuli with differing amplitude and phase patterns. Cross-correlations were computed between individual trials and a wave form template (smoothed wave V for BAER, pure tone stimulus sinusoids for FFR). Trials were included in the analysis only if values of r2 exceeded 0.5 (negative values of r were thus included, which controlled for the chance occurrence of positive correlations). Although brain-stem recordings are noisy, requiring as many as 1000 stimuli/average, correlation analysis consistently identified more positive than negative trials (approximately 2:1 ratio). Trials were also deleted if the lag associated with the selected r2 was at the maximum shift position ('extreme lag'). Averaging trials that satisfied the correlation and lag criteria led to sizeable enhancement of BAER (mean = 114%) and FFR (mean = 68% for 230 Hz stimulus) amplitudes. LC analysis resulted in additional, albeit smaller, increases in amplitude (approximately 10%). FFRs to harmonically complex stimuli were characterized by a clear periodicity at the missing fundamental frequency (230 Hz). However, amplitudes varied according to the modulation depth of the stimulus and, in certain cases, actually exceeded that of the FFR response to a 230 Hz pure tone. The results demonstrate the effectiveness of cross-correlation and, to a lesser degree, latency compensation analysis, applied to two classes of brain-stem potentials. It is anticipated that such techniques will prove useful in the study of auditory signal processing at the level of the brain-stem.     

Effects of acoustic and sensory variables on masking tuning curves of the offset auditory brain-stem response in the rodent

Simultaneous sinusoidal masking of the auditory brain-stem response (ABR) which is generated by the offset of a tone produces a W-shaped masking tuning curve (TC) in the gerbil, rat, mouse, and guinea pig. The probe stimulus offset must be very rapid in most animals. Lesions of the contralateral ear, strychnine blockage of the olivocochlear bundle, or removal of the ipsilateral outer ear do not alter the basic properties of the offset masking TC. Increasing the simultaneous masker duration selectively increases the tuning of the offset masking TC peak. Masking only the latter portions of the probe stimulus does not alter the shape of the offset masking TC.     

Brain-stem auditory evoked potentials in squirrel monkey (Saimiri sciureus)

To more fully characterize brain-stem auditory evoked potentials (BAEPs) in non-human primates, BAEPs were recorded from chronically implanted epidural electrodes in 10 squirrel monkeys (Saimiri sciureus). The effects of stimulus intensity, repetition rate, and anesthesia (ketamine 20 mg/kg i.m.) on peak latencies and inter-peak intervals were evaluated. Monkey wave forms consisted of approximately 7 peaks (I-VII), each exhibiting similar latencies across sessions, with later peaks exhibiting greater variability. In some subjects, additional peaks (IIa, IIIa) and slow potentials were recorded. The slow potentials provided a substratum for peaks IV through VII. As with human, monkey peaks exhibited systematic changes in latency with changes in stimulus intensity or repetition rate. These shifts included significant decreases in latency with increasing intensity for peaks I-IV and increases in latency with increases in repetition rate for peaks III, V, and VI. Inter-peak intervals were similar to those observed in human. Furthermore, ketamine anesthesia significantly delayed the latencies of most peaks (except I, V, and VII). Some differences between monkey and human BAEPs were evident in the relative amplitude of specific peaks. For example, peak V is typically most prominent in human, while this was true for peak III in monkey. The similarities between unanesthetized monkey and human inter-peak intervals suggest that the times required for impulses to reach particular brain-stem areas are conserved across primate species that vary in brain size. This supports the hypothesis that comparably numbered BAEP peaks in monkey and human index homologous processes. The data also suggest that the differences between animal and human BAEPs commonly reported may result from the use of anesthetics. In summary, unanesthetized monkey BAEPs resemble human BAEPs in morphology, number of peaks, polarity, latency variability, inter-peak intervals, slow potentials superimposed on the high-frequency peaks, and variations in morphology, amplitude, and resolution of peaks as a function of recording site. Thus, unanesthetized monkey BAEPs may be an excellent model for investigating the neural substrates of human BAEP or for determining species differences in acoustic processing among primates.     

