Dissociated lateralization of transient and sustained blood oxygen level-dependent signal components in human primary auditory cortex

Among other auditory operations, the analysis of different sound levels received at both ears is fundamental for the localization of a sound source. These so-called interaural level differences, in animals, are coded by excitatory-inhibitory neurons yielding asymmetric hemispheric activity patterns with acoustic stimuli having maximal interaural level differences. In human auditory cortex, the temporal blood oxygen level-dependent (BOLD) response to auditory inputs, as measured by functional magnetic resonance imaging (fMRI), consists of at least two independent components: an initial transient and a subsequent sustained signal, which, on a different time scale, are consistent with electrophysiological human and animal response patterns. However, their specific functional role remains unclear. Animal studies suggest these temporal components being based on different neural networks and having specific roles in representing the external acoustic environment. Here we hypothesized that the transient and sustained response constituents are differentially involved in coding interaural level differences and therefore play different roles in spatial information processing. Healthy subjects underwent monaural and binaural acoustic stimulation and BOLD responses were measured using high signal-to-noise-ratio fMRI. In the anatomically segmented Heschl's gyrus the transient response was bilaterally balanced, independent of the side of stimulation, while in opposite the sustained response was contralateralized. This dissociation suggests a differential role at these two independent temporal response components, with an initial bilateral transient signal subserving rapid sound detection and a subsequent lateralized sustained signal subserving detailed sound characterization.

Differential patterns of multisensory interactions in core and belt areas of human auditory cortex

The auditory cortex is anatomically segregated into a central core and a peripheral belt region, which exhibit differences in preference to bandpassed noise and in temporal patterns of response to acoustic stimuli. While it has been shown that visual stimuli can modify response magnitude in auditory cortex, little is known about differential patterns of multisensory interactions in core and belt. Here, we used functional magnetic resonance imaging and examined the influence of a short visual stimulus presented prior to acoustic stimulation on the spatial pattern of blood oxygen level-dependent signal response in auditory cortex. Consistent with crossmodal inhibition, the light produced a suppression of signal response in a cortical region corresponding to the core. In the surrounding areas corresponding to the belt regions, however, we found an inverse modulation with an increasing signal in centrifugal direction. Our data suggest that crossmodal effects are differentially modulated according to the hierarchical core-belt organization of auditory cortex.

Steady streaming in a two-dimensional box model of a passive cochlea

Acoustic stimulation of the cochlea leads to a travelling wave in the cochlear fluids and on the basilar membrane (BM). It has long been suspected that this travelling wave leads to a steady streaming flow in the cochlea. Theoretical investigations suggested that the steady streaming might be of physiological relevance. Here, we present a quantitative study of the steady streaming in a computational model of a passive cochlea. The structure of the streaming flow is illustrated and the sources of streaming are closely investigated. We describe a source of streaming which has not been considered in the cochlea by previous authors. This source is also related to a steady axial displacement of the BM which leads to a local stretching of this compliant structure. We present theoretical predictions for the streaming intensity which account for these new phenomena. It is shown that these predictions compare well with our numerical results and that there may be steady streaming velocities of the order of millimetres per second. Our results indicate that steady streaming should be more relevant to low-frequency hearing because the strength of the streaming flow rapidly decreases for higher frequencies.

Terapias auditivas para acúfenos (tinnitus)

Un acúfeno (tinnitus) es la percepción de un sonido en ausencia de estimulación acústica externa, es decir, la experiencia consciente de un sonido que se origina en la propia cabeza del paciente. En colaboración con el departamento de acústica (CAEND) del Consejo Superior de Investigaciones Científicas (CSIC), se pretende revertir (de forma paliativa) las molestias, con ayuda de terapias sonoras que estimulan el sistema auditivo. Primero, se analizan los tratamientos existentes que se utilizan para atender a los pacientes diagnosticados. Por último, se diseñan dos aplicaciones informáticas referentes a las terapias: Auditory Discrimination Training (ADT) y Enriched Acoustic Environment (EAE). Abstract Tinnitus is the perception of sound in the absence of external acoustic stimulation, in addition, the conscious experience a sound originating from the patient’s own head. In collaboration with the department of acoustic (CAEND) of the Consejo Superior de Investigaciones Científicas (CSIC), is to reverse (for palliation) discomfort, using sound therapies that stimulate the auditory system. First, we analyze the existing treatments are used to treat patients diagnosed. Finally, two applications are designed regarding therapies: Auditory Discrimination Training (ADT) and Enriched Acoustic Environment (EAE).

