Determination and evaluation of clinically efficient stopping criteria for the multiple auditory steady-state response technique

Background: Although the auditory steady-state response (ASSR) technique utilizes objective statistical detection algorithms to estimate behavioural hearing thresholds, the audiologist still has to decide when to terminate ASSR recordings introducing once more a certain degree of subjectivity. Aims: The present study aimed at establishing clinically efficient stopping criteria for a multiple 80-Hz ASSR system. Methods: In Experiment 1, data of 31 normal hearing subjects were analyzed off-line to propose stopping rules. Consequently, ASSR recordings will be stopped when (1) all 8 responses reach significance and significance can be maintained for 8 consecutive sweeps; (2) the mean noise levels were ≤ 4 nV (if at this “≤ 4-nV” criterion, p-values were between 0.05 and 0.1, measurements were extended only once by 8 sweeps); and (3) a maximum amount of 48 sweeps was attained. In Experiment 2, these stopping criteria were applied on 10 normal hearing and 10 hearing-impaired adults to asses the efficiency. Results: The application of these stopping rules resulted in ASSR threshold values that were comparable to other multiple-ASSR research with normal hearing and hearing-impaired adults. Furthermore, in 80% of the cases, ASSR thresholds could be obtained within a time-frame of 1 hour. Investigating the significant response-amplitudes of the hearing-impaired adults through cumulative curves indicated that probably a higher noise-stop criterion than “≤ 4 nV” can be used. Conclusions: The proposed stopping rules can be used in adults to determine accurate ASSR thresholds within an acceptable time-frame of about 1 hour. However, additional research with infants and adults with varying degrees and configurations of hearing loss is needed to optimize these criteria

Mapping Auditory Nerve Firing Density using the Compound Action Potential and High-pass Noise Masking

A critical barrier to future implementation of regenerative treatments for sensorineural hearing loss is the lack of diagnostic tools that can specify the target(s) within the cochlea and auditory nerve for delivery of therapeutic agents. This study used a gerbil model to test the idea of mapping auditory nerve firing density by tracking the amplitude of high-level compound action potentials (CAPs) while varying the bandwidth of simultaneous masking noise. The distributions of neural firing, obtained by calculating the derivative of the equation describing CAP amplitude growth as a function of distance along the cochlea, indicated that high-level chirp stimuli trigger widespread neural firing along the cochlea that is unaltered by sensory outer hair cell pathology. These results suggest that CAP-derived neural density functions for high-level chirp stimuli may provide reliable maps of auditory nerve density in impaired ears

A Novel EEG Paradigm to Simultaneously and Rapidly Assess the Functioning of Auditory and Visual Pathways

Objective assessment of the sensory pathways is crucial for understanding their development across the lifespan and how they may be affected by neurodevelopmental disorders (e.g., autism) and neurological pathologies (e.g., stroke, multiple sclerosis, etc.). Quick and passive measurements, for example using electroencephalography (EEG), are especially important when working with infants and young children, and with patient populations having communication deficits (e.g., aphasia). However, many EEG paradigms are limited to measuring activity from one sensory domain at a time, may be time consuming, and target only a subset of possible responses from that particular sensory domain (e.g., only auditory brainstem responses or only auditory P1-N1-P2 evoked potentials). Thus, we developed a new multisensory paradigm that enables simultaneous, robust, and rapid (6-12 minute) measurements of both auditory and visual EEG activity, including auditory brainstem responses (ABRs), auditory and visual evoked potentials, as well as auditory and visual steady-state responses. This novel method allows us to examine neural activity at various stations along the auditory and visual hierarchies with an ecologically valid continuous speech stimulus, while an unrelated video is playing. Both the speech stimulus and the video can be customized for any population of interest. Furthermore, by using two simultaneous visual steady-state stimulation rates, we demonstrate the ability of this paradigm to track both parafoveal and peripheral visual processing concurrently. We report results from twenty-five healthy young adults, which validate this new paradigm

Neural Correlates of Binaural Interaction Using Aggregate-System Stimulation in Cochlear Implantees

