High Stimulation Rates Research Articles

Combined-electrical optogenetic stimulation but not channelrhodopsin kinetics improves the fidelity of high rate stimulation in the auditory pathway in mice

Novel stimulation methods are needed to overcome the limitations of contemporary cochlear implants. Optogenetics is a technique that confers light sensitivity to neurons via the genetic introduction of light-sensitive ion channels. By controlling neural activity with light, auditory neurons can be activated with higher spatial precision. Understanding the behaviour of opsins at high stimulation rates is an important step towards their translation. To elucidate this, we compared the temporal characteristics of auditory nerve and inferior colliculus responses to optogenetic, electrical, and combined optogenetic-electrical stimulation in virally transduced mice expressing one of two channelrhodopsins, ChR2-H134R or ChIEF, at stimulation rates up to 400 pulses per second (pps). At 100 pps, optogenetic responses in ChIEF mice demonstrated higher fidelity, less change in latency, and greater response stability compared to responses in ChR2-H134R mice, but not at higher rates. Combined stimulation improved the response characteristics in both cohorts at 400 pps, although there was no consistent facilitation of electrical responses. Despite these results, day-long stimulation (up to 13 h) led to severe and non-recoverable deterioration of the optogenetic responses. The results of this study have significant implications for the translation of optogenetic-only and combined stimulation techniques for hearing loss.

A Mixed-Rate Strategy on a Bilaterally-Synchronized Cochlear Implant Processor Offering the Opportunity to Provide Both Speech Understanding and Interaural Time Difference Cues.

Background/Objective: Bilaterally implanted cochlear implant (CI) users do not consistently have access to interaural time differences (ITDs). ITDs are crucial for restoring the ability to localize sounds and understand speech in noisy environments. Lack of access to ITDs is partly due to lack of communication between clinical processors across the ears and partly because processors must use relatively high rates of stimulation to encode envelope information. Speech understanding is best at higher stimulation rates, but sensitivity to ITDs in the timing of pulses is best at low stimulation rates. Methods: We implemented a practical "mixed rate" strategy that encodes ITD information using a low stimulation rate on some channels and speech information using high rates on the remaining channels. The strategy was tested using a bilaterally synchronized research processor, the CCi-MOBILE. Nine bilaterally implanted CI users were tested on speech understanding and were asked to judge the location of a sound based on ITDs encoded using this strategy. Results: Performance was similar in both tasks between the control strategy and the new strategy. Conclusions: We discuss the benefits and drawbacks of the sound coding strategy and provide guidelines for utilizing synchronized processors for developing strategies.

Optimization of signal-to-noise ratio in short-duration SEP recordings by variation of stimulation rate

ObjectiveThe intraoperative averaging of the somatosensory evoked potential (SEP) requires reliable recordings within the shortest possible duration. We here systematically optimized the repetition rate of stimulus presentation. MethodsWe recorded medianus and tibial nerve SEP during 22 surgeries and varied the rate of stimulus presentation between 2.7 Hz and 28.7 Hz. We randomly sampled a number of sweeps corresponding to recording durations up to 20 s and calculated the signal-to-noise ratio (SNR). ResultsFor the medianus nerve at 5 s recording duration, SEP stimulation rate at 12.7 Hz obtained the highest median SNR = 22.9 for the N20, which was higher than for rate 4.7 Hz (p = 1.5e-4). When increasing the stimulation rate, latency increased and amplitude decayed for cortical but not for peripheral recording sites. For the tibial nerve, the rate 4.7 Hz achieved the highest SNR for all durations. ConclusionsWe determined the time-dependence of SNR for N20 and elucidated the underlying physiology. For short recordings, rapid reduction of noise through averaging at high stimulation rate outweighs the disadvantage of smaller amplitude. SignificanceFor a short duration of medianus nerve SEP recording only, it may be advantageous to stimulate with a repetition rate of 12.7 Hz.

Lateralization of interaural time differences with mixed rates of stimulation in bilateral cochlear implant listeners.

