The synaptic physiology of cochlear hair cells

Mechanosensory hair cells of the vertebrate inner ear are so-called 'short' receptors that communicate to the central nervous system by way of chemical synapses with afferent neurons. In turn, hair cells are the targets of olivocochlear fibers that carry efferent inhibitory feedback from the brain. These synaptic activities contribute to, or modulate the hair cell's receptor potentials through the gating of associated ion channels. Thus for example, voltage-gated calcium channels open to trigger vesicle fusion and release of transmitter by entry of extracellular calcium. The inward calcium current also depolarizes the membrane and could lead to generation of 'all-or-none' action potentials. However, regenerative depolarization is prevented in most hair cells by prominent voltage-gated potassium conductances that rapidly repolarize the membrane. The magnitude and speed of these delayed potassium conductances determine the size and shape of the resulting receptor potential, and subsequent transmitter release, produced by sound. Efferent feedback is provided by the release of acetylcholine (ACh) from olivocochlear nerve fibers onto outer hair cells in the mammalian cochlea. The hair cell's ACh receptors are ligand-gated cation channels related to the nicotinic receptors of nerve and muscle. Calcium influx through the ACh receptors activates nearby calcium-gated potassium channels, resulting in hyperpolarization and inhibition of the hair cell. Calcium influx during efferent inhibition is regulated by a 'synaptic cistern' that also may act as a calcium store that is triggered by ACh under some conditions.     

Recent advances in cochlear blood flow measurements

Changes in blood flow to the inner ear have been thought to influence or underlie a number of cochlear diseases, including some forms of noise-induced hearing loss, sudden hearing loss, and Meniere's disease. Recently, important advances have been made in two technologies for the study of cochlear blood flow. The first is in the area of vital microscopic studies of cochlear microcirculation, and the second is based on the introduction of laser technology in the form of laser Doppler flowmetry. In this report, measurements are given of changes in cochlear circulation caused by carbon dioxide breathing, intravenous phenylephrine injection, systemic hemodilution, positive end expiratory pressure, and direct electrical stimulation of the cochlea. From these changes, we observe that cochlear blood circulation responds to systemic blood pressure alterations and is subject to local flow control mechanisms. Linearity and speed of response of the laser Doppler instrumentation also are shown. These advances show promise for contributing to our knowledge of control mechanisms of inner ear blood flow and for revealing the influence of various pharmacologic agents of potential clinical value.     

脱髓鞘疾病的听力学研究进展

脱髓鞘疾病是一大类病因不同、临床表现各异、但又有相似特征的疾病,其共同特点是神经纤维的髓鞘脱失而神经细胞相对保持完整.国内外有些学者在对此病患者的研究报道中,显示有不同程度的听神经损害,但迄今尚未有病理证实,尚不能明确具体病变部位.现就近年来这方面的研究进行综述.     

Longitudinal changes in children's speech and voice physiology after cochlear implantation

