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Sound localization is necessary for social interaction and remains challenging for bilateral cochlear implant (CI) users. This study investigated the influence of fine structure processing (FSP) coding strategies on temporal accuracy and source localization. The ability to discriminate between different interaural time differences (ITD) was measured objectively and compared.Fifteen normal-hearing subjects and five CI users participated in this study. Electrophysiological recording of mismatch negativity (MMN) and psychoacoustic tests with headphones and loudspeakers were conducted to measure and compare the discrimination of ITDs.In normal-hearing subjects the discrimination threshold for ITD was 83-117 µs. Localization ability in a free sound field was below the limit of resolution. A significant MMN was measured. CI users showed a mean angle detection error of more than 30° and a discrimination threshold between 1100 and 2100 µs. Due to artifacts, no clear MMN component could be recorded.This study shows that MMN can be used as an objective measure of ITD discrimination in normal-hearing participants. An indication that improvements in directional hearing can be achieved with the transfer of fine structure could not be provided by this study.

Outer hair cells play a major role in the hearing process: they amplify the motion of the basilar membrane up to a 1000-fold and at the same time sharpen the excitation patterns. These patterns are converted by inner hair cells into action potentials of the auditory nerve. Outer hair cells are delicate structures and easily damaged, e. g., by overexposure to noise. Hearing aids can amplify the amplitude of the excitation patterns, but they cannot restore their degraded frequency selectivity. Noise overexposure also leads to delayed degeneration of auditory nerve fibers, particularly those with low a spontaneous rate, which are important for the coding of sound in noise. However, this loss cannot be diagnosed by pure-tone audiometry.

Within the context of treatment with cochlear implants (CIs), different electrical and electrophysiological diagnostic procedures are applied both intra- and postoperatively. These assess electrical measures from the CI and electrophysiological measures from CI patients, respectively. The electrophysiological diagnostic procedures comprise measurement of electrically evoked compound action potentials of the auditory nerve, the registration of electrically evoked auditory brainstem potentials and the assessment of electrically evoked auditory cortical potentials. These potentials reflect auditory nerve excitation and stimulus processing in different parts of the ascending auditory pathway for intracochlear electrical stimulation via a CI. For current CIs, assessment of electrode position and examination of the implant's coupling to the auditory nerve are important domains of application for electrophysiological diagnostic procedures. Another substantial application area is the examination of stimulus processing in the auditory pathway. However, the main field of application of these procedures is supporting the fitting of CI speech processors in infants and toddlers on the basis of electrophysiological thresholds.

It is not unusual for a neurological expert to have problems defining the precise anatomical location and the required objective proof of damage, especially if the medical history and the neurological report released by the clinic prove inadequate in terms of providing a reliable assessment. This may well result from somatoform disorders, dissociation, aggravation and simulation, as well as dissimulation and complex organic diagnostic findings. A range of standardised neurophysiologic procedures is available for the objective measuring of motor, vegetative and sensory systems; a brief summary of the most frequent occurrences is given here, along with their significance for appraising damage resulting from an accident. Target groups primarily include surgeons, orthopaedists, lawyers and insurance specialists. Structural improvements and measures to integrate immigrant doctors is essential.

Objective methods based on the measurement of otoacoustic emissions (OAE) and auditory evoked potentials (AEP) are indispensable in pediatric audiology especially for the early detection and therapy of congenital hearing impairment. The correct and efficient use requires knowledge and skills which are beyond the basic equipment of many users and require continuous updating. In the present review many aspects relevant for the safe handling of the methods and interpretation of the results are addressed. The presentation does not focus on the methods themselves but on the core problem of the practical daily routine, namely the qualitative and quantitative description of hearing loss in terms of its extent, the frequency range affected and the identity with respect to the type and site of the lesion. The certainty of the diagnosis can be optimized by observing few and simple rules. Central importance is attached to the thorough discussion of the interrelated parameters residual noise, signal-to-noise ratio and reproducibility in order to promote their correct use. Further subjects of this article are the recognition of pitfalls, the description of new developments, such as chirp and auditory steady-state responses (ASSR) and finally the consideration of the extraordinarily important aspect of maturation.

Auditory evoked potentials (AEPs) are elicited at various levels of the auditory system following acoustic stimulation. Electrocochleography is a technique for recording AEPs of the inner ear. The recording is performed by means of a needle electrode placed on the promontory or non-invasive with tympanic membrane or ear canal electrodes. Clinically, electrocochleography is used for the diagnosis of auditory neuropathy spectrum disorder (ANSD) and endolymphatic hydrops. According to their latencies, AEPs of the central auditory pathway are subdivided into early, middle and late (cortical) AEPs. These AEPs are recorded via surface scalp electrodes. Normally, the larger EEG masks AEPs. For unmasking the AEP, several techniques are applied. Early AEPs or auditory brainstem responses (ABR) are the most widely used AEPs for functional evaluation of the auditory pathway. In contrast to otoacoustic emissions, early AEPs can detect ANSD. Thus, they are more suitable for hearing screening in newborns. For this purpose automated procedures are implemented.

Examination of the sense of hearing is a technically difficult undertaking especially with functional magnetic resonance imaging because the machine causes a high noise level during the measurement. This article describes the technical conditions which, nevertheless, allow the auditory capabilities to be tested. Furthermore, every switch point of the auditory pathway and the cortical areas involved, which are technically accessible in an investigation of the sense of hearing are pictorially described.