While listeners with bilateral cochlear implants (BiCIs) are able to access information in both ears, they still struggle to perform well on spatial hearing tasks when compared to normal hearing listeners. This performance gap could be attributed to the high stimulation rates used for speech representation in clinical processors. Prior work has shown that spatial cues, such as interaural time differences (ITDs), are best conveyed at low rates. Further, BiCI listeners are sensitive to ITDs with a mixture of high and low rates. However, it remains unclear whether mixed-rate stimuli are perceived as unitary percepts and spatially mapped to intracranial locations. Here, electrical pulse trains were presented on five, interaurally pitch-matched electrode pairs using research processors, at either uniformly high rates, low rates, or mixed rates. Eight post-lingually deafened adults were tested on perceived intracranial lateralization of ITDs ranging from 50 to 1600 μs. Extent of lateralization depended on the location of low-rate stimulation along the electrode array: greatest in the low- and mixed-rate configurations, and smallest in the high-rate configuration. All but one listener perceived a unitary auditory object. These findings suggest that a mixed-rate processing strategy can result in good lateralization and convey a unitary auditory object with ITDs.

Implantable AC-driven CMOS chip for distributed multichip retinal prosthesis capable of high-rate stimulation

Implantable retinal prostheses are stimulation devices used to compensate for the light sensitivity loss of retinal cells. In this study, we propose and demonstrate a novel method to significantly reduce the setting time for the stimulation conditions of a retinal prosthesis chip capable of multi-electrode stimulation. The efficiency of the control method is increased while using only two wires, as in our previous work. The chip comprises an 8 bit ID and 7 electrodes, and the stimulation current value can be set from 50 to 1550 μA. The fabricated chip requires only 32 pulses to set the stimulation conditions, which is approximately 1/65 of that of our previous chip. Furthermore, it is equipped with a complementary metal–oxide–semiconductor rectifier to enable it to be driven by a rectangular AC power supply. The effectiveness of the chip is demonstrated by setting the stimulation conditions at approximately 18 μs per electrode at a clock frequency of 2.3 MHz.

On the Effect of High Stimulation Rates on Temporal Loudness Integration in Cochlear Implant Users.

Long stimuli have lower detection thresholds or are perceived louder than short stimuli with the same intensity, an effect known as temporal loudness integration (TLI). In electric hearing, TLI for pulse trains with a fixed rate but varying number of pulses, i.e. stimulus duration, has mainly been investigated at clinically used stimulation rates. To study the effect of an overall effective stimulation rate at 100% channel crosstalk, we investigated TLI with (a) a clinically used single-channel stimulation rate of 1,500 pps and (b) a high stimulation rate of 18,000 pps, both for an apical and a basal electrode. Thresholds (THR), a line of equal loudness (BAL), and maximum acceptable levels (MALs) were measured in 10 MED-EL cochlear implant users. Stimulus durations varied from a single pulse to 300 ms long pulse trains. At 18,000 pps, the dynamic range (DR) increased by dB for the 300 ms pulse train. Amplitudes at THR, BAL, and MAL decreased monotonically with increasing stimulus duration. The decline was fitted with high accuracy with a power law function (). Threshold slopes were and dB per doubling of duration for the low and high rate, respectively, and were shallower than for acoustic hearing. The electrode location did not affect the amplitudes or slopes of the TLI curves. THR, BAL, and MAL were always lower for the higher rate and the DR was larger at the higher rate at all measured durations.

Temporal frequency dependence of the polarity inversion between upper and lower visual field in the pattern-onset steady-state visual evoked potential

PurposeAccording to the cruciform model, the upper and lower halves of the visual field representation in the primary visual cortex are located mainly on the opposite sides of the calcarine sulcus. Such a shape would have consequences for the surface-recorded visual evoked potential (VEP), as V1 responses to stimulation of the upper and lower hemifield manifest with opposite polarity (i.e., polarity inversion). However, the steady-state VEP results from a complex superposition of response components from different cortical sources, which can obscure the inversion of polarity. The present study assesses the issue for different stimulation frequencies which result in different patterns of superposition in the steady-state response.MethodsSequences of brief pattern-onset stimuli were presented at different stimulation rates ranging from 2 Hz (transient VEP) to 13 Hz (steady-state VEP). The upper and lower hemifields were tested separately and simultaneously. The data were assessed both in the time domain and in the frequency domain.ResultsComparing the responses to the stimulation of upper and lower hemifield, polarity inversion was present within a limited time interval following individual stimulus onsets. With increasing frequency, this resulted in an approximate inversion of the full steady-state response and consequently in a phase shift of approximately 180° in the time-domain response. Polarity inversion was more prominent at electrode Pz, also for transient responses. Our data also demonstrated that the sum of the hemifield responses is a good approximation of the full-field response.ConclusionWhile the basic phenomenon of polarity inversion occurs irrespective of the stimulus frequency, its relative impact on the steady-state response as a whole is the largest for high stimulation rates. We propose that this is because longer-lasting response components from other visual areas are not well represented in the steady-state VEP at higher frequencies.

