Development of a feline model for preclinical research of a new translabyrinthine auditory nerve implant

Cochlear implants are among the most successful neural prosthetic devices to date but exhibit poor frequency selectivity and the inability to consistently activate apical (low frequency) spiral ganglion neurons. These issues can limit hearing performance in many cochlear implant patients, especially for understanding speech in noisy environments and in perceiving or appreciating more complex inputs such as music and multiple talkers. For cochlear implants, electrical current must pass through the bony wall of the cochlea, leading to widespread activation of auditory nerve fibers. Cochlear implants also cannot be implanted in some individuals with an obstruction or severe malformations of the cochlea. Alternatively, intraneural stimulation delivered via an auditory nerve implant could provide direct contact with neural fibers and thus reduce unwanted current spread. More confined current during stimulation can increase selectivity of frequency fiber activation. Furthermore, devices such as the Utah Slanted Electrode Array can provide access to the full cross section of the auditory nerve, including low frequency fibers that are difficult to reach using a cochlear implant. However, further scientific and preclinical research of these Utah Slanted Electrode Array devices is limited by the lack of a chronic large animal model for the auditory nerve implant, especially one that leverages an appropriate surgical approach relevant for human translation. This paper presents a newly developed transbullar translabyrinthine surgical approach for implanting the auditory nerve implant into the cat auditory nerve. In our first of a series of studies, we demonstrate a surgical approach in non-recovery experiments that enables implantation of the auditory nerve implant into the auditory nerve, without damaging the device and enabling effective activation of the auditory nerve fibers, as measured by electrode impedances and electrically evoked auditory brainstem responses. These positive results motivate performing future chronic cat studies to assess the long-term stability and function of these auditory nerve implant devices, as well as development of novel stimulation strategies that can be translated to human patients.

Rib detection using pitch-catch ultrasound and classification algorithms for a novel ultrasound therapy device

BACKGROUND

Noninvasive ultrasound (US) has been used therapeutically for decades, with applications in tissue ablation, lithotripsy, and physical therapy. There is increasing evidence that low intensity US stimulation of organs can alter physiological and clinical outcomes for treatment of health disorders including rheumatoid arthritis and diabetes. One major translational challenge is designing portable and reliable US devices that can be used by patients in their homes, with automated features to detect rib location and aid in efficient transmission of energy to organs of interest. This feasibility study aimed to assess efficacy in rib bone detection without conventional imaging, using a single channel US pitch-catch technique integrated into an US therapy device to detect pulsed US reflections from ribs.

METHODS

In 20 healthy volunteers, the location of the ribs and spleen were identified using a diagnostic US imaging system. Reflected ultrasound signals were recorded at five positions over the spleen and adjacent ribs using the therapy device. Signals were classified as between ribs (intercostal), partially over a rib, or fully over a rib using four models: threshold-based time domain classification, threshold-based frequency domain classification, logistic regression, and support vector machine (SVM).

RESULTS

SVM performed best overall on the All Participants cohort with accuracy up to 96.25%. All models' accuracies were improved by separating participants into two cohorts based on Body Mass Index (BMI) and re-fitting each model. After separation into Low BMI and High BMI cohorts, a simple time-thresholding approach achieved accuracies up to 100% and 93.75%, respectively.

CONCLUSION

These results demonstrate that US reflection signal classification can accurately provide low complexity, real-time automated onboard rib detection and user feedback to advance at-home therapeutic US delivery.

Gradients of response latencies and temporal precision of auditory neurons extend across the whole inferior colliculus

Neural responses to acoustic stimulation have long been studied throughout the auditory system to understand how sound information is coded for perception. Within the inferior colliculus (IC), a majority of the studies have focused predominantly on characterizing neural responses within the central region (ICC), as it is viewed as part of the lemniscal system mainly responsible for auditory perception. In contrast, the responses of outer cortices (ICO) have largely been unexplored, though they also function in auditory perception tasks. Therefore, we sought to expand on previous work by completing a three-dimensional (3-D) functional mapping study of the whole IC. We analyzed responses to different pure tone and broadband noise stimuli across all IC subregions and correlated those responses with over 2,000 recording locations across the IC. Our study revealed there are well-organized trends for temporal response parameters across the full IC that do not show a clear distinction at the ICC and ICO border. These gradients span from slow, imprecise responses in the caudal-medial IC to fast, precise responses in the rostral-lateral IC, regardless of subregion, including the fastest responses located in the ICO. These trends were consistent at various acoustic stimulation levels. Weaker spatial trends could be found for response duration and spontaneous activity. Apart from tonotopic organization, spatial trends were not apparent for spectral response properties. Overall, these detailed acoustic response maps across the whole IC provide new insights into the organization and function of the IC.NEW & NOTEWORTHY Study of the inferior colliculus (IC) has largely focused on the central nucleus, with little exploration of the outer cortices. Here, we systematically assessed the acoustic response properties from over 2,000 locations in different subregions of the IC. The results revealed spatial trends in temporal response patterns that span all subregions. Furthermore, two populations of temporal response types emerged for neurons in the outer cortices that may contribute to their functional roles in auditory tasks.

Topographic and widespread auditory modulation of the somatosensory cortex: potential for bimodal sound and body stimulation for pain treatment

OBJECTIVE

There has been growing interest in understanding multisensory integration in the cortex through activation of multiple sensory and motor pathways to treat brain disorders, such as tinnitus or essential tremors. For tinnitus, previous studies show that combined sound and body stimulation can modulate the auditory pathway and lead to significant improvements in tinnitus symptoms. Considering that tinnitus is a type of chronic auditory pain, bimodal stimulation could potentially alter activity in the somatosensory pathway relevant for treating chronic pain. As an initial step towards that goal, we mapped and characterized neuromodulation effects in the somatosensory cortex (SC) in response to sound and/or electrical stimulation of the body.

APPROACH

We first mapped the topographic organization of activity across the SC of ketamine-anesthetized guinea pigs through electrical stimulation of different body locations using subcutaneous needle electrodes or with broadband acoustic stimulation. We then characterized how neural activity in different parts of the SC could be facilitated or suppressed with bimodal stimulation.

MAIN RESULTS

The topography in the SC of guinea pigs in response to electrical stimulation of the body aligns consistently to that shown in previous rodent studies. Interestingly, auditory broadband noise stimulation primarily excited SC areas that typically respond to stimulation of lower body locations. Although there was only a small subset of SC locations that were excited by acoustic stimulation alone, all SC recording sites could be altered (facilitated or suppressed) with bimodal stimulation. Furthermore, specific regions of the SC could be modulated by stimulating an appropriate body region combined with broadband noise.

SIGNIFICANCE

These findings show that bimodal stimulation can excite or modulate firing across a widespread yet targeted population of SC neurons. This approach may provide a non-invasive method for altering or disrupting abnormal firing patterns within certain parts of the SC for chronic pain treatment.

Quantifying Rheumatoid Arthritis Disease Activity using a Multimodal Sensing Knee Brace

OBJECTIVE

Rheumatoid arthritis (RA) is a chronic inflammatory syndrome that features painful and destructive joint disease. Aggressive disease-modifying treatment can result in reduced symptoms and protection from irreversible joint damage; however, assessment of treatment efficacy is currently based largely on subjective measures of patient and physician impressions. In this work, we address this compelling need to provide an accurate and quantitative capability for monitoring joint health in patients with RA.

METHODS

Joint acoustic emissions (JAEs), electrical bioimpedance (EBI), and kinematics were measured noninvasively from 11 patients with RA over the course of three weeks using a custom multimodal sensing brace, resulting in 49 visits with JAE recordings and 43 with EBI recordings. Features derived from all sensing modalities were fed into a linear discriminant analysis (LDA) model to predict disease activity according to the validated disease activity index (the DAS28-ESR). Erythrocyte sedimentation rate (ESR) was predicted using ridge regression and classified into a high or low class using LDA.

RESULTS

DAS28-ESR level was predicted with an area under the receiver operating characteristic curve (AUC) of 0.82. With JAEs alone, we were able to track intrasubject differences in the disease activity score as well as classify ESR level with an AUC of 0.93. The majority of patients reported both an interest and ability to use the brace at home for longitudinal monitoring.

