Ipsilateral Ear Research Articles

Selectivity of Monaural Synaptic Inputs Underlying Binaural Auditory Information Integration in the Central Nucleus of Inferior Colliculus.

Neurons in the central nucleus of the inferior colliculus (ICC) receive ascending inputs from the ipsilateral and contralateral auditory pathway. However, the contributions of excitatory or inhibitory synaptic inputs evoked by ipsilateral and contralateral stimuli to auditory responses of ICC neurons remain unclear. Using in vivo whole-cell voltage-clamp recordings, we investigated excitatory and inhibitory synaptic currents in neurons of the ICC in response to binaural stimulation by performing an intensity-intensity scan. To systematically analyze the contribution of the ipsilateral and contralateral ear, the sound intensity was randomly delivered to each side from 0 dB sound pressure level (SPL) to 70 dB SPL. Although the synaptic responses were dominated by contralateral inputs at weak sound intensities, they could be increased (or decreased) by additional ipsilateral stimulation at higher intensities. Interestingly, the synaptic responses to contralateral acoustic inputs were not linearly superimposed with the ipsilateral ones. By contrast, the responses showed either a contralateral or ipsilateral profile, depending on which one was more dominant. This change occurred at a certain intensity “switch” point. Thus, the binaural auditory responses of the ICC neurons were not simply mediated by the summation of the inputs evoked by ipsilateral and contralateral stimulations. This suggested that the ICC might inherit the acoustic information integrated at the brainstem, causing the selectivity of monaural excitation and inhibition to underlie the neuronal binaural acoustic response.

Specific synaptic input strengths determine the computational properties of excitation-inhibition integration in a sound localization circuit.

During the computation of sound localization, neurons of the lateral superior olive (LSO) integrate synaptic excitation arising from the ipsilateral ear with inhibition from the contralateral ear. We characterized the functional connectivity of the inhibitory and excitatory inputs onto LSO neurons in terms of unitary synaptic strength and convergence. Unitary IPSCs can generate large conductances, although their strength varies over a 10-fold range in a given recording. By contrast, excitatory inputs are relatively weak. The conductance associated with IPSPs needs to be at least 2-fold stronger than the excitatory one to guarantee effective inhibition of action potential (AP) firing. Computational modelling showed that strong unitary inhibition ensures an appropriate slope and midpoint of the tuning curve of LSO neurons. Conversely, weak but numerous excitatory inputs filter out spontaneous AP firing from upstream auditory neurons. The lateral superior olive (LSO) is a binaural nucleus in the auditory brainstem in which excitation from the ipsilateral ear is integrated with inhibition from the contralateral ear. It is unknown whether the strength of the unitary inhibitory and excitatory inputs is adapted to allow for optimal tuning curves of LSO neuron action potential (AP) firing. Using electrical and optogenetic stimulation of afferent synapses, we found that the strength of unitary inhibitory inputs to a given LSO neuron can vary over a ∼10-fold range, follows a roughly log-normal distribution, and, on average, causes a large conductance (9nS). Conversely, unitary excitatory inputs, stimulated optogenetically under the bushy-cell specific promoter Math5, were numerous, and each caused a small conductance change (0.7nS). Approximately five to seven bushy cell inputs had to be active simultaneously to bring an LSO neuron to fire. In double stimulation experiments, the effective inhibition window caused by IPSPs was short (1-3ms) and its length depended on the inhibitory conductance; an ∼2-fold stronger inhibition than excitation was needed to suppress AP firing. Computational modelling suggests that few, but strong, unitary IPSPs create a tuning curve of LSO neuron firing with an appropriate slope and midpoint. Furthermore, weak but numerous excitatory inputs reduce the spontaneous AP firing that LSO neurons would otherwise inherit from their upstream auditory neurons. Thus, the specific connectivity and strength of unitary excitatory and inhibitory inputs to LSO neurons is optimized for the computations performed by these binaural neurons.

The effect of variation of reverberation parameters in contralateral versus ipsilateral ear signals on perceived externalization of a lateral sound source in a listening room.