Recording human auditory steady-state responses (ASSR) at different frequencies allows objective assessment of auditory thresholds. Common practice has been to record ASSR to pure tones that are sinusoidally modulated in amplitude and frequency. Recently, optimized chirp stimuli have been proposed to evoke transient as well as steady-state responses. Because of the resulting uncertainty about the different methods, this paper aims to reconsider the terminology of transient and steady-state responses.Two experiments demonstrate the smooth transition between transient and steady-state responses. In experiment 1, click-evoked auditory brainstem responses (ABR) were recorded over a wide range of stimulus repetition rates (24/s to 72/s). In experiment 2, auditory steady-state responses were recorded for the same stimulus repetition rates, using three different stimulus types: an amplitude modulated 1-kHz tone (AM), a 1-kHz tone-burst (TB) and a flat-spectrum chirp.Experiment 1 demonstrates the merging of the typical ABR wave complexes at higher repetition rates, forming a steady-state response. This effect can only be observed if the time window is extended far beyond the window traditionally used for clinical ABR recordings. Experiment 2 reveals similar ASSR amplitude spectra regardless of the stimulus type and repetition rate used.Steady-state responses can be evoked for a large variety of stimulus types and repetition rates. Thus, from a clinician's point of view, steady-state responses cannot be considered a new type of evoked responses. They differ from transient responses primarily in the frequency response method and the longer timeframe required.

Modern computer-based methods to monitor anesthesia are widespread. They are used in order to avoid awareness, to reduce consumption of anesthetics, to optimize recovery times and to detect prolonged times of deep anesthesia and associated immunsuppression, mortality and morbidity. This review illustrates the evidence with which these goals were achieved until now. Finally, a recommendation for each indication is given. The useage of EEG-monitoring may help to avoid awareness and allows a reduced of consumption of anesthetics. The question if a cumulated time of deep anesthesia is associated with elevated mortality might be of a certain importance in the future.

Wilson's disease is a rare autosomal recessive disorder of hepatic copper transport leading to hepatic but also to highly variable neurological symptoms with basal ganglia and cerebellar manifestation. Symptoms, signs and results of investigations can overlap with those of other central nervous system disorders such as multiple sclerosis and sometimes delay diagnosis.We report on a 38-year-old male patient who was diagnosed with a hepatic form of Wilson's disease at age 12 and with multiple sclerosis at age 38. Intravenous radio copper test confirmed the diagnosis of Wilson's disease. Multiple sclerosis was diagnosed after occurrence of transient sensory disturbances in both legs, based on typical changes on MRI over the course of 2 years, in the cerebrospinal fluid and in multimodal evoked potentials.Although Wilson's disease and multiple sclerosis are known as distinct diseases with a completely different pathophysiology, symptoms and results of evoked potentials overlap, and they share a common historic background. Similarities and differences of both disorders are discussed.

The simple insight in the central serotonergic activity would allow a more specific pharmacotherapy of disorders with serotonergic deficits and could thus serve as a predictive parameter. An antidepressive treatment could be chosen due to the verification or falsification of such a deficit with a serotonergic or noradrenergic substance. In search of predictive parameters we have investigated the loudness dependence of auditory evoked potentials (LDAEP), a parameter that has already been discussed concerning this matter, and serotonin levels in the human blood serum regarding their correlation.Eight outpatients of a lithium clinics were investigated neurophysiologically after blood samples had been taken.A significant negative correlation between LDAEP and serotonin level in the serum was found, a low serotonin level correlates with a high LDAEP.The result of this pilot study justifies further investigations with larger sample sizes. In case of further and stable evidence the use of serotonin levels in the serum as a predicitve parameter is conceivable.

A cortical dysbalance has a pivotal role in the pathophysiology of migraine. Numerous electrophysiological and transcranial magnetic stimulation (TMS) studies have investigated the interictal excitability level in migraineurs and have shown a consistent lack of habituation during repetitive stimulation. There is some controversy in the current literature over whether this deficit is based on a lowered or an elevated preactivation level. However, the current discussion may be misguided. It seems that multiple external and intrinsic factors influence the level of cortical excitability and the frequency and intensity of attacks: Habituation is specific neither to migraine nor even to pain; the same phenomenon is found in tinnitus patients, for example. Cortical hyperexcitability is presumably the result of chronicity and the concomitant central sensitisation process.

One of the most important mandates of the anaesthesiologist is to control the depth of anaesthesia. An unsolved problem is that a straight definition of the depth of anaesthesia does not exist. Concerning this it is rational to separate hypnosis from analgesia, from muscle relaxation and from block of cardiovascular reactions. Clinical surrogate parameters such as blood pressure and heart rate are not well-suited for a valid statement about the depth of hypnosis. To answer this question the brain has become the focus of interest as the target of anaesthesia. It is possible to visualize the brain's electrical activity from anelectroencephalogram (EEG). The validity of the spontaneous EEG as an anesthetic depth monitor is limited by the multiphasic activity, especially when anaesthesia is induced (excitation) and in deep anaesthesia (burst suppression). Recently, various commercial monitoring systems have been introduced to solve this problem. These monitoring systems use different interpretations of the EEG or auditory-evoked potentials (AEP). These derived and calculated variables have no pure physiological basis. For that reason a profound knowledge of the algorithms and a validation of the monitoring systems is an indispensable prerequisite prior to their routine clinical use. For the currently available monitoring systems various studies have been reported. At this time it is important to know that the actual available monitors can only value the sedation and not the other components of anaesthesia. For example, they cannot predict if a patient will react to a painful stimulus or not. In the future it would be desirable to develop parameters which allow an estimate of the other components of anaesthesia in addition to the presently available monitoring systems to estimate sedation and muscle relaxation. These could be sensoric-evoked potentials to estimate analgesia and AEPs for the detection of awareness.