CONCLUSION

This work demonstrates the ability to detect RA disease activity using noninvasive sensing.

SIGNIFICANCE

This system has the potential to improve RA disease activity monitoring by giving treating clinicians objective data that can be acquired independent of a face-to-face clinic visit.

A pre-admission triaging tool to predict severe COVID-19 cases: ABCD score

INTRODUCTION

Isolation of SARS-CoV-2-infected individuals is an important COVID-19 pandemic control measure. While most cases have uncomplicated infection, a small proportion of them has developed life-threatening disease. We set up a retrospective study to determine preadmission triaging tool to predict the development of severe COVID-19.

MATERIALS AND METHODS

A retrospective study was conducted from 1 October 2020 to 31 January 2021 with enrolment of all SARS-CoV-2 PCR-confirmed persons aged ≥13 years. The disease severity was assessed on admission and daily throughout the hospitalisation. Test-positive individuals were considered as having "severe COVID-19" if they had ≥1 of the following: room air oxygen saturation 30 breaths/minute, signs of severe respiratory distress, or received mechanical ventilation and/or vasopressor therapy. Uni- and multi-variate analyses using SPSS Statistics Ver. 26 were performed.

RESULTS

We showed that age ≥ 60 years, BMI ≥ 30.0, presentation on days 7-12 of illness, and ≥1 comorbidity were associated with development of severe COVID-19. A scoring system based on the four variables is a useful COVID-19 risk assessment tool. A total score ≥2 had a sensitivity of 60.9%, specificity of 88.2%, positive predictive value of 37.8% and negative predictive value of 95.0%.

CONCLUSION

Development of preadmission triaging tool can help health care providers (HCPs) decide on the placement of test-positive individuals to appropriate isolation facilities according to the risk of developing severe COVID-19.

Single-step label-free nanowell immunoassay accurately quantifies serum stress hormones within minutes

A non-faradaic label-free cortisol sensing platform is presented using a nanowell array design, in which the two probe electrodes are integrated within the nanowell structure. Rapid and low volume (≤5 μl) sensing was realized through functionalizing nanoscale volume wells with antibodies and monitoring the real-time binding events. A 28-well plate biochip was built on a glass substrate by sequential deposition, patterning, and etching steps to create a stack nanowell array sensor with an electrode gap of 40 nm. Sensor response for cortisol concentrations between 1 and 15 μg/dl in buffer solution was recorded, and a limit of detection of 0.5 μg/dl was achieved. Last, 65 human serum samples were collected to compare the response from human serum samples with results from the standard enzyme-linked immunosorbent assay (ELISA). These results confirm that nanowell array sensors could be a promising platform for point-of-care testing, where real-time, laboratory-quality diagnostic results are essential.

The effect of input noises on the activity of auditory neurons using GLM-based metrics

CONTEXT

The auditory system is extremely efficient in extracting auditory information in the presence of background noise. However, people with auditory implants have a hard time understanding speech in noisy conditions. Understanding the mechanisms of perception in noise could lead to better stimulation or preprocessing strategies for such implants.

OBJECTIVE

The neural mechanisms related to the processing of background noise, especially in the inferior colliculus (IC) where the auditory midbrain implant is located, are still not well understood. We thus wish to investigate if there is a difference in the activity of neurons in the IC when presenting noisy vocalizations with different types of noise (stationary vs. non-stationary), input signal-to-noise ratios (SNR) and signal levels.

APPROACH

We developed novel metrics based on a generalized linear model (GLM) to investigate the effect of a given input noise on neural activity. We used these metrics to analyze neural data recorded from the IC in ketamine-anesthetized female Hartley guinea pigs while presenting noisy vocalizations.

MAIN RESULTS

We found that non-stationary noise clearly contributes to the multi-unit neural activity in the IC by causing excitation, regardless of the SNR, input level or vocalization type. However, when presenting white or natural stationary noises, a great diversity of responses was observed for the different conditions, where the multi-unit activity of some sites was affected by the presence of noise and the activity of others was not.

SIGNIFICANCE

The GLM-based metrics allowed the identification of a clear distinction between the effect of white or natural stationary noises and that of non-stationary noise on the multi-unit activity in the IC. This had not been observed before and indicates that the so-called noise invariance in the IC is dependent on the input noisy conditions. This could suggest different preprocessing or stimulation approaches for auditory midbrain implants depending on the noisy conditions.

Bimodal neuromodulation combining sound and tongue stimulation reduces tinnitus symptoms in a large randomized clinical study

Tinnitus is a phantom auditory perception coded in the brain that can be bothersome or debilitating, affecting 10 to 15% of the population. Currently, there is no clinically recommended drug or device treatment for this major health condition. Animal research has revealed that sound paired with electrical somatosensory stimulation can drive extensive plasticity within the brain for tinnitus treatment. To investigate this bimodal neuromodulation approach in humans, we evaluated a noninvasive device that delivers sound to the ears and electrical stimulation to the tongue in a randomized, double-blinded, exploratory study that enrolled 326 adults with chronic subjective tinnitus. Participants were randomized into three parallel arms with different stimulation settings. Clinical outcomes were evaluated over a 12-week treatment period and a 12-month posttreatment phase. For the primary endpoints, participants achieved a statistically significant reduction in tinnitus symptom severity at the end of treatment based on two commonly used outcome measures, Tinnitus Handicap Inventory (Cohen’s d effect size: −0.87 to −0.92 across arms; P < 0.001) and Tinnitus Functional Index (−0.77 to −0.87; P < 0.001). Therapeutic improvements continued for 12 months after treatment for specific bimodal stimulation settings, which had not previously been demonstrated in a large cohort for a tinnitus intervention. The treatment also achieved high compliance and satisfaction rates with no treatment-related serious adverse events. These positive therapeutic and long-term results motivate further clinical trials toward establishing bimodal neuromodulation as a clinically recommended device treatment for tinnitus.

Noninvasive Bimodal Neuromodulation for the Treatment of Tinnitus: Protocol for a Second Large-Scale Double-Blind Randomized Clinical Trial to Optimize Stimulation Parameters

Background

There is increasing evidence from animal and human studies that bimodal neuromodulation combining sound and electrical somatosensory stimulation of the tongue can induce extensive brain changes and treat tinnitus.

Objective

The main objectives of the proposed clinical study are to confirm the efficacy, safety, and tolerability of treatment demonstrated in a previous large-scale study of bimodal auditory and trigeminal nerve (tongue) stimulation (Treatment Evaluation of Neuromodulation for Tinnitus - Stage A1); evaluate the therapeutic effects of adjusting stimulation parameters over time; and determine the contribution of different features of bimodal stimulation in improving tinnitus outcomes.

Methods

This study will be a prospective, randomized, double-blind, parallel-arm, comparative clinical trial of a 12-week treatment for tinnitus using a Conformité Européenne (CE)–marked device with a pre-post and 12-month follow-up design. Four treatment arms will be investigated, in which each arm consists of two different stimulation settings, with the first setting presented during the first 6 weeks and the second setting presented during the next 6 weeks of treatment. The study will enroll 192 participants, split in a ratio of 80:80:16:16 across the four arms. Participants will be randomized to one of four arms and stratified to minimize baseline variability in four categories: two separate strata for sound level tolerance (using loudness discomfort level as indicators for hyperacusis severity), high tinnitus symptom severity based on the Tinnitus Handicap Inventory (THI), and tinnitus laterality. The primary efficacy endpoints are within-arm changes in THI and Tinnitus Functional Index as well as between-arm changes in THI after 6 weeks of treatment for the full cohort and two subgroups of tinnitus participants (ie, one hyperacusis subgroup and a high tinnitus symptom severity subgroup). Additional efficacy endpoints include within-arm or between-arm changes in THI after 6 or 12 weeks of treatment and in different subgroups of tinnitus participants as well as at posttreatment assessments at 6 weeks, 6 months, and 12 months. Treatment safety, attrition rates, and compliance rates will also be assessed and reported.

