Changes In Auditory Evoked Potentials Research Articles

A cross-sectional study of severe acute malnutrition impact on auditory evoked potentials in children age 6–59 months

Background: Malnutrition is a public health concern in India. According to NFHS-5, the number of children under 5 years who are stunted (less height-for-age) and underweight (less weight-for-age) in India, are 35.5% and 32.1%, respectively. Many researchers reported that malnutrition affects myelination and neural maturation of the auditory brainstem pathway. Aims and Objectives: In this study, auditory evoked potential (AEP) parameters were studied in severly acute malnutrition (SAM) children of 6 months to <5 years of age. Materials and Methods: Fifty children, with severely malnourished (Their weighted age was 51–60% of the expected weight, and height for age <85% of the expected height) and 50 healthy children (with weight >80% of expected with normal height for their age), aged 6–59 months were included in the study. The parameters of AEPs were recorded using RMS-EMG EP MARK II, a 4-channel machine. Results: In our study, 30 (60%) males and 20 (40%) females had severe acute malnutrition. There were significant differences in the mean latencies of the waves I to V and the mean interpeak latencies (IPLs) of the waves I-III and I-V on the right and left ears between the study and control groups (P<0.05). The mean IPLs of I-III and I-V on the right side were found to be longer in the SAM group than in the control group (P<0.05. While the mean absolute peak latencies of wave, I found prolonged on both ears in the children with SAM (P<0.05). Conclusion: In the present study, severely acute malnourished children showed changes in AEPs characterized by absolute wave prolonged latencies and interpeak intervals compared with normally nourished children.

32. BAEPs and their application in monitoring the auditory pathway

We discuss cases with cerebellopontine angle surgery and intraoperative monitoring with auditory evoked potentials. The aim of neuromonitoring is to provide the surgical team with an additional instrument to assess the functional state of the hearing pathway with objective neurophysiological criteria, during surgery near the eighth cranial nerve. Changes in latency, amplitude or total loss of the responses during a neurovascular decompression of the trigeminal nerve, can be avoided by the surgeon modifying the surgical technique. Monitoring is challenging in chronic lesions with poor basal studies. In cases of acoustic neuroma with preserved, but low voltage potentials, the outcome is good. In other cases, latency increments and transient amplitude attenuation, with normalization at the end of surgery, the postoperative results were good with hearing preservation. The relationship between intraoperative auditory evoked potentials changes and eighth nerve integrity with hearing preservation, are consistent with patient prognosis.

From bird to sparrow: Learning-induced modulations in fine-grained semantic discrimination

Recognition of environmental sounds is believed to proceed through discrimination steps from broad to more narrow categories. Very little is known about the neural processes that underlie fine-grained discrimination within narrow categories or about their plasticity in relation to newly acquired expertise. We investigated how the cortical representation of birdsongs is modulated by brief training to recognize individual species. During a 60-minute session, participants learned to recognize a set of birdsongs; they improved significantly their performance for trained (T) but not control species (C), which were counterbalanced across participants. Auditory evoked potentials (AEPs) were recorded during pre- and post-training sessions. Pre vs. post changes in AEPs were significantly different between T and C i) at 206–232ms post stimulus onset within a cluster on the anterior part of the left superior temporal gyrus; ii) at 246–291ms in the left middle frontal gyrus; and iii) 512–545ms in the left middle temporal gyrus as well as bilaterally in the cingulate cortex. All effects were driven by weaker activity for T than C species. Thus, expertise in discriminating T species modulated early stages of semantic processing, during and immediately after the time window that sustains the discrimination between human vs. animal vocalizations. Moreover, the training-induced plasticity is reflected by the sharpening of a left lateralized semantic network, including the anterior part of the temporal convexity and the frontal cortex. Training to identify birdsongs influenced, however, also the processing of C species, but at a much later stage. Correct discrimination of untrained sounds seems to require an additional step which results from lower-level features analysis such as apperception. We therefore suggest that the access to objects within an auditory semantic category is different and depends on subject’s level of expertise. More specifically, correct intra-categorical auditory discrimination for untrained items follows the temporal hierarchy and transpires in a late stage of semantic processing. On the other hand, correct categorization of individually trained stimuli occurs earlier, during a period contemporaneous with human vs. animal vocalization discrimination, and involves a parallel semantic pathway requiring expertise.

