Microelectronic circuits for noninvasive ear type assistive devices

An ear type system and its circuit realization with application as new assistive devices are investigated. The auditory brainstem responses obtained from clinical hearing measurements are utilized for which the ear type systems mimicking the physical and behavioral characteristics of the individual auditory system are developed. In the case that effects from the hearing loss and disorder can be detected via the measured responses, differentiations between normal and impaired characteristics of the human auditory system are made possible from which the new noninvasive way of correcting these undesired effects is proposed. The ear type system of auditory brainstem response is developed using an adaptation of the nonlinear neural network architecture and the system for making a correction is realized using the derived inverse of neural network. Microelectronic circuits of the systems are designed and simulated showing a possibility of developing into a hearing aid type device which potentially helps hearing impaired patients in an alternate and noninvasive useful way

Comparison of efficacy and safety of intranasal Midazolam with syrup Chloral hydrate for procedural sedation of children undergoing Auditory Brainstem evoked Response audiometry: A Randomized, Double-blinded, Placebo controlled trial

OBJECTIVE: The objective of this study was to evaluate the efficacy and safety of intranasal Midazolam compared to syrup Chloral hydrate for procedural sedation in children undergoing Auditory Brainstem evoked Response audiometry (ABR). METHODS: A prospective, randomized, double-blinded placebo controlled trial was carried out in the audiology lab of a tertiary care hospital over a period of 18 months. 82 children between the age group of 1 to 6 years (mean 2 years) irrespective of their developmental maturity, belonging to ASA class I and II who were referred for ABR testing were recruited. Children were randomized to receive either midazolam spray with oral placebo or syrup chloral hydrate with nasal placebo spray. The nasal spray was dosed at 0.5 mg/kg delivered as 100mcg per spray and oral syrup at a dose of 50 mg/kg. Those children who did not show onset of sedation at 30 minutes were administered the second dose at half the initial dose. Randomization was computer generated and allocation concealment was achieved by opaque sequentially numbered sealed envelopes that were employed serially to the participating children. The primary outcome measured were safety which was measured in terms of heart rate, respiratory rate, oxygen saturation and efficacy was measured in terms of level of consciousness (uninterrupted sleep without movement) and successful completion of the procedure. The various secondary outcomes were time to onset of sedation, time to parental separation, nature of parental separation, duration of procedure, parental satisfaction, audiologist’s satisfaction, time to recovery and number of attempts. RESULTS: The trial was completed over a period of 18 months when 41 children were studied in each arm. Both the drugs were found to be safe with no major adverse events. One child who had received Midazolam developed transient hypoxia. It was corrected with appropriate head positioning. Minor side effects noted were sneezing, hiccups and crying. Children on Chloral hydrate had an earlier onset of sedation (66% of children) at or less than 30 minutes as compared to only 33% from the Midazolam group. Developmentally delayed children had an earlier onset of sedation compared to developmentally normal group irrespective of the drug they received. Parental separation was earlier for chloral hydrate group at 20 minutes than for midazolam at 30 minutes. There was no statistically significant difference in the duration of procedure. There was a significant difference noted in the time to recovery (Chloral hydrate children (78 minutes) as compared to Midazolam children (105 minutes). Parental and audiologists satisfaction were higher for Chloral hydrate (95% and 75% respectively) than for Midazolam (49% and 29%). A larger number of patients (80%) slept with the first dose of Chloral hydrate as against Midazolam children who required a second dose. Overall, sedation was successful among 95% of children who received chloral hydrate compared to 51% of children who received Midazolam. Once sedation was achieved, both the drugs were efficacious in maintaining sedation with no intra-procedural interruption in sedation. CONCLUSION: Intranasal Midazolam and oral Chloral hydrate are both safe and efficacious for pediatric procedural sedation in ABR. However, Chloral hydrate had a superior efficacy to intranasal Midazolam with an earlier time to onset of sedation, a faster recovery, better parental and audiologist’s satisfaction and successful sedation even with the first attempt. There was no difference in the duration of the procedure. Developmentally delayed children showed an earlier onset of sedation and faster recovery compared to their normal counterparts irrespective of the drug regimen they received

Aerospace Medicine and Biology: A continuing bibliography with indexes (supplement 314)

This bibliography lists 139 reports, articles, and other documents introduced into the NASA scientific and technical information system in August, 1988

Electrically Evoked Auditory Event-Related Responses in Patients with Auditory Brainstem Implants: Morphological Characteristics, Test–Retest Reliability, Effects of Stimulation Level, and Association with Auditory Detection

This study aimed to 1) characterize morphological characteristics of the electrically-evoked cortical auditory event-related potentials (eERP) and explore the potential association between onset eERP morphology and auditory vs non-auditory stimulation; 2) assess test-retest reliability of onset eERPs; 3) investigate effects of stimulation level on onset eERPs; and 4) explore the feasibility of using the onset eERP to estimate the lowest stimulation level that can be detected for individual stimulating electrodes in patients with auditory brainstem implants (ABIs)

Assessing brain activity related to speech production and perception using tonal stimuli