As Picton demonstrated with case reports in 1978, thresholds of click-evoked potentials do not match to pure tone thresholds if hearing loss differs across the test frequencies. Thus, he developed a stimulation with brief tone pips masked by a notched noise that over the years became the standard method for frequency specific threshold estimation. Currently, new technologies like auditory steady-state responses and Chirp-evoked potentials promise to overcome some disadvantages of the NN-BERA.Thus, a systematic review about the NN-BERA was needed to further compare the competitive technologies. Literature research was performed according to the present guidelines for evidence based medicine. It was found that a meta-analysis with data pooling was impossible because of massive discrepancies of methods and subjects across the retrieved publications.The differences of means between pure tone thresholds and NN-BERA-thresholds were up to 12 dB. Standard deviations were 2 to 16 dB and generally higher at 0.5 und 1 kHz compared to 2 and 4 kHz. Correlations were r = 0.84 to r = 0.97.The NN-BERA faces a growing competition by auditory steady state potentials, chirp-evoked potentials, and distortion product otoacoustic emissions but serves still as the standard for an objective threshold estimation since it's accuracy is well evaluated and the interpretation is independent from statistical tests which accuracy is not sufficiently evaluated at present.

Central auditory processing disorders (CAPD) are associated with reduced discriminatory abilities of the auditory system. One of these abilities is directional hearing, which is based on the evaluation of interaural signal differences. Since these differences affect also the binaural difference potentials (BDP), these derived evoked potentials could be suitable for the objective detection of disabilities in acoustic localization.Auditory brainstem responses (ABR) evoked by monaural and binaural stimulation were recorded in 32 adult normal-hearing volunteers at stimulus levels between 10 and 80 dB nHL and the BDP were derived. Additionally, a test of directional hearing was performed and evaluated.BDP are detectable at all stimulus levels without difficulties, with acceptable examination times and with satisfactory reliability in a routine clinical environment. The electrodes can be positioned at the mastoid (A1 and A2) and vertex (Cz) as for conventional ABR recording. Normal ranges are given for latency and amplitude as well as for their lateral differences.The spectrum in directional hearing ability as covered by normal-hearing subjects is not mirrored in the parameters of their BDP. Nevertheless, it cannot be ruled out that a real impairment of directional hearing goes along with significantly altered BDP.

Intraoperative wakefulness is not only limited to adults and can also be found at a similar percentage (0.8%) in paediatric anaesthesia. For prevention of awareness neurophysiologic methods like auditory evoked potentials might be helpful. We report a case of a 2-year-old boy receiving balanced anaesthesia with sevoflurane and alfentanil. Midlatency auditory evoked potentials (MLAEPs) were recorded continuously before, during and after the surgical procedure. During the surgical procedure sevoflurane was withdrawn unintentionally. After a short period of time the boy started coughing and moved his legs, which was interpreted as insufficient analgesia. Several boli of alfentanil did not lead to the expected clinical effect on the depth of anaesthesia. After a recheck of the anaesthetic ventilator the error was determined and delivery of the volatile anaesthetic restored. The postoperative evaluation of the MLAEPs revealed the inadequate suppression of auditory processing during this incident with latencies comparable to the awake state. After reapplication of sevoflurane the MLAEPs were almost completely suppressed demonstrating adequate anesthetic depth. Exemplarily this case suggests that MLAEPs could be used to detect intraoperative awareness also in paediatric anaesthesia. Investigations to prove the validity and reproducibility of MLAEPs in children will be necessary.

The prognosis after traumatic coma is often unclear. We investigated the prognostic value of somatosensory (SSEP) and early acoustic (EAEP) evoked potentials on comatose patients in the intensive care unit regarding long-term outcome. Different evaluation systems were investigated.This was a retrospective analysis of 100 patients. SSEP and EAEP were examined at different times and analysed according to the Riffel score. Combinations of the different types of potentials were evaluated regarding possible improvement of outcome prediction.The positive predictive value of at least one missing peak V of the EAEP regarding a fatal prognosis was 83%. The negative predictive value of the EAEP was 96%. A good outcome (GOS 4+5) could be predicted by bilateral normal SSEP and EAEP with a positive predictive value of 98%.Early evaluation of SSEP and EAEP allows reliable prognostic predictions regarding a later outcome in patients with severe traumatic brain injury and should therefore be used more often for intensive care patients.

High doses of acetylsalicylic acid (ASS) induce tinnitus and hearing loss. This ototoxic side effect of ASS is characterized by a decrease in spontaneous and evoked otoacoustic emissions. A decrease in otoacoustic emissions is found not only in mammals, but also in non-mammalian ears without electromotile outer hair cells. The molecular mechanism underlying ASS ototoxicity seems to be competitive binding to and a block of the motor molecule prestin. In non-mammalian species, ASS ototoxicity is possibly explained by an effect on the hair bundle.The present data from the outer hair cells of the adult guinea pig cochlea show a reduction in the membrane capacitance by maximally 42%, probably as a result of ASS binding competitively to the motor molecule. However, spontaneous and evoked receptor currents were not modulated by ASS.The results suggest an influence of ASS on outer hair cell somatic electromotility, without a concomitant effect on hair-bundle function.

Auditory evoked responses to tone-pips in notched-noise provide frequency specific estimations of thresholds. Most often, test frequencies are 0.5-4 kHz. Thresholds are expected to match with a high degree to behavioral thresholds. However, only few studies are available containing data on stimulus and averaging parameters, especially at a test frequency of 0.25 kHz. In order to find "optimal" parameters for a widely used device (Nicolet Spirit Version 1.6), we designed five experiments on stimulus polarity (Exp.I), sweep frequency (Exp.II), stimulus duration (Exp.III), notched noise level (Exp.IV), and threshold estimation (Exp.V). The experiments also included a low test frequency of 0.25 kHz. These experiments were applied to 29 healthy volunteers (n=29, aged 20-41 years with normal hearing and no history of illness of the ear). We found that alternating stimulus polarity and a sweep frequency of 43.5/s evoked responses that were highest with respect to amplitudes (0.2-0.4 mV) and correlations (0.49-0.91). A novel finding of the study was that the highest amplitudes and correlations could be achieved if stimulus durations and notched-noise-levels were specifically adjusted to the test frequencies (stimulus durations 0.25 kHz: 4 ms, 0.5 Hz: 2 ms, 1-4 kHz: 1 ms, notched-noise-levels 0.25-0.5 Hz: +10 dB, 1-4 kHz: +/-0 dB). Deviations from behavioral thresholds did not exceed +/-5 dB in 93% of the measures. The results indicate that frequency specific auditory evoked responses provide reliable threshold estimations. Future experiments are required to confirm the threshold deviations for hard of hearing individuals.