It is well known that reverberation plays an important role in perceived externalization of three-dimensional audio over headphones. In the case of the externalization of a frontal sound source, the reverberation heard by both ears is equally important. Relatively little is known about the relative influence of reverberation at the contralateral versus the ipsilateral ear on perceived externalization of a lateral sound source. For a lateral sound source, the direct sound energy is much higher at the ipsilateral ear than at the contralateral ear due to the shadowing effect, which dominates at mid to high frequencies. The reverberant energy does not have a major difference between two ears. Therefore, the direct-to-reverberant energy ratio is much lower for the contralateral ear than for the ipsilateral ear. In addition, the frequency-to-frequency variability, which describes the frequency variability in the magnitude spectrum, is more pronounced in the contralateral ear than in the ipsilateral ear. The results of two listening experiments and the analysis of short-term binaural cues suggested that the reverberation at the contralateral ear has more influence on perceived externalization of a lateral sound source than that at the ipsilateral ear.

Electric-acoustic stimulation suppresses tinnitus in a subject with high-frequency single-sided deafness

Background: A suggested solution to suppress tinnitus is to restore the normal sensory input. This is based on the auditory deprivation hypothesis. It is known that hearing aids can provide sufficient activation of the auditory nervous system and reduce tinnitus in subjects with mild to moderate hearing loss and that cochlear implantation can reduce tinnitus in subjects with severe to profound hearing loss. This applies to subjects with single-sided deafness (SSD) or bilateral hearing loss.Aim: To investigate if electric-acoustic stimulation (EAS) can reduce severe tinnitus in a subject with residual hearing in the ipsilateral ear and contralateral normal hearing (high-frequency SSD) by restoring the auditory input.Methods: Tinnitus reduction was investigated for 1 year after implantation in a subject with high-frequency SSD, who uses EAS, and was compared to 11 subjects with a cochlear implant (CI) with SSD. The Visual Analogue Scale (VAS) and the Tinnitus Questionnaire (TQ) were administered pre-operatively and at 1, 3, 6, and 12 months after implantation.Results: Significant tinnitus reduction was observed 1 month after implantation on the VAS in the subjects with SSD using a CI. Tinnitus reduction was also observed in the subject with high-frequency SSD using EAS. A further decrease was observed 3 months after implantation. The TQ and VAS scores remained stable up to 1 year after implantation.Conclusion: A CI can significantly reduce ipsilateral severe tinnitus in a subject with SSD. Ipsilateral severe tinnitus can also be reduced using EAS in subjects with high-frequency SSD.

Click-Evoked Auditory Efferent Activity: Rate and Level Effects.

There currently are no standardized protocols to evaluate auditory efferent function in humans. Typical tests use broadband noise to activate the efferents, but only test the contralateral efferent pathway, risk activating the middle ear muscle reflex (MEMR), and are laborious for clinical use. In an attempt to develop a clinical test of bilateral auditory efferent function, we have designed a method that uses clicks to evoke efferent activity, obtain click-evoked otoacoustic emissions (CEOAEs), and monitor MEMR. This allows for near-simultaneous estimation of cochlear and efferent function. In the present study, we manipulated click level (60, 70, and 80dB peak-equivalent sound pressure level [peSPL]) and rate (40, 50, and 62.5Hz) to identify an optimal rate-level combination that evokes measurable efferent modulation of CEOAEs. Our findings (n = 58) demonstrate that almost all click levels and rates used caused significant inhibition of CEOAEs, with a significant interaction between level and rate effects. Predictably, bilateral activation produced greater inhibition compared to stimulating the efferents only in the ipsilateral or contralateral ear. In examining the click rate-level effects during bilateral activation in greater detail, we observed a 1-dB inhibition of CEOAE level for each 10-dB increase in click level, with rate held constant at 62.5Hz. Similarly, a 10-Hz increase in rate produced a 0.74-dB reduction in CEOAE level, with click level held constant at 80dB peSPL. The effect size (Cohen's d) was small for either monaural condition and medium for bilateral, faster-rate, and higher-level conditions. We were also able to reliably extract CEOAEs from efferent eliciting clicks. We conclude that clicks can indeed be profitably employed to simultaneously evaluate cochlear health using CEOAEs as well as their efferent modulation. Furthermore, using bilateral clicks allows the evaluation of both the crossed and uncrossed elements of the auditory efferent nervous system, while yielding larger, more discernible, inhibition of the CEOAEs relative to either ipsilateral or contralateral condition.