TH-298. High stimulation rate improves somatosensory evoked potentials for short recording duration

TH-298. High stimulation rate improves somatosensory evoked potentials for short recording duration

A Diagnostic Dilemma: Normal Repetitive Nerve Stimulation in Lambert-Eaton Myasthenic Syndrome

It is important for the diagnosis of Lambert-Eaton myasthenic syndrome (LEMS) to confirm the incremental response at high-rate stimulation or after brief exercise in the repetitive nerve stimulation (RNS) test. Therefore, it may be difficult to diagnose LEMS if the RNS test is normal initially. We report a patient with LEMS whose diagnosis was delayed due to normal RNS findings. We believe that anti-P/Q-type voltage-gated calcium channel antibody testing is crucial in the diagnosis of LEMS.

Underutilization of advanced presurgical studies and high rates of vagus nerve stimulation for drug-resistant epilepsy: a single-center experience and recommendations.

Epilepsy surgery continues to be profoundly underutilized despite its safety and effectiveness. We sought to investigate factors that may contribute to this phenomenon, with a particular focus on the antecedent underutilization of appropriate preoperative studies. We reviewed patient data from a pediatric epilepsy clinic over an 18-month period. Patients with drug-resistant epilepsy (DRE) were categorized according to brain magnetic resonance imaging (MRI) findings (lesional, MRI-negative, or multifocal abnormalities) and type of epilepsy diagnosis based on semiology and electroencephalography (EEG) (focal or generalized). We then analyzed the rates of diagnostic test utilization, surgical referral, and subsequent epilepsy surgery as well as vagus nerve stimulation (VNS). Of the 249 patients with a diagnosis of epilepsy, 138 (55.4%) were found to have DRE. Excluding the 10 patients with DRE who did not undergo MRI, 76 patients (59.4%) were found to be MRI-negative (non-lesional epilepsy), 37 patients (28.9%) were found to have multifocal abnormalities, and 15 patients (11.7%) were found to have a single epileptogenic lesion on MRI (lesional epilepsy). Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) were each completed in nine patients (7.0%) and magnetoencephalography (MEG) in four patients (3.1%). Despite the low utilization rate of adjunctive studies, over half (56.3%) ultimately underwent VNS alone, and 8.6% ultimately underwent definitive intracranial resection or disconnection surgery. The underutilization of appropriate non-invasive, presurgical testing in patients with focal DRE may in part explain the continued underutilization of definitive, resective/disconnective surgery. For patients without access to a high-volume, multidisciplinary surgical epilepsy center, adjunctive presurgical studies [e.g., PET, SPECT, MEG, electrical source imaging (ESI), EEG-functional magnetic resonance imaging (fMRI)], even when available, are rarely ordered, and this may contribute to excessive rates of VNS in lieu of definitive intracranial surgery.

Neuromuscular junction disorders beyond myasthenia gravis.

To give an overview of the recent data on three autoimmune neuromuscular junction disorders with the recent Food Drug Administration (FDA) approval of amifampridine [3,4-Diaminopyridine (3,4-DAP) and 3,4-diaminopyridine phosphate (3,4-DAPP) for the treatment of Lambert-Eaton myasthenic syndrome (LEMS). In LEMS, the most important recent development is the introduction of FDA approved amifampridine for the symptomatic treatment. Randomized controlled studies showed an extremely effective improvement with amifampridine with daily dose of ≤ 80 mg with minimal side reactions. The next important development is in the electrodiagnostic criteria. Now 10 s exercise and an incremental response ≥ 60% either after 10 s exercise or at the high-rate stimulation in the repetitive nerve stimulation test are recommended as the standard tests.In 2016, myasthenia-gravis Lambert-Eaton overlap syndrome (MLOS) was coined as new syndrome for patients with myasthenia gravis and LEMS combined symptoms in same patients.In Isaacs syndrome, voltage gated calcium channel antibody order is no longer recommended because of low specificity for immunotherapy responsive disorders. Instead, ' leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated like-2 (CASPR2) autoantibody tests' are recommended. In LEMS, amifampridine (3,4 DAP and 3,4-DAPP) is approved by the FDA as an effective symptomatic treatment. MLOS is coined as new syndrome recently. In Isaacs syndrome, LGI1 and CASPR2 antibody tests are recommended.