The importance of binaural cues in auditory stream formation and sound source differentiation is widely accepted. When treating one ear with a cochlear implant (CI) the peripheral auditory system gets partially replaced and processing delays get added potentially, thus important interaural time encoding gets altered. This is a crucial problem because factors like the interaural time delay between the receiving ears are known to be responsible for facilitating such cues, e.g., sound source localization and separation. However, these effects are not fully understood, leaving a lack of systematic binaural fitting strategies with respect to an optimal binaural fusion. To gain new insights into such alterations, we suggest a novel method of free-field evoked auditory brainstem response (ABR) analysis in CI users. As a result, this method does not bypass the technically induced intrinsic delays of the hearing device while leaving the complete electrode array active, thus the most natural way of stimulation is provided and the comparable testing of real world stimuli gets facilitated. Unfortunately, ABRs acquired in CI users are additionally affected by the prominent artifact caused by their electrical stimulation, which severely distorts the desired neural response, thus challenging their analysis. To circumvent this problem, we further introduce a novel narrowband filtering CI artifact removal technique capable of obtaining neural correlates of ABRs in CI users. Consequently, we were able to compare brainstem-level responses collected of 12 CI users and 12 normal hearing listeners using two different stimuli (i.e., chirp and click) at four different intensities each, what comprises an adaption of the prominent brainstem evoked response audiometry serving as an additional evaluation criterion. We analyzed the responses using the average of 2,000 trials in combination with synchronized regularizations across them and found consistent results in their deflections and latencies, as well as in single trial relationships between both groups. This method provides a novel and unique perspective into the natural CI users’ brainstem-level responses and can be practical in future research regarding binaural interaction and fusion. Furthermore, the binaural interaction component (BIC), i.e., the arithmetical difference between the sum of both monaurally evoked ABRs and the binaurally evoked ABR, has been previously shown to be an objective indicator for binaural interaction. This component is unfortunately known to be rather fragile and as a result, a reliable, objective measure of binaural interaction in CI users does not exist to the present date. It is most likely that implantees would benefit from a reliable analysis of brainstem-level and subsequent higher-level binaural interaction, since this could objectively support fitting strategies with respect to a maximization of interaural integration. Therefore, we introduce a novel method capable of obtaining neural correlates of binaural interaction in bimodal CI users by combining recent advances in the field of fast, deconvolution-based ABR acquisitions with the introduced narrowband filtering technique. The proposed method shows a significant improvement in the magnitude of resulting BICs in 10 bimodal CI users and a control-group of 10 normal hearing subjects when compensating the interaural latency difference caused by the technical devices. In total, both proposed studies objectively demonstrate technical-driven interaural latency mismatches. Thus, they strongly emphasize potential benefits when balancing these interaural delays to improve binaural processing by significant increases in associated neural correlates of successful binaural interaction. These results and also the estimated latency differences should be investigated in larger group sizes to further consolidate the results, but confirm the demand for rather binaural solutions than treating hearing losses in an isolated monaural manner.Zusammenfassung Die Notwendigkeit binauraler Verarbeitungsprozesse in der auditorischen Wahrnehmung ist weitestgehend akzeptiert. Bei der Therapie eines Ohres mit einem Cochlea-Implantat (engl. cochlear implant (CI)) wird das periphere auditorische System teilweise ersetzt und verändert, sodass