Precisely timed inhibition facilitates action potential firing for spatial coding in the auditory brainstem

The integration of excitatory and inhibitory synaptic inputs is fundamental to neuronal processing. In the mammalian auditory brainstem, neurons compare excitatory and inhibitory inputs from the ipsilateral and contralateral ear, respectively, for sound localization. However, the temporal precision and functional roles of inhibition in this integration process are unclear. Here, we demonstrate by in vivo recordings from the lateral superior olive (LSO) that inhibition controls spiking with microsecond precision throughout high frequency click trains. Depending on the relative timing of excitation and inhibition, neuronal spike probability is either suppressed or—unexpectedly—facilitated. In vitro conductance-clamp LSO recordings establish that a reduction in the voltage threshold for spike initiation due to a prior hyperpolarization results in post-inhibitory facilitation of otherwise sub-threshold synaptic events. Thus, microsecond-precise differences in the arrival of inhibition relative to excitation can facilitate spiking in the LSO, thereby promoting spatial sensitivity during the processing of faint sounds.

Electric-acoustic forward masking in cochlear implant users with ipsilateral residual hearing

In order to investigate the temporal mechanisms of the auditory system, psychophysical forward masking experiments were conducted in cochlear implant users who had preserved acoustic hearing in the ipsilateral ear. This unique electric-acoustic stimulation (EAS) population allowed the measurement of threshold recovery functions for acoustic or electric probes in the presence of electric or acoustic maskers, respectively. In the electric masking experiment, the forward masked threshold elevation of acoustic probes was measured as a function of the time interval after the offset of the electric masker, i.e. the masker-to-probe interval (MPI). In the acoustic masking experiment, the forward masked threshold elevation of electric probe stimuli was investigated under the influence of a preceding acoustic masker. Since electric pulse trains directly stimulate the auditory nerve, this novel experimental setup allowed the acoustic adaptation properties (attributed to the physiology of the hair cells) to be differentiated from the subsequent processing by more central mechanisms along the auditory pathway. For instance, forward electric masking patterns should result more from the auditory-nerve response to electrical stimulation, while forward acoustic masking patterns should primarily be the result of the recovery from adaptation at the hair-cell neuron interface.Electric masking showed prolonged threshold elevation of acoustic probes, which depended significantly on the masker-to-probe interval. Additionally, threshold elevation was significantly dependent on the similarity between acoustic stimulus frequency and electric place frequency, the electric-acoustic frequency difference (EAFD). Acoustic masking showed a reduced, but statistically significant effect of electric threshold elevation, which did not significantly depend on MPI. Lastly, acoustic masking showed longer decay times than electric masking and a reduced dependency on EAFD.In conclusion, the forward masking patterns observed for combined electric-acoustic stimulation provide further insights into the temporal mechanisms of the auditory system. For instance, the asymmetry in the amount of threshold elevation, the dependency on EAFD and the time constants for the recovery functions of acoustic and electric masking all indicate that there must be several processes with different latencies (e.g. neural adaptation, depression of spontaneous activity, efferent systems) that are involved in forward masking recovery functions.

Ultra Long-Term Audiometric Outcomes in the Treatment of Vestibular Schwannoma With the Middle Cranial Fossa Approach.

Define the long-term audiometric outcomes of vestibular schwannomas treated using the middle cranial fossa (MCF) approach. Retrospective records review. University-based tertiary referral center. Patients undergoing treatment of small vestibular schwannomas using the MCF approach. MCF exposure and treatment of small vestibular schwannomas. Demographic and audiometric variables were assessed. Thirteen subjects demonstrated audiometric data for review. The average time between surgery and the most recent audiometric testing was 14 years (range 10-18 yr). The mean baseline pure-tone average (PTA) was 36 dB HL and the most recent PTA was 59 dB HL in the operated ear. The mean baseline PTA was 16 dB HL and the most recent PTA was 37 dB HL in the nonoperated ear. The mean change from baseline to most recent follow-up was a threshold elevation of 22 and 19 dB HL in the operated and nonoperated ears, respectively. The mean baseline speech discrimination score (SDS) was 83% and the most recent SDS was 73% in the operated ear. The mean baseline SDS was 98% and the most recent SDS was 94% in the nonoperated ear. The mean changes from baseline to most recent follow-up were 10 and 0% SDS depression in the operated and nonoperated ears, respectively. The rates of changes in PTA and SDS were not statistically different between the operated and nonoperated ears. Surgically preserved hearing is maintained in the majority of patients more than 10 years following surgery. PTA and SDS changes were similar between the ipsilateral and contralateral ears.