Brain-stem auditory evoked potential abnormalities with unilateral brain-stem lesions demonstrated by magnetic resonance imaging

We correlated the brain-stem auditory evoked potential (BAEP) abnormalities in 24 patients with discrete unilateral brain-stem lesions demonstrated by magnetic resonance imaging. In 18 patients who had BAEP abnormalities either confined to or more severe on stimulation of one ear, the lesion on magnetic resonance imaging was in the brain stem ipsilateral to the corresponding ear. Mesencephalic lesions produced amplitude abnormalities of the IV/V complex while pontine lesions resulted in abnormalities of earlier components (wave II and/or III). Prolongation of the I-III interpeak latency tended to occur with pontine lesions and of the III-V interpeak latency with mesencephalic lesions. Unilateral brain-stem lesions, particularly at the mesencephalic level, often produced BAEP abnormalities on both ipsilateral and contralateral monaural stimulation.     

Quantitative analysis of reversible dysfunction of brain-stem midline structures caused by disturbance of basilar artery blood flow with the auditory brain-stem responses

To clarify the effects of disturbances in basilar artery blood flow, basilar artery angiospasm was induced in 2 cats and 4 guinea pigs and auditory brain-stem responses (ABRs) were continuously recorded preceding, during and following the angiospasm. The angiospasm caused specific ABR changes in that waves II (P2-N2) and III (P3-N3) were attenuated without any corresponding amplitude reduction of P4. Those changes were equivalent following stimulation of either ear. Moreover, the ABR changes gradually recovered within 5 h. On the basis of the animal experiments, 52 patients with subarachnoid hemorrhage, supratentorial tumor showing increased intracranial pressure or hydrocephalus were selected for repeated ABR examinations. ABR abnormalities similar to those observed in the animal experiment were obtained especially from the patients exhibiting grade 3 or 4 symptomatology with subarachnoid hemorrhage. In these cases, the wave III to wave IV-V amplitude ratio was significantly decreased. In some cases the ABR abnormalities and the wave III to wave IV-V amplitude ratio recovered as the clinical course improved. These results support the conclusion that specific ABR changes (wave III to wave IV-V amplitude ratio) reflect transient ischemic dysfunction of the midline portion of the brain-stem caused by disturbances of basilar artery blood flow.     

A developmental study on the effect of stimulus rate on the auditory evoked brain-stem response

Four groups of subjects were presented auditory stimuli differing only in repetition rate. One group was adults, another term newborns, and the other 2 groups were preterm newborns tested at respectively, 32 and 36 weeks postconceptional age. All 4 groups were judged to be audiologically and neurologically normal at the time of testing. Six stimulus repetition rates were presented to each subject, 10, 20, 40, 50, 66 2/3, and 80/sec. Auditory evoked brain-stem responses (ABRs) were recorded to each stimulus. Increasing repetition rate increased ABR wave form latencies and decreased ABR wave form amplitudes at all ages tested. For the most reliable measurement, wave V latency, a linear function effectively described the latency-rate function for individual subjects at all ages. The slope of the wave V latency-rate function increased with decreasing age. It was 300 microseconds decade change in rate at 32 weeks, 227 microseconds/decade at 36 weeks, 162 microseconds/decade at term, and 86 microseconds/decade in adults. Wave V latencies were more prolonged by rate than waves I and III and the differences in the rate effects between waves V and I and III increased with decreasing age. Amplitude was a less reliable measurement and amplitude-rate effects were less consistent than latency-rate effects.     

Auditory brain-stem responses in adrenomyeloneuropathy

We studied three patients with adrenomyeloneuropathy. Complete audiologic assessment was obtained: two patients showed unimpaired peripheral hearing and one showed a mild high-frequency hearing loss. Auditory brain-stem responses were abnormal in both ears of all subjects, with one subject showing no response above wave I, and the other two having significant wave I to III and wave III to V interval prolongations. We concluded that auditory brain-stem response testing provides a simple, valid, reliable method for demonstrating neurologic abnormality in adrenomyeloneuropathy even prior to evidence of clinical signs.     

Auditory brain-stem, middle- and long-latency evoked potentials in mild cognitive impairment.

