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Conclusion: This paper reviews psychoacoustical and electrophysiological evidence for reorganization of the human central auditory system in case of auditory deprivation and rehabilitation., Objective: To investigate the plasticity of cortical tonotopic maps in cochlear-damaged subjects., Methods: Frequency discrimination scores were analysed in subjects with high frequency hearing loss to test for potential perceptual correlates of auditory deprivation- and rehabilitation-induced plasticity. In cochlear implant patients, electrically evoked auditory cortical responses were obtained using EEG to study scalp potential maps., Results: Perceptual changes in frequency discrimination were observed at the lesion-edge frequency of steeply sloping hearing loss. Although these results are not direct proof of cortical plasticity, no peripheral phenomenon has been found to explain them. The reversal of such auditory deprivation-induced plasticity, a phenomenon that may be termed rehabilitation plasticity, can be studied in hearing-impaired subjects fitted with a hearing aid. Cochlear implant subjects provide another interesting model for studying rehabilitation plasticity in that even profound to total deafness is made partially reversible by cochlear implantation. We found that the auditory cortex of deaf subjects with at least 3 months of cochlear implant experience is organized in a way similar to the tonotopy described in normal-hearing subjects.

Objective: Previous studies reported that the consequences of auditory rehabilitation were lateralized, with the right ear (RE) showing more improvement than the left ear (LE) over the time course of hearing aid (HA) use in elderly patients with symmetrical presbyacusis. It has been suggested that this asymmetry is linked to a change in speech lateralization. The aim of this study was to explore the consequences of HA use on interaural asymmetry in symmetrical sensorineural hearing impairment patients before and 4 months after binaural HA fitting., Material and Methods: Two types of perceptual task were chosen in order to measure speech lateralization: two dichotic listening tasks; and an identification task for a voice onset time continuum. Seven elderly, right-handed patients suffering from symmetrical presbyacusis were selected and tested before HA fitting and 4 months after. All measurements were made without the use of the HA, and the listeners were all first-time HA wearers., Results: Dichotic listening scores for words improved significantly over the course of HA use. Moreover, the dichotic listening task for syllables revealed an increase in auditory asymmetry after 4 months of HA use. Concerning the identification task, a significant difference between ears was found, with only the R E showing significant improvement with HA use., Conclusion: These results suggest that auditory rehabilitation is lateralized, with greater change as a result of HA use occurring in the RE than the LE in right-handed patients.

It is well known that the large inter-individual susceptibility to noise exposure makes it impossible to predict the degree of hearing loss which will develop after any given intense noise exposure. The acoustic trauma which sometimes occurs affects cochlear mechanisms, the damage being most probably due to deactivation of the active processes of the outer hair cells (OHCs), which receive direct efferent innervation. The present report is of a follow-up study involving young military personnel recovering auditively from impulse noise exposure, and seeks to assess changes in cochlear status by means of otoacoustic emissions (OAEs) and their modulation by the medial olivocochlear (MOC) system. The study investigated the relationship between recovery of cochlear function and variables that could serve as predictors of vulnerability to noise-induced hearing loss (NIHL). Thirty-six subjects with unilateral NHIL above 4 kHz were included. Normal and affected ears were compared with respect to click-evoked and spontaneous OAEs (CEOAEs and SOAEs, respectively) and for contralateral CEOAE suppression. Measurements were obtained: (i) just after the traumatic exposure (D0); (ii) 3 days after this first measurement (D3); and (iii) 30 days after (D30). Significant improvement in the 4, 6 and 8 kHz thresholds was observed for the affected ear, with large inter-subject variability. No significant change was observed in CEOAE amplitude or MOC suppression, whereas incidence of SOAE was found to increase in the affected ear, leading to higher SOAE prevalence on this side I month after the intense noise exposure. There was no significant correlation between NIHL at 4, 6 and 8 kHz and MOC functioning on D0, but significant correlations were obtained between audiometric threshold improvement by D3 and contralateral CEOAE suppression, with better recovery in subjects with greater MOC suppressive action. The MOC system could be an underlying mechanism in post-traumatic auditory threshold recovery.