Influence of dose and duration of isoflurane anesthesia on the auditory brainstem response in the rat

Objective: Isoflurane anesthesia can have significant effects on processing of sounds at the peripheral and central levels, manifesting in changes in auditory-evoked potentials. The current study tested whether duration of isoflurane anesthesia changes thresholds, amplitudes, and latencies of the auditory brainstem response (ABR). Design: The study tested ABRs in a rat animal model under isoflurane anesthesia. Study variables were duration of isoflurane anesthesia, stimulus frequency, stimulus level, and the dose of isoflurane. Rats were anesthetized with 1.5% or 2% isoflurane. ABRs were collected from 90 to 5 dB SPL at 5–40 kHz. Three full ABR series were collected over a 105-minute period. Thresholds were assigned, and ABR wave amplitudes and latencies were measured at each stimulus frequency and level. Study sample: Ten Sprague-Dawley rats were tested in a repeated measures design. Results: Statistical analyses revealed no significant effects of dose or duration on threshold, but a series of significant interactions between test variables for the amplitude and latency measurements. Conclusions: In the rat, dose and duration of isoflurane anesthesia induced inconsistent changes in latency and amplitude of the ABR. At 40 kHz, isoflurane dose had more powerful effects on latency and amplitude than occurred at other frequencies.

Alterations in early auditory evoked potentials and brainstem transmission time associated with tinnitus residual inhibition induced by auditory electrical stimulation.

Residual inhibition (RI) is the temporary inhibition of tinnitus by use of masking stimuli when the device is turned off. The main aim of this study was to evaluate the effects of RI induced by auditory electrical stimulation (AES) in the primary auditory pathways using early auditory-evoked potentials (AEPs) in subjective idiopathic tinnitus (SIT) subjects. A randomized placebo-controlled study was conducted on forty-four tinnitus subjects. All enrolled subjects based on the responses to AES, were divided into two groups of RI and Non-RI (NRI). The results of the electrocochleography (ECochG), auditory brain stem response (ABR) and brain stem transmission time (BTT) were determined and compared pre- and post-AES in the studied groups. The mean differences in the compound action potential (CAP) amplitudes and III/V and I/V amplitude ratios were significantly different between the RI, NRI and PES controls. BTT was significantly decreased associated with RI. The observed changes in AEP associated with RI suggested some peripheral and central auditory alterations. Synchronized discharges of the auditory nerve fibers and inhibition of the abnormal activity of the cochlear nerve by AES may play important roles associated with RI. Further comprehensive studies are required to determine the mechanisms of RI more precisely.

Effect of psychological care on changes in auditory evoked potential and hemodynamics during anesthetic induction with remifentanil

Objective To explore psychological care on changes in auditory evoked potential (AEP) and hemodynamics during anesthetic induction with remifentanil. Methods 30 ASA Ⅰ-Ⅱ patients were divided into study group and conrol group. The study group received psychological care one day before surgery, a intravenous injection of remifentanil of 1μg/kg 4 min before anaesthestic induction, and then a continuous infusion of remifentanil 0.1 μg/kg/min, which was decreased to 0.05μg/kg/min during anesthetic induction; while the control group received esmolol of 300μg/kg/min, which was reduced to 200 μg/kg/min during induction. The medications were terminated 10 min after intubation. AEP, ECC, HR, SBP, and RPP were compared between the two groups and then analyzed statistically. Results AEP did not differ significantly between the two groups at different time points (P>0.05). SBP, HR, and RPP changed slightly in the study group after intubation. Conclusions Psychological care is helpful in making remifentanil more effectively suppress the adverse cardiovascular reactions during intubation. Key words: Remifentanil; Tracheal intubation; Vecuronium bromide; Fentanil; Haemodynamics; Psychological care