OBJECTIVE: Mild cognitive impairment (MCI) is a selective episodic memory deficit in the elderly with a high risk of Alzheimer's disease. The amplitudes of a long-latency auditory evoked potential (P50) are larger in MCI compared to age-matched controls. We tested whether increased P50 amplitudes in MCI were accompanied by changes of middle-latency potentials occurring around 50 ms and/or auditory brain-stem potentials. METHODS: Auditory evoked potentials were recorded from age-matched controls (n = 16) and MCI (n = 17) in a passive listening paradigm at two stimulus presentation rates (2/s, 1/1.5 s). A subset of subjects also received stimuli at a rate of 1/3 s. RESULTS: Relative to controls, MCI subjects had larger long-latency P50 amplitudes at all stimulus rates. Significant group differences in N100 amplitude were dependent on stimulus rate. Amplitudes of the middle-latency components (Pa, Nb, P1 peaking at approximately 30, 40, and 50 ms, respectively) did not differ between groups, but a slow wave between 30 and 49 ms on which the middle-latency components arose was significantly increased in MCI. ABR Wave V latency and amplitude did not differ significantly between groups. CONCLUSIONS: The increase of long-latency P50 amplitudes in MCI reflects changes of a middle-latency slow wave, but not of transient middle-latency components. There was no evidence of group difference at the brain-stem level. SIGNIFICANCE: Increased slow wave occurring as early as 50 ms may reflect neurophysiological consequences of neuropathology in MCI.     

Brain-stem auditory evoked responses to hypercarbia in preterm infants

To determine the effect of acute hypercarbia on brain-stem function in preterm neonates, we compared brain-stem auditory evoked responses (BAERs) during 8% CO₂ breathing to those elicited during room air breathing in 12 healthy preterm infants during the first week of life. End-tidal CO₂ (ETpCO₂), respiratory rate and depth were monitored throughout the protocol. Absolute wave latencies and interpeak intervals of the BAERs were ana;yzed from duplicate trials. During 8% CO₂ breathing, ETpCO₂, respiratory rate depth of respiration increased significantly (p < 0.05). The absolute latency of wave V was prolonged (P < 0.025). Values of absolute peak latencies I and III were unaffected by the hypercarbic state. These data demonstrate that elevations in pCO₂ which elicit ventilatory responses also effect the BAER. The specific effects on ventilatory pattern, peak V latency and interpeak interval III–V indicate brain-stem responsiveness and alterations in the more central components of the auditory pathway. These findings raise important considerations regarding the influence of hypercarbia on brain-stem function preterm infants and the clinical management of such infants with abnormalities of gas exchange.     

Brain-stem auditory evoked potentials in adults with Down's syndrome.

Brain-stem auditory evoked potentials (BAEPs) were examined in 37 adult patients with Down's syndrome and in 37 age-matched normal subjects. All absolute and interpeak latencies except for the interpeak latency IV-V were shorter in patients than in normal subjects. The amplitude of wave V and the amplitude ratio V/I were smaller in patients than in normal subjects. Short latencies in patients were considered to be due to the smaller size of the brain-stem or to faster conduction velocity. The prolonged interpeak latency IV-V and the smaller wave V may indicate physiological dysfunctions between the upper pons and the lower midbrain.     

BAEP amplitudes and amplitude ratios: relation to click polarity, rate, age and sex.

BAEP amplitudes and amplitude ratios in 47 healthy subjects aged 4-58 years have been investigated with respect to the simultaneous influence of stimulus polarity, rate, sex and age. The sex effect (larger amplitudes in women than in men) seemed to be most pronounced for wave IV-V amplitude, while the age effects (decreasing amplitudes with age) seem to be largest for the early waves. The amplitude reductions which followed an increment in the stimulus rate from 10 to 50 Hz were generally larger than the reduction following a change in the stimulus polarity from R to C clicks. The rate-induced amplitude reductions depend on click polarity for waves II and V. Thus, adaptation may be different in C click responding neurons as compared to R click responding neurons. The IV-V/I and IV-V/III amplitude ratios were both independent of sex, but the IV-V/I ratio increased significantly with age. Polarity and rate effects depended on age (wave III) but not on sex. Thus, aging may involve alterations of neural function, while the sex-related amplitude differences may be explained by non-neural factors.     