Experience-dependent corticofugal adjustment of midbrain frequency map in bat auditory system

Recent studies of corticofugal modulation of auditory information processing indicate that cortical neurons mediate both a highly focused positive feedback to subcortical neurons “matched” in tuning to a particular acoustic parameter and a widespread lateral inhibition to “unmatched” subcortical neurons. This cortical function for the adjustment and improvement of subcortical information processing is called egocentric selection. Egocentric selection enhances the neural representation of frequently occurring signals in the central auditory system. For our present studies performed with the big brown bat (Eptesicus fuscus), we hypothesized that egocentric selection adjusts the frequency map of the inferior colliculus (IC) according to auditory experience based on associative learning. To test this hypothesis, we delivered acoustic stimuli paired with electric leg stimulation to the bat, because such paired stimuli allowed the animal to learn that the acoustic stimulus was behaviorally important and to make behavioral and neural adjustments based on the acquired importance of the acoustic stimulus. We found that acoustic stimulation alone evokes a change in the frequency map of the IC; that this change in the IC becomes greater when the acoustic stimulation is made behaviorally relevant by pairing it with electrical stimulation; that the collicular change is mediated by the corticofugal system; and that the IC itself can sustain the change evoked by the corticofugal system for some time. Our data support the hypothesis.

Caracterização do potencial evocado auditivo cortical P1-N1-P2 em crianças com estimulação bimodal

Introdução: O implante coclear (IC) amplamente aceito como forma de intervenção e (re) habilitação nas perdas auditivas severas e profundas nas diversas faixas etárias. Contudo observa-se no usuário do IC unilateral queixas como localização e compreensão sonora em meio ao ruído, gerado pelo padrão anormal de estimulação sensorial. A fim de fornecer os benefícios da audição binaural, é preconizado a estimulação bilateral, seja por meio do IC bilateral ou com a adaptação de um aparelho de amplificação sonora individual (AASI) contralateralmente ao IC. Esta última condição é referida como estimulação bimodal, quando temos, concomitantemente dois modos de estimulação: Elétrica (IC) e acústica (AASI). Não há dados suficientes na literatura voltados à população infantil que esclareça ou demonstre o desenvolvimento do córtex auditivo na audição bimodal. Ressalta-se que não foram encontrados estudos em crianças. Objetivo: Caracterizar o PEAC complexo P1, N1 P2 em usuários da estimulação bimodal e verificar se há correlação com testes de percepção de fala. Metodologia: Estudo descritivo de séries de casos, com a realização do PEAC em cinco crianças usuárias da estimulação bimodal, a partir da metodologia proposta por Ventura (2008) utilizando o sistema Smart EP USB Jr da Intelligent Hearing Systems. Foi utilizado o som de fala /da/, apresentado em campo livre. O exame será realizado em três situações: Somente IC, IC e AASI e somente AASI. A análise dos dados dos potenciais corticais foi realizada após a marcação da presença ou ausência dos componentes do complexo P1-N1-P2 por dois juízes com experiência em potenciais evocados. Resultados: Foi obtida a captação do PEAC em todas as crianças em todas as situações de teste, além do que foi possível observar a correlação destes com os testes de percepção auditiva da fala. Foi possível verificar que o registro dos PEAC é um procedimento viável para a avaliação da criança com estimulação bimodal, porém, ainda não há dados suficientes quanto a utilização deste para a avaliação e indicação do IC bilateral.