In humans, administration of benzodiazepines (BZD) has been shown to have an asymmetrical effect on the medial olivocochlear system. Indeed, a decrease of evoked otoacoustic emission suppression by contralateral acoustic stimulation, which explores the medial olivocochlear efferent system, was observed in the right ear, with no left ear effect. This result suggests a possible left-right auditory pathway BZD receptor asymmetry. Given the anatomical link between auditory centers and the medial olivocochlear system, the existence of a larger volume of cortical connecting fibers in the left hemisphere, and the possible link between BZD receptor density and neuronal density, we tested the hypothesis of an asymmetrical localization of BZD receptors in the auditory system in 10 right-handed subjects using [11C]flumazenil positron emission tomography. Semi-quantitative measurements of flumazenil binding were evaluated in Heschl's gyrus showing a left-right asymmetry in favor of left auditory cortex. This result indicates a higher density of neurons in left auditory cortex. The possible link between neurochemical asymmetry and functional asymmetry, and the perceptual outcome of BZD administration, will be discussed.

The present study aimed to test whether central, across-channel, informational auditory processing abilities are altered by hearing loss. The informational masking effect exerted on a 1 kHz tone-pip by a simultaneous four-tone masker, whose spectral content changed within as well as across trials, was measured in the left and right ears of normal-hearing subjects and hearing-impaired subjects with either symmetrical or asymmetrical hearing loss between the two ears. In the subjects with normal-hearing or symmetrical hearing loss, the level of the masker was set to 40 dB SL in each ear, in the subjects with asymmetrical hearing loss, the masker was set to 40 dB SL in the best ear and loudness-balanced in the other ear. The results failed to reveal significant differences in informational masking between normal-hearing and hearing-impaired subjects. However, in subjects with asymmetric hearing loss, less informational masking was observed in the ear with the more elevated absolute thresholds than in the opposite ear. Since the latter finding can be explained in terms of across-ear differences in loudness recruitment, it is suggested that central, across-channel, informational processing abilities are not substantially different in hearing-impaired than in normal-hearing ears.

Electrically evoked auditory brainstem responses (EABRs) and loudness functions were measured in 14 subjects equipped with an MXM Digisonic cochlear implant. EABRs were evoked by 75-Hz pulse trains presented on the apical electrode. Loudness functions at the same rate and at a rate more conventional for psychoacoustic measurements (300 Hz) were measured using a categorical loudness-scaling procedure. The results revealed a significant difference in the loudness functions measured at 75 and 300 Hz, loudness increasing more steeply with stimulus intensity for the latter rate. Significant correlations between EABR wave V thresholds and perceptual thresholds measured at both 75 and 300 Hz were observed. Furthermore, in 8 out of the 14 patients, EABR wave V saturated at a stimulus level corresponding precisely to the loudest bearable, i.e. "Too loud" level for the 300-Hz stimulation rate; this same level corresponded to the "Comfortable" loudness level for the 75-Hz stimulation rate. On average, an almost linear relationship was observed over the first half of the loudness range between the stimulus intensity, expressed as a pulse duration in log units, and wave V amplitude in dB. Although further investigation is required before maximum comfort levels can be predicted reliably from EABR measures in individual subjects, these results indicate new directions regarding the estimation of perceptual dynamic range limits on the basis of EABR measures in cochlear implantees.

The aim of this study was to test for differences between normal-hearing and hearing-impaired listeners regarding two fundamental aspects of intensity perception: loudness integration and loudness summation. Loudness functions for three different stimuli were measured using categorical loudness scaling in 8 normal-hearing and 12 hearing-impaired subjects. The results indicated that temporal loudness integration, defined as the difference in SPL between 16.25-ms and 300-ms noise bursts of equal loudness, was larger in the hearing-impaired than in the normal-hearing listeners. Loudness summation, defined as the difference in SPL between a 300-ms, 1,600-Hz tone pip and a white noise burst of the same duration and loudness, did not differ between the two groups. Implications of these results for hearing aid fitting strategies based on loudness normalization are discussed.