The effect of click rate on latency and interpeak interval of the brain-stem auditory evoked potentials in children from birth to 6 years.

Latency and interpeak interval of the brain-stem auditory evoked potentials at different click rates were measured in 80 healthy children from birth to 6 years, and 21 adults. Clicks were presented at 10, 30, 50, 70 and 90/sec, and 70, 40 and 20 dB HL. At high stimulus intensity (70 dB SL), all latencies of waves I, III and V and the I-V, I-III and III-V intervals showed a progressive prolongation with increasing repetition rate. The latency- and the interval-rate functions were similar for all age groups but their slopes were slightly steeper in younger than in older. As click rate increased from 10/sec to 90/sec, the latencies of waves I, III and V at different age groups were prolonged by 4-10%, 9-13% and 12-15% respectively, and the intervals of I-V, I-III and III-V were prolonged by 15-16%, 8-16% and 14-24% respectively. The mean increments of wave V latency and I-V interval in different age groups were 0.404-0.575 and 0.332-0.526 msec respectively with increasing click rate from 10 to 50/sec, and 0.697-1.009 and 0.629-0.776 msec respectively with increasing click rate from 10 to 90/sec. The younger the age the larger the absolute increments for all these BAEP parameters, but the increasing rates for a BAEP measure were similar among different age groups, exhibiting no age-dependent differences.(ABSTRACT TRUNCATED AT 250 WORDS)     

Anesthesia effects: auditory brain-stem response

Auditory brain-stem responses (ABRs) were measured in the awake state and with ketamine and xylazine anesthesia in adult gerbils. Surface recorded vertex-positive components of the ABR were analyzed with respect to the awake and anesthetized states as a function of stimulus frequency. ABR thresholds were not altered with ketamine/xylazine. Small increases in peak latency were associated with anesthesia for all components except wave P1. Increases in absolute latency were progressively greater for successive peaks, reaching an average shift of 0.41 msec for wave P6. Amplitude changes with anesthesia were more variable, with increases generally seen for waves P4 and P6. Significant anesthesia effects on peak latency and amplitude were independent of stimulus frequency. These data confirm previously reported ABR sensitivity to non-barbiturate anesthesia. Direct comparisons of ABR interpeak intervals or amplitude ratios from awake versus anesthetized animals must account for the effects of barbiturate and non-barbiturate agents. However, the stability of response threshold and the small magnitude of latency and amplitude changes with a ketamine and xylazine regimen demonstrate that accurate electrophysiological measures of hearing sensitivity and auditory brain-stem activity can be obtained in anesthetized animals, provided that temperature and other parameters are maintained within normal physiological limits.     

脑干听觉诱发电位在脑干肿瘤手术中的监护

用双耳刺激、双侧记录的脑干听觉诱发电位(简称bBAEP)对16例脑干肿瘤进行术中监护。发现所有病人在手术操作时,均出现bBAEP改变,按其改变程度大致可分为轻、中、重三种改变。认为bBAEP更适用于手术中监护;bBAEP改变程度能反映脑干功能受影响程度;术中bBAEP监护有助于提高手术效果,且能预测预后;Ⅲ波和(或)Ⅴ波的潜伏期(PL),Ⅰ～Ⅲ、Ⅰ～Ⅴ、Ⅲ～Ⅴ的峰间潜伏期(IPL)延长超过1.5ms,或者全部波形消失,是脑干功能受到不可逆损害的具体指标。     

Far-field recorded frequency-following responses: correlates of low pitch auditory perception in humans.

The recent demonstration that auditory frequency-following responses (FFR) can be recorded by signal averaging from the human scalp, opened the way for studies correlating FFR with auditory experience. This report describes FFR amplitude changes as a function of stimulus intensity and the addition of masking noise. The first experiment revealed a high degree of consistency both within and across subjects in the latency, phase and waveform of averaged FFR. This experiment also demonstrated a monotonic relationship between average FFR amplitude and stimulus intensity between 40 and 65 dB SL. Results of the second experiment showed a close correlation between the detectability of a tone in a noise masker and FFR amplitude. FFR amplitude diminishes precipitously as noise intensity approaches or exceeds the threshold for masking of the tone. These results are interpreted as emphasizing the role of neural periodicity mechanisms in the preception of low frequencies.     