Beat-by-Beat Cardiomyocyte T-Tubule Deformation Drives Tubular Content Exchange.

The sarcolemma of cardiomyocytes contains many proteins that are essential for electromechanical function in general, and excitation-contraction coupling in particular. The distribution of these proteins is nonuniform between the bulk sarcolemmal surface and membrane invaginations known as transverse tubules (TT). TT form an intricate network of fluid-filled conduits that support electromechanical synchronicity within cardiomyocytes. Although continuous with the extracellular space, the narrow lumen and the tortuous structure of TT can form domains of restricted diffusion. As a result of unequal ion fluxes across cell surface and TT membranes, limited diffusion may generate ion gradients within TT, especially deep within the TT network and at high pacing rates. We postulate that there may be an advective component to TT content exchange, wherein cyclic deformation of TT during diastolic stretch and systolic shortening serves to mix TT luminal content and assists equilibration with bulk extracellular fluid. Using electron tomography, we explore the 3-dimensional nanostructure of TT in rabbit ventricular myocytes, preserved at different stages of the dynamic cycle of cell contraction and relaxation. We show that cellular deformation affects TT shape in a sarcomere length-dependent manner and on a beat-by-beat time-scale. Using fluorescence recovery after photobleaching microscopy, we show that apparent speed of diffusion is affected by the mechanical state of cardiomyocytes, and that cyclic contractile activity of cardiomyocytes accelerates TT diffusion dynamics. Our data confirm the existence of an advective component to TT content exchange. This points toward a novel mechanism of cardiac autoregulation, whereby the previously implied increased propensity for TT luminal concentration imbalances at high electrical stimulation rates would be countered by elevated advection-assisted diffusion at high mechanical beating rates. The relevance of this mechanism in health and during pathological remodeling (eg, cardiac hypertrophy or failure) forms an exciting target for further research.

Differential Responses to High-Frequency Electrical Stimulation in Brisk-Transient and Delta Retinal Ganglion Cells.

Retinal microprostheses strive to evoke a sense of vision in individuals blinded by outer retinal degenerative diseases, by electrically stimulating the surviving retina. It is widely suspected that a stimulation strategy that can selectively activate different retinal ganglion cell types will improve the quality of evoked phosphenes. Previous efforts towards this goal demonstrated the potential for selective ON and OFF brisk-transient cell activation using high-rate (2000 pulses per second, PPS) stimulation. Here, we build upon this earlier work by testing an additional rate of stimulation and additional cell populations. We find considerable variability in responses both within and across individual cell types, but show that the sensitivity of a ganglion cell to repetitive stimulation is highly correlated to its single-pulse threshold. Consistent with this, we found thresholds for both stimuli to be correlated to soma size, and thus likely mediated by the properties of the axon initial segment. The ultimate efficacy of high-rate stimulation will likely depend on several factors, chief among which are (a) the residual ganglion types, and (b) the stimulation frequency.

Forward masking patterns by low and high-rate stimulation in cochlear implant users: Differences in masking effectiveness and spread of neural excitation

The goal of the present study was to compare forward masking patterns by stimulation of low and high rates in cochlear implant users. Postlingually deafened Cochlear Nucleus® device users participated in the study. In experiment 1, two maskers of different rates (250 and 1000 pulses per second) were set at levels that produced equal masking for a probe presented at the same electrode as the maskers. This aligned the two masking functions at the on-site probe location. Then their forward masking patterns for the far probes were compared. Results showed that slope of the masked probe-threshold decay as a function of probe-masker separation was steeper for the high-rate than the low-rate masker. A linear model indicated that this difference in spread of neural excitation (SOE) was accounted for by two factors that were not correlated with each other. One factor was that the low-rate masker required a considerably higher current level to be equally effective in masking as the high-rate masker. The second factor was the effect of stimulation rate on loudness, i.e., integration of multiple pulses. This was consistent with our hypothesis that if an increase in stimulation rate does not result in an increased total neural response, then it is unlikely that the change in rate would change spatial distribution of the neural activity. Interestingly, the difference in masking effectiveness of the maskers predicted subjects’ speech recognition. Poorer performers were those who showed more comparable masking effects by maskers of different rates. The difference in the masking effectiveness may indirectly measure the auditory neurons’ excitability, which predicts speech recognition. In experiment 2, SOE of the high-rate and low-rate maskers were compared at a level that is clinically relevant, i.e., equal loudness. At equal loudness, high-rate stimulation not only produced an overall greater amount of forward masking, but also a shallower decay of masking with probe-masker separation (wider SOE), compared to low rate. The difference in SOE was the opposite to the findings from experiment 1. Whether the maskers were calibrated for equal masking or loudness, the absolute current level was always higher for the low-rate masker, which suggests that the SOE patterns cannot be explained by current spread alone. The fact that high-rate stimulation produced greater masking and wider SOE at equal loudness may explain why using high stimulation rates has not produced consistent benefits for speech recognition, and why lowering stimulation rate from the manufacturer’s default sometimes results in improved speech recognition for subjects.

