1,721,164 research outputs found
Hearing aids for auditory neuropathy patients
No full textAuditory Neuropathy (AN) is a hearing disorder characterized by disruption of temporal coding of acoustic signals in auditory nerve fibers resulting from lesions involving the nerve fibers themselves, the inner hair cells or their synapses with auditory nerve terminals. In contrast, outer hair cell activities are preserved (cochlear microphonic and otoacoustic emissions, OAEs). AN may be underlain by genetic disorders or result from a wide range of other etiologies. The disruption of auditory nerve discharge underlies both the absence of auditory brainstem responses (ABRs) and the impairment of speech perception. These alterations show high variability depending on etiology, site of lesion and stage of the disease. Cochlear implantation constitutes the only rehabilitative tool able to restore speech perception in patients with genetic AN. Nevertheless, some patients benefit from the use of auditory input delivered by hearing aids before cochlear implantation. Differently from subjects affected by genetic AN, hearing-impaired children discharged from Neonatal Intensive Care Units (NICUs) with absent ABRs and presence of OAEs may be successful hearing aid users.
In this presentation I shall report the outcome of hearing aid use in patients with genetic AN and in a group of children discharged from NICUs with the clinical picture of AN
Meccanismi neurofisiologici alla base degli acufeni: effetti inaspettati della plasticità neuronale
No full textClassicamente gli acufeni sono stati classificati in periferici e centrali sulla base della presunta localizzazione della lesione a livello della periferia uditiva o del sistema nervoso centrale. Tale lesione determinerebbe l’insorgenza di un segnale neurale “aberrante” responsabile della erronea percezione sonora (Eggermont, 2003; Baguley, 2002). In realtà, il problema è troppo complesso per poter essere risolto in questi termini. I dati forniti dalla ricerca di base e dalla ricerca clinica inducono attualmente a ritenere che nella stragrande maggioranza dei casi la lesione debba essere localizzata a livello della periferia uditiva e riguardi in particolare le cellule ciliate (Noreña e Eggermont, 2003, Jastreboff, 1990; Liberman e Kiang, 1978). La conseguente modificazione del pattern di scarica a livello delle fibre del nervo rappresenta comunque una condizione necessaria ma non sufficiente per l’insorgenza di una illusione della percezione uditiva. La realizzazione di questa condizione dipende infatti strettamente dalle modalità con cui la nuova configurazione della scarica neurale periferica viene elaborata dai centri nervosi immediatamente dopo l’instaurarsi del danno e, in una fase successiva, dopo l’innesco dei fenomeni di plasticità neuronale
Information from cochlear potentials and genetic mutations helps localize the lesion site in auditory neuropathy
Full text linkAuditory neuropathy (AN) is a disorder characterized by disruption of auditory nerve activity resulting from lesions involving the auditory nerve (postsynaptic AN), inner hair cells and/or the synapses with auditory nerve terminals (presynaptic AN). Affected subjects show impairment of speech perception beyond that expected for the hearing loss, abnormality of auditory brainstem potentials and preserved outer hair-cell activities. Furthermore, AN can be identified either as an isolated disorder or as an associated disorder with multisystem involvement including peripheral and optic neuropathies (non-isolated AN). Mutations in several nuclear and mitochondrial genes have been identified as underlying these forms of AN. Recently, new genes have been identified as involved in both isolated (DIAPH3, OTOF) and non-isolated AN (OPA1). Moreover, abnormal cochlear potentials have been recorded from patients with specific gene mutations by using acoustic stimuli or electrical stimulation through cochlear implant. In this review, different types of genetically based auditory neuropathies are discussed and the proposed molecular mechanisms underlying AN are reviewe
L’utilizzo della elettrococleografia nella diagnosi della neuropatia uditiva
No full textTre pazienti (due bambini e un giovane adulto) sono stati inquadrati nel gruppo di disordini denominato neuropatia uditiva per l’assenza di risposta ABR associata alla conservazione delle otoemissioni acustiche. Due casi presentavano una perdita uditiva di entità moderata e una grave compromissione della percezione verbale che appariva sproporzionatamente ridotta rispetto al grado di ipoacusia. L’altro paziente, dell’età di un anno, era affetto da ipoacusia profonda. In un caso era associata una atrofia ottica bilaterale.
Al fine di ottenere una stima della funzionalità della periferia uditiva, i tre soggetti sono stati sottoposti alla registrazione dell’elettrococleografia con elettrodo transtimpanico in risposta alla stimolazione con clicks presentati in campo libero a varie intensità di stimolazione. In tutti e tre i casi è stata evidenziata una lesione cocleare. Nel paziente con ipoacusia profonda solo il potenziale microfonico era identificabile nella registrazione elettrococleografica ottenuta alla massima intensità di stimolazione, mentre non era riconoscibile il potenziale di azione del nervo. Un altro dei soggetti presentava il potenziale microfonico, il potenziale di sommazione e forse una attività neurale che, se presente, appariva comunque destrutturata. Il quadro elettrococleografico dell’ultimo soggetto era tipico di una cocleopatia con una soglia uditiva situata a medi livelli di intensità che non giustificava l’assenza della risposta ABR
Transtympanic electrocochleography in auditory neuropathy
No full textAuditory neuropathy is a disorder identified by the absence or the severe impairment of auditory brainstem responses (ABRs) with the preservation of otoacoustic emissions. It is generally accepted that the lesion should be localized at the level of the inner hair cells, the auditory nerve fibers or the synapse in between. The presence of otoacoustic emissions indicates that the outer hair cells are spared and possibly they are functional.
