Auditory Middle Latency Responses Research Articles

Effects of isoflurane on auditory middle latency (MLRs) and steady-state (SSRs) responses recorded from the temporal cortex of the rat

Auditory steady-state responses (SSRs) are believed to result from superimposition of middle latency responses (MLRs) evoked by individual stimuli during repetitive stimulation. Our previous studies showed that besides linear addition of MLRs, other phenomena, mainly related to the adaptive properties of neural sources, interact in a complex way to generate the SSRs recorded from the temporal cortex of awake rats. The aim of this study was to evaluate the effects of the inhalational general anesthetic, isoflurane, on MLRs and SSRs at several repetition rates (30–60 Hz) recorded from the temporal cortex of rats. Auditory evoked potentials were obtained by means of epidural electrodes in the awake condition and during anesthesia at three isoflurane concentrations (0.38, 0.76 and 1.13 vol.% in oxygen). MLR latency significantly increased during anesthesia in a concentration-dependent manner, while MLR amplitude, even when significantly attenuated with respect to the mean awake baseline value, failed to correlate with isoflurane concentration. SSRs decreased in amplitude and increased in phase during anesthesia in a concentration-dependent manner and the anesthetic-induced decrease of SSR amplitude appeared to be higher than the corresponding MLR attenuation. SSR prediction curves synthesized by linear addition of MLRs failed to predict SSRs in both amplitude and phase. Moreover, phase discrepancies proved to be higher during anesthesia. Our results suggest that MLRs and SSRs recorded from the temporal cortex of the rat exhibit differential sensitivity to isoflurane and that isoflurane could enhance the role of rate-dependent effects in SSR generation.

Effects of Isoflurane on the Auditory Brainstem Responses and Middle Latency Responses of Rats

Objective—To evaluate the effects of a volatile anesthetic, isoflurane, on auditory brainstem responses (ABRs) and middle latency responses (MLRs) recorded in rats.Material and Methods—ABRs and MLRs evoked by click stimuli were simultaneously recorded in eight rats in the awake condition and during anesthesia with isoflurane at clinically relevant concentrations.Results—Vertex-recorded ABRs showed a significant increase in the latency of waves I–IV during anesthesia and the latency changes appeared to be significantly related to the isoflurane concentration. The I–IV interval also appeared to be significantly increased in comparison to the awake condition, while minor changes in ABR amplitudes were induced by isoflurane. MLRs, which were recorded by means of epidural electrodes implanted over the auditory cortex, appeared to be attenuated in amplitude and increased in latency during anesthesia. Only latency changes appeared to be significantly related to the isoflurane concentration. Moreover, “bursts” of high amplitude MLRs were observed during anesthesia at each concentration.Conclusion—The present findings indicate that both ABR and MLR latencies are increased by isoflurane in a concentration-dependent manner, whilst the anesthetic-induced attenuation in amplitude does not appear to be related to the isoflurane concentration.

Neurophysiology of cochlear implant users I: effects of stimulus current level and electrode site on the electrical ABR, MLR, and N1-P2 response.

As the need for objective measures with cochlear implant users increases, it is critical to understand how electrical potentials behave when stimulus parameters are systematically varied. The purpose of this study was to record and evaluate the effects of implanted electrode site and stimulus current level on latency, amplitude, and threshold measures of electrically evoked auditory potentials, representing brainstem and cortical levels of the auditory system. The electrical auditory brainstem response (EABR), electrical auditory middle latency response (EAMLR), and the electrical late auditory response (ELAR) were recorded from the same experimental subjects, 11 adult Clarion cochlear implant users. The Waves II, III, and V of the EABR, the Na-Pa complex of the EAMLR and the N1-P2 complex of the ELAR were investigated relative to electrode site (along the intra-cochlear electrode array) and stimulus current level. Evoked potential measures were examined for statistical significance using analysis of variance (ANOVA) for repeated measures. For the EABR, Wave V latency was significantly longer for the basal electrode (7) compared with the mid (4) and apical (1) electrodes. For the EAMLR and ELAR, there were no significant differences in latency by electrode site. For all subjects and each of the evoked potentials, the apical electrodes tended to have the largest amplitude and the basal electrodes the smallest amplitude, although amplitude differences did not reach statistical significance. In general, decreases in stimulus current level resulted in statistically significant decreases in the amplitude of Wave V, Na-Pa and N1-P2. The evoked potential thresholds for Wave V, Na-Pa, and N1-P2 were significantly higher for the basal Electrode 7 than for Electrodes 4 and 1. Electrophysiologic responses of Waves II, III, and V of the EABR, Na-Pa of the EAMLR, and N1-P2 of the ELAR were characterized as functions of current level and electrode site. Data from this study may serve as a normative reference for expected latency, amplitude and threshold values for the recording of electrically evoked auditory brainstem and cortical potentials. Responses recorded from cochlear implant users show many similar patterns, yet important distinctions, compared with auditory potentials elicited with acoustic signals.