Testing of phytotoxicity of mining waste to determine the direction of future development

Energy industry and coal mining produce large amounts of mining waste. The material is accumulated on dumps and heaps which alter the landscape appearance. As the material is waste from mining, there are concerns from possible environmental contamination. On the other hand, some scientific publications mention favorable properties of this material and claim that it can be possibly used for example in land reclamation. This research is focused on the testing of phytotoxicity of samples collected from mining waste heaps. The pH values of tested samples ranged from 7.00 to 8.67. In the phytotoxicity tests, vital seeds of plants Sinapis alba. L., Hordeum vulgare L., and Cannabis sativa L. were used. The tests did not exhibit high phytotoxicity. Contrariwise, many results showed a high rate of growth stimulation (nearly 80%). Average values (median) of growth inhibition observed in individual samples for all three plant species in the share of 100% (with no addition of OECD soil) ranged from −13.96% to −33.73%. The obtained results can confirm the positive properties of mining waste in terms of phytotoxicity, resp. the experiments did not confirm the phytotoxic effects on the tested plants. Mining waste/material could have a positive effect on plants and thanks to its properties it could be used e.g., in land reclamation.

ABR findings in musicians with normal audiogram and otoacoustic emissions: evidence of cochlear synaptopathy?

Purpose: Although findings in human studies trying to identify signs of cochlear synaptopathy (CS) are still controversial, several methodological restrictions exist, including inconsistencies in participants profiles, definition of study groups and inclusion criteria, diverse electrophysiological measurements settings and noise exposure history metrics and participants’ age range, which question the reliability of conclusions.Method: Two groups of individuals aged 18–41 participated in this study. The first group consisted of 24 musicians with well documented occupational noise exposure and the second one of 24 healthy controls. Groups were matched for age and gender. Inclusion criteria were normal and symmetrical pure tone audiometry and extended high frequency audiometry thresholds, as well as present and normal TEOAEs and DPOAEs. Outcome measures included SNR scores of speech in bubble audiometry and auditory brainstem response waves I, II and V amplitudes and latencies at three different presentation rates: 11, 33 and 44 clicks/s.Results: Wave I amplitude in musicians was significantly lower compared to controls at all presentation rates (11/s: p .043, 33/s: p .007 and 44/s: p .014). There was also a significantly greater reduction in wave I amplitude as well as in wave Ι/V amplitude ratio in the 33/s stimulus presentation in musicians compared to the control group (p .02 and .01, respectively). Finally, lower wave I amplitudes were found in musicians with auditory symptoms compared to musicians without symptoms at the 44/s presentation rate (p = .002).Conclusion: The ABR findings in our study are suggestive of possible increased prevalence of CS in musicians. Wave I amplitude was lower in Musicians group compared to matched controls. Furthermore, there was a greater reduction of wave I amplitude and wave Ι/V amplitude ratio at higher stimulation rates, which would support their use in CS studies.

Increased Vulnerability to Atrial Fibrillation Is Associated With Increased Susceptibility to Alternans in Old Sheep.

BackgroundAtrial fibrillation (AF) is common in the elderly, but rare in the young; however, the changes that occur with age that promote AF are not fully understood. Action potential (AP) alternans may be involved in the initiation of AF. Using a translationally relevant model, we investigated whether age‐associated atrial vulnerability to AF was associated with susceptibility to AP alternans.Methods and Results AF was induced in conscious young and old sheep using 50 Hz burst pacing. Old sheep were more vulnerable to AF. Monophasic and cellular APs were recorded from the right atrium in vivo and from myocytes isolated from the left and right atrial appendages. AP alternans occurred at lower stimulation frequencies in old sheep than young in vivo (old, 3.0±0.1 Hz; young, 3.3±0.1 Hz; P<0.05) and in isolated myocytes (old, 1.6±0.1 Hz; young, 2.0±0.1 Hz; P<0.05). Simultaneous recordings of [Ca2+]i and membrane potential in myocytes showed that alternans of APs and [Ca2+]i often occurred together. However, at low stimulation rates [Ca2+]i alternans could occur without AP alternans, whereas at high stimulation rates AP alternans could still be observed despite disabling Ca2+ cycling using thapsigargin.ConclusionsWe have shown, for the first time in a large mammalian model, that aging is associated with increased duration of AF and susceptibility to AP alternans. We suggest that instabilities in Ca2+ handling initiate alternans at low stimulation rates, but that AP restitution alone can sustain alternans at higher rates.