Results

This study protocol was approved by the Tallaght University Hospital/St. James’s Hospital Joint Research Ethics Committee in Dublin, Ireland. The first participant was enrolled on March 20, 2018. The data collection and database lock are expected to be completed by February 2020, and the data analysis and manuscript submission are expected to be conducted in autumn of 2020.

Conclusions

The findings of this study will be disseminated to relevant research, clinical, and health services and patient communities through publications in peer-reviewed journals and presentations at scientific and clinical conferences.

Trial Registration

ClinicalTrials.gov NCT03530306; https://clinicaltrials.gov/ct2/show/NCT03530306

International Registered Report Identifier (IRRID)

DERR1-10.2196/13176

Peripheral Focused Ultrasound Stimulation (pFUS): New Competitor in Pharmaceutical Markets?

A new study published in Nature Communications outlines our group's results using focused ultrasound stimulation within peripheral organs to precisely activate autonomic nerve circuits. The concept is demonstrated by modulating two different (and potentially therapeutic) targets in animal models, a neuroimmune connection in the spleen (that modulates blood cytokine concentrations) and a nutrient sensory pathway within the liver (that modulates metabolism). Connected to this work is a companion Nature Communications publication that utilizes an ultrasound stimulus focused on the spleen to reduce disease severity in a serum-transferred rodent model of inflammatory arthritis. These reports highlight the growing evidence that ultrasound energy (previously shown to enable activation or modulation of central nervous system pathways) may be used to perform peripheral neuromodulation. In this commentary, we highlight the main findings and discuss their implications for new forms of ultrasound-based therapy. Though challenges remain, a new noninvasive method for precision neuromodulation could solve many of the challenges facing the nascent field of bioelectronic medicine. That is, the use of ultrasound to directly modulate neurophysiological systems therapeutically may provide alternatives to traditional pharmaceuticals. However, to alter the current pharmaceutical paradigm, the field will need to develop a new understanding of how traditional drug concepts (such as dose and pharmacokinetics-pharmacodynamics) relate to the parameters, protocols, and outcomes of this new stimulation technology.

Frequency-specific activation of the peripheral auditory system using optoacoustic laser stimulation

Hearing impairment is one of the most common sensory deficits in humans. Hearing aids are helpful to patients but can have poor sound quality or transmission due to insufficient output or acoustic feedback, such as for high frequencies. Implantable devices partially overcome these issues but require surgery with limited locations for device attachment. Here, we investigate a new optoacoustic approach to vibrate the hearing organ with laser stimulation to improve frequency bandwidth, not requiring attachment to specific vibratory structures, and potentially reduce acoustic feedback. We developed a laser pulse modulation strategy and simulated its response at the umbo (1-10 kHz) based on a convolution-based model. We achieved frequency-specific activation in which non-contact laser stimulation of the umbo, as well as within the middle ear at the round window and otic capsule, induced precise shifts in the maximal vibratory response of the umbo and neural activation within the inferior colliculus of guinea pigs, corresponding to the targeted, modelled and then stimulated frequency. There was also no acoustic feedback detected from laser stimulation with our experimental setup. These findings open up the potential for using a convolution-based optoacoustic approach as a new type of laser hearing aid or middle ear implant.

Noninvasive ultrasound stimulation of the spleen to treat inflammatory arthritis

Targeted noninvasive control of the nervous system and end-organs may enable safer and more effective treatment of multiple diseases compared to invasive devices or systemic medications. One target is the cholinergic anti-inflammatory pathway that consists of the vagus nerve to spleen circuit, which has been stimulated with implantable devices to improve autoimmune conditions such as rheumatoid arthritis. Here we report that daily noninvasive ultrasound (US) stimulation targeting the spleen significantly reduces disease severity in a mouse model of inflammatory arthritis. Improvements are observed only with specific parameters, in which US can provide both protective and therapeutic effects. Single cell RNA sequencing of splenocytes and experiments in genetically-immunodeficient mice reveal the importance of both T and B cell populations in the anti-inflammatory pathway. These findings demonstrate the potential for US stimulation of the spleen to treat inflammatory diseases.

Ultrasound Produces Extensive Brain Activation via a Cochlear Pathway

Ultrasound (US) can noninvasively activate intact brain circuits, making it a promising neuromodulation technique. However, little is known about the underlying mechanism. Here, we apply transcranial US and perform brain mapping studies in guinea pigs using extracellular electrophysiology. We find that US elicits extensive activation across cortical and subcortical brain regions. However, transection of the auditory nerves or removal of cochlear fluids eliminates the US-induced activity, revealing an indirect auditory mechanism for US neural activation. Our findings indicate that US activates the ascending auditory system through a cochlear pathway, which can activate other non-auditory regions through cross-modal projections. This cochlear pathway mechanism challenges the idea that US can directly activate neurons in the intact brain, suggesting that future US stimulation studies will need to control for this effect to reach reliable conclusions.

A Streaming PCA VLSI Chip for Neural Data Compression

Neural recording system miniaturization and integration with low-power wireless technologies require compressing neural data before transmission. Feature extraction is a procedure to represent data in a low-dimensional space; its integration into a recording chip can be an efficient approach to compress neural data. In this paper, we propose a streaming principal component analysis algorithm and its microchip implementation to compress multichannel local field potential (LFP) and spike data. The circuits have been designed in a 65-nm CMOS technology and occupy a silicon area of 0.06 mm. Throughout the experiments, the chip compresses LFPs by 10 at the expense of as low as 1% reconstruction errors and 144-nW/channel power consumption; for spikes, the achieved compression ratio is 25 with 8% reconstruction errors and 3.05-W/channel power consumption. In addition, the algorithm and its hardware architecture can swiftly adapt to nonstationary spiking activities, which enables efficient hardware sharing among multiple channels to support a high-channel count recorder.

Improving neural decoding in the central auditory system using bio-inspired spectro-temporal representations and a generalized bilinear model

We study the impact of different encoding models and spectro-temporal representations on the accuracy of Bayesian decoding of neural activity recorded from the central auditory system. Two encoding models, a generalized linear model (GLM) and a generalized bilinear model (GBM), are compared along with three different spectro-temporal representations of the input stimuli: a spectrogram and two bio-inspired representations, i.e. a gammatone filter bank (GFB) and a spikegram. Signal to noise ratios between the reconstructed and original representations are used to evaluate the decoding, or reconstruction accuracy. We experimentally show that the reconstruction accuracy is best with the spikegram representation and worst with the spectrogram representation and, furthermore, that using a GBM instead of a GLM significantly increases the reconstruction accuracy. In fact, our results show that the spikegram reconstruction accuracy with a GBM fitting yields an SNR that is 3.3 dB better than when using the standard decoding approach of reconstructing a spectrogram with GLM fitting.

A new concept for noninvasive tinnitus treatment utilizing multimodal pathways

Current noninvasive treatments for tinnitus have shown mixed results. There have been encouraging developments in using invasive brain or vagal nerve stimulation to modulate neural populations driving the tinnitus percept. However, these invasive treatments can only be used in a small patient population with severe conditions. In this preliminary study, we present a new treatment option we call Multimodal Synchronization Therapy (MST), which attempts to achieve synchronized and localized brain activation without invasive neural stimulation. MST combines multiple sensory, motor, limbic, and cognitive inputs to elicit activation of multimodal neurons to potentially modulate specific neurons driving the tinnitus percept. We present preliminary data in a guinea pig model showing activation of somatosensory and auditory pathways to alter neural activity within the inferior colliculus, a multimodal integration region that has shown pathological changes in animals and patients with tinnitus. Electrical stimulation of different body locations induced excitatory responses in the inferior colliculus, eliciting responses in up to 41% of all recording sites for a given somatic site. Paired somatic and acoustic stimulation resulted in enhanced or suppressed acoustic-driven neural activity in the inferior colliculus that varied depending on stimulation and recording location. Similar modulation effects were observed in the auditory cortex, which may relate to changes in auditory perception. Further studies need to incorporate multiple multimodal pathways and must also confirm that MST can suppress the abnormal neural patterns that directly drive the tinnitus percept.