More than 30% of all otogenic vestibular disorders are related to isolated macular dysfunction. Videooculographic examination techniques for the otolith-ocular reflex, e. g. by means of eccentric rotation tests, are not widely used in clinical routine as these put a considerable strain on technical and staff resources. Thus, there is a considerable risk of "false negative" classification of vertigo disorders being labelled as "non-otogenic". By means of vestibular-evoked myogenic potentials (VEMPs) and caloric irrigation in prone and supine position, several examination techniques for a side-related investigation of macula-induced vestibulo-ocular reflexes are available. The objective of this study is to compare and evaluate these techniques as screening tests.In 32 patients with vestibular disorders we performed investigations for VEMPs, eccentric rotation tests, as well as caloric irrigation for macular reaction in prone and supine position. In addition, we performed other audiologic and vestibular function tests which were complemented by the clinical course in order to differentiate each case between otogenic and non-otogenic vertigo with or without macular affection.The technical feasibility as well as patients' acceptance for VEMP testing is better than for eccentric rotation tests. The sensitivity index for VEMPs (89%) as well as for caloric irrigation in prone and supine position for macular examination (71%) is satisfactory. However, the specificity of VEMPs is inferior (53%) to eccentric rotation (100%).Both the examination for VEMPs as well as caloric macular testing in prone and supine position carry features which make them feasible for screening, even though these two procedures test for two different parts of the otolith system. However, to confirm a diagnosis and to set up a therapeutic concept for macular function disorders, eccentric rotation should be added.

Since Dohlmann's investigations the extremely variable interindividual natural course of Menière's disease has been documented. The description of sub-entities of Menière's disease shows, the localisation of dysfunction within the labyrinth is of considerable importance. The selective investigation of crista and macula sensor organs and its time-dependent progression even provides information for the disease's staging.In the retrospective trial presented here, 126 patients suffering from vertigo were tested by the methods described above. 10 of these patients who showed a triad of symptoms including vertigo attacks, unilateral sudden hearing loss and tinnitus were selected for this study. All 10 patients were tested within 48 hours after the last acute vertigo attack by means of caloric irrigation and VEMPs.The function loss verified in saccular testing could be found in Menière's disease progression at an earlier stage than the utricular function loss. Most patients with a long history of vertigo attacks also suffered from a dysfunction of the semicircular canals.The differential testing of the otolith function is a valid tool for the recognition of early labyrinth dysfunction in Menière's disease and could lead to an earlier onset of specific therapy. It also provides the base for a differentiated staging prior to therapy planning.

The speech recognition performances in postlingually deaf patients, which had a long duration of deafness, seem to be poorer than in patients with a short duration of deafness. The reason could be a functional reorganization in the auditory cortex. A long time of auditory deprivation may decrease neuronal activity in the auditory related cortices. As the late acoustically evoked potentials are generated in this region, we compared the speech recognition performances and also the late acoustically evoked potentials with the individual duration of deafness in a series of postlingually deaf patients.In 9 patients (cochlear implant (CI), MED EL) with postlingual deafness the late acoustically evoked potentials and the HSM-set-test on the quiet were measured. Additionally 1 patient with prelingual deafness was examined. The CI-operation was done, when he was 14 years old. The relations between the late acoustically evoked potentials and the speech recognition performances in dependence of the duration of deafness were examined.Typical late acoustically evoked potentials could be measured in 3 patients only. The speech recognition in these patients was very good. The longest time of deafness in these patients was 6 years. In 6 patients the minimum duration of deafness was 12 years. Here were measured the N1-potentials only, the P2- and the N2-potentials were absent. In these patients the scores of the HSM-set-test were lower than in the others. In the 15-years old patient with prelingual deafness the speech recognition was absent. The late acoustically evoked potentials of this patient showed an atypical form.The results of this study showed a correlation between the duration of deafness, the forms of the late acoustically evoked potentials and the speech perception. The duration of deafness preceding CI-implantation should be very small in deaf children and in postlingually deaf patients.

Neurophysiologic intraoperative monitoring (NIM) has gone through a renaissance since the advent of computer technology. Currently, both motor and sensory cranial nerves, including the IInd and VIIIth cranial nerves, can be intraoperatively controlled by means of small and mobile systems.In order to estimate the value of NIM using the new generation of computer systems, we analyzed the records of 379 patients who underwent skull base surgery since 1996. These comprised NIM of the IInd, VIIth, VIIIth cranial nerves in most cases and of the IXth, Xth, XIth, and XIIth cranial nerves in selected cases.Whereas 72% of these cases demonstrated changes in the recorded intraoperative NIM signals, only 29% of them gave evidence of either clinical or electrophysiological neural function alterations during the postoperative follow-up.NIM is the only available system capable of providing the surgeon with instant intraoperative neural status-related feedback.