natürliche, interaurale Zeitauflösungen beeinflusst werden. Dieses Problem ist entscheidend, denn Faktoren wie interaurale Laufzeitunterschiede zwischen den aufnehmenden Ohren sind verantwortlich für die Umsetzung der erwähnten binauralen Verarbeitungsprozesse, z.B. Schallquellenlokalisation und -separation. Allerdings sind diese Effekte nicht ausreichend verstanden, weshalb bis heute binaurale Anpassstrategien mit Rücksicht auf eine optimale Fusionierung fehlen. Um neue Einsichten in solche zeitlichen Verzerrungen zu erhalten, schlagen wir ein neues Verfahren der Freifeld evozierten auditorischen Hirnstammpotentiale (engl. auditory brainstem response (ABR)) in CI-Nutzern vor. Diese Methode beinhaltet explizit technisch-induzierte Laufzeiten verwendeter Hörhilfen, sodass eine natürliche Stimulation unter Verwendung von realitätsnahen Stimuli ermöglicht wird. Unglücklicherweise sind ABRs von CI-Nutzern zusätzlich mit Stimulationsartefakten belastet, wodurch benötigte neurale Antworten weiter verzerrt werden und eine entsprechende Analyse der Signale deutlich erschwert wird. Um dieses Problem zu umgehen, schlagen wir eine neue Artefakt- Reduktionstechnik vor, welche auf spektraler Schmalbandfilterung basiert und somit den Erhalt entsprechender, neuraler ABR Korrelate ermöglicht. Diese Methoden erlaubten die Interpretation neuraler Korrelate auf Hirnstammebene unter Verwendung von zwei verschiedenen Stimuli (Chirps und Klicks) unter vier verschiedenen Lautstärken in 12 CI-Nutzern und 12 normalhörenden Probanden. Die beschriebene Prozedur adaptiert somit die weitläufig bekannte Hirnstammaudiometrie (engl. brainstem evoked response audiometry (BERA)), deren Ergebnisse zur zusätzlichen Evaluation des vorgestellten Verfahrens dienten. Die Untersuchung der aus 2000 Einzelantworten erhaltenen Mittelwerte in Kombination mit der Analyse synchronisierter Regularitäten über den Verlauf der Einzelantworten ergab dabei konsistente Beobachtungen in gefundenen Amplituden, Latenzen sowie in Abhängigkeiten zwischen Einzelantworten in beiden Gruppen. Das vorgestellte Verfahren erlaubt somit auf einzigartige Weise neue und ungesehene Einsichten in natürliche, neurale Antworten auf Hirnstammebene von CI-Nutzern, welche in zukünftigen Studien verwendet werden können, um binaurale Interaktionen und Fusionen weiter untersuchen zu können. Interessanterweise hat sich, die auf ABRs basierende, binaurale Interaktionskomponente (engl. binaural interaction component (BIC)) als objektiver Indikator binauraler Integration etabliert. Diese Komponente (d.h. die arithmetische Differenz zwischen der Summe der monauralen Antworten und der binauralen Antwort) ist leider sehr fragil, wodurch ein sicherer und objektiver Nachweis in CI-Nutzern bis heute nicht existiert. Dabei ist es sehr wahrscheinlich, dass gerade Implantatsträger von einer entsprechenden Analyse auf Hirnstammebene und höherrangigen Ebenen deutlich profitieren würden, da dies objektiv Anpassstrategien mit Rücksicht auf eine bestmögliche binaurale Integration ermöglichen könnte. Deshalb stellen wir ein weiteres, neuartiges Verfahren zum Erhalt von neuralen Korrelaten binauraler Interaktion in bimodal versorgten CI-Trägern vor, welches jüngste Erfolge im Bereich der schnellen, entfalltungsbasierten ABR Akquisition und der bereits vorgestellten Schmalband- filterung zur Reduktion von Stimulationsartefakten kombiniert. Basierend auf diesem Verfahren konnten signifikante Verbesserungen in der BIC-Amplitude in 10 bimodal versorgten Patienten sowie 10 normalhörenden Probanden, basierend auf umgesetzte, interaurale Laufzeitkompensationen technischer Hörhilfen, aufgezeigt werden. Insgesamt demonstrieren beide vorgestellten Studien technisch-induzierte, interaurale Laufzeitunterschiede und betonen demnach sehr deutlich potenzielle Vorteile in assoziierten neuralen Korrelaten binauraler Interaktionen, wenn solche Missverhältnisse zeitlich ausgeglichen werden. Die aufgezeigten Ergebnisse sowie die getätigte Abschätzungen technischer Laufzeiten sollte in größeren Gruppen weiter untersucht werden, um die Aussagekraft weiter zu steigern. Dennoch unterstreichen diese Einsichten das Verlangen nach binauralen Lösungsansätzen in der zukünftigen Hörrehabilitation, statt bisheriger isolierter und monauraler Therapien