Positron Emission Tomography Imaging Reveals Auditory and Frontal Cortical Regions Involved with Speech Perception and Loudness Adaptation

Considerable progress has been made in the treatment of hearing loss with auditory implants. However, there are still many implanted patients that experience hearing deficiencies, such as limited speech understanding or vanishing perception with continuous stimulation (i.e., abnormal loudness adaptation). The present study aims to identify specific patterns of cerebral cortex activity involved with such deficiencies. We performed O-15-water positron emission tomography (PET) in patients implanted with electrodes within the cochlea, brainstem, or midbrain to investigate the pattern of cortical activation in response to speech or continuous multi-tone stimuli directly inputted into the implant processor that then delivered electrical patterns through those electrodes. Statistical parametric mapping was performed on a single subject basis. Better speech understanding was correlated with a larger extent of bilateral auditory cortex activation. In contrast to speech, the continuous multi-tone stimulus elicited mainly unilateral auditory cortical activity in which greater loudness adaptation corresponded to weaker activation and even deactivation. Interestingly, greater loudness adaptation was correlated with stronger activity within the ventral prefrontal cortex, which could be up-regulated to suppress the irrelevant or aberrant signals into the auditory cortex. The ability to detect these specific cortical patterns and differences across patients and stimuli demonstrates the potential for using PET to diagnose auditory function or dysfunction in implant patients, which in turn could guide the development of appropriate stimulation strategies for improving hearing rehabilitation. Beyond hearing restoration, our study also reveals a potential role of the frontal cortex in suppressing irrelevant or aberrant activity within the auditory cortex, and thus may be relevant for understanding and treating tinnitus.

Pairing broadband noise with cortical stimulation induces extensive suppression of ascending sensory activity

OBJECTIVE

The corticofugal system can alter coding along the ascending sensory pathway. Within the auditory system, electrical stimulation of the auditory cortex (AC) paired with a pure tone can cause egocentric shifts in the tuning of auditory neurons, making them more sensitive to the pure tone frequency. Since tinnitus has been linked with hyperactivity across auditory neurons, we sought to develop a new neuromodulation approach that could suppress a wide range of neurons rather than enhance specific frequency-tuned neurons.

APPROACH

We performed experiments in the guinea pig to assess the effects of cortical stimulation paired with broadband noise (PN-Stim) on ascending auditory activity within the central nucleus of the inferior colliculus (CNIC), a widely studied region for AC stimulation paradigms.

MAIN RESULTS

All eight stimulated AC subregions induced extensive suppression of activity across the CNIC that was not possible with noise stimulation alone. This suppression built up over time and remained after the PN-Stim paradigm.

SIGNIFICANCE

We propose that the corticofugal system is designed to decrease the brain's input gain to irrelevant stimuli and PN-Stim is able to artificially amplify this effect to suppress neural firing across the auditory system. The PN-Stim concept may have potential for treating tinnitus and other neurological disorders.

Investigating a new neuromodulation treatment for brain disorders using synchronized activation of multimodal pathways

Neuromodulation is an increasingly accepted treatment for neurological and psychiatric disorders but is limited by its invasiveness or its inability to target deep brain structures using noninvasive techniques. We propose a new concept called Multimodal Synchronization Therapy (mSync) for achieving targeted activation of the brain via noninvasive and precisely timed activation of auditory, visual, somatosensory, motor, cognitive, and limbic pathways. In this initial study in guinea pigs, we investigated mSync using combined activation of just the auditory and somatosensory pathways, which induced differential and timing dependent plasticity in neural firing within deep brain and cortical regions of the auditory system. Furthermore, by varying the location of somatosensory stimulation across the body, we increased or decreased spiking activity across different neurons. These encouraging results demonstrate the feasibility of systematically modulating the brain using mSync. Considering that hearing disorders such as tinnitus and hyperacusis have been linked to abnormal and hyperactive firing patterns within the auditory system, these results open up the possibility for using mSync to decrease this pathological activity by varying stimulation parameters. Incorporating multiple types of pathways beyond just auditory and somatosensory inputs and using other activation patterns may enable treatment of various brain disorders.

Auditory midbrain implant: research and development towards a second clinical trial

The cochlear implant is considered one of the most successful neural prostheses to date, which was made possible by visionaries who continued to develop the cochlear implant through multiple technological and clinical challenges. However, patients without a functional auditory nerve or implantable cochlea cannot benefit from a cochlear implant. The focus of the paper is to review the development and translation of a new type of central auditory prosthesis for this group of patients that is known as the auditory midbrain implant (AMI) and is designed for electrical stimulation within the inferior colliculus. The rationale and results for the first AMI clinical study using a multi-site single-shank array will be presented initially. Although the AMI has achieved encouraging results in terms of safety and improvements in lip-reading capabilities and environmental awareness, it has not yet provided sufficient speech perception. Animal and human data will then be presented to show that a two-shank AMI array can potentially improve hearing performance by targeting specific neurons of the inferior colliculus. A new two-shank array, stimulation strategy, and surgical approach are planned for the AMI that are expected to improve hearing performance in the patients who will be implanted in an upcoming clinical trial funded by the National Institutes of Health. Positive outcomes from this clinical trial will motivate new efforts and developments toward improving central auditory prostheses for those who cannot sufficiently benefit from cochlear implants. This article is part of a Special Issue entitled <Lasker Award>.

Suppression and facilitation of auditory neurons through coordinated acoustic and midbrain stimulation: investigating a deep brain stimulator for tinnitus

OBJECTIVE

The inferior colliculus (IC) is the primary processing center of auditory information in the midbrain and is one site of tinnitus-related activity. One potential option for suppressing the tinnitus percept is through deep brain stimulation via the auditory midbrain implant (AMI), which is designed for hearing restoration and is already being implanted in deaf patients who also have tinnitus. However, to assess the feasibility of AMI stimulation for tinnitus treatment we first need to characterize the functional connectivity within the IC. Previous studies have suggested modulatory projections from the dorsal cortex of the IC (ICD) to the central nucleus of the IC (ICC), though the functional properties of these projections need to be determined.

APPROACH

In this study, we investigated the effects of electrical stimulation of the ICD on acoustic-driven activity within the ICC in ketamine-anesthetized guinea pigs.

MAIN RESULTS

We observed ICD stimulation induces both suppressive and facilitatory changes across ICC that can occur immediately during stimulation and remain after stimulation. Additionally, ICD stimulation paired with broadband noise stimulation at a specific delay can induce greater suppressive than facilitatory effects, especially when stimulating in more rostral and medial ICD locations.

SIGNIFICANCE

These findings demonstrate that ICD stimulation can induce specific types of plastic changes in ICC activity, which may be relevant for treating tinnitus. By using the AMI with electrode sites positioned with the ICD and the ICC, the modulatory effects of ICD stimulation can be tested directly in tinnitus patients.

Effects of location and timing of co-activated neurons in the auditory midbrain on cortical activity: implications for a new central auditory prosthesis

OBJECTIVE

An increasing number of deaf individuals are being implanted with central auditory prostheses, but their performance has generally been poorer than for cochlear implant users. The goal of this study is to investigate stimulation strategies for improving hearing performance with a new auditory midbrain implant (AMI). Previous studies have shown that repeated electrical stimulation of a single site in each isofrequency lamina of the central nucleus of the inferior colliculus (ICC) causes strong suppressive effects in elicited responses within the primary auditory cortex (A1). Here we investigate if improved cortical activity can be achieved by co-activating neurons with different timing and locations across an ICC lamina and if this cortical activity varies across A1.

APPROACH

We electrically stimulated two sites at different locations across an isofrequency ICC lamina using varying delays in ketamine-anesthetized guinea pigs. We recorded and analyzed spike activity and local field potentials across different layers and locations of A1.

RESULTS

Co-activating two sites within an isofrequency lamina with short inter-pulse intervals (<5 ms) could elicit cortical activity that is enhanced beyond a linear summation of activity elicited by the individual sites. A significantly greater extent of normalized cortical activity was observed for stimulation of the rostral-lateral region of an ICC lamina compared to the caudal-medial region. We did not identify any location trends across A1, but the most cortical enhancement was observed in supragranular layers, suggesting further integration of the stimuli through the cortical layers.