Speech processing was studied by looking at brain processes underlying speech perception and production. Existing models of speech and empirical data propose that producing speech decreases neural activity relative to perceiving speech (termed Speech-Induced Suppression - SIS). SIS is associated with monitoring the intended auditory targets against perceived speech output. SIS has been frequently reported at cortical levels but not at subcortical levels. If SIS occurs at subcortical levels, then speech processing models would be expanded to incorporate these in the internal sensory prediction (i.e. the intended auditory targets). Auditory tonal stimuli were used in this thesis. Such stimuli are commonly used in research on subcortical activity during speech perception. Knowing what the benchmark response (i.e. subcortical activity to tones in speech perception) looks like, allows us to compare our findings made during speech production to speech perception research. The first four studies recorded cortical activity using EEG, a common method in studying SIS. The same experimental conditions were used across the studies to facilitate comparison. The results showed a large variation in the magnitude and direction of the SIS effect across conditions and experiments. Even though mean amplitudes appeared to indicate than the cortical activity was indeed suppressed in some cases, when the random effects were controlled for using linear mixed models, the suppression was not significant. A potential explanation of this result might be that the alien voice auditory stimuli played during the experimental tasks were not recognised as one’s own. This mismatch would preclude occurrence of SIS. SIS was tested for the first time using functional near-infrared spectroscopy (fNIRS) using the same experimental conditions that were used in the EEG studies. The suppression of the fNIRS signal (HbO peaks) was not significant. However, the haemoglobin concentration plots suggested that the responses to conditions that involved vocalisation differed from those that did not. This thesis also describes attempts at recording subcortical responses (FFR) during speech production. SIS has been reported at the brainstem level in the past (Papanicolaou, Raz, Loring, & Eisenberg, 1986) but this required further exploration because of procedural issues in the study. Recording FFRs during vocalisation was attempted here to test whether subcortical activity is suppressed. This required the development of a processing pipeline to extract clean signals (FFR) from brainstem recordings during speech production. Recording FFRs during speech production turned out to be very challenging. Methodological improvements introduced in the later experiments improved signal quality but it was far from the standard achieved during speech perception. Combining these two strands of research, i.e. SIS on cortical and subcortical level, led to methodological improvements. The main theoretical contribution of the thesis is the finding that SIS cannot be consistently observed when an external audio stimulus is presented whilst speech production occurs concurrently. This result agrees with a previous finding which described that less prototypical speech sounds are less suppressed (Niziolek, Nagarajan, & Houde, 2013). These results support speech models which postulate that suppression is due to matching predicted and perceived feedback

Computational modelling of neural mechanisms underlying natural speech perception

Humans are highly skilled at the analysis of complex auditory scenes. In particular, the human auditory system is characterized by incredible robustness to noise and can nearly effortlessly isolate the voice of a specific talker from even the busiest of mixtures. However, neural mechanisms underlying these remarkable properties remain poorly understood. This is mainly due to the inherent complexity of speech signals and multi-stage, intricate processing performed in the human auditory system. Understanding these neural mechanisms underlying speech perception is of interest for clinical practice, brain-computer interfacing and automatic speech processing systems. In this thesis, we developed computational models characterizing neural speech processing across different stages of the human auditory pathways. In particular, we studied the active role of slow cortical oscillations in speech-in-noise comprehension through a spiking neural network model for encoding spoken sentences. The neural dynamics of the model during noisy speech encoding reflected speech comprehension of young, normal-hearing adults. The proposed theoretical model was validated by predicting the effects of non-invasive brain stimulation on speech comprehension in an experimental study involving a cohort of volunteers. Moreover, we developed a modelling framework for detecting the early, high-frequency neural response to the uninterrupted speech in non-invasive neural recordings. We applied the method to investigate top-down modulation of this response by the listener's selective attention and linguistic properties of different words from a spoken narrative. We found that in both cases, the detected responses of predominantly subcortical origin were significantly modulated, which supports the functional role of feedback, between higher- and lower levels stages of the auditory pathways, in speech perception. The proposed computational models shed light on some of the poorly understood neural mechanisms underlying speech perception. The developed methods can be readily employed in future studies involving a range of experimental paradigms beyond these considered in this thesis.Open Acces

The utility of the auditory brainstem response in children with atypical saccadic eye movements