Contralateral Interference Caused by Binaurally Presented Competing Speech in Adult Bilateral Cochlear-Implant Users

Bilateral cochlear implants (BI-CIs) are intended to improve sound localization and speech understanding in the presence of interfering sounds. For normal-hearing listeners, improved speech understanding in the presence of interfering sounds can be achieved with monaural head shadow and binaural unmasking. While some BI-CI listeners experience binaural unmasking under certain testing conditions, others appear to not. This study tested a group of BI-CI users with hearing histories that have been linked to poor binaural processing-early onset of deafness or long duration of deafness in just one ear. We predicted that these listeners would experience the opposite of binaural unmasking (i.e., contralateral interference) when trying to understand speech in the presence of a competing talker. Nine adult BI-CI users who were deafened early in life or had an asymmetric hearing history (e.g., a much longer duration of deafness in one ear) participated in this study. The coordinate response measure corpus was used to assess speech understanding for a male target talker in quiet or in the presence of one male competing talker. Experiment 1 measured binaural unmasking in a paradigm that provided no head-shadow component. The target was always presented monaurally, while the interferer was presented either monaurally or diotically. Experiment 2 measured spatial release from masking in a paradigm that included both a head-shadow component and possible binaural-unmasking component. Nonindividualized head-related transfer functions were used to simulate talker locations in the front or 90° to the left or right. In experiment 1, all nine listeners experienced contralateral interference (9 dB on average). Four listeners demonstrated roughly symmetric contralateral interference; five listeners experienced asymmetrical contralateral interference. In experiment 2, the listeners experienced only 1 dB of spatial release from masking on average; this small amount was possibly a result of the contralateral interference observed in experiment 1. The results were best explained by individual differences in speech understanding in quiet, which significantly correlated with the duration of deafness in the ipsilateral ear. Specifically, instances of asymmetrical contralateral interference could correspond to asymmetrical hearing histories. Bilateral cochlear implantation should provide a hearing benefit to the recipient. For the BI-CI listeners specifically recruited for this study, there seems to be a conflict with processing the auditory information across the two ears, which produced the opposite of the desired hearing benefit. This suggests that there may be a subset of potential BI-CI users for whom contralateral interference offsets much of the potential head-shadow benefit. If so, earlier implantation in the second implanted ear might have produced larger binaural benefits, which is important information for clinicians advising patients considering bilateral implantation.

Clinical features and response to botulinum toxin in primary and secondary hemifacial spasm.

Hemifacial spasm (HFS) is a hyperkinetic movement disorder of adults. The condition is usually primary, but may be secondary to facial nerve damage, and responds well to botulinum toxin therapy. To study the demographic and clinical features of primary and secondary HFS and assess its response to botulinum toxin therapy. A retrospective study of 40 patients of primary (33) and secondary (7) HFS, who attended our botulinum toxin clinic over the last 18 months, was conducted. We collected the data including the demographic profile, clinical features of primary and secondary HFS, severity measured by Likert scale, etiology, details of magnetic resonance imaging (MRI) of the brain, and a detailed account of the botulinum toxin injection. Thirty-three out of the 40 patients had primary HFS. The mean age at presentation was 48.4 ± 12.6 years whereas the mean duration of symptoms was 57.4 ± 39.3 (6-144) months. The onset of spasm on the upper part of face was seen in 31 patients (77.5%). An ipsilateral ear click was found in 17 (42.5%) patients. Mild spasms were seen in 18 patients, whereas 12 patients had severe spasms. The severity of spasm was lower in patients with secondary HFS. Five out of 22 magnetic resonance imaging (MRI) results showed an abnormality. The mean dosage of botulinum toxin was 21.86 ± 4.19 units in primary spasm and 17 ± 4.16 units in secondary spasm (P =0.018). The mean duration of response was 112.6 ± 55.7 days (median: 90 days; range: 30-240 days) in primary spasm and 135 ± 63.6 days (median: 135 days; range: 90-180 days) in secondary spasm (P = 0.29). Ipsilateral auditory clicks are fairly common in primary and secondary HFS. The patients with secondary HFS have a milder intensity of disease and they may have the onset of spasm from the upper part of face. Both primary as well as secondary HFS patients respond well to botulinum toxin injection; however, the adverse effects are more likely to occur in secondary HFS, and therefore, these patients require lower dosages of toxin.