Effects of nootropic drugs for demented patients—a study using LORETA

To evaluate the efficacy of nootropic drugs on higher brain function in terms of time and space, electrical field distributions of the scalp map and low-resolution electromagnetic tomography (LORETA) were applied for evoked potentials (EPs) and spontaneous eyes-closed EEG. The studies were carried out on demented patients. We examined them before and after the administration of nicotine with a patch and nefiracetam, which is a pyrrolidine derivative agonist. We recorded event-related potentials (ERPs) with auditory “oddball” paradigm, auditory middle latency response (MLR) and spontaneous eyes-closed resting EEG. Multichannel EPs and EEG data were measured and averaged using a Biologic Brain Atlas. LORETA was used to compute the three-dimensional intracerebral distribution of electric activity of the EPs and the EEG frequency bands. Psychological examinations were also performed. After treatment with nefiracetam, the potential distribution of P3 differed clearly between before and after the administration. This change showed improvement towards normal values. For nicotine, significant effects were found in the MLR P1 component and in some EEG frequency bands. In addition, LORETA for EEG indicated inhibitory, normal and excitatory activity. These findings were supported by significant improvements of the performance test. We conclude that the spatial distribution of inhibitory, normal and excitatory activity, obtained from multichannel EPs and EEG data, allows the assessment of the complex effect of nootropic drugs.

Amplitude–intensity functions for auditory middle latency responses in hearing-impaired subjects

Results from animal studies show that hearing loss can result in increased neural responsiveness within the central auditory system. This study employed auditory middle latency evoked responses to compare central auditory responsiveness in human males with and without hearing loss. Measurements of auditory middle latency responses (MLRs) recorded from 14 normal hearing males were compared with MLR measures from 14 males with high-frequency, sensorineural hearing loss. Sixteen toneburst stimuli (four frequencies×four intensities) were used. Slopes of the amplitude–intensity functions for the several components of the MLR were obtained for each subject at frequencies below, near, and above the audiometric edge. Analysis of variance (ANOVA) revealed a significant group effect for MLR component Pa–Na, with less steep slopes at all frequencies for the hearing-impaired group. The ANOVA also showed a trend towards a significant group effect for Pb–Nb. Two-sample t-tests performed for Pb–Nb for each of the four tonebursts showed a frequency-specific effect. For Pb–Nb there was a statistically greater mean slope for the hearing-impaired group at the toneburst frequency associated with the audiometric edge.

Effects of Stimulus Rate and Gender on the Auditory Middle Latency Response

The effects of stimulus rate and gender on the auditory middle latency response (AMLR) waveforms were examined in 20 young adult male and female subjects. Four different repetition rates were presented to subjects (1.1/sec, 4.1/sec, 7.7/ sec, and 11.3/sec). Stimulus repetition rate had a significant effect on Pa latency, Pa amplitude, and Pb amplitude. Pa and Pb amplitudes decreased with increasing the stimulus rate, and Pa latency significantly increased with increasing the stimulus rate. No significant differences were seen on Pb latency or site of recording. Gender had a significant effect on Pa latency and Pa amplitude. Pa latencies were longer in male subjects, and Pa amplitudes were larger in female subjects. Gender did not have a significant effect on the Pb waveform.