Neutral condition event related potentials (NC-ERP) are not suitable for differentiating between children suffering from auditory processing disorders (APD) alone and APD-children with attention deficit disorder. Other factors beside severity of APD may cause "pathological" NC-ERP. Here we raise the question of whether maturational factors may be responsible for disordered NC-ERP.NC-ERP data from 142 APD children (range 5.4-17.2 years; mean 9.8 years) were analysed. Data were grouped according to age of children (I:7.11 years n=34; II: 8.0-9.11 years n=46; III: 10.0-11.11 years n=39; IV:12.0 years n=23).Pathological NC-ERP were found in 82.3% (group I), 56.6% (group II), 46.2% (group III) and 8.8% (group IV). Additional analyses confirmed no correlation with ADHD.Although there is a whole body of evidence that late auditory evoked potential may mature with age, it is not known if NC-ERP are also age dependent. Our results that NC-ERP mature with age are consistent with data for other late auditory evoked potentials. Since normative date of NC-ERP for different age groups are still lacking, NC-ERP results in children should be interpreted very cautiously.

Mismatch negativity (MMN) represents an event-related component of the auditory evoked potentials at about 100-250 ms, evoked by discernible changes in an ongoing uniform acoustic stimulation. The current paper reviews all recently published MMN studies in the field of schizophrenia research. A reduced MMN in schizophrenic patients is found in the majority of the studies. This deficit is likely to be related to the disorder, since antipsychotic medication seems to have little influence on these results. Interestingly, a reduced MMN is also found in first-degree relatives of patients. Clear evidence for a hemispheric lateralization of the MMN reduction in schizophrenic patients is lacking. A hypofunction of the N-methyl-D-aspartate (NMDA) receptor is discussed as a possible explanation of this deficit.

Auditory processing disorders (APD) result from dysfunctions of processes dedicated to audition and affect processing of information in the auditory modality. Children with APD exhibit symptoms similar to those with attention deficit disorders (ADHD). With regard to therapeutic strategies it seems mandatory to employ diagnostic procedures able to differentiate between APD and ADHD. Recently it was found that auditory evoked neutral condition event-related potentials (NC-ERP) correlate with results from psychoacoustic measures suitable to unveil dysfunctions of auditory processing, thus confirming APD. Here we investigated whether NC-ERP may be used as a tool to differentiate between APD and ADHD.In a retrospective analysis, NC-ERP data from 99 children with (+ADHD) and 43 without ADHD symptoms (-ADHD) were examined. All patients suffered from symptoms consistent with information processing deficits in the auditory modality. Analysis of variance was applied.+ADHD children and -ADHD children did not show a significantly different distribution pattern of pathological NC-ERP.Since the probability of pathological NC-ERP is equally distributed in children with or without ADHD, all of whom suffered from auditory processing deficits, it seems fair to conclude that NC-ERP are not suitable to differentiate between APD and ADHD. This may be due to methodological limitations. Alternatively, APD and ADHD may indeed be overlapping entities with a common yet unidentified origin.

The psychophysiological measuring method for the determination of the auditory order threshold (OT) is steadily gaining in importance, both for the diagnosis and treatment of speech disorders. Observed intraindividual variability of (macro-) vigilance led to the hypothesis of discontinuous cognitive processing in the central nervous system. The base for the variability of microvigilance is hypothesized to be in the phase difference of the alpha rhythm. To test for this hypothesis, we developed an EEG-comparator, which allows for a phase-dependent triggering of external stimuli. In direct comparison with stochastic (i.e. non-phase-dependent) stimulus presentation, the threshold in phase-dependent OT-testing is distinctly lower. Optimal results occurred at phase angels of phi = 90 degrees and phi = 270 degrees. Our findings support the hypothesis of a correlation between alpha rhythm and vigilance processes. Furthermore, there seems to be evidence that memory processes go with changes in vigilance, and in this context the alpha phase correlation seems to be important.

Event-related auditory evoked potentials can contribute to the evaluation of discrimination abilities of cochlear implant users. Auditory P300 potentials to a frequency contrast were obtained in six post-lingually deaf adults using a cochlear implant and in a control group of normal hearing subjects. The aim of this study was to investigate how these potentials were determined by the stimulation pattern of the cochlear implant. To visualise these stimulation patterns colour-coded plots (stimulograms) were calculated based on the stimulus and the fitting file of the individual subject as inputs. These stimulograms were used to evaluate the influence of various stimulation parameters on the stimulation contrast used in an oddball paradigm. The influence of discrimination difficulty on the P300 response is demonstrated.

Recording procedure of transiently evoked otoacoustic emissions is an important part of diagnostics in pediatric audiology. As a rule of thumb measurable TEOAE excludes more than slight hearing impairment. Nevertheless any interpretation of these measurements in a clinical setting must consider supposed false positive findings (so called pseudoemissions) and real false positive findings in cases of profound hearing loss with reproducible TEOAE and missing auditory evoked potentials.TEOAE recordings in 512 patients were evaluated for recording procedure failure. Possible types of recording procedure failure were divided into failures conditioned by the patients and stimulus or probe dependent failures. In case of insufficient test procedure and absent TEOAE recording procedure was improved and repeated.In 2 patients with severe to profound hearing loss we discovered reproducible TEOAE whereas auditory evoked potentials were missing. As a stimulus and probe dependent recording procedure failure we saw reproducible pseudoemissions in 3 other patients with profound hearing loss.These results indicate that conclusions concerning hearing ability on the base of TEOAE should keep in mind possible pseudoemissions as a result of recording procedure failure. Reported cases with absent auditory evoked potentials and reproducible TEOAE showed that TEOAE recordings in these cases indicate substantially preserved outer hair-cell function independent of profound hearing loss.