Full version unavailable due to 3rd party copyright restrictionsLesions in the brainstem result in widespread damage to a number of sensorimotor systems including oculomotor and auditory neural circuits. Although these systems are spatially separate and highly specialised, they are also co-located. This thesis, investigates whether lesions in the oculomotor system will also cause co-morbid dysfunction in the auditory pathways. Specifically, we investigated the usefulness of the Auditory Brainstem Response (ABR) in two oculomotor conditions: slow saccades in Gaucher disease (GD) and opsoclonus in Dancing Eye Syndrome (DES). We present four empirical studies. In our first study we systematically investigated the ABR in GD. We found that multimodal testing can better delineate underlying neurological deficits in neuronopathic GD (nGD) and distinguish between phenotypes. In the second study we examined the ABR's utility as a longitudinal, objective marker of disease burden and in a randomised clinical control trial. ABRs continued to deteriorate regardless of treatment. In our third study we assessed audiological function in DES. We found that at least 43% of DES patients have hyperacusis. We also found subtle abnormalities in the auditory brainstem, as shown by the ABR. Our final study explored the onset-offset response in the ABR and assessed its utility as a clinical marker. Overall, this thesis provides new evidence that auditory pathways are also affected in diseases which are traditionally assumed to be ‘oculomotor’ in nature. We believe that there is sufficient evidence to warrant the inclusion of audiological testing, such as the ABR, as part of the standard assessment of newly diagnosed GD patients and that they undergo these tests prior to commencing treatment. These tests may also have a wider application as longitudinal outcome measures for use in clinical trials or as markers of neurological burden in GD and we believe may be useful in other metabolic diseases; we found that current therapies for GD have low efficacy. Understanding the underlying neurological deficits in these debilitating illnesses can only help to improve treatments and the long-term outlook for these patients

Individual differences in supra-threshold auditory perception - mechanisms and objective correlates

Thesis (Ph.D.)--Boston UniversityTo extract content and meaning from a single source of sound in a quiet background, the auditory system can use a small subset of a very redundant set of spectral and temporal features. In stark contrast, communication in a complex, crowded scene places enormous demands on the auditory system. Spectrotemporal overlap between sounds reduces modulations in the signals at the ears and causes masking, with problems exacerbated by reverberation. Consistent with this idea, many patients seeking audiological treatment seek help precisely because they notice difficulties in environments requiring auditory selective attention. In the laboratory, even listeners with normal hearing thresholds exhibit vast differences in the ability to selectively attend to a target. Understanding the mechanisms causing these supra-threshold differences, the focus of this thesis, may enable research that leads to advances in treating communication disorders that affect an estimated one in five Americans. Converging evidence from human and animal studies points to one potential source of these individual differences: differences in the fidelity with which supra-threshold sound is encoded in the early portions of the auditory pathway. Electrophysiological measures of sound encoding by the auditory brainstem in humans and animals support the idea that the temporal precision of the early auditory neural representation can be poor even when hearing thresholds are normal. Concomitantly, animal studies show that noise exposure and early aging can cause a loss (cochlear neuropathy) of a large percentage of the afferent population of auditory nerve fibers innervating the cochlear hair cells without any significant change in measured audiograms. Using behavioral, otoacoustic and electrophysiological measures in conjunction with computational models of sound processing by the auditory periphery and brainstem, a detailed examination of temporal coding of supra-threshold sound is carried out, focusing on characterizing and understanding individual differences in listeners with normal hearing thresholds and normal cochlear mechanical function. Results support the hypothesis that cochlear neuropathy may reduce encoding precision of supra-threshold sound, and that this manifests as deficits both behaviorally and in subcortical electrophysiological measures in humans. Based on these results, electrophysiological measures are developed that may yield sensitive, fast, objective measures of supra-threshold coding deficits that arise as a result of cochlear neuropathy

Cortical And Subcortical Mechanisms For Sound Processing

The auditory cortex is essential for encoding complex and behaviorally relevant sounds. Many questions remain concerning whether and how distinct cortical neuronal subtypes shape and encode both simple and complex sound properties. In chapter 2, we tested how neurons in the auditory cortex encode water-like sounds perceived as natural by human listeners, but that we could precisely parametrize. The stimuli exhibit scale-invariant statistics, specifically temporal modulation within spectral bands scaled with the center frequency of the band. We used chronically implanted tetrodes to record neuronal spiking in rat primary auditory cortex during exposure to our custom stimuli at different rates and cycle-decay constants. We found that, although neurons exhibited selectivity for subsets of stimuli with specific statistics, over the population responses were stable. These results contribute to our understanding of how auditory cortex processes natural sound statistics. In chapter 3, we review studies examining the role of different cortical inhibitory interneurons in shaping sound responses in auditory cortex. We identify the findings that support each other and the mechanisms that remain unexplored. In chapter 4, we tested how direct feedback from auditory cortex to the inferior colliculus modulated sound responses in the inferior colliculus. We optogenetically activated or suppressed cortico-collicular feedback while recording neuronal spiking in the mouse inferior colliculus in response to pure tones and dynamic random chords. We found that feedback modulated sound responses by reducing sound selectivity by decreasing responsiveness to preferred frequencies and increasing responsiveness to less preferred frequencies. Furthermore, we tested the effects of perturbing intra-cortical inhibitory-excitatory networks on sound responses in the inferior colliculus. We optogenetically activated or suppressed parvalbumin-positive (PV) and somatostatin-positive (SOM) interneurons while recording neuronal spiking in mouse auditory cortex and inferior colliculus. We found that modulation of neither PV- nor SOM-interneurons affected sound-evoked responses in the inferior colliculus, despite significant modulation of cortical responses. Our findings imply that cortico-collicular feedback can modulate responses to simple and complex auditory stimuli independently of cortical inhibitory interneurons. These experiments elucidate the role of descending auditory feedback in shaping sound responses. Together these results implicate the importance of the auditory cortex in sound processing