Human auditory middle latency responses: influence of stimulus type and intensity

Human auditory middle latency responses (MLR) to click and tone pip stimuli of different intensities were recorded by means of magnetoencephalography (MEG) and electroencephalography (EEG). Clicks elicited larger responses with significantly shorter latencies than the tone pips at the same intensity in dB sensation level (SL). Most MLR amplitudes increased and their latencies decreased with increasing stimulus intensity for both types of stimulation. Pa and Nb amplitudes saturated at intensities of 60 dB SL in the case of click stimulation. The shorter latencies of MLR evoked by the click were explained by its short rise time and the high frequency content of its spectrum. MEG source analysis yielded MLR sources which were clearly different from those of the slow cortical wave N1. They seem to be located in primary auditory areas along Heschl’s gyrus.

Effect of Stimulus Intensity Level on Auditory Middle Latency Response Brain Maps in Human Adults

Auditory middle latency response (AMLR) brain maps were obtained in 11 young adults with normal hearing. AMLR waveforms were elicited with monaural clicks presented at three stimulus intensity levels (50, 70, and 90 dB nHL). Recordings were made for right and left ear stimulus presentations. All recordings were obtained in an eyes open/awake status for each subject. Peak-to-peak amplitudes and absolute latencies of the AMLR Pa and Pb waveforms were measured at the Cz electrode site. Pa and Pb waveforms were present 100 percent of the time in response to the 90 dB nHL presentation. The prevalence of Pa and Pb to the 70 dB nHL presentation varied from 86 to 95 percent. The prevalence of Pa and Pb to the 50 dB nHL stimulus never reached 100 percent, ranging in prevalence from 77 to 68 percent. No significant ear effect was seen for amplitude or latency measures of Pa or Pb. AMLR brain maps of the voltage field distributions of Pa and Pb waveforms showed different topographic features. Scalp topography of the Pa waveform was altered by a reduction in stimulus intensity level. At 90 dB nHL, the Pa brain map showed a large positivity midline over the frontal and central scalp areas. At lower stimulus intensity levels, frontal positivity was reduced, and scalp negativity over occipital regions was increased. Pb scalp topography was also altered by a reduction in stimulus intensity level. Varying the stimulus intensity significantly altered Pa and Pb distributions of amplitude and latency measures. Pa and Pb distributions were skewed regardless of stimulus intensity.

Suppression of the auditory middle-latency response and evoked gamma-band response in a paired-click paradigm.

When two clicks are presented within 500 ms and the clicks are separated by several seconds, a typical finding is a suppression of the amplitude of the P50 component of the middle-latency auditory-evoked response. In the present study, we investigated whether only the P50 or also the earlier components Po, Na, Pa and Nb, and the exogenous components N100 and P200 exhibit an amplitude suppression to the second click. In addition, we studied the suppression behaviour of the auditory-evoked 40-Hz gamma-band response in the time and frequency domain. We found a significant amplitude suppression to the second click for all components of the auditory-evoked potential following Po, which was most pronounced at electrode Cz. When testing the successive peaks and troughs of the evoked 40-Hz gamma-band response in the time domain, we found a significant amplitude suppression for peaks and troughs with the same latency and polarity as the middle-latency components following Po, which was most pronounced at electrodes Fz and Cz. Consequently, the amplitude of the 40-Hz evoked gamma-band response in the frequency domain paralleled the findings of the time domain, with a significant amplitude suppression to the second tone, which was most pronounced at electrodes Fz and Cz. Results are discussed with reference to the early sensory-gating hypothesis.

Electrically Evoked Potentials Recorded in Adult and Pediatric Clarion® Implant Users

The purpose of this study was to record electrical auditory brain stem responses (EABRs) and electrical middle latency responses (EMLRs) in the clinic from 3 adult CLARION Multi-Strategy Cochlear Implant subjects and to record EABRs in the operating room from 3 pediatric subjects. For 2 of the 3 adult subjects, EABR thresholds were within the subject's behavioral dynamic range, whereas 1 adult subject's EABR thresholds were either absent or, when present, exceeded the upper limit of the dynamic range. For this subject, EMLRs were absent or of poor morphology for the channels tested. Moreover, this subject was not able to understand speech in an open-set, auditory-only format. The EABR thresholds obtained with children were within the behavioral dynamic range for 2 of the 3 subjects, but exceeded comfortable loudness levels for 1 subject. Although the EABR thresholds were measured at stimulus levels that were audible for all subjects, the relationship of the EABR threshold levels to behavioral measures of loudness varied. Evoked potentials that originate more centrally, such as the EMLR, should be investigated further to determine the possible relationship to postimplant performance.