We performed an audiologic evaluation in three patients showing distortion product otoacoustic emissions and absent ABRs. Since these findings could be attributed both to a selective damage involving the peripheral afferent component and/or to a de-synchronization of brainstem neural generators, patients underwent the recording of transtympanic electrocochleography (ECochG). The results were:
1) The first patient (aged 1) with hyperbilirubinemia at birth showed only the cochlear microphonic in the electrocochleographic recording;
2) The second patient (aged 17) had a severe impairment of speech discrimination out of proportion of the auditory threshold. The ECochG performed in this subject consisted in the summating potential followed by a neural activity highly desynchronized which was identifiable at stimulation intensities lower than the hearing threshold;
3) The third patient (aged 5) showed a moderate hearing loss at low frequencies and a severe impairment in speech discrimination associated with bilateral optic nerve atrophy. A compound action potential with normal amplitude and latency was identifiable in the ECochG recording till to a stimulation intensity corresponding to the PTA threshold.
On the basis of ECochG recordings the lesion should be localized at the level of the cochlear afferent component only in the first two subjects. The presence of a CAP response at high to moderate stimulus intensities together with an absent ABR point to a superimposed brainstem lesion in the third patient. These results suggest that electrocochleography can be useful in the assessment of the auditory neuropathy since only the CAP detection in ECochG recordings is a reliable estimate of the auditory peripheral function in the presence of a de-synchronized ABR
Electrocochleography in Auditory Neuropathy
No full textAuditory neuropathy (AN) is a disorder characterized by the absence or the severe impairment of the auditory brainstem responses (ABRs) together with the preservation of otoacoustic emissions and/or cochlear microphonic (CM). We recorded transtympanic electrocochleography (ECohG) evoked by 0.1 ms clicks in one young adult and in four children having distortion product otoacoustic emissions and absent ABRs. In all but one patient CM and summating potential (SP) were present with normal threshold, and their amplitudes appeared comparable to or higher than the values obtained from subjects with normal hearing. The compound action potential (CAP) was absent in two patients while in one subject CM and SP were followed by a highly desynchronized neural activity. A broad CAP was found in two children and the threshold appeared clearly elevated in one of them, while it showed only a mild elevation in the other. No correlation was found between CAP and behavioral thresholds. These results suggest that ECohG can be useful in AN diagnoses since it is the only reliable tool in evaluating the auditory peripheral function in the presence of a desynchronized ABR
Generation of auditory steady-state responses: linearity assessment.
No full textThe linear summation of the responses elicited by individual stimuli can be considered the main mechanism underlying SSR generation. Moreover other phenomena become involved so that individual responses elicited at fast repetition rates (LCRs) are different from those recorded at stimulus rates preventing their overlapping (MLRs). First, phenomena related to the recovery cycle can determine parameters of individual responses within the SSR causing a reduction in amplitude and an increase in latency with increasing repetition rates. Second, other mechanisms related to the resonant frequency of the auditory system come into play enhancing the contribution of individual responses during 40 Hz steady state stimulation. Assuming linearity and admitting that the system behaves as a damped harmonic oscillator having resonant frequency of 40 Hz and damping ratio between 0 and 1, one can speculate that, for a given damping value, the output modulus depends on the frequency components of the input as well as on the system resonant frequency. The increase in the input of the frequency components close to the system resonant frequency causes the output modulus to increase and this make more likely the appearance of further oscillations in the system output.
In conclusion it seems that the surface recorded SSR results from the linear summation of the responses to individual stimuli and these responses are different from MLRs since they can be enhanced or depressed by resonant and adaptation phenomena. The interplay between these effects is strictly dependent on the stimulus repetition rate
La neuropatia uditiva
No full textNel corso degli ultimi decenni le alterazioni della percezione verbale causate da una disfunzione del sistema uditivo non riconducibili a una lesione cocleare “classica” sono state oggetto di un crescente interesse emergendo dal gruppo indistinto ed eterogeneo dei disturbi psichiatrici, neuropsicologici e del linguaggio in cui erano state confinate. La spinta alla individuazione di alterazioni del “processing” del segnale uditivo si è svolta lungo due direttive principali. Nel 1996 Arnold Starr e collaboratori hanno riportato le caratteristiche cliniche di un gruppo di pazienti che presentavano una severa compromissione della percezione verbale a fronte di una perdita uditiva lieve o moderata. Tali reperti erano associati alla presenza delle otoemissioni acustiche (otoacoustic emissions, OAEs) e all’assenza delle risposte evocate uditive del tronco encefalico (auditory brainstem responses, ABRs). L’assenza di coinvolgimento del sistema nervoso centrale e il riscontro di una neuropatia periferica riscontrate nella maggioranza dei pazienti ha indotto gli autori a ipotizzare che la lesione responsabile della compromissione della percezione verbale e dell’assenza della risposta ABR fosse riconducibile a fenomeni di demielinizzazione delle fibre del nervo uditivo (auditory neuropathy, AN) o in alternativa, a lesioni delle cellule ciliate interne (inner hair cells, IHCs) o delle sinapsi interposte. Le basi neurofisiologiche della ridotta percezione verbale sarebbero pertanto da ricercare in una alterata codifica dell’informazione uditiva da parte del compartimento afferente periferico con conservazione della funzionalità delle cellule ciliate esterne (outer hair cells. OHCs)
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