Update On Hearing Loss

Update on Hearing Loss encompasses both the theoretical background on the different forms of hearing loss and a detailed knowledge on state-of-the-art treatment for hearing loss, written for clinicians by specialists and researchers. Realizing the complexity of hearing loss has highlighted the importance of interdisciplinary research. Therefore, all the authors contributing to this book were chosen from many different specialties of medicine, including surgery, psychology, and neuroscience, and came from diverse areas of expertise, such as neurology, otolaryngology, psychiatry, and clinical and experimental audiology

Amazon Nights II: Electric Boogaloo-Neural Adaptations for Communication in Three Species of Weakly Electric FIsh

Sensory systems have to extract useful information from environments awash in noise and confounding input. Studying how salient signals are encoded and filtered from these natural backgrounds is a key problem in neuroscience. Communication is a particularly tractable tool for studying this problem, as it is a ubiquitous task that all organisms must accomplish, easily compared across species, and is of significant ethological relevance. In this chapter I describe the current knowledge of what is both known and still unknown about how sensory systems are adapted for the challenges of encoding conspecific signals, particularly in environments complicated by conspecific-generated noise. The second half of this chapter describes why weakly electric fish are particularly suited to investigating how communication can shape the nervous system to accomplish this task

Role of the Cochlear Nucleus Circuitry in Tinnitus and Hyperacusis

Tinnitus is the disorder of phantom sound perception, while hyperacusis is abnormally increased loudness growth. Tinnitus and hyperacusis are both associated with hearing loss, but hearing loss does not always occur with either condition, implicating central neural activity as the basis for each disorder. Furthermore, while tinnitus and hyperacusis can co-occur, either can occur exclusively, suggesting that separate pathological neural processes underlie each disorder. Mounting evidence suggests that pathological neural activity in the cochlear nucleus, the first central nucleus in the auditory pathway, underpins hyperacusis and tinnitus. The cochlear nucleus is comprised of a ventral and dorsal subdivision, which have separate principal output neurons with distinct targets. Previous studies have shown that dorsal cochlear nucleus fusiform cells show tinnitus-related increases in spontaneous firing with minimal alterations to sound-evoked responses. In contrast, sound-evoked activity in ventral cochlear nucleus bushy cells is enhanced following noise-overexposure, putatively underlying hyperacusis. While the fusiform-cell contribution to tinnitus has been well characterized with behavioral and electrophysiological studies, the bushy-cell contribution to tinnitus or hyperacusis has been understudied. This dissertation examines how pathological neural activity in cochlear nucleus circuitry relates to tinnitus and hyperacusis in the following three chapters. In the first chapter, I characterize the development of a high-throughput tinnitus behavioral model, which combines and optimizes existing paradigms. With this model, I show that animals administered salicylate, a drug that reliably induces tinnitus at high doses in both humans and animals, show behavioral evidence of tinnitus in two separate behavioral tests. Moreover, in these same animals, I show that dorsal-cochlear-nucleus fusiform cells exhibit frequency-specific increases in spontaneous firing activity, consistent with the increased spontaneous firing observed in animal models of noise-induced tinnitus. In the second chapter, I show that following noise-overexposure, ventral-cochlear-nucleus bushy cells demonstrate hyperacusis-like neural firing patterns, but not tinnitus-specific increases in spontaneous activity. I contrast the bushy-cell neural activity with established fusiform-cell neural signatures of tinnitus, to highlight the bushy-cell, but not fusiform-cell contribution to hyperacusis. These analyses suggest that tinnitus and hyperacusis likely arise from distinct neural substrates. In the third chapter, I use computational modelling of the auditory periphery and bushy-cell circuitry to examine potential mechanisms that underlie hyperacusis-like neural firing patterns demonstrated in the second chapter. I then relate enhanced bushy-cell firing patterns to alterations in the auditory brainstem response, a sound-evoked electrical potential generated primarily by bushy cells. Findings in this chapter suggest that there are multiple hyperacusis subtypes, arising from separate mechanisms, which could be diagnosed through fine-tuned alterations to the auditory brainstem response.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163087/1/damartel_1.pd