Area-Under-the-Curve Measure of the Auditory Middle Latency Response (AMLR) From Birth to Early Adulthood.

The area-under-the-curve (AUC) measure of the auditory middle latency response (AMLR) waveform was derived and analyzed from recordings in 50 subjects with normal hearing. The AUC metric is believed to represent the total amount of neural energy contributing to the evoked response. This proposed method of measure, therefore, may provide an alternative method of quantifying the response. The subjects were divided into five age groups (n = 10 for each group): infants, children, preteens, teens, and adults. Ipsilateral and contralateral recordings of the AMLR were obtained at two stimulus levels (70 and 40 dB nHL) and at two stimulus rates (11.3 and 3.3/s). AUC measures were obtained for each recording at 70 and 40 dB nHL and at 3.3 and 11.3 clicks/s. These area measurements were compared among the five age groups for significant differences due to age. According to the results, no significant differences in the AUC of the AMLR waveform existed as a function of age.

Ear Extinctionを示す片側脳損傷者における聴性中間潜時反応

Ear Extinctionを示す片側脳損傷者における聴性中間潜時反応

Individual differences in auditory middle latency responses in elderly adults and patients with Alzheimer's disease

Previous research has suggested that the Pb component of the middle-latency auditory evoked response (MLAER) is differentially abnormal in patients with Alzheimer's disease relative to control subjects. In the present study, this putative abnormality was examined in vertex-recorded MLAERs elicited by monaural stimulation in 14 patients with Alzheimer's disease (six females) and 22 age-matched control subjects (10 females). A sex difference in Pb elicitation was revealed in control subjects; Pb area was twice as large in females than males ( P<0.05). Pb and Pa amplitudes and latencies did not differ between male and female control subjects. Comparisons of Pb between patients and controls were conducted within each sex. There was no main effect of group on Pb area, amplitude, or latency. Pa amplitude was significantly larger in patients than control subjects; there was no group difference in Pa latency. This study did not replicate previous reports of differences in Pb between patients with Alzheimer's disease and elderly control subjects. We demonstrated that Pb elicitation may be unreliable in elderly control subjects and found evidence of a possible sex difference. The effects of inter-subject variables (e.g. age, sex) must be understood more fully before MLAERs can be exploited as meaningful markers of brain dysfunction. © 1997 Elsevier Science B.V.

Effects of unilateral cerebral lesions on auditory middle latency responses from seven locations on the scalp

Effects of unilateral cerebral lesions on auditory middle latency responses from seven locations on the scalp

Ketamine increases the amplitude of the 40-Hz auditory steady-state response in humans

The auditory middle latency response (AMLR) and the 40-Hz auditory steady-state response (40-Hz ASSR) are evoked potentials which possibly arise from the same generators in the primary auditory cortex. Both responses are attenuated by most general anaesthetics. Ketamine, however, has been reported to have no effect on the AMLR. Our aim was to evaluate the effects of ketamine on the 40-Hz ASSR. Spectral analysis of the electroencephalogram (EEG) was also conducted to independently examine the effects of ketamine. Ketamine 1.5 mg kg-1 was given to 12 patients for induction of general anaesthesia. Recordings of the 40-Hz ASSR and EEG were obtained every minute from 3 min before administration of ketamine to 5 min after injection, when the study was terminated. Similar recordings were obtained in three control subjects under identical conditions except that no medication was administered. Consciousness, defined as responsiveness to verbal commands, was assessed before each recording. Ketamine caused an increase in the amplitude of the 40-Hz ASSR (P < 0.01). Using published AMLR data, we conducted a simulation experiment that suggested that the effect of ketamine on the AMLR can explain its effects on the amplitude of the 40-Hz ASSR. There was a pronounced increase in relative theta (3.9-7.9 Hz) EEG power and a decrease in relative alpha (8.0-12.8 Hz) power (P < 0.001). These changes were not observed in the control group. Ketamine produced unconsciousness until the end of the study in five patients and transient unconsciousness in five patients. Two patients did not lose consciousness after administration of ketamine. The 40-Hz ASSR and EEG revealed no consistent differences between conscious and unconscious patients. No relationship could be demonstrated between the increase in amplitude of the 40-Hz ASSR or of relative theta power (the hallmark of ketamine effect) and loss of responsiveness to commands. We conclude that ketamine, unlike other anaesthetics, increases the amplitude of the 40-Hz ASSR.