Source derivation of the brain-stem auditory evoked potential

This study described the results of applying source derivation to the brain-stem auditory evoked potential. Unilateral stimulation gives rise to current sinks, associated with waves I and III, which are located in the vicinity of the ipsilateral mastoid. Waves II and V are associated with a pair of current sinks which appear bilaterally in the vicinity of each mastoid.     

Clinical correlates of brain-stem auditory evoked potential variables in multiple sclerosis. Relation to click polarity.

The correlations between clinical signs and BAEP latency, amplitude and dispersion variables were investigated in 98 multiple sclerosis patients. A new dispersion variable, the wave IV-V "shape ratio" (SR IV-V), correlated most strongly with brain-stem signs (i.e., nystagmus). Severely reduced wave IV-V amplitude was frequently found in patients with vertical nystagmus or internuclear ophthalmoplegia, and interpeak latency (IPL) III-V correlated most strongly with cerebellar dysfunction (i.e., ataxia). The results may reflect different localizing ability among the various BAEP variables. The association between ataxia and increased IPL III-V was significantly stronger for BAEP to C clicks than to R clicks. Patients with abnormal BAEPs to one polarity (C or R) but not to the other, had significantly more clinical dysfunction than patients with normal BAEPs to both C and R clicks. Hence, C vs. R discordance may be interpreted to indicate possible brain-stem dysfunction.     

Auditory brain-stem responses in hydrocephalic patients

Auditory brain-stem response (ABR) was measured in 40 patients (80 ears) with confirmed hydrocephalus. Eighty-eight percent of these patients showed some form of ABR abnormality. Responses indicative of brain-stem dysfunction consisted of prolonged I-V interwave latency (38%), reduced V/I amplitude ratio (33%), and abnormalities in wave-shape of components III (27%) and V (53%). In addition, 70% of the patients had elevated ABR thresholds; 45% had responses in excess of 20 dB HL and the remaining 25% had no ABR activity. The etiology of the hydrocephalus, head circumference and brain-stem symptoms were not associated with particular ABR abnormalities. Communicating hydrocephalus correlated significantly with both prolonged I-V conduction time and absence of ABR activity, compared with non-communicating hydrocephalus. Four of the 9 patients retested showed ABR improvement on follow-up; one patient showed deterioration. The results were compared to our prior studies of ABR in 60 post-meningitic patients and in 100 severely neurologically impaired institutionalized children in whom the incidence of intrinsic brainstem abnormalities was one-third and two-thirds that of the hydrocephalic group, respectively. The results of this study suggest that ABR can be used to document clinically unsuspected brain-stem pathology that may accompany hydrocephalus. Auditory brain-stem dysfunction is likely to complicate the assessment of hearing sensitivity in hydrocephalic patients.     

Normal variability of the brain-stem auditory evoked response in young and old adult subjects.

The brain-stem auditory evoked response was studied under three combinations of intensity and rate of click stimulation in 25 young and 25 old adult subjects. The responses show a great intra and inter subject variability. Waves 1, 3 and 5 are constant and reproducible markers of the response while waves 2, 4, 6, and 7 are variable and frequently asymmetrical or absent. Wave peak latencies increase with an increase in stimulation rate, a decrease in stimulus intensity and an increase in age. Interpeak conduction times, except those involving wave 2, are unaffected by a change in stimulus intensity. Wave 1-3 time increases with an increase in stimulus rate and an increase in age while wave 3-5 time is not affected by any change in stimulus parameters or age. Wave amplitude alone is not a reliable measure of normality. Normal values for peak latencies, interpeak conduction times and interear symmetry are presented. One tailed 95 and 99% confidence intervals for normal interpeak conduction times are presented with appropriate corrections for stimulus rate used and patient age. No corrections need to be made for changes in stimulus intensity. This suggests that no correction is necessary when studying patients with conductive type hearing deficits. Laboratories using the same stimulation technique appear to produce equivalent normative conduction time values.