Auditory system hemispheric asymmetry in language processing is well-established, and there are many indications of lateralization as of the peripheral auditory system i.e., as of the cochlea. The left ear is more susceptible to noise damage; tinnitus is more predominant there, while spontaneous otoacoustic emissions (SOAEs) are more often found in the right ear. The present study addressed the following two questions: Does this right-ear SOAE prevalence exist as early as preterm birth? Is there any functional asymmetry in the medial olivo-cochlear (MOC) efferent system, known to modulate outer hair cell contractions? The study involved 483 preterm neonates (gestional age: 24-37 weeks) and 70 right-handed adults (age: 18-31 years). In each ear, SOAEs and evoked otoacoustic emissions (EOAEs) were recorded and analysed, and, for the adults, functional MOC system assessment was made. Results showed SOAEs and EOAE amplitude to be right-predominant and in adults a right MOC functional predominance. These results indicate peripheral auditory system lateralisation, and an early origin thereof. The MOC system being thought to play a protective role, its physiological lateralisation may be relevant to the left prevalence of tinnitus and of auditory fatigue.

In a previous study, the authors described a technique for recording ipsilateral EABRs using the DIGISONIC MXM cochlear implant (Gallégo et al, Acta Otolaryngol (Stockh) 1996; 116: 228-33) and showed that the EABR input/output functions were very similar across electrodes. In the present study a test of electrode functioning based on the recording of surface potentials is presented. Then, for each electrode the relationship between EABR thresholds and hearing thresholds was determined. Lastly, the relationship between EABR parameters and patients' performances was studied. The results show that the functioning of each implanted electrode can be assessed quickly, accurately and objectively. Furthermore it is demonstrated that a strong correlation between EABR and hearing threshold can be obtained using an automatic EABR wave detection technique. Finally it is shown that EABR inter-peak intervals are related to patient performance. These results are of the utmost importance for cochlear implant setting in children as they indicate a method of objective assessment of the functioning of each electrode and of the corresponding hearing threshold.

Ipsilateral ABR recording technique was developed with the MXM DIGISONIC DX10 cochlear implant, involving, firstly, setting of recording variables with regard to implant and ABR constraints, and, secondly, enhancement of recording quality by signal processing. The resulting recording quality then enabled us to characterize ABR latency, amplitude and wave reproductibility according to stimulus intensity and stimulation site (electrode stimulated). The findings agree with those of the literature on contralateral human and ipsilateral animal studies. Waves III and V amplitude increased with stimulus intensity. Waves III and V latency was insensitive to stimulus intensity or site. ABR quality diminished basally.

Tinnitus is characterized by the continuous or intermittent auditory perception of various sounds (buzzing, whistling, etc.) in the absence of any external stimulus. Perilymphatic hyperpressure is one of the numerous mechanisms which could hypothetically be involved in tinnitus generation. In the present experiment, perilymphatic pressure was measured indirectly using the tympanic membrane displacement technique. Twenty-five tinnitus patients were investigated at 10, 15 and 20 dB above the acoustic reflex threshold with ipsilateral stimulation. The variables Vi (inward tympanic displacement), Vm (mean tympanic displacement) and their variations according to stimulus level were compared between tinnitus sufferers and age-matched or hearing-matched controls. Tympanic displacement was measured in sitting and supine positions so as to evaluate cochlear aqueduct patency. No systemic changes in response occurred in tinnitus patients, except at a high stimulation level, perhaps due to hearing impairment.

We examined several members of the same family with unilateral sensorineural hearing loss. The defect showed dominant inheritance. Clinical examination and auditory tests, including high-definition audiogram and otoacoustic emission recording, were done to characterize the physiopathological process of hearing loss, and to investigate possible asymptomatic auditory features in the normal ear of affected subjects and nonaffected siblings. Hypotheses as to the underlying mechanisms are discussed, eg, variable expression of bilateral isolated hereditary deafness, incomplete Klein-Waardenburg syndrome with stria vascularis anomalies and highly variable gene expression, or unilateral cochlear aplasia. The phenomenon may also be related to the delayed progressive unilateral loss in patients with bilateral hereditary deafness, involving perhaps unilateral vascular disorders or a genetically induced degeneration of cochlear cells or auditory neurons.