The diagnostic significance of vestibular evoked myogenic potentials in different types of vertigo

To study the parameters of vestibular evoked myogenic potentials (VEMPs) in different types of vertigo. Seventy-seven patients, 35 men and 42 women, aged 43.7±12.5 years, with vestibular vertigo and unsteadiness were examined. The activity of the stemocleidomastoid muscle in response to auditory stimulation of the ipsilateral ear was recorded using surface electromyography. There were a trend towards the increase in the N2 latency, the significant reduction of the P1-N2 amplitude (p<0,005) on both sides and significant changes in the coefficient of asymmetry. Compared to healthy people, the P1 latency and asymmetry in P1 latency were significantly increased in patients with peripheral type of vertigo (p<0,005 and р=0,0007, respectively). There were no differences in the P1 latency and N2 in patients with unsteadiness. In patients with peripheral vertigo, central vertigo and unsteadiness, vestibular-spinal reflex was disturbed at different levels of vestibular analyzer.

A Masquerader

An elderly male presented to ENT outpatient department with left sided firm post aural swelling and ipsilateral ear discharge. Radiological evaluation revealed a vascular tumour with otomastoiditis. Patient was operated and excision was done via Fisch approach. Histopathology revealed a benign myoepithelioma of parotid.

Intracochlear Measurements of Interaural Time and Level Differences Conveyed by Bilateral Bone Conduction Systems.

Intracochlear pressures (PIC) and stapes velocity (Vstap) elicited by bilaterally placed bone-anchored hearing devices (BAHD) will be systematically modulated by imposed interaural time (ITD) and level differences (ILD), demonstrating the potential for users of bilateral BAHD to access these binaural cues. BAHD are traditionally implanted unilaterally under the assumption that transcranial cross-talk limits interaural differences. Recent studies have demonstrated improvements in binaural and spatial performance with bilateral BAHD; however, objective measures of binaural cues from bilateral BAHDs are lacking. Bone-conduction transducers were coupled to both mastoids of cadaveric specimens via implanted titanium abutments. PIC and Vstap were measured using intracochlear pressure probes and laser Doppler vibrometry, respectively, during stimulation with pure-tone stimuli of varied frequency (250-4000 Hz) under ipsilateral, contralateral, and bilateral ITD (-1 to 1 ms) and ILD (-20 to 20 dB) conditions. Bilateral stimulation produced constructive and destructive interference patterns that varied dramatically with ITD and stimulus frequency. Variation of ITD led to large variation of PIC and Vstap, with opposing effects in ipsilateral and contralateral ears expected to lead to "ITD to ILD conversion." Variation of ILD produced more straightforward (monotonic) variations of PIC and Vstap, with ipsilateral-favoring ILD producing higher PIC and Vstap than contralateral-favoring. Variation of ITDs and ILDs conveyed by BAHDs systematically modulated cochlear inputs. While transcranial cross-talk leads to complex interactions that depend on cue type and stimulus frequency, binaural disparities potentiate binaural benefit, providing a basis for improved sound localization and speech-in-noise perception.

Hearing Loss in Children With Craniofacial Microsomia.

To evaluate the association between craniofacial phenotype and hearing loss in children with craniofacial microsomia. Retrospective cohort study. Tertiary care children's hospital. Individuals with craniofacial microsomia. Ear-specific audiograms and standardized phenotypic classification of facial characteristics. A total of 79 participants were included in the study. The mean age was 9 years (range, 1 to 23 years) and approximately 60% were boys. Facial anomalies were bilateral in 39 participants and unilateral in 40 participants (24 right, 16 left). Microtia (hypoplasia of the ear) was the most common feature (94%), followed by mandibular hypoplasia (76%), soft tissue deficiency (60%), orbital hypoplasia or displacement (53%), and facial nerve palsy (32%). Sixty-five individuals had hearing loss (12 bilateral and 53 unilateral). Hearing loss was conductive in 73% of affected ears, mixed in 10%, sensorineural in 1%, and indeterminate in 16%. Hypoplasia of the ear or mandible was frequently associated with ipsilateral hearing loss, although contralateral hearing loss occurred in 8% of hemifaces. Hearing loss is strongly associated with malformations of the ipsilateral ear in craniofacial microsomia and is most commonly conductive. Hearing loss can occur contralaterally to the side with malformations in children with apparent hemifacial involvement. Children with craniofacial microsomia should receive early diagnostic hearing assessments.