Case 261.

History A 29-year-old woman presented with a 6-month history of progressive general fatigue, fluctuating limb weakness, and difficulty climbing stairs. She initially experienced occasional episodes of transient diplopia that developed while reading in the evening. She subsequently started to experience dry eyes and mouth, difficulty chewing, and mild dysphagia that worsened throughout the day. Her medical history included hypothyroidism from Hashimoto thyroiditis and pneumonia with left pleural effusion. She had no smoking history, and her body mass index was normal (23.8 kg/m2). No medication use was reported at admission. Physical examination revealed mild bilateral ptosis, reduced muscle tone and strength that worsened in proximal leg muscles, and decreased deep tendon reflexes. An edrophonium test revealed improvement in muscle strength and eyelid ptosis. Repetitive nerve stimulation revealed low amplitude of compound muscle action potential at rest (0.21 mV), with a marked increase (700%; normal increase, <60%) at high-rate stimulation (50 Hz). Laboratory work-up was unremarkable except for detection of acetylcholine receptor antibodies in the serum (21.30 nmol/L) and P/Q-type voltage-gated calcium channel antibodies (220 pmol/L). Recent MRI of the brain and spine at an outside hospital showed no abnormal findings. At admission, the patient underwent CT of the chest, abdomen, and pelvis ( Fig 1 ) followed by thoracic MRI ( Figs 2 , 3 ) to further evaluate CT findings. [Figure: see text][Figure: see text][Figure: see text][Figure: see text][Figure: see text][Figure: see text][Figure: see text][Figure: see text].

Examination of Prosody and Timbre Perception in Adults With Cochlear Implants Comparing Different Fine Structure Coding Strategies.

This study aimed to investigate whether adults with cochlear implants benefit from a change of fine structure (FS) coding strategies regarding the discrimination of prosodic speech cues, timbre cues, and the identification of natural instruments. The FS processing (FSP) coding strategy was compared to 2 settings of the FS4 strategy. A longitudinal crossover, double-blinded study was conducted. This study consisted of 2 parts, with 14 participants in the first part and 12 participants in the second part. Each part lasted 3 months, in which participants were alternately fitted with either the established FSP strategy or 1 of the 2 newly developed FS4 settings. Participants had to complete an intonation identification test; a timbre discrimination test in which 1 of 2 isolated cues changed, either the spectral centroid or the spectral irregularity; and an instrument identification test. A significant effect was seen in the discrimination of spectral irregularity with 1 of the 2 FS4 settings. The improvement was seen in the FS4 setting in which the upper envelope channels had a low stimulation rate. This improvement was not seen with the FS4 setting that had a higher stimulation rate on the envelope channels. In general, the FSP strategy and the 2 settings of the FS4 strategy provided similar levels in the perception of prosody and timbre cues, as well as in the identification of instruments.

Mixed stimulation rates to improve sensitivity of interaural timing differences in bilateral cochlear implant listeners.

Normal hearing listeners extract small interaural time differences (ITDs) and interaural level differences (ILDs) to locate sounds and segregate targets from noise. Bilateral cochlear implant listeners show poor sensitivity to ITDs when using clinical processors. This is because common clinical stimulation approaches use high rates [∼1000 pulses per-second (pps)] for each electrode in order to provide good speech representation, but sensitivity to ITDs is best at low rates of stimulation (∼100-300 pps). Mixing rates of stimulation across the array is a potential solution. Here, ITD sensitivity for a number of mixed-rate configurations that were designed to preserve speech envelope cues using high-rate stimulation and spatial hearing using low rate stimulation was examined. Results showed that ITD sensitivity in mixed-rate configurations when only one low rate electrode was included generally yielded ITD thresholds comparable to a configuration with low rates only. Low rate stimulation at basal or middle regions on the electrode array yielded the best sensitivity to ITDs. This work provides critical evidence that supports the use of mixed-rate strategies for improving ITD sensitivity in bilateral cochlear implant users.