Objective audiometric methods such as the measurement of otoacoustic emissions and auditory evoked potentials (click evoked and notched-noise auditory evoked brainstem potentials, auditory evoked cortical potentials) can provide helpful information. However, information derived from the individual test is limited and each method contains specific restrictions. To illustrate the possible audiometric pitfalls this work presents a case history.The puretone audiometry showed a severe hearing loss at low frequencies up to 2 kHz, a slight hearing loss for higher frequencies up to 6 kHz and almost normal hearing thresholds above 6 kHz. Transitory evoked otoacoustic emissions could not be detected. While the auditory evoked brainstem responses (ABR) using click-stimuli showed a normal pattern no reproducible responses could be derived using the notched-noise technique. Auditory evoked cortical potentials exhibited a normal N1/P2-complex and were detectable down to stimulus levels 0-20 dB above the individual hearing threshold.Click-evoked auditory evoked brainstem potentials are widely regarded as the "gold-standard" of objective audiometry. The example presented in this work shows that in special cases it may provide false negative results. In these special cases auditory tone-evoked cortical potentials may provide better objective information. When objectively assessing the determination of the hearing threshold it may be necessary not only to use all electrophysiological measurements but also to know their methodical restrictions and pitfalls.

The main objectives of the study presented here were to prove the early auditory evoked potentials (EAEPs) as an objective procedure to confirm the diagnosis of otitis media in the rabbit. Therefore, in a clinical study the latencies and amplitudes of the EAEPs of 67 (ear) healthy rabbits were determined at sound pressure levels (SPLs) of 80, 60 and 40 dB. In comparison, the EAEPs of 9 rabbits with otitis media/interna were measured and the deviation of the latencies and amplitudes statistically analysed. The rabbits (no clinical signs of ear disease) showed at 80 dB SPLs the following latencies: potential 0 appeared with 0.53 ms (= average latency, +/- 0.12 ms standard deviation), potential I with an average latency from 1.26 (+/- 0.13) ms, potential II with 2.04 (+/- 0.14) ms, potential III with 2.71 (+/- 0.13) ms, potential IV with 3.72 (+/- 0.17) ms and potential V, which often was difficult to recognize, had an average latency of 4.62 (+/- 0.30) ms. In comparison to these results the rabbits with otitis media showed significant longer latencies at a sound pressure level of 80 dB for potential II, III and IV. Altogether, all mean values of latencies were prolonged in the affected rabbits. The amplitudes of the potentials of the rabbits without clinical signs of ear disease had a broad mean variation with large individual differences. The comparison of the results of EAEPs between rabbits with and without otitis media showed some differences of the latencies but these differences were not obviously enough to confirm the diagnosis of otitis media. Overall, the results showed that EAEPs with only three different sound pressure levels give no convincing results, although extensively prolonged latencies could lead suspicion on the diagnosis of otitis media. Further studies about the ascertainment of the objectively acoustic threshold in the rabbit with otitis media are necessary. The comparison of the latencies and amplitudes in the EAEPs between male and female rabbits showed longer latencies of potential III for male rabbits at 80 and 60 dB SPLs. Furthermore the results of latencies and amplitudes were compared between dwarf rabbits and other breeds. In dwarf rabbits (with an average body weight of 1420 g) significant higher amplitudes for the potentials I, II, IV and V were detectable than in other breeds (with an average body weight of 2852 g). This can be due to different body mass or different headsize.

A sudden unilateral hearing loss in childhood is commonly regarded as an unusual event.In this paper, we report of a 10 year old girl suffering from a unilateral right-sided sudden hearing loss following an acute infection with Mycoplasma pneumoniae, which is also rarely observed. Maximum hearing loss was estimated around 30 dB (0.25-6 kHz), which resolved after infusions using plasma expanders. Both transitory and distortion product otoacoustic emissions remained absent, while latencies of acoustically evoked potentials were normal.This suggests a damage of outer hair cell function as an explanation for the observed hearing loss. The coincidence of two rare events for children such as a spontaneous sudden unilateral hearing loss combined with an infection with Mycoplasma pneumoniae gives rise to the hypothesis of a causal relationship that is discussed according to the literature.

Amplitude modulation following responses (AMFR) allows good estimation of the hearing threshold due to the very narrow band excitation of the cochlea. Audiological use of AMFR requires knowledge of the relationship of these responses to the state of vigilance. The few studies published compared only qualitatively the amplitude of AMFR recorded in awake subjects to that recorded in sleeping subjects. A quantitative determination of the level of vigilance on the basis of recorded physiological parameters has not yet been carried out. In the present study, the relationship between the amplitude of AMFR and the level of vigilance was investigated quantitatively.In eight adults with normal hearing, the relationship between the AMFR amplitude and EEG amplitude in the delta- and theta-band was determined. The amplitude in both frequency bands was used to indicate the state of vigilance. The subjects were studied during natural and drug-induced sleep. A 1-kHz carrier tone with a sinusoidally modulated amplitude of 40 Hz or 80 Hz was used as stimulus.At 40-Hz modulation frequency, the AMFR amplitude correlates with the EEG amplitude both in natural and drug-induced sleep. An increase in EEG activity is paralleled by a significant reduction of AMFR amplitude. At 80-Hz modulation frequency, no relationship between AMFR amplitude and EEG activity could be detected. Under all conditions, the amplitudes of AMFR evoked by a modulation frequency of 80 Hz were significantly lower than those evoked by 40 Hz.These results suggest that for an audiological use of the 40-Hz AMFR the state of vigilance should be stabilised at a constantly high level. In spite of the lower influence of vigilance on the 80-Hz AMFR, this response appears less ideal for threshold estimation in adults due to the significantly smaller amplitudes.

Synchronized neural activity in animal visual cortex in the frequency range above 20 Hz, the gamma band, has been proposed as a signature of temporal feature binding. More and more research in humans by means of noninvasive electrophysiological recordings was stimulated by these studies. Here, research on evoked and induced gamma band activity in human EEG and MEG mainly in the auditory and visual modality is reviewed and their role in perceptual processes, feature integration and language processing is discussed. In addition, research on the attentional modulation of gamma band activity is reviewed. In contrast to evoked gamma band activity, which occurs right after stimulus onset, induced gamma band activity can be recorded with a latency of 200 to 400 ms and a frequency range of 30 to 95 Hz. Cumulative consistent experimental evidence allows us to conclude that gamma band activity in the human cortex is related to neuronal information processing and cognitive functions, e.g. memory processes. The findings are discussed in the light of different functional theories of induced gamma band activity.