Although some findings suggest that auditory efferent fibers are involved in perception in noise, their function remains controversial. The contralateral suppression of evoked otoacoustic emissions (EOAEs) has recently provided a means of exploring the medial olivocochlear system (MOCS) in humans. In an experiment based on this paradigm, the present study examined the relationships between variations of both EOAEs and detection-in-noise thresholds, induced in the same subjects by a contralateral 50-dB-SPL broad-band noise masker. EOAEs were recorded in response to a burst of a multitone complex composed of 1, 1.5 and 2-kHz components. The detection thresholds of this 3-component complex were measured at 2 ipsilateral noise levels: 50 and 70 dB SPL. The main finding was a significant correlation between EOAE suppression and threshold variations under contralateral masking. A relationship was also found between the contralateral suppression of EOAEs and threshold variation induced by the increase in ipsilateral noise level. These findings support the notion that the MOCS is involved in the detection of multicomponent stimuli in noise.

This study compared the influence of an auditory attention task and of repetitive measures on the peripheral auditory system, using evoked otoacoustic emissions (EOAEs). The experimental task protocol comprised three sessions (pre-control, attention and post-control conditions) with, in each session, six measurements of EOAEs, at intervals of about 60 seconds, while the other ear was receiving two pure tones of 2,500 and 750 Hz, with a probability of appearance of 20% and 80%, respectively. In the contralateral attention condition, the subject had to count the number of the less frequent high pitched sounds. A long duration protocol (20 min for the total experiment) was used in order to examine a possible time-effect on EOAEs. An increase in EOAE amplitude during the second and third sessions, with linear saturation around the last measurements, was observed. While no attention effect could be identified, a time-effect seemed to be present. Possible explanations for the influence of repeated measurements on EOAEs are discussed. Moreover, EOAE amplitudes of subjects presenting spontaneous otoacoustic emissions were compared to those of subjects without SOAEs: significant differences were found, showing the particularity of cochleas emitting SOAEs.

The aim of this study was to investigate the functional development of cochlear active mechanisms and of the medial efferent olivocochlear system. Otoacoustic emissions (evoked and spontaneous) were recorded in 42 preterm neonates (conceptional age ranging form 33 to 39 weeks) and a control group of 20 young normal-hearing adults. Medial olivocochlear system activity was examined by coupling evoked otoacoustic emission recording to a contralateral stimulation. Otoacoustic emission recordings were carried out using the Otodynamic ILO88 software and hardware. The stimuli were unfiltered clicks and the contralateral stimulation was broad band noise of 50 and 70 dBSPL delivered by an Adam generator. The results revealed the presence of EOAEs and SOAEs from at least 33 weeks in humans, suggesting that the functional maturation of the outer hair cells is nearly complete at that age. The study further revealed that the contralateral stimulation had no effect on evoked otoacoustic emissions in preterm neonates. The lack of activity observed in medial olivocochlear system indicated functional immaturity here, at least before full-term birth.

A possible role of the efferent system in the mechanisms of tinnitus generation has been put forward by several authors. A simple method for studying the functioning of this system is to compare the amplitudes of otoemissions with and without mild contralateral stimulation. In a recent communication, Veuillet et al. (1991) reported that, on the side of tinnitus, the efferent system of patients suffering from unilateral tinnitus seems to be less efficient than on the other side. The results presented here correspond to those obtained in the very first tinnitus patients submitted to a research protocol exploring systematically the efferent system. When possible, the effectiveness was tested in two ways: globally, using evoked otoacoustic emissions (EOAEs) and, very precisely in the frequency zone of the tinnitus, using cubic distortion product 2f1-f2. Preliminary results obtained in bilateral and unilateral tinnitus sufferers show that a majority of them exhibits, at least in the proximity of the tinnitus, a lack of effectiveness of the efferent system. In some of them, instead of the suppressive effect, an increasing one was even observed.