SIGNIFICANCE

The topographic organization identified by this study provides further evidence for the presence of functional zones across an ICC lamina with locations consistent with those identified by previous studies. Clinically, these results suggest that co-activating different neural populations in the rostral-lateral ICC rather than the caudal-medial ICC using the AMI may improve or elicit different types of hearing capabilities.

Response features across the auditory midbrain reveal an organization consistent with a dual lemniscal pathway

The central auditory system has traditionally been divided into lemniscal and nonlemniscal pathways leading from the midbrain through the thalamus to the cortex. This view has served as an organizing principle for studying, modeling, and understanding the encoding of sound within the brain. However, there is evidence that the lemniscal pathway could be further divided into at least two subpathways, each potentially coding for sound in different ways. We investigated whether such an interpretation is supported by the spatial distribution of response features in the central nucleus of the inferior colliculus (ICC), the part of the auditory midbrain assigned to the lemniscal pathway. We recorded responses to pure tone stimuli in the ICC of ketamine-xylazine-anesthetized guinea pigs and used three-dimensional brain reconstruction techniques to map the location of the recording sites. Compared with neurons in caudal-and-medial regions within an isofrequency lamina of the ICC, neurons in rostral-and-lateral regions responded with shorter first-spike latencies with less spiking jitter, shorter durations of spiking responses, a higher proportion of spikes occurring near the onset of the stimulus, lower thresholds, and larger local field potentials with shorter latencies. Further analysis revealed two distinct clusters of response features located in either the caudal-and-medial or the rostral-and-lateral parts of the isofrequency laminae of the ICC. Thus we report substantial differences in coding properties in two regions of the ICC that are consistent with the hypothesis that the lemniscal pathway is made up of at least two distinct subpathways from the midbrain up to the cortex.

Investigation of a new electrode array technology for a central auditory prosthesis

Ongoing clinical studies on patients recently implanted with the auditory midbrain implant (AMI) into the inferior colliculus (IC) for hearing restoration have shown that these patients do not achieve performance levels comparable to cochlear implant patients. The AMI consists of a single-shank array (20 electrodes) for stimulation along the tonotopic axis of the IC. Recent findings suggest that one major limitation in AMI performance is the inability to sufficiently activate neurons across the three-dimensional (3-D) IC. Unfortunately, there are no currently available 3-D array technologies that can be used for clinical applications. More recently, there has been a new initiative by the European Commission to fund and develop 3-D chronic electrode arrays for science and clinical applications through the NeuroProbes project that can overcome the bulkiness and limited 3-D configurations of currently available array technologies. As part of the NeuroProbes initiative, we investigated whether their new array technology could be potentially used for future AMI patients. Since the NeuroProbes technology had not yet been tested for electrical stimulation in an in vivo animal preparation, we performed experiments in ketamine-anesthetized guinea pigs in which we inserted and stimulated a NeuroProbes array within the IC and recorded the corresponding neural activation within the auditory cortex. We used 2-D arrays for this initial feasibility study since they were already available and were sufficient to access the IC and also demonstrate effective activation of the central auditory system. Based on these encouraging results and the ability to develop customized 3-D arrays with the NeuroProbes technology, we can further investigate different stimulation patterns across the ICC to improve AMI performance.

Neural representation in the auditory midbrain of the envelope of vocalizations based on a peripheral ear model

The auditory midbrain implant (AMI) consists of a single shank array (20 sites) for stimulation along the tonotopic axis of the central nucleus of the inferior colliculus (ICC) and has been safely implanted in deaf patients who cannot benefit from a cochlear implant (CI). The AMI improves lip-reading abilities and environmental awareness in the implanted patients. However, the AMI cannot achieve the high levels of speech perception possible with the CI. It appears the AMI can transmit sufficient spectral cues but with limited temporal cues required for speech understanding. Currently, the AMI uses a CI-based strategy, which was originally designed to stimulate each frequency region along the cochlea with amplitude-modulated pulse trains matching the envelope of the bandpass-filtered sound components. However, it is unclear if this type of stimulation with only a single site within each frequency lamina of the ICC can elicit sufficient temporal cues for speech perception. At least speech understanding in quiet is still possible with envelope cues as low as 50 Hz. Therefore, we investigated how ICC neurons follow the bandpass-filtered envelope structure of natural stimuli in ketamine-anesthetized guinea pigs. We identified a subset of ICC neurons that could closely follow the envelope structure (up to ß100 Hz) of a diverse set of species-specific calls, which was revealed by using a peripheral ear model to estimate the true bandpass-filtered envelopes observed by the brain. Although previous studies have suggested a complex neural transformation from the auditory nerve to the ICC, our data suggest that the brain maintains a robust temporal code in a subset of ICC neurons matching the envelope structure of natural stimuli. Clinically, these findings suggest that a CI-based strategy may still be effective for the AMI if the appropriate neurons are entrained to the envelope of the acoustic stimulus and can transmit sufficient temporal cues to higher centers.

Frequency representation within the human brain: stability versus plasticity

A topographical representation for frequency has been identified throughout the auditory brain in animals but with limited evidence in humans. Using a midbrain implant, we identified an ordering of pitch percepts for electrical stimulation of sites across the human inferior colliculus (IC) that was consistent with the IC tonotopy shown in animals. Low pitches were perceived by the subject for stimulation of superficial IC sites while higher pitches were perceived for stimulation of deeper sites. Interestingly, this pitch ordering was not initially observed for stimulation across the IC, possibly due to central changes caused by prior hearing loss. Daily implant stimulation for about 4 months altered the pitch percepts from being predominantly low to exhibiting the expected ordering across the stimulated IC. A presumably normal tonotopic representation may have been maintained within the IC or accessible through IC stimulation that helped form this pitch ordering perceived in higher centers.

Neural integration and enhancement from the inferior colliculus up to different layers of auditory cortex

While the cochlear implant has successfully restored hearing to many deaf patients, it cannot benefit those without a functional auditory nerve or an implantable cochlea. As an alternative, the auditory midbrain implant (AMI) has been developed and implanted into deaf patients. Consisting of a single-shank array, the AMI is designed for stimulation along the tonotopic gradient of the inferior colliculus (ICC). Although the AMI can provide frequency cues, it appears to insufficiently transmit temporal cues for speech understanding because repeated stimulation of a single site causes strong suppressive and refractory effects. Applying the electrical stimulation to at least two sites within an isofrequency lamina can circumvent these refractory processes. Moreover, coactivation with short intersite delays (<5 ms) can elicit cortical activation which is enhanced beyond the summation of activity induced by the individual sites. The goal of our study was to further investigate the role of the auditory cortex in this enhancement effect. In guinea pigs, we electrically stimulated two locations within an ICC lamina or along different laminae with varying interpulse intervals (0-10 ms) and recorded activity in different locations and layers of primary auditory cortex (A1). Our findings reveal a neural mechanism that integrates activity only from neurons located within the same ICC lamina for short spiking intervals (<6 ms). This mechanism leads to enhanced activity into layers III-V of A1 that is further magnified in supragranular layers. This integration mechanism may contribute to perceptual coding of different sound features that are relevant for improving AMI performance.

Tonotopic and localized pathways from primary auditory cortex to the central nucleus of the inferior colliculus

Descending projections from the cortex to subcortical structures are critical for auditory plasticity, including the ability for central neurons to adjust their frequency tuning to relevant and meaningful stimuli. We show that focal electrical stimulation of primary auditory cortex in guinea pigs produces excitatory responses in the central nucleus of the inferior colliculus (CNIC) with two tonotopic patterns: a narrow tuned pattern that is consistent with previous findings showing direct frequency-aligned projections; and a broad tuned pattern in which the auditory cortex can influence multiple frequency regions. Moreover, excitatory responses could be elicited in the caudomedial portion along the isofrequency laminae of the CNIC but not in the rostrolateral portion. This descending organization may underlie or contribute to the ability of the auditory cortex to induce changes in frequency tuning of subcortical neurons as shown extensively in previous studies.