The fetal magnetoencephalogram with a 31 chanal biomagnetometer made by Philips was measured in a fetal 1F-phase in 20 normotroph unimpaired and in 14 growth retarded fetuses with a birth weight5 percentile after completed 36th gestational week. Trough defined acoustic stimulations, which were applied over the maternal abdominal wall, it was possible to measure acoustic evoked cerebromagnetic field changes using a special computer programs. The registrated evoked cerebromagnetic field changes had a latence time of 112.8 +/- 18.4 ms in normotroph fetuses and 130.9 +/- 18.5 ms in hypotroph fetuses. The difference was significant (p0.01). The presented results lead to the conclusions that the fetal magnetoencephalography makes a differentiation between normal and disturbed fetal cerebral integrity possible.

The cause of stuttering is unknown. For clinical purposes it proved to be useful to assume a multifactorial genesis with organic psychological and social aspects. A longstanding organic theory focussed on the failure to develop left-hemispheric dominance for speech, whereas others favoured deficits of the speech motor system. Positron emission tomography (PET) studies support organic theories for the development of stuttering. The purpose of this study was to find out whether in stutterers auditory cortical potentials evoked by pure tones, noise and words are different to those of healthy controls.10 young adults having suffered from stuttering since infancy were examined. The potentials were measured and analysed as previously described.No correlation of clinical and electrophysiological findings were found. In one case the evoked potentials were normal, in all other patients heterogeneous results were obtained in respect of tone-evoked and both noise- and speech-evoked potentials. Cortical hemispheric differences could be detected.In agreement with PET findings reported in the literature the data obtained in this study indicate an organic, central nervous cause of stuttering. Obviously both speech motoric components and perception elements are affected. These facts have to be taken into account whenever a psychological cause of stuttering is suspected. Nevertheless, psychosomatic aspects of the disturbances must be considered since they influence the patients' ability to cope with their symptom.

Electrophysiological parameters are well-suited to detect changes in cerebral function. The present study investigates whether balanced anaesthesia with remifentanil during nociceptive stimulation is associated with changes in clinical and electrophysiological parameters indicating inadequate depth of anaesthesia. Following IRB approval and written informed consent, 23 patients (ASA: I; age: 36 +/- 11) scheduled for elective gynaecological laparoscopy were included in the study. Without any premedication, anaesthesia was induced with remifentanil (1.0 microgram/kg bolus injection), propofol (0.5 mg/kg added by repetitive (10 mg) bolus injections every 10 s until unconciousness) and vecuronium (0.1 mg/kg). Following endotracheal intubation (normoventilation: PetCO2: 36 bis 38 mmHg), remifentanil infusion was started with continuous doses of 0.5 microgram/kg/min over 5 minutes and maintained with 0.25 microgram/kg/min during surgery. Remifentanil was randomly combined with propofol (group 1: 100 micrograms/kg/min; n = 7), enflurane (group 2: 0.5 MAC; n = 8) or isoflurane (group 3: 0.5 MAC; n = 8). Monitoring included: heart rate (beats/min), mean arterial pressure (mmHg), oxygen saturation (%), endtidal CO2 (mmHg) and endtidal enflurane and isoflurane (%). EEG: 2-channel recordings of Fz versus mastoid and ECG (artefact control) during steady-state anaesthesia and surgery. Following fast-fourier-transformation (4 s; 256/s; 0.5 to 35.0 Hz), spectral power densities were calculated for the selected frequency bands. Auditory evoked potentials (AEP; middle latency) were registered simultaneously after binaural stimulation via head-phones click-stimulation (6 Hz; 75 dB above hearing threshold; 512 stimulations per average). Bandpass was 0.01 to 2.0 kHz.Na, Pa, Nb (latencies; ms) and peak-to-peak amplitudes (NaPa, PaNb; microV). EEG and AEP recording technique [15]. The study protocol included baseline values from pre-intubation, pre-surgery, the respective post-stimulation values (1 min, 3 min, 5 min) and all data at five-minute intervals during surgery until emergence from anaesthesia. During steady-state study conditions with defined remifentanil applications, mean data indicate that in response to nociceptive stimuli no changes in clinical or electrophysiological parameters were observed. In contrast to other studies using different anaesthetic techniques, the present data from remifentanil indicate very stable haemodynamic and electrophysiological parameters (EEG, AEP) during noxious stimulations. Adjustable and with no plasma accumulation, remifentanil demonstrates potent antinociceptive effects resulting in signs of adequate anaesthesia.

The problem of inherited deafness in various breeds of dogs and cats catches more and more attention in concerned breeders and owners. This article presents an update in the current knowledge of prevalence, aetiology and genetics of sensorineural deafness and its differentiation against acquired forms of hearing disorders. An electrophysiological method (Auditory Evoked Potentials) to obtain an objective diagnosis of hearing disorders is presented. The usefulness of Auditory Evoked Potentials as an instrument for genetic investigations in inherited deafness is discussed.

The current adjustment of cochlear implant (CI) speech processors is based on a knowledge of the lower and upper limits (T- and C-levels) for electrical stimulus currents. These data are usually acquired from subjective classifications of individual patients. In cases with non-reliable patient responses, objective methods are necessary. Especially for the estimation of correct T-levels, auditory evoked potentials (AEP) can be applied, since they allow the determination of response thresholds in a frequency-specific manner. By determining the AEP of different latencies, late cortical responses can be registered almost without artifact contamination. These patients have been examined in 20 patients provided with 22- or 8-channel CI-systems (Nucleus or Med-EI implants). In all cases, clear responses and clearly discernible threshold transitions could be detected. By making use of acoustical stimulation in a free sound field, subjective hearing threshold and the T-levels of electrical stimulation could be verified. Since late responses are generated in the primary auditory cortex, their assessment permits a nearly integral functional control of the aided hearing system. To date, no problems have occurred from maturation or attentional effects in either pediatric or adult patients. The applicability in very young children remains to be explored.