Hemisphere specific EEG related to alternate nostril yoga breathing

BackgroundPreviously, forced unilateral nostril breathing was associated with ipsilateral, or contralateral cerebral hemisphere changes, or no change. Hence it was inconclusive. The present study was conducted on 13 normal healthy participants to determine the effects of alternate nostril yoga breathing on (a) cerebral hemisphere asymmetry, and (b) changes in the standard EEG bands.MethodsParticipants were randomly allocated to three sessions (a) alternate nostril yoga breathing (ANYB), (b) breath awareness and (c) quiet sitting, on separate days. EEG was recorded from bilaterally symmetrical sites (FP1, FP2, C3, C4, O1 and O2). All sites were referenced to the ipsilateral ear lobe.ResultsThere was no change in cerebral hemisphere symmetry. The relative power in the theta band was decreased during alternate nostril yoga breathing (ANYB) and the beta amplitude was lower after ANYB. During quiet sitting the relative power in the beta band increased, while the amplitude of the alpha band reduced.ConclusionThe results suggest that ANYB was associated with greater calmness, whereas quiet sitting without specific directions was associated with arousal. The results imply a possible use of ANYB for stress and anxiety reduction.

Progression of Unilateral Hearing Loss in Children With and Without Ipsilateral Cochlear Nerve Canal Stenosis: A Hazard Analysis.

To investigate the risk of hearing loss progression in each ear among children with unilateral hearing loss associated with ipsilateral bony cochlear nerve canal (BCNC) stenosis. Tertiary pediatric referral center. Children diagnosed with unilateral hearing loss who had undergone temporal bone computed tomography imaging and had at least 6 months of follow-up audiometric testing were identified from a prospective audiological database. Two pediatric radiologists blinded to affected ear evaluated imaging for temporal bone anomalies and measured bony cochlear canal width independently. All available audiograms were reviewed, and air conduction thresholds were documented. Progression of hearing loss was defined by a 10 dB increase in air conduction pure-tone average. One hundred twenty eight children met inclusion criteria. Of these, 54 (42%) had a temporal bone anomaly, and 22 (17%) had ipsilateral BCNC stenosis. At 12 months, rates of progression in the ipsilateral ear were as follows: 12% among those without a temporal bone anomaly, 13% among those with a temporal bone anomaly, and 17% among those with BCNC stenosis. Children with BCNC stenosis had a significantly greater risk of progression in their ipsilateral ear compared with children with no stenosis: hazard ratio (HR) 2.17, 95% confidence interval (CI) (1.01, 4.66), p value 0.046. When we compared children with BCNC stenosis to those with normal temporal bone imaging, we found that the children with stenosis had nearly two times greater risk estimate for progression, but this difference did not reach significance, HR 1.9, CI (0.8, 4.3), p = 0.1. No children with BCNC stenosis developed hearing loss in their contralateral year by 12 months of follow-up. Children with bony cochlear nerve canal stenosis may be at increased risk for progression in their ipsilateral ear. Audiometric and medical follow-up for these children should be considered.

Superiority in Robustness of Multifield Optimization Over Single-Field Optimization for Pencil-Beam Proton Therapy for Oropharynx Carcinoma: An Enhanced Robustness Analysis

To compare the difference in robustness of single-field optimized (SFO) and robust multifield optimized (rMFO) proton plans for oropharynx carcinoma patients by an improved robustness analysis. We generated rMFO proton plans for 11 patients with oropharynx carcinoma treated with SFO intensity modulated proton therapy with simultaneous integrated boost prescription.Doses from both planning approaches were compared for the initial plans and the worst cases from 20 optimization scenarios of setup errors and range uncertainties. Expected average dose distributions per range uncertainty were obtained by weighting the contributions from the respective scenarios with their expected setup error probability, and the spread of dose parameters for different range uncertainties were quantified. Using boundary dose distributions created from 56 combined setup error and range uncertainty scenarios and considering the vanishing influence of setup errors after 30 fractions, we approximated realistic worst-case values for the total treatment course. Error bar metrics derived from these boundary doses are reported for the clinical target volumes (CTVs) and organs at risk (OARs). The rMFO plans showed improved CTV coverage and homogeneity while simultaneously reducing the average mean dose to the constrictor muscles, larynx, and ipsilateral middle ear by 5.6Gy, 2.0Gy, and 3.9Gy, respectively. We observed slightly larger differences during robustness evaluation, as well as a significantly higher average brainstem maximum and ipsilateral parotid mean dose for SFO plans. For rMFO plans, the range uncertainty-related spread in OAR dose parameters and many error bar metrics were found to be superior. The SFO plans showed a lower global maximum dose for single-scenario worst cases and a slightly lower mean oral cavity dose throughout. An enhanced robustness analysis has been proposed and implemented into clinical systems. The benefit of better CTV coverage and OAR dose sparing in oropharynx carcinoma patients by rMFO compared with SFO proton plans is preserved in a robustness analysis with consideration of setup error and range uncertainty.