Assessment of auditory sensory processing in a neurodevelopmental animal model of schizophrenia—Gating of auditory-evoked potentials and prepulse inhibition

The use of translational approaches to validate animal models is needed for the development of treatments that can effectively alleviate cognitive impairments associated with schizophrenia, which are unsuccessfully treated by the current available therapies. Deficits in pre-attentive stages of sensory information processing seen in schizophrenia patients, can be assessed by highly homologues methods in both humans and rodents, evident by the prepulse inhibition (PPI) of the auditory startle response and the P50 (termed P1 here) suppression paradigms. Treatment with the NMDA receptor antagonist PCP on postnatal days 7, 9, and 11 reliably induce cognitive impairments resembling those presented by schizophrenia patients. Here we evaluate the potential of early postnatal PCP (20mg/kg) treatment in Lister Hooded rats to induce post-pubertal deficits in PPI and changes, such as reduced gating, in the P1 suppression paradigm in the EEG. The results indicate that early postnatal PCP treatment to rats leads to a reduction in PPI of the acoustic startle response. Furthermore, treated animals were assessed in the P1 suppression paradigm and produced significant changes in auditory-evoked potentials (AEP), specifically by an increased P1 amplitude and reduced P2 (P200 in humans) gating. However, the treatment neither disrupted normal P1 gating nor reduced N1 (N100 in humans) amplitude, representing two phenomena that are usually found to be disturbed in schizophrenia. In conclusion, the current findings confirm measures of early information processing to show high resemblance between rodents and humans, and indicate that early postnatal PCP-treated rats show deficits in pre-attentional processing, which are distinct from those observed in schizophrenia patients.

The Auditory System Involvement in Parkinson Disease: Electrophysiological and Neuropsychological Correlations

In the course of Parkinson disease (PD), apart from motor symptoms, presence of mental disturbances such as dementia and depression is common. The aims of this study were to assess the auditory system involvement in patients with PD using electrophysiological and neuropsychological tests and to correlate the cognitive impairment and the auditory evoked potentials tests results. The auditory and cognitive functions were studied in 53 patients with idiopathic PD, mean age 65.8 +/- 9.1 years; mean disease duration 7.8 +/- 5.0 years; mean motor disability score 2.5 +/- 0.8 points in Hoehn-Yahr scale compared with a control group matched for age and sex. In patients and controls, cognitive functions were analyzed electrophysiologically using middle latency auditory evoked potentials (MLAEP) and long latency (event-related potentials, P300) auditory evoked potentials. Neuropsychological testing consisted of Wisconsin Card Sorting Test (WCST). According to WCST results, patients with PD were divided into 2 subgroups: patients with normal and abnormal WCST performance (WCST(-) and WCST(+) subgroups, respectively). Sixteen of 46 patients (34.8%) showed cognitive impairment when evaluated with WCST. Statistically significant differences in middle latency auditory evoked potentials and P300 results between WCST(-) and WCST(+) groups were found consisting of P300 abnormalities in 93.8% patients in WCST(+) and 57.7% in WCST(-) group. Middle latency auditory evoked potentials were abnormal in 71.4% and 63% patients in WCST(+) and WCST(-) group, respectively. P300 was absent significantly more often (P < 0.01) in the subgroup with cognitive impairment. The difference in middle latency auditory evoked potentials results between these subgroups was statistically insignificant. The auditory evoked potentials changes were more common among patients with abnormal WCST performance. According to our results, the auditory evoked potentials of different latencies are helpful in the assessment of cognitive changes accompanying PD.