O efeito da estimulação top-down e bottom-up no potencial evocado auditivo de tronco encefálico com estímulo complexo

Introdução: Crianças com transtorno fonológico (TF) apresentam dificuldade na percepção de fala, em processar estímulos acústicos quando apresentados de forma rápida e em sequência. A percepção dos sons complexos da fala, dependem da integridade no processo de codificação analisado pelo Sistema Nervoso Auditivo. Por meio do Potencial Evocado Auditivo de Tronco Encefálico com estímulo complexo (PEATEc) é possível investigar a representação neural dos sons em níveis corticais e obter informações diretas sobre como a estrutura do som da sílaba falada é codificada no sistema auditivo. Porém, acredita-se que esse potencial sofre interferências tanto de processos bottom-up quanto top-down, o que não se sabe é quanto e como cada um desses processos modifica as respostas do PEATEc. Uma das formas de investigar a real influência dos aspectos top-down e bottom-up nos resultados do PEATEc é estimulando separadamente esses dois processos por meio do treinamento auditivo e da terapia fonoaudiológica. Objetivo: Verificar o impacto da estimulação sensorial (processamento bottom-up) e cognitiva (processamento top-down), separadamente, nos diferentes domínios da resposta eletrofisiológica do PEATEc. Método: Participaram deste estudo 11 crianças diagnosticadas com TF, com idades entre 7 e 10:11, submetidas a avaliação comportamental e eletrofisiológica e então dividas nos grupos Bottom-up (B-U) (N=6) e Top-down T-D (N=5). A estimulação bottom-up foi voltada ao treinamento das habilidades sensoriais, através de softwares de computador. A estimulação top-down foi realizada por meio de tarefas para estimular as habilidades cognitiva por meio do Programa de Estimulação Fonoaudiológica (PEF). Ambas as estimulações foram aplicadas uma vez por semana, num período de aproximadamente 45 minutos por 12 semanas. Resultados: O grupo B-U apresentou melhoras em relação aos domínios onset e harmônicos e no valor da pontuação do escore após ser submetido à estimulação bottom-up. Por sua vez, após serem submetidos à estimulação top-down, o grupo T-D apresentou melhoras em relação aos domínios onset, espectro-temporal, fronteiras do envelope e harmônicos e para os valores da pontuação do escore. Conclusão: Diante dos resultados obtidos neste estudo, foi possível observar que a estimulação sensorial (processamento bottom-up) e a estimulação cognitiva (processamento top-down) mostraram impactar de forma diferente a resposta eletrofisiológica do PEATEc

Design of a semi-implantable hearing device for direct acoustic cochlear stimulation

A new hearing therapy based on direct acoustic cochlear stimulation was developed for the treatment of severe to profound mixed hearing loss. The device efficacy was validated in an initial clinical trial with four patients. This semi-implantable investigational device consists of an externally worn audio processor, a percutaneous connector, and an implantable microactuator. The actuator is placed in the mastoid bone, right behind the external auditory canal. It generates vibrations that are directly coupled to the inner ear fluids and that, therefore, bypass the external and the middle ear. The system is able to provide an equivalent sound pressure level of 125 dB over the frequency range between 125 and 8000 Hz. The hermetically sealed actuator is designed to provide maximal output power by keeping its dimensions small enough to enable implantation. A network model is used to simulate the dynamic characteristics of the actuator to adjust its transfer function to the characteristics of the middle ear. The geometry of the different actuator components is optimized using finite-element modeling.