Assessment of Ipsilateral Efferent Effects in Human via ECochG.

Development of electrophysiological means to assess the medial olivocochlear (MOC) system in humans is important to further our understanding of the function of that system and for the refinement and validation of psychoacoustical and otoacoustic emission methods which are thought to probe the MOC. Based on measurements in anesthetized animals it has been hypothesized that the MOC-reflex (MOCR) can enhance the response to signals in noise, and several lines of evidence support such a role in humans. A difficulty in these studies is the isolation of efferent effects. Efferent activation can be triggered by acoustic stimulation of the contralateral or ipsilateral ear, but ipsilateral stimulation is thought to be more effective. However, ipsilateral stimulation complicates interpretation of effects since these sounds can affect the perception of other ipsilateral sounds by mechanisms not involving olivocochlear efferents. We assessed the ipsilaterally evoked MOCR in human using a transtympanic procedure to record mass-potentials from the cochlear promontory or the niche of the round window. Averaged compound action potential (CAP) responses to masked probe tones of 4 kHz with and without a precursor (designed to activate the MOCR but not the stapedius reflex) were extracted with a polarity alternating paradigm. The masker was either a simultaneous narrow band noise masker or a short (20-ms) tonal ON- or OFF-frequency forward masker. The subjects were screened for normal hearing (audiogram, tympanogram, threshold stapedius reflex) and psychoacoustically tested for the presence of a precursor effect. We observed a clear reduction of CAP amplitude by the precursor, for different masking conditions. Even without an MOCR, this is expected because the precursor will affect the response to subsequent stimuli via neural adaptation. To determine whether the precursor also activated the efferent system, we measured the CAP over a range of masker levels, with or without precursor, and for different types of masker. The results show CAP reduction consistent with the type of gain reduction caused by the MOCR. These results generally support psychoacoustical paradigms designed to probe the efferent system as indeed activating the MOCR system, but not all observations are consistent with this mechanism.

Microsecond interaural time differences of acoustic transients are decoded by inhibitory-excitatory interactions in neurons of the lateral superior olive

The lateral superior olive (LSO) in the auditory brainstem generates sensitivity to interaural level differences (ILD), an important cue for sound localization, by comparing excitatory (E) input from the ipsilateral ear with inhibitory (I) input from the contralateral ear. Large axosomatic synapses (e.g., calyx of Held) point to the importance of precise temporal processing, but that is not easily reconciled with ILD detection. We propose that the IE interaction allows detection of interaural time differences (ITD) of acoustic transients, to which humans are exquisitely sensitive. We obtained in vivo whole cell recordings of LSO and MSO neurons in the gerbil, while presenting monaural and binaural clicks. We found that ITD functions to clicks in the LSO are surprisingly steep, in contrast to MSO neurons, which are considered the main ITD detectors. Intracellular LSO recordings show EPSPs generated by the ipsilateral click and IPSPs by the contralateral click, where IPSPs often arrive earlier. Binaural spiking is maximally suppressed when the EPSP coincides with the falling slope rather than the peak of the IPSP. We conclude that LSO neurons are more sensitive to ITDs of transients than MSO neurons. This clarifies the importance of timing specializations in the LSO circuit.

Perceived amount of reverberation consistent with binaural summation model

Although perceived amount of reverberation (PAR) is known to be dependent on the physical amount of reverberation present at the two ears, the extent to which this information may be combined across the ears is not well understood. Previous work using virtual auditory space techniques has demonstrated that when physical reverberation is reduced in the ear nearest a sound source while the contralateral ear is left unchanged, listeners do not report a change in PAR. Reducing physical reverberation equally in both ears, however, elicits a decrease in PAR. To better understand this phenomenon, the present study examines how PAR is affected by three additional listening conditions: scaling the contralateral ear while leaving ipsilateral fixed, scaling the contralateral ear only with no ipsilateral signal (monaural), and scaling the ipsilateral ear only with no contralateral signal (monaural). This study also examines how PAR is affected by an increase in physical reverberation present at the ears in the two li...