OBJECTIVES: The purposes of this investigation were 1) to describe speech/voice physiological characteristics of prelingually deafened children before and after cochlear implantation and determine whether they fall into a range that would be considered deviant, 2) to determine whether selected deviant articulatory and phonatory behaviors of children with cochlear implants persist despite long-term cochlear implant use and continued participation in aural rehabilitation services, and 3) to determine whether further development of deviant articulatory and phonatory behaviors occurs postimplantation. DESIGN: Seven prelingually deafened children who received cochlear implants after 5 yr of age were followed from shortly before implantation until 5 to 6 yr postimplantation. These children received their early education in a Total Communication environment and used the Nucleus 22-electrode cochlear implant. All of them initially used the MPEAK speech processing strategy, and five of them eventually upgraded to the SPEAK speech processing strategy. Speech/voice physiological measurements that were obtained periodically from the children included intraoral air pressure (P(o)), nasal and phonatory air flow, voice onset time (VOT), and fundamental frequency (F(o)). Data from the deaf children were compared with a database from 56 children with normal hearing to determine when the deaf children exhibited "deviant" speech/voice behaviors. Speech/voice behaviors were considered "deviant" if they never occurred for children with normal hearing or were associated with z-scores that were outside the range of +/-2.0. RESULTS: The deaf children showed a wide range of deviant speech and voice behaviors both pre- and post-cochlear implant. The most frequently occurring atypical behaviors were use of negative P(o), high P(o) for [b, m], long and short VOT for [p], and high F(o). Some deviant behaviors improved post-cochlear implant. However, deviant behaviors often persisted for several years post-cochlear implant. There was considerable evidence of further development of deviant behaviors post-cochlear implant. All of the deaf children demonstrated deviancy on at least two of our measures at the last data collection interval (5 to 6 yr post-cochlear implant). CONCLUSIONS: Children who received cochlear implants after 5 yr of age and who were educated in a Total Communication setting showed persistence and further development of deviant speech/voice behaviors for several years post-cochlear implant. Although our findings cannot be generalized to other populations of children with cochlear implants (i.e., those who were implanted earlier, those educated in auditory-oral programs), it seems wisest at the present time not to assume that children's deviant speech/voice behaviors will remit spontaneously with continued cochlear implant use. Our data provide an important comparative database for future investigations of pediatric cochlear implant users who have had shorter periods of auditory deprivation and who have received cochlear implants with more current technological features. Longitudinal Changes in Children's Speech and Voice Physiology after Cochlear Implantation     

Multichannel cochlear implants. Current status and future developments.

The University of Califorina, San Francisco has been active in the development of the multichannel cochlear implants for rehabilitation of total sensory deafness for the past 8 years. Patients implanted with experimental prototypes of the devices now in use have demonstrated that speech discrimination of 40% to 50% is possible for common everyday words and sentence material. These devices provide the same stimulation to each of the 8 bipolar pairs in the cochlea. They have an internal disconnect device which allows for replacement and upgrading of implanted receiver-drivers without disturbing the scala tympani electrodes. Application of these devices in a larger deaf population is currently underway. The present report discusses the current status of implants and the future developments we feel are necessary to achieve improved speech discrimination.     

Recent developments with the nucleus 22-electrode cochlear implant: a new two formant speech coding strategy and its performance in background noise

A clinical evaluation of speech processing strategies for the Nucleus 22-electrode cochlear implant showed improvements in understanding speech using the new FOF1F2 speech coding strategy instead of the F0F2 strategy. Significant improvement in closed-set speech recognition in the presence of background noise was an additional advantage of the new speech processing strategy.     

声带的细胞生理学研究进展

声带由不同类型组织组成，包括上皮、固有层、横纹肌、神经、血管和软骨，为多层结构，每层都有不同的作用。固有层是其中的重要结构，分为浅层、中层和深层，浅层下为任克间隙，中层主要由弹性纤维组成，而深层主要由胶原纤维组成，后两层合称声韧带。深层的深面为甲杓肌，形成声带的主体。在声带的前端，固有层的中间层增厚形成一卵圆形的结构，称为前黄斑，由弹性纤维、纤维母细胞和基质组成，形成一网状结构。两边的前黄斑之间主要由胶原纤维组成，成为前联合。声带膜部的后端，固有层的中间层在这里又形成卵圆结构，成为后黄斑，结构与前黄斑相似，与杓状软骨的声带突相连。     

The physiology of the normal and pathological cochlear neurones--some recent advances

This is the first of two auditory science tutorials designed for otolaryngologists, audiologists, and others dealing with deafness and its consequences. This tutorial is intended as an update on recent advances in the understanding of cochlear function both in the normal person and in patients with hearing loss of cochlear origin. It draws largely on studies involving electrophysiological recordings from cochlear nerve fibres in "animal models" of cochlear hearing loss. These data allow considerable insight into the underlying causes, for example, loudness recruitment, tinnitus, and poor speech intelligibility. Areas of scientific ignorance are also mentioned. This is not an exhaustive review of the literature but rather a general overview. The style of the tutorial is not starchily scientific, contains minimum jargon, and is intended to make easy reading.     