Electrically evoked auditory middle latency responses versus perception abilities in cochlear implant users.

Electrical auditory middle latency responses (EAMLRs) were recorded in a group of 12 postlingually and 4 congenitally deaf cochlear implant users. The EAMLRs of the postlingually deaf cochlear implant users were compared to behavioral measures of speech perception. All the cochlear implant users showed pronounced EAMLR morphology and amplitude. EAMLRs of congenitally deaf cochlear implant users were remarkably similar to those of postlingually deaf cochlear implant users. The difference in speech perception ability between congenitally deaf and postlingually deaf cochlear implant users did not seem to be caused by integrity differences of the neural generators of the auditory middle latency response. For the postlingually deaf subjects, EAMLR amplitude variation and interlatency variation seemed to be related to specific aspects of speech perception. The poorer performers demonstrated more diversity in the amplitude of the EAMLR component peaks and a more diffuse EAMLR peak latency organization across the electrodes than the better performers.

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PS-9-6 Effects of unilateral cerebral lesions on auditory middle latency responses

PS-9-6 Effects of unilateral cerebral lesions on auditory middle latency responses

Possible modulation of auditory middle latency responses by nitric oxide in the inferior colliculus of anaesthetized rats

Nitric oxide (NO) is a short-lived radical species endowed with intercellular signalling functions in the mammalian brain. In the present study we have investigated the effects of focal injection into one inferior colliculus of N ω-nitro- L-arginine methyl ester ( L-NAME), a nitric oxide synthase inhibitor, on the acoustic middle latency responses (MLRs) evoked by click stimuli and recorded from the auditory cortex in anaesthetized rats. Microinfusion of L-NAME (1.0 mM) did not alter the latency of MLRs nor did it affect the evoked brain stem responses (ABRs). By contrast, L-NAME reduced P 1a—N 1 amplitude of MLRs by 51.7 ± 6.6% (mean ± SEM; n = 5) and almost complete recovery to background amplitude was obtained 15–25 min after treatment. The less active isomer, D-NAME (1.0 mM; n = 5), failed to produce consistent effects on the evoked MLRs. A higher concentration of L-NAME (5.0 mM; n = 5) yielded a 69.0 ± 13.3% inhibition whereas maximum inhibition produced by 0.5 mM ( n = 3) L-NAME was ≌10% of control value. The inhibitory effect typically evoked by 1.0 mM L-NAME was prevented by treating rats with L-arginine (5.0 mM; n = 5), the endogenous precursor of NO synthesis. Reduction of MLR amplitude was also obtained in rats receiving intracollicular injection of dizocilpine (MK801; 1.0 μM) and LY274614 (1.0 mM), two selective [ N-methyl- D-aspartate (NMDA) receptor antagonists. In conclusion, the present data support a role for intracollicular NO in the processing and transmission of the acoustic input to the auditory cortex in the rat.

Middle latency response in children with learning disabilities: Preliminary findings

The objective of this investigation was to determine if auditory middle latency responses (MLR) obtained from children with learning disabilities (LD) differ from those obtained from children without LD. Simultaneous recordings of auditory brainstem and middle latency responses were obtained in both vertex-ipsilateral (V-I) and vertex-contralateral derivations (V-C) in 22 children (11 LD and 11 normal) in the age range of eight to twelve years whose peripheral hearing was within normal limits to bilateral. The results indicate that for specific recording conditions, the latencies of middle latency responses differ significantly between children with LD and a normal group of children.