In contrast to auditory brainstem potentials (ABR), a more apically defined generation of middle latency evoked potentials (MLR) can be assumed due to the longer integration time present. To date, the effect of stimulus frequency spectra on MLR has not been completely known. By using masking with high-pass filtered white noise in 12 normal-hearing adults, we measured the dependence of amplitude and latency of ABR and MLR on filter frequency. No differences were found between the masking effects for ABR and MLR evoked by tone bursts of 0.5 and 2 kHz. The high-pass masking of click stimuli showed a greater influence on the amplitude and latency of the ABR than on MLR. These different qualities have to be considered clinically when evaluating the methods and results of hearing testing with acoustic evoked potentials. Our findings show that MLR evoked by tone bursts should be used for the frequency selective diagnosis of hearing thresholds, especially in low-frequency ranges.

Hearing impairment is a rare but characteristic symptom of vertebrobasilar occlusive disease. Two patients with anterior inferior cerebellar artery (AICA) infarction and hearing loss as presenting complaint, are described. In patient 1 progressive bilateral AICA infarction was caused by occlusion of the basilar artery, verified by transcranial Doppler sonography. Initial dizziness and bilateral hearing loss were followed by ataxia, dysarthria, dysphagia and right facial sensory impairment. Hearing loss improved during the second week, parallel to a temporary partial recanalisation of the basilar artery, but the patient subsequently developed further progressive brain stem symptoms and died. A right-sided AICA-infarction was diagnosed in patient 2. Initial symptoms were right-sided deafness and dizziness. Neurological examination revealed nystagmus, ataxia and involvement of th 5th and 6th cranial nerve. A progressive improvement of hearing loss and total recovery of the other brain stem symptoms was evident. In conclusion every patient with sudden hearing loss should be examined for additional brain stem symptoms since this can be the presenting sign of a life-threatening basilar artery thrombosis.

Transient click-evoked otoacoustic emissions (TEOAE) and distortion-product otoacoustic emissions (DPOAE) are produced by an active biomechanical process in the cochlea, presumably related to outer hair-cell activity. Although it is generally accepted that in most cases of hearing loss with absent auditory evoked potentials neither TEOAE nor DPOAE can be found, some cases with such a constellation have been described. Here we report another four cases of children with severe to profound hearing loss where we discovered reproducible TEOAE and DPAOE, whereas auditory evoked potentials were missing. TEOAE and DPOAE recordings in these cases indicate substantially preserved outer hair-cell function independent of profound pre-sensineural hearing loss. Since the incidence of children with preserved otoacoustic emissions together with impairment of synaptic or postsynaptic function of the first neuron is not known, the unconditioned use of TEOAE nor DPOAE as a screening instrument must be seriously questioned. Secondly, in conjunction with subjective audiometry and brain-stem-evoked potentials, emission recordings is an indispensable measurement prior to cochlear implantation and use of high-power hearing aids.

Evoked potentials are used for intraoperative monitoring to assess changes of cerebral function. This prospective randomised study assesses the influence of surgical stimulation on midlatency components of somatosensory (SEPs) and auditory evoked potentials (AEPs) in anaesthetised patients.After approval of the Ethics Committee and written informed consent 36 orthopaedic patients (34 +/- 15 y, 73 +/- 14 kg. 1.71 +/- 0.07 m, ASA I-II) were randomly included in the study. Anaesthesia was induced with 1.5 micrograms/kg fentanyl, 0.3 mg/kg etomidate and 0.1 mg/kg vecuronium. The lungs were intubated and patients normoventilated in steady state anaesthesia with isoflurane (end-tidal 0.6%) and 66% nitrous oxide. 18 patients (group 1) were assigned to the SEP group: median nerve stimulation, recording at Erb, C 6 and the contralateral somatosensory cortex (N20, P25, N35) vs Fz. AEPs were recorded in group 2 (n = 18): binaural stimulation, recording at Cz versus linked mastoid (V, Na, Pa, Nb). Recordings were performed during 30 min before the start of surgery (baseline: BL), at skin incision (SURG1) and at the preparation of the periost (SURG2). Heart rate, mean arterial blood pressure, oxygen saturation, endtidal pCO2 and isoflurane (PetISO) concentrations were registered simultaneously. Data were analysed by one-way analysis of variance. Post hoc comparison were made by Mann-Whitney U-Wilcoxon Rank Sum Test with p0.05 significant.During steady state isoflurane anaesthesia surgical stimulation (SURG2) resulted in significant increases of N20 P25 amplitudes compared with BL (BL: 1.4 +/- 0.7 microV; SURG2: 2.0 +/- 0.8 microV; p0.05). Latencies of SEPs and midlatency components of AEPs did not change over time. There were no differences in autonomic parameters between SEP and AEP groups. MAP increased from 76 +/- 6 mmHg at BL to 93 +/- 16 mmHg at SURG1 and 96 +/- 17 mmHg at SURG2 (n = 36; p0.05). HR increased from BL (60 +/- 8 beats/min) to SURG2 (76 +/- 12 beats/min). Increases of amplitudes of midlatency SEP amplitudes indicate increased nociceptive signal transmission which is not blunted by isoflurane-nitrous oxide anaesthesia. In contrast, unchanged AEPs indicate adequate levels of the hypnotic components of anaesthesia.