Some Aspects of Balance Disorder in Patients with Multiple Sclerosis

The aim of this study was to analyze: frequency of balance disorder (vertigo and disequilibrium), frequency of abnormalities in auditory evoked potentials (AEP) and magnetic resonance imaging (MRI) changes of the brain in multiple sclerosis (MS) patients with balance disorder, relation of patient's disability status to balance disorder and relation of the changes in MRI of the brainstem to AEP abnormalities. It was analyzed 60 patients with relapsing-remitting form of MS. Two groups of patients were made consecutively under Expanded Disability Status Scale score (EDSS): A (EDSS < or =4,5) and B (EDSS > or =5,0). The study was retrospective-prospective. After the neurological exam AEP and MRI of the brain have been done. Balance disorder has been verified as initial symptom in 29 (48,4%) and out of them disequilibrium experienced 24 (83,4%) patients. During the relapses balance disorder experienced 48 (80%) patients and in 37 (77,1%) it was disequilibrium. Among them 33 (68,7%) were with lower EDSS (< or =4,5) and 15 (31,3%) with higher EDSS score (> or =5). There is no correlation between disability status and vertigo which means that vertigo is not more frequent in more disabled patients and vice-versa. The AEP were pathological in 57 (95%) patients. Of all 29 patients with vertigo AEP were pathological in 28 (96,5%) while in 31 patients without vertigo pathological AEP were in 29 (93,5%) but it is not statistical significant. The most frequent characteristic of AEP changes were prolonged inter-peak latency III-V waves (48 patients or 80%). The plaque in brainstem visualized by MRI was found in 41 (71,8%) of patients (38 or 92,6% of them had pathological AEP and in three patients AEP were normal). In group of patients with pathological AEP, 38 (66,6%) of them had plaque in brainstem. In other three patients with normal AEP it was visualized plaque in brainstem. In the group of 29 patients with balance disorder, 20 (68,9%) had plaque in brainstem as well as 21 (67,7%) out of 31 patients without balance disorder had plaque in the brainstem. This difference is not statistical significant. It is concluded that the vertigo (including disequilibrium) is relatively often (48,4%) initial symptom of MS. Vertigo is not more frequent in patients with higher EDSS score and vice-versa. Pathological AEP are frequent neurophysiologic finding in both (95%) patients with (96,5%) and without (93,5%) vertigo. The most often pathological characteristic of AEP are prolonged interpeak latency of III-V waves (78,5%), as well as abnormalities of V and than IV wave. MS plaques in brainstem visualized by MRI technique are frequent in both groups of patients with and without pathological finding of the AEP.

Intensity dependence of auditory evoked dipole source activity in polydrug ecstasy users: evidence from an 18 months longitudinal study

Numerous animal studies have been able to demonstrate neurotoxic damage to central serotonergic systems after exposure to 3,4-methylenedioxymethamphetamine (MDMA, ecstasy). It has been suggested that a high loudness dependence of auditory evoked potentials (LDAEP) and, particularly, of the tangential N1/P2 source activity is associated with a low functioning of serotonergic activity. Therefore, the LDAEP may be used as a non-invasive indicator for a possible neurotoxic damage caused by the long-term use of ecstasy in recreational users. We recorded auditory evoked potentials (AEP) with a passive listening paradigm in 18 polydrug ecstasy users at baseline (t1) and after 18 months (t2). Several aspects of ecstasy use, such as frequency of use, cumulative lifetime dose or period of abstinence were associated with the LDAEP for several tangential dipoles at both measuring times. However, we failed to demonstrate any significant relationship between drug use reported at follow-up and AEP changes from baseline to follow-up. Despite some incertitude these data suggest, yet do not unambiguously con.rm, the hypothesis that abstinent ecstasy users present with diminished central serotonergic activity. This feature of information processing is potentially related to the neurotoxic potential of ecstasy. However, alternative interpretations of these data refer to possible preexisting traits and the potential impact of other illicit drugs, particularly amphetamine, since ecstasy users typically exhibit polydrug use patterns. Thus, further research with larger sample sizes and prospective study designs are needed to definitively establish a causative link between ecstasy use and neurotoxicity-related dysfunctions in sensory processing.