Association of fatty acid composition in serum phospholipids with metabolic syndrome and arterial stiffness

BACKGROUND AND AIM

We examined the association of fatty acid (FA) composition in serum phospholipids with the features of metabolic syndrome (MetS) and arterial stiffness.

METHODS

Korean men (n = 593, 30-79 yrs) were categorized based on the number of MetS risk factors (RFs) and measured for the markers of MetS, serum phospholipid FA composition and brachial-ankle pulse wave velocity (baPWV), an index for the severity of arterial stiffness.

RESULTS

Insulin resistance (HOMA-IR), baPWV, LDL size, and adiponectin were significantly altered corresponding to the number of MetS RFs. The proportions of total monounsaturated FA, palmitoleic acid (16:1), oleic acid (18:1ω-9) and dihomo-γ-linolenic acid (DGLA, 20:3ω-6) in serum phospholipids, and DGLA/linoleic acid (LA) (20:3ω-6/18:2ω-6), deta9-desaturase activity (D9D-16: 16:1/16:0 and D9D-18: 18:1ω-9/18:0) significantly increased corresponding to the number of MetS RFs, but D5D (20:4ω-6/20:3ω-6) decreased. baPWV positively correlated with HOMA-IR, palmitic acid (16:0), oleic acid, D6D (18:3ω-6/18:2ω-6), DGLA/LA and D9D-18, and negatively with adiponectin, LDL size, LA, docosahexaenoic acid (DHA, 22:6ω-3) and D5D. Multiple stepwise regression models revealed that baPWV was significantly influenced by systolic blood pressure, age, body weight, triglyceride and LA in serum phospholipids (R(2) = 0.378). Interestingly, baPWV (1419 ± 1 cm/s) and MetS (22%) were highest in individuals with lower proportion of LA (< 12.361%) and higher proportion of DGLA (≥ 1.412%) in serum phospholipid FAs.

CONCLUSION

The features of MetS significantly related to serum phosopholipid FA composition. Particularly, arterial stiffness was associated with LA additively together with DLGA. It may suggest a potential benefit of sufficient amounts of LA in serum or in diet can reduce cardiovascular risk.

Neuromodulation for brain disorders: challenges and opportunities

The field of neuromodulation encompasses a wide spectrum of interventional technologies that modify pathological activity within the nervous system to achieve a therapeutic effect. Therapies including deep brain stimulation, intracranial cortical stimulation, transcranial direct current stimulation, and transcranial magnetic stimulation have all shown promising results across a range of neurological and neuropsychiatric disorders. While the mechanisms of therapeutic action are invariably different among these approaches, there are several fundamental neuroengineering challenges that are commonly applicable to improving neuromodulation efficacy. This paper reviews the state-of-the-art of neuromodulation for brain disorders and discusses the challenges and opportunities available for clinicians and researchers interested in advancing neuromodulation therapies.

Three-dimensional brain reconstruction of in vivo electrode tracks for neuroscience and neural prosthetic applications

The brain is a densely interconnected network that relies on populations of neurons within and across multiple nuclei to code for features leading to perception and action. However, the neurophysiology field is still dominated by the characterization of individual neurons, rather than simultaneous recordings across multiple regions, without consistent spatial reconstruction of their locations for comparisons across studies. There are sophisticated histological and imaging techniques for performing brain reconstructions. However, what is needed is a method that is relatively easy and inexpensive to implement in a typical neurophysiology lab and provides consistent identification of electrode locations to make it widely used for pooling data across studies and research groups. This paper presents our initial development of such an approach for reconstructing electrode tracks and site locations within the guinea pig inferior colliculus (IC) to identify its functional organization for frequency coding relevant for a new auditory midbrain implant (AMI). Encouragingly, the spatial error associated with different individuals reconstructing electrode tracks for the same midbrain was less than 65 μm, corresponding to an error of ~1.5% relative to the entire IC structure (~4–5 mm diameter sphere). Furthermore, the reconstructed frequency laminae of the IC were consistently aligned across three sampled midbrains, demonstrating the ability to use our method to combine location data across animals. Hopefully, through further improvements in our reconstruction method, it can be used as a standard protocol across neurophysiology labs to characterize neural data not only within the IC but also within other brain regions to help bridge the gap between cellular activity and network function. Clinically, correlating function with location within and across multiple brain regions can guide optimal placement of electrodes for the growing field of neural prosthetics.

Coactivation of different neurons within an isofrequency lamina of the inferior colliculus elicits enhanced auditory cortical activation

The phenomenal success of the cochlear implant (CI) is attributed to its ability to provide sufficient temporal and spectral cues for speech understanding. Unfortunately, the CI is ineffective for those without a functional auditory nerve or an implantable cochlea required for CI implementation. As an alternative, our group developed and implanted in deaf patients a new auditory midbrain implant (AMI) to stimulate the central nucleus of the inferior colliculus (ICC). Although the AMI can provide frequency cues, it appears to insufficiently transmit temporal cues for speech understanding. The three-dimensional ICC consists of two-dimensional isofrequency laminae. The single-shank AMI only stimulates one site in any given ICC lamina and does not exhibit enhanced activity (i.e., louder percepts or lower thresholds) for repeated pulses on the same site with intervals <2-5 ms, as occurs for CI pulse or acoustic click stimulation. This enhanced activation, related to short-term temporal integration, is important for tracking the rapid temporal fluctuations of a speech signal. Therefore, we investigated the effects of coactivation of different regions within an ICC lamina on primary auditory cortex activity in ketamine-anesthetized guinea pigs. Interestingly, our findings reveal an enhancement mechanism for integrating converging inputs from an ICC lamina on a fast scale (<6-ms window) that is compromised when stimulating just a single ICC location. Coactivation of two ICC regions also reduces the strong and long-term (>100 ms) suppressive effects induced by repeated stimulation of just a single location. Improving AMI performance may require at least two shanks implanted along the tonotopic gradient of the ICC that enables coactivation of multiple regions along an ICC lamina with the appropriate interstimulus delays.

Optoacoustic induced vibrations within the inner ear

An acoustic transient can be generated inside an absorbing tissue as a result of laser-tissue interaction after pulsed laser irradiation. Herein we report a novel application of this physical process, the optoacoustic wave generation in the inner ear and subsequently the induction of basilar membrane vibrations. These laser induced vibrations show a direct correlation to the laser energy and an indirect correlation to the distance from the irradiation focus. Through these characteristics they may be used, in a new generation of cochlear implants, to improve the frequency specific cochlear activation and consequently improve speech perception in hearing impaired patients with residual hearing.

Auditory midbrain implant: a review

The auditory midbrain implant (AMI) is a new hearing prosthesis designed for stimulation of the inferior colliculus in deaf patients who cannot sufficiently benefit from cochlear implants. The authors have begun clinical trials in which five patients have been implanted with a single shank AMI array (20 electrodes). The goal of this review is to summarize the development and research that has led to the translation of the AMI from a concept into the first patients. This study presents the rationale and design concept for the AMI as well a summary of the animal safety and feasibility studies that were required for clinical approval. The authors also present the initial surgical, psychophysical, and speech results from the first three implanted patients. Overall, the results have been encouraging in terms of the safety and functionality of the implant. All patients obtain improvements in hearing capabilities on a daily basis. However, performance varies dramatically across patients depending on the implant location within the midbrain with the best performer still not able to achieve open set speech perception without lip-reading cues. Stimulation of the auditory midbrain provides a wide range of level, spectral, and temporal cues, all of which are important for speech understanding, but they do not appear to sufficiently fuse together to enable open set speech perception with the currently used stimulation strategies. Finally, several issues and hypotheses for why current patients obtain limited speech perception along with several feasible solutions for improving AMI implementation are presented.