Otoacoustic emission (OAE) generation mechanisms reside in the active micromechanical properties of the organ of Corti, and especially in the outer hair cells (OHCs). OHCs are strongly innervated by medial efferent olivo-cochlear fibres. Decrease of the intensity of transiently evoked otoacoustic emissions (TOAEs) and modification of spontaneous otoacoustic emissions (SOAEs) during acoustic stimulation of the contralateral ear have already been shown in humans. Similar results were obtained in guinea pigs with a decrease of 2F1-F2 acoustic distortion products (DPOAEs) and a suppression of the effect with sectioning of the floor of the fourth ventricle. The present study sought to investigate the influence of contralateral auditory stimulation on DPOAEs recorded in humans. It shows a decrease in DPOAE intensity for all frequencies, at levels above 45 dB SPL of contralateral broad band noise. This effect was found at levels of contralateral BBN well below the acoustic reflex threshold, and in subjects without acoustic reflex. Moreover, the influence of transcranial transmission could be ruled out since no effect was found when contralateral BBN applied to the altered ear of totally unilaterally deaf patients. Thus, the contralateral acoustic stimulation effect on DPOAEs provides a new means of functional exploration of the medial efferent system in humans. The effect obtained is more ample at low primary frequency levels. Moreover, as DPOAEs are known to be stronger and to show more irregular input/output function patterns in the vicinity of an SOAE, the influence of contralateral auditory stimulation was studied for DPOAEs recorded at 10 Hz, 50 Hz and 150 Hz from an SOAE frequency.

Evoked otoacoustic emissions (EOAE) and sound evoked olivocochlear feedback were performed in 200 subjects (noise induced hearing loss (NIHL), n = 109; sensori-neural hearing loss (SNHL), n = 91). Intensity of EOAE is greater in NIHL than in SNHL. This result does not seem to be related to the medial olivocochlear system since sound olivocochlear feedback was not significantly different between the two groups. No correlations were seen between temporary threshold shifts (TTS) and sound-olivocochlear feedback in the NIHL group.

This study sought to clarify the clinical relevance of spontaneous otoacoustic emissions (SOAEs) and to define the hearing loss level (and frequency) at which absence of SOAE is found. Findings from 126 ears of patients with sensori-neural hearing loss showed an incidence of SOAEs in 18.25% of the cases (23 out of 126 ears). SOAEs were never found when hearing loss at 1,000 Hz exceeded 10 dB. The presence of SOAE seems to indicate a good cochlear functioning at least in the mid-frequencies. Although the incidence of SOAEs is markedly lower than that of evoked otoacoustic emissions (EOAEs), SOAE recording is shown to be a good test, rapid, non-invasive for audiological screening, the presence of SOAE confirming a hearing threshold of less than 10 dB at 1,000 Hz, the absence of SOAE being inconclusive.

The clinical usefulness of the brainstem evoked response (BAER) derives from the high inter- and intra-subject reproducibility of V-wave latency. Attentiveness represents one possible cause of variation. To evaluate the effect of auditory or visual attention tasks and their repetition, we recorded BAERs during six repetitions of each of these two tasks. Each BAER was evoked by 2 000, 40 dB Hearing Level clicks. The results show that, at the 0.05 level, the difference in V-wave latency for auditory and for visual tasks is not significant. Moreover, repetition of the attention tasks fails to bring about any significant (p less than 0.05) change in this difference. In agreement with some researchers, but not with others, we show that attentiveness has little effect on BAER V-wave latency.

One thousand four hundred and ninety-one cases of acute appendicitis during infancy and childhood are reviewed, 137 were revealed by peritonitis. Complications following appendicitis with perforation (15%) are higher than acute appendicitis (2%). Many complications are reported, but the most serious of them are the 5th day syndrome after appendectomy. Early diagnosis, often difficult in infancy, and early operation before diffusion are the only means of prevention. Ultrasonography may reveal pelvic or intraperitoneal abscess. Treatment is a large drainage with antibiotics; enteral or parenteral nutrition may be associated.

The effects of stimulus intensity variation on brainstem auditory evoked potentials have been studied on 111 preterm, 36 fullterm neonates and 50 adults. When intensity decreases the lengthening of latencies is greater in preterm neonates. This effect is clearer with wave I than waves III and V and suggests an immaturity of the basal part of the human cochlea in preterm neonates.