Induction of LTP in the human auditory cortex by sensory stimulation

High-frequency, repetitive, auditory stimulation was used to determine whether induction of a long-lasting increase of the human auditory evoked potential (AEP) was possible. Recording non-invasively with electroencephalogram scalp electrodes, stable increases in amplitude were observed in the N1 component of the AEP, which is thought to reflect activity within auditory cortex (N1). The increase was maintained over an hour and was shown to be independent of alterations in the state of arousal. This is the first demonstration of the induction of long-lasting plastic changes in AEPs, and suggest that this represents the first direct demonstration of long-term potentiation in the auditory cortex of normal, intact humans.

Effects of Hypericum Extract (LI160) on the Change of Auditory Evoked Potentials by Cortisol Administration

Target symptoms treated with Hypericum extract, i.e. somatisation, fatigue and depression could be related to an increased activity of glucocorticoids in the brain. One potential mechanism is the increased permeability of the blood-brain barrier for glucocorticoids. Hypericum extract LI160 reduces intracerebral glucocorticoid concentration possibly by its action to induce the expression of the transport protein P-glycoprotein (P-gp). To test this hypothesis directly, we performed a randomised double-blind crossover study to examine the effect of intravenously administered cortisol on auditory evoked potentials (AEPs) and salivary cortisol concentration. Nineteen healthy subjects were treated for 2 weeks with 300 mg LI160 twice a day or placebo. On the 14th day, AEPs were recorded every 30 min, at times –60, –30 and 0 min before the start of the infusion and at +30, +60 and +90 min after starting the infusion. The rate of infusion was 20 mg cortisol/h. No changes in the AEP, especially the N₁-P₂ component, could be observed under cortisol infusion and consequently no modification with the treatment of Hypericum extract. The salivary concentration of cortisol under cortisol infusion was slightly but significantly decreased in the Hypericum condition compared to placebo. The results of the present study are therefore inconclusive with respect to the influence of LI160 treatment on the expected cortisol-induced AEP changes, but support the concept of an action of Hypericum on P-gp function by the observed changes in salivary cortisol.

Maturation of human central auditory system activity: separating auditory evoked potentials by dipole source modeling

Objectives: Previous studies have shown that observed patterns of auditory evoked potential (AEP) maturation depend on the scalp location of the recording electrodes. Dipole source modeling incorporates the AEP information recorded at all electrode locations. This should provide a more robust description of auditory system maturation based on age-related changes in AEPs. Thus, the purpose of this study was to evaluate central auditory system maturation based dipole modeling of multi-electrode long-latency AEPs recordings. Methods: AEPs were recorded at 30 scalp-electrode locations from 118 subjects between 5 and 20 years of age. Regional dipole source analysis, using symmetrically located sources, was used to generate a spatio-temporal source model of age-related changes in AEP latency and magnitude. Results: The regional dipole source model separated the AEPs into distinct groups depending on the orientation of the component dipoles. The sagittally oriented dipole sources contained two AEP peaks, comparable in latency to Pa and Pb of the middle latency response (MLR). Although some magnitude changes were noted, latencies of Pa and Pb showed no evidence of age-related change. The tangentially oriented sources contained activity comparable to P 1, N 1b, and P 2. There were various age-related changes in the latency and magnitude of the AEPs represented in the tangential sources. The radially oriented sources contained activity comparable to the T-complex, including Ta, and Tb, that showed only small latency changes with age. In addition, a long-latency component labeled TP 200 was observed. Conclusions: It is possible to distinguish 3 maturation groups: one group reaching maturity at age 6 and comprising the MLR components Pa and Pb, P 2, and the T-complex. A second group that was relatively fast to mature (50%/year) was represented by N 2. A third group was characterized by a slower pattern of maturation with a rate of 11–17%/year and included the AEP peaks P 1, N 1b, and TP 200. The observed latency differences combined with the differences in maturation rate indicate that P 2 is not identical to TP 200. The results also demonstrated the independence of the T-complex components, represented in the radial dipoles, from the P 1, N 1b, and P 2 components, contained in the tangentially oriented dipole sources.