Green laser light activates the inner ear

The hearing performance with conventional hearing aids and cochlear implants is dramatically reduced in noisy environments and for sounds more complex than speech (e. g. music), partially due to the lack of localized sensorineural activation across different frequency regions with these devices. Laser light can be focused in a controlled manner and may provide more localized activation of the inner ear, the cochlea. We sought to assess whether visible light with parameters that could induce an optoacoustic effect (532 nm, 10-ns pulses) would activate the cochlea. Auditory brainstem responses (ABRs) were recorded preoperatively in anesthetized guinea pigs to confirm normal hearing. After opening the bulla, a 50-microm core-diameter optical fiber was positioned in the round window niche and directed toward the basilar membrane. Optically induced ABRs (OABRs), similar in shape to those of acoustic stimulation, were elicited with single pulses. The OABR peaks increased with energy level (0.6 to 23 microJ/pulse) and remained consistent even after 30 minutes of continuous stimulation at 13 microJ, indicating minimal or no stimulation-induced damage within the cochlea. Our findings demonstrate that visible light can effectively and reliably activate the cochlea without any apparent damage. Further studies are in progress to investigate the frequency-specific nature and mechanism of green light cochlear activation.

Atherogenecity of LDL and unfavorable adipokine profile in metabolically obese, normal-weight woman

OBJECTIVE

The relationship of visceral adiposity with adipocytokines and low-density lipoprotein (LDL) particle distribution and oxidation in Asian metabolically obese, normal-weight (MONW) individuals has not been evaluated. We aimed to investigate the association between visceral adiposity and adipocytokines and cardiovascular disease (CVD) risk factors in MONW Korean women with normal glucose tolerance.

METHODS AND PROCEDURES

We examined the metabolic characteristics of 135 non-obese (BMI <25 kg/m(2)) women aged 25-64 years. Twenty-five women (BMI <25 kg/m(2) and visceral fat adiposity (VFA) > or =100 cm(2)) were classified as MONW and 25 women (BMI <25 kg/m(2) and VFA <100 cm(2)), pair-matched for age, weight, height, and menopausal status, as control group. Plasma lipid profiles and adipocytokines were evaluated in these two groups.

RESULTS

MONW subjects had higher systolic (P < 0.05) and diastolic blood pressure (P < 0.005) and higher concentrations of triacylglycerol (TG) (P < 0.005), insulin (P < 0.01), and free fatty acid (FFA) (P < 0.05) than control subjects. There was no significant difference between two groups in LDL-cholesterol (LDL-C) concentrations; however, MONW subjects had smaller LDL particles (P < 0.01) and higher concentrations of oxidized LDL (ox-LDL) (P < 0.05) compared with controls. Moreover, MONW subjects had higher concentrations of tumor necrosis factor-alpha (TNF-alpha) (P < 0.05), interleukin-6 (IL-6) (P < 0.05) and leptin (P < 0.05), and lower plasma adiponectin concentrations (P < 0.05). Higher intake of saturated fat with lower ratio of polyunsaturated fatty acids (PUFAs) to saturated fatty acids (SFA) and lower fiber intake than normal subjects were found in MONW women.

DISCUSSION

We found an unfavorable inflammatory profile and a more atherogenic LDL profile in MONW female subjects even in the absence of a known CVD risk factors. Moreover, MONW consumed more saturated fat and less fiber than the control group.

Effects of phase duration and pulse rate on loudness and pitch percepts in the first auditory midbrain implant patients: Comparison to cochlear implant and auditory brainstem implant results

The auditory midbrain implant (AMI), which is designed for stimulation of the inferior colliculus (IC), is now in clinical trials. The AMI consists of a single shank array (20 contacts) and uses a stimulation strategy originally designed for cochlear implants since it is already approved for human use and we do not yet know how to optimally activate the auditory midbrain. The goal of this study was to investigate the effects of different pulse rates and phase durations on loudness and pitch percepts because these parameters are required to implement the AMI stimulation strategy. Although each patient was implanted into a different region (i.e. lateral lemniscus, central nucleus of IC, dorsal cortex of IC), they generally exhibited similar threshold versus phase duration, threshold versus pulse rate, and pitch versus pulse rate curves. In particular, stimulation with 100 mus/phase, 250 pulse per second (pps) pulse trains achieved an optimal balance among safety, energy, and current threshold requirements while avoiding rate pitch effects. However, we observed large differences across patients in loudness adaptation to continuous pulse stimulation over long time scales. One patient (implanted in dorsal cortex of IC) even experienced complete loudness decay and elevation of thresholds with daily stimulation. Comparing these results with those of cochlear implant and auditory brainstem implant patients, it appears that stimulation of higher order neurons exhibits less and even no loudness summation for higher rate stimuli and greater current leakage for longer phase durations than that of cochlear neurons. The fact that all midbrain regions we stimulated, which includes three distinctly different nuclei, exhibited similar loudness summation effects (i.e. none for pulse rates above 250 pps) suggests a possible shift in some coding properties that is affected more by which stage along the auditory pathway rather than the types of neurons are being stimulated. However, loudness adaptation occurs at multiple stages from the cochlea up to the midbrain.

The auditory midbrain implant: effects of electrode location

The auditory midbrain implant (AMI) is a new hearing prosthesis designed for stimulation of the inferior colliculus in patients who do not receive sufficient benefit from cochlear or brainstem prostheses. We have begun clinical trials in which three patients have been implanted with the AMI. Although the intended target was the central nucleus of the inferior colliculus (ICC), the electrode array was implanted into different locations across patients (i.e., ICC, dorsal cortex of inferior colliculus, lateral lemniscus). In this paper, we will summarize the effects of electrical stimulation of these different midbrain regions on various psychophysical properties and speech perception performance. The patient implanted within the intended target, the ICC, exhibited the greatest improvements in hearing performance. However, this patient has not yet achieved open-set speech perception to the performance level typically observed for cochlear implant patients, which we believe is partially due to the location of the array within the ICC. We will present findings from previous AMI studies in guinea pigs demonstrating the existence of spatially distinct functional output regions within the ICC and suggesting that further improvements in performance may be achieved by stimulating within a rostral-ventral region. Remaining questions include if a similar organization exists in the human ICC and if stimulation of its rostral-ventral region with currently available strategies (i.e., those designed for cochlear implants) can restore sufficient speech perception.

Spatially distinct functional output regions within the central nucleus of the inferior colliculus: implications for an auditory midbrain implant

The inferior colliculus central nucleus (ICC) has potential as a new site for an auditory prosthesis [i.e., auditory midbrain implant (AMI)] for deaf patients who cannot benefit from cochlear implants (CIs). We have previously shown that ICC stimulation achieves lower thresholds, greater dynamic ranges, and more localized, frequency-specific primary auditory cortex (A1) activation than CI stimulation. However, we also observed that stimulation location along the caudorostral (isofrequency) dimension of the ICC affects thresholds and frequency specificity in A1, suggesting possible differences in functional (output) organization within the ICC. In this study, we electrically stimulated different regions along the isofrequency laminas of the ICC and recorded the corresponding A1 activity in ketamine-anesthetized guinea pigs using multisite probes to systematically assess ICC stimulation location effects. Our results indicate that stimulation of more rostral and somewhat ventral regions within an ICC lamina achieves lower thresholds, smaller discriminable level steps, and larger evoked potentials in A1. We also observed longer first spike latencies, which correlated with reduced spiking precision, when stimulating in more caudal and dorsal ICC regions. These findings suggest that at least two spatially distinct functional output regions exist along an ICC lamina: a caudal-dorsal region and a rostral-ventral region. The AMI will be implanted along the tonotopic axis of the ICC to achieve frequency-specific activation. However, stimulation location along the ICC laminas affects response properties that have shown to be important for speech perception performance, and needs to be considered when implanting future AMI patients.