A Novel Implantable Hearing System with Direct Acoustic Cochlear Stimulation

A new implantable hearing system, the direct acoustic cochlear stimulator (DACS) is presented. This system is based on the principle of a power-driven stapes prosthesis and intended for the treatment of severe mixed hearing loss due to advanced otosclerosis. It consists of an implantable electromagnetic transducer, which transfers acoustic energy directly to the inner ear, and an audio processor worn externally behind the implanted ear. The device is implanted using a specially developed retromeatal microsurgical approach. After removal of the stapes, a conventional stapes prosthesis is attached to the transducer and placed in the oval window to allow direct acoustical coupling to the perilymph of the inner ear. In order to restore the natural sound transmission of the ossicular chain, a second stapes prosthesis is placed in parallel to the first one into the oval window and attached to the patient's own incus, as in a conventional stapedectomy. Four patients were implanted with an investigational DACS device. The hearing threshold of the implanted ears before implantation ranged from 78 to 101 dB (air conduction, pure tone average, 0.5-4 kHz) with air-bone gaps of 33-44 dB in the same frequency range. Postoperatively, substantial improvements in sound field thresholds, speech intelligibility as well as in the subjective assessment of everyday situations were found in all patients. Two years after the implantations, monosyllabic word recognition scores in quiet at 75 dB improved by 45-100 percent points when using the DACS. Furthermore, hearing thresholds were already improved by the second stapes prosthesis alone by 14-28 dB (pure tone average 0.5-4 kHz, DACS switched off). No device-related serious medical complications occurred and all patients have continued to use their device on a daily basis for over 2 years. Copyright (c) 2008 S. Karger AG, Basel.

Improvement of cardiac function with device-based diaphragmatic stimulation in chronic heart failure patients: the randomized, open-label, crossover Epiphrenic II Pilot Trial.

AIMS Device-based pacing-induced diaphragmatic stimulation (PIDS) may have therapeutic potential for chronic heart failure (HF) patients. We studied the effects of PIDS on cardiac function and functional outcomes. METHODS AND RESULTS In 24 chronic HF patients with CRT, an additional electrode was attached to the left diaphragm. Randomized into two groups, patients received the following PIDS modes for 3 weeks in a different sequence: (i) PIDS off (control group); (ii) PIDS 0 ms mode (PIDS simultaneously with ventricular CRT pulse); or (iii) PIDS optimized mode (PIDS with optimized delay to ventricular CRT pulse). For PIDS optimization, acoustic cardiography was used. Effects of each PIDS mode on dyspnoea, power during exercise testing, and LVEF were assessed. Dyspnoea improved with the PIDS 0 ms mode (P = 0.057) and the PIDS optimized mode (P = 0.034) as compared with the control group. Maximal power increased from median 100.5 W in the control group to 104.0 W in the PIDS 0 ms mode (P = 0.092) and 109.5 W in the PIDS optimized mode (P = 0.022). Median LVEF was 33.5% in the control group, 33.0% in the PIDS 0 ms mode, and 37.0% in the PIDS optimized mode (P = 0.763 and P = 0.009 as compared with the control group, respectively). PIDS was asymptomatic in all patients. CONCLUSION PIDS improves dyspnoea, working capacity, and LVEF in chronic HF patients over a 3 week period in addition to CRT. This pilot study demonstrates proof of principle of an innovative technology which should be confirmed in a larger sample. TRIAL REGISTRATION NCT00769678.

Listening to nature : acoustic monitoring of the environment

The requirement to monitor the rapid pace of environmental change due to global warming and to human development is producing large volumes of data but placing much stress on the capacity of ecologists to store, analyse and visualise that data. To date, much of the data has been provided by low level sensors monitoring soil moisture, dissolved nutrients, light intensity, gas composition and the like. However, a significant part of an ecologist’s work is to obtain information about species diversity, distributions and relationships. This task typically requires the physical presence of an ecologist in the field, listening and watching for species of interest. It is an extremely difficult task to automate because of the higher order difficulties in bandwidth, data management and intelligent analysis if one wishes to emulate the highly trained eyes and ears of an ecologist. This paper is concerned with just one part of the bigger challenge of environmental monitoring – the acquisition and analysis of acoustic recordings of the environment. Our intention is to provide helpful tools to ecologists – tools that apply information technologies and computational technologies to all aspects of the acoustic environment. The on-line system which we are building in conjunction with ecologists offers an integrated approach to recording, data management and analysis. The ecologists we work with have different requirements and therefore we have adopted the toolbox approach, that is, we offer a number of different web services that can be concatenated according to need. In particular, one group of ecologists is concerned with identifying the presence or absence of species and their distributions in time and space. Another group, motivated by legislative requirements for measuring habitat condition, are interested in summary indices of environmental health. In both case, the key issues are scalability and automation.