Changes of auditory-evoked potentials in response to behaviorally meaningful tones induced by acute ethanol intake in altricial nestlings at the stage of formation of natural behavior

Acute ethanol's influence on field L auditory-evoked potentials (AEP) was studied in 4–7-days-old altricial nestlings of the pied flycatcher. Nestlings were presented with behaviorally meaningful tone pips (2.0 and 5.0 kHz) and control tone pips (3.0 kHz). Ethanol ingestion was found to reduce the N 1 amplitude and maturity index (MI) of the AEP in response to “behavioral” but not to control frequencies. This effect was first observed on day 5, when the nestlings' behavior became more complex (their eyes opened and defence behavior appeared), and when previously formed feeding behavior was undergoing modifications. The MI increase during the early postembryonic ontogeny was probably due to the selective involvement of neurons with newly formed behavioral specializations into the subserving of new behavioral patterns, while the decrease of the MI under alcohol was due to the depression of activity in these neurons.

Effect of noise on higher nervous activity

The effects of continuous, regular and irregular intermittent white noises consisting of three kinds of unpleasant noises (frying pan noise (FN), synthesizer noise (SN) and white noise (WN)), pure tones of 125, 250, 500, 1k, 2k, 4k and 8k Hz, and band-limited noises with the same center frequencies as pure tones were estimated by using electroencephalograms (EEG) and auditory evoked potential (AEP), to make clear the relationship between the unpleasantness of noise and brain activity. The results obtained were as follows. Alpha-wave appearance rate differed in continuous, regular and irregular intermittent white noise exposures. Psychologically unpleasant noises, estimated by the method of paired comparisons and a rating scale, brought about changes in brain waves that corresponded to the degree of unpleasantness. Changes in the number and the total power of the peak frequency in brain waves of the subjects exposed to pure tones showed a tendency to be similar to the equal loudness contour. Changes in the AEP components of N 1 and P 2 latencies and P 2 amplitude due to both pure tones and band noises with the same center frequency as each pure tone showed the same pattern, with the shortest latency and amplitude between the frequencies of 1 kHz and 2 kHz. The changes in AEP were also similar to the equal loudness contour.

EFFECTS OF NITROUS OXIDE ON AUDITORY CORTICAL EVOKED POTENTIALS AND SUBJECTIVE THRESHOLDS

This study has examined the effects of inhaled nitrous oxide on the N1 and P2 components of the cortical auditory evoked potentials (AEP) in the latency interval 80-300 ms after the stimulus. The amplitudes, latencies and thresholds of the AEP were measured at a range of end-tidal nitrous oxide concentrations (0%, 10%, 20%, 40%) in 10 subjects with normal hearing. Systematic decreases in amplitude and latency were observed with an increase in threshold. A study of the effect of stimulus intensity on AEP amplitude showed that the amplitude change with nitrous oxide was accounted for largely by systematic increase in evoked potential threshold. Subjective pure tone thresholds were not affected by the concentrations of nitrous oxide used, indicating that the AEP changes were independent of subjective hearing level.

Electrocorticogram (ECoG) and auditory evoked potential (AEP) in rats intoxicated with lead acetate.

ECoG and AEP of male Sprague-Dawley rats were recorded to elucidate the effect of lead acetate on the central nervous system. Lead acetate (1.0 x 10-2M) in distilled water, 1 m//100 g body weight, was administered intraperitoneally for four consecutive days to an experimental group of rats. On the 11th day after injection, the rats were decapitated and the content of lead in the whole brain was measured in addition to the blood lead concentration and the hematocrit. The body weights and hematocrit values of rats in the experimental group decreased remarkably although they tended to recover by the end of the experimental period. The blood lead concentration of rats in the experimental group increased through-out the experimental period and their whole brain lead amount was twelve times that of the control group. No changes in the ECoG of rats given lead acetate were found in this experiment, but the changes in AEP of the rats in the experi-mental group were delayed P2 peak latency and increased P1-N1 peak to peak amplitude.