The auditory midbrain implant: a new auditory prosthesis for neural deafness-concept and device description

The auditory midbrain implant (AMI) is a new central auditory prosthesis designed for penetrating stimulation of the human inferior colliculus. The major group of candidates for the AMI consists of neurofibromatosis type 2 (NF2) patients who develop neural deafness because of growth and/or surgical removal of bilateral acoustic neuromas. Because of the absence of a viable auditory nerve, these patients cannot benefit from cochlear implants. An alternative solution has been the auditory brainstem implant (ABI), which stimulates the cochlear nucleus. However, speech perception performance in NF2 ABI patients has been limited. The fact that the ABI is able to produce high levels of speech perception in nontumor patients (with inaccessible cochleae or posttraumatic damage to the cochlear nerve) suggests that limitations in ABI performance in NF2 patients may be associated with cochlear nucleus damage caused by the tumors or the tumor removal process. Thus, stimulation of the auditory midbrain proximal to the damaged cochlear nucleus may be a better alternative for hearing restoration in NF2 patients. We propose the central nucleus of the inferior colliculus (ICC) as the potential site. A penetrating electrode array aligned along the well-defined tonotopic gradient of the ICC should selectively activate different frequency regions, which is an important elementfor supporting good speech understanding. The goal of this article is to present the ICC as an alternative site for an auditory implant for NF2 patients and to describe the design of the first human prototype AMI. Practical considerations for implementation of the AMI will also be discussed.

Antidromic Activation Reveals Tonotopically Organized Projections From Primary Auditory Cortex to the Central Nucleus of the Inferior Colliculus in Guinea Pig

The inferior colliculus (IC) is highly modulated by descending projections from higher auditory and nonauditory centers. Traditionally, corticofugal fibers were believed to project mainly to the extralemniscal IC regions. However, there is some anatomical evidence suggesting that a substantial number of fibers from the primary auditory cortex (A1) project into the IC central nucleus (ICC) and appear to be tonotopically organized. In this study, we used antidromic stimulation combined with other electrophysiological techniques to further investigate the spatial organization of descending fibers from A1 to the ICC in ketamine-anesthetized guinea pigs. Based on our findings, corticofugal fibers originate predominantly from layer V of A1, are amply scattered throughout the ICC and only project to ICC neurons with a similar best frequency (BF). This strict tonotopic pattern suggests that these corticofugal projections are involved with modulating spectral features of sound. Along the isofrequency dimension of the ICC, there appears to be some differences in projection patterns that depend on BF region and possibly isofrequency location within A1 and may be indicative of different descending coding strategies. Furthermore, the success of the antidromic stimulation method in our study demonstrates that it can be used to investigate some of the functional properties associated with corticofugal projections to the ICC as well as to other regions (e.g., medial geniculate body, cochlear nucleus). Such a method can address some of the limitations with current anatomical techniques for studying the auditory corticofugal system.

Auditory Midbrain Implant

HYPOTHESIS

The lateral suboccipital approach is a well-established route for safe removal of vestibular schwannomas in neurofibromatosis Type 2 (NF2) patients. The goal of this study was to assess if this approach can be extended to a lateral supracerebellar infratentorial approach to enable insertion of an auditory midbrain implant (AMI) penetrating array along the tonotopic gradient of the inferior colliculus central nucleus (ICC).

BACKGROUND

The AMI is a new auditory prosthesis designed for penetrating stimulation of the ICC in patients with neural deafness. The initial candidates are NF2 patients who, because of the growth and/or surgical removal of bilateral acoustic neuromas, develop neural deafness and are unable to benefit from cochlear implants. The ideal surgical approach in NF2 patients must first enable safe removal of vestibular schwannomas and then provide sufficient exposure of the midbrain for AMI implantation.

METHODS

This study was performed on formalin-fixed and fresh cadaver specimens. Computed tomography scan and magnetic resonance imaging were used to study the heads of the specimens and for surgical navigation.

RESULTS

The lateral suboccipital craniotomy enabled sufficient exposure of the cerebellopontine angle and internal auditory canal for tumor removal. It could then be extended to a lateral supracerebellar infratentorial approach that provided good exposure of the dorsolateral aspect of the tentorial hiatus and mesencephalon for implantation of the AMI along the tonotopic gradient of the ICC. This approach did not endanger the trochlear nerve or any major midline venous structures in the quadrigeminal cistern.

CONCLUSION

This modified lateral suboccipital approach ensures safe removal of large vestibular schwannomas and provides sufficient exposure of the inferior colliculus for ideal AMI implantation.

Electrophysiological validation of a human prototype auditory midbrain implant in a guinea pig model

The auditory midbrain implant (AMI) is a new treatment for hearing restoration in patients with neural deafness or surgically inaccessible cochleae who cannot benefit from cochlear implants (CI). This includes neurofibromatosis type II (NF2) patients who, due to development and/or removal of vestibular schwannomas, usually experience complete damage of their auditory nerves. Although the auditory brainstem implant (ABI) provides sound awareness and aids lip-reading capabilities for these NF2 patients, it generally only achieves hearing performance levels comparable with a single-channel CI. In collaboration with Cochlear Ltd. (Lane Cove, Australia), we developed a human prototype AMI, which is designed for electrical stimulation along the well-defined tonotopic gradient of the inferior colliculus central nucleus (ICC). Considering that better speech perception and hearing performance has been correlated with a greater number of discriminable frequency channels of information available, the ability of the AMI to effectively activate discrete frequency regions within the ICC may enable better hearing performance than achieved by the ABI. Therefore, the goal of this study was to investigate if our AMI array could achieve low-threshold, frequency-specific activation within the ICC, and whether the levels for ICC activation via AMI stimulation were within safe limits for human application. We electrically stimulated different frequency regions within the ICC via the AMI array and recorded the corresponding neural activity in the primary auditory cortex (A1) using a multisite silicon probe in ketamine-anesthetized guinea pigs. Based on our results, AMI stimulation achieves lower thresholds and more localized, frequency-specific activation than CI stimulation. Furthermore, AMI stimulation achieves cortical activation with current levels that are within safe limits for central nervous system stimulation. This study confirms that our AMI design is sufficient for ensuring safe and effective activation of the ICC, and warrants further studies to translate the AMI into clinical application.

Auditory cortical responses to electrical stimulation of the inferior colliculus: implications for an auditory midbrain implant

The success and limitations of cochlear implants (CIs) along with recent advances in deep brain stimulation and neural engineering have motivated the development of a central auditory prosthesis. In this study, we investigated the effects of electrical stimulation of the inferior colliculus central nucleus (ICC) on primary auditory cortex (A1) activity to determine the potential benefits of an auditory midbrain implant (AMI). We recorded multiunit activity in A1 of ketamine-anesthetized guinea pigs in response to single-pulse (200 micros/phase) monopolar stimulation of the ICC using multisite silicon-substrate probes. We then compared measures of threshold, dynamic range, and tonotopic spread of activation for ICC stimulation with that of published data for CI stimulation. Our results showed that compared with cochlear stimulation, ICC stimulation achieved: 1) thresholds about 8 dB lower; 2) dynamic ranges > or = 4 dB greater; and 3) more localized, frequency-specific activation, even though frequency specificity was partially lost at higher stimulus levels for low-frequency ICC regions. Our results also showed that stimulation of rostral ICC regions elicited lower thresholds but with greater activation spread along the tonotopic gradient of A1 than did stimulation of more caudal regions. These results suggest that an AMI may improve frequency and level coding with lower energy requirements compared with CIs. However, a trade-off between lower perceptual thresholds and better frequency discrimination may exist that depends on location of stimulation along the caudorostral dimension of the ICC. Overall, this study provides the foundation for future AMI research and development.

Tophaceous gout causing atlanto-axial subluxation mimicking rheumatoid arthritis: a case report

This is a case report of an extremely rare condition of atlanto-axial subluxation secondary to gouty arthritis, which mimicked rheumatoid arthritis at presentation. Gouty arthritis involving the spine is a rare condition. We highlight a case of gouty arthritis involving the atlanto-axial joint resulting in joint instability, subluxation, and neurological deficit. A 66-year-old obese woman who had a polyarticular disease for the previous 3 years presented with neck pain and progressive neurology. A 2-stage procedure was performed: posterior decompression and occipitocervical fusion followed by further anterior trans-oral decompression. However, after an initial neurological improvement, she succumbed to aspirational pneumonia and septicaemia. Atlanto-axial subluxation caused by gouty arthritis can present in the same way as rheumatoid arthritis. Therefore, the possibility of this as a differential diagnosis should be kept in mind.