Altered phonatory physiology with short-term deactivation of children's cochlear implants.

OBJECTIVES: The purposes of this investigation were 1) to determine whether short-term auditory deprivation results in systematic phonatory changes for prelingually deafened children who use cochlear implants (CIs) and 2) to determine whether such changes are similar to those that have been reported for postlingually deafened adults. DESIGN: Participants were two 6-yr-old children with CIs. Both children had been prelingually deafened, had good to excellent speech production and speech perception skills, and had been using their CIs for 2.5 yr. A single-subject design was used. Intraoral air pressure (Po), phonatory air flow (Vl), electroglottograph (EGG) cycle width, fundamental frequency (F0), and intensity were measured during syllable production over two baseline days and three experimental days. Data were collected twice on each baseline day while the children wore their CIs, with a 1 hr break between data collection sessions. On experimental days, data were collected while the children wore their CIs (ON condition) and after their CIs had been removed for 1 hr (OFF condition). RESULTS: Both children demonstrated highly variable phonatory behaviors in baseline. The child with the more proficient speech production and perception skills showed consistent and significant reductions in Po, F0, and intensity in the OFF condition. These findings were dissimilar to those that occurred with repeated testing in the baseline condition and so were attributed to the sudden loss of auditory feedback. The other child showed a consistent and significant increase in mean Vl in the OFF condition. However, this child exhibited a similar finding with repeated testing in the baseline condition. Therefore, increased Vl in the OFF condition may have represented a practice effect. She also showed a small and consistent decrease in F0 in the OFF condition when F0 was derived from acoustic data, but this effect was not reliable in another data set when F0 was derived from the EGG signal. Our results with prelingually deafened children were inconsistent with reports of increased intensity and F0 in the absence of auditory feedback for postlingually deafened adults with CIs. CONCLUSIONS: Some prelingually deafened children who are successful CI users appear to use auditory feedback to self-monitor phonation. We suggest that the participant in our investigation who showed systematic phonatory changes in response to diminished auditory feedback was using auditory feedback primarily to stabilize her phonatory behaviors. She may not have had adequate experience with auditory feedback or adequate flexibility in her use of feedback mechanisms to implement the phonatory compensations that late-deafened adults use when auditory feedback suddenly is diminished. We further suggest that the phonatory changes that she exhibited during short-term auditory deprivation reflected disruption of her typical speaking strategies or apprehension about speaking when her ability to self-monitor auditorily was compromised.     

The Bone-Anchored Hearing Aid for children: Recent developments

In 1984 the Bone-Anchored Hearing Aid, or BAHA, system was introduced. Its transducer is coupled directly to the skull percutaneously to form a highly effective bone-conduction hearing device. Clinical studies on adults with conductive hearing loss have shown that the BAHA system outperforms conventional bone-conduction hearing aids. Therefore, the next step was to apply the BAHA system in children with congenital or acquired conductive hearing loss. Reviewed data showed that, on average, such children benefited significantly more from the BAHA than from reconstructive surgery. Thus, BAHA application appears to be the best option to achieve normal communication and speech and language development in children with bilateral conductive hearing loss. However, in children under the age of three to four years, a conventional solution must be applied, e.g. a bone conductor with a transcutaneous coupling, because they are too young to undergo BAHA implant surgery. In the case of unilateral congenital conductive hearing loss, there is no convincing evidence in the clinical literature for early intervention.

In summary, the BAHA system can be considered a new, indispensable tool for children with bilateral conductive hearing loss.     

定量检测LASIK手术对视网膜影响的研究进展

准分子激光原位角膜磨镶术(LASIK)是近年来发展迅速的治疗屈光不正的角膜屈光手术,但LASIK术中眼压急剧变化、激光切削的冲击力等因素可能会对视网膜和视神经产生不良影响。基础研究表明,超过30s的负压吸引有可能对视网膜神经纤维层(RNFL)及视网膜微观结构有一定的影响;临床研究显示,目前的LASIK手术对RNFL厚度影响不明显,但可有一过性的黄斑中心凹视网膜厚度增加。