Impact of endolymphatic hydrops on the function of the horizontal canal during caloric stimulation in Ménière's disease.

PURPOSE: When a dizzy patient with episodic vertigo has an abnormal caloric and a normal video head impulse test (vHIT), this caloric-vHIT dissociation provides vital information for a diagnosis of Ménière's disease (MD). Endolymphatic hydrops (EH), a histological marker of MD, is hypothesized to be involved in the caloric-vHIT dissociation in MD through hydropic duct distension of the horizontal semicircular canal (SC). This study was designed to determine the impact of EH on the function of horizontal SC during caloric stimulation. METHODS: Caloric test and vHIT were used to evaluate the function of horizontal SC every six months, annual magnetic resonance imaging (MRI) was used to evaluate the degree of EH size in the vestibule, and monthly vertigo and hearing evaluation was done for 12 months. EH shrinkage was defined as the size change of vestibular EH from significant to none. RESULTS: Among 133 MD patients evaluated for eligibility, 67 patients with caloric-vHIT dissociation entered the study. Fifteen participants had EH shrinkage (G-I), while 52 participants had no remarkable EH change (G-II). Average values (IQR) of the maximum slow phase velocity in G-I and G-II were 29.6 (13.0-34.0) and 25.9 (17.3-31.3), respectively, at baseline, 26.1 (9.0-38.0) and 23.6 (18.0-28.3) at 12 months. Two-factor repeated-measures ANOVA showed no significant differences between the groups (P = 0.486). The values of vestibulo-ocular reflex gain of the horizontal SC in G-I and G-II remained above 0.8 during the study period. CONCLUSIONS: EH detected by MRI shows limited correlation with caloric stimulation results.

Auditory steady state responses elicited by silent gaps embedded within a broadband noise.

BACKGROUND: Auditory temporal processing plays an important role in speech comprehension. Usually, behavioral tests that require subjects to detect silent gaps embedded within a continuous sound are used to assess the ability of auditory temporal processing in humans. To evaluate auditory temporal processing objectively, the present study aimed to measure the auditory steady state responses (ASSRs) elicited by silent gaps of different lengths embedded within a broadband noise. We presented a broadband noise with 40-Hz silent gaps of 3.125, 6.25, and 12.5 ms. RESULTS: The 40-Hz silent gaps of 3.125, 6.25, and 12.5 ms elicited clear ASSRs. Longer silent gaps elicited larger ASSR amplitudes and ASSR phases significantly differed between conditions. CONCLUSION: The 40 Hz gap-evoked ASSR contributes to our understanding of the neural mechanisms underlying auditory temporal processing and may lead to the development of objective measures of auditory temporal acuity in humans.

Manipulation of Auditory Inputs as Rehabilitation Therapy for Maladaptive Auditory Cortical Reorganization.

Neurophysiological and neuroimaging data suggest that the brains of not only children but also adults are reorganized based on sensory inputs and behaviors. Plastic changes in the brain are generally beneficial; however, maladaptive cortical reorganization in the auditory cortex may lead to hearing disorders such as tinnitus and hyperacusis. Recent studies attempted to noninvasively visualize pathological neural activity in the living human brain and reverse maladaptive cortical reorganization by the suitable manipulation of auditory inputs in order to alleviate detrimental auditory symptoms. The effects of the manipulation of auditory inputs on maladaptively reorganized brain were reviewed herein. The findings obtained indicate that rehabilitation therapy based on the manipulation of auditory inputs is an effective and safe approach for hearing disorders. The appropriate manipulation of sensory inputs guided by the visualization of pathological brain activities using recent neuroimaging techniques may contribute to the establishment of new clinical applications for affected individuals.

Broadened population-level frequency tuning in the auditory cortex of tinnitus patients.

Tinnitus is a phantom auditory perception without an external sound source and is one of the most common public health concerns that impair the quality of life of many individuals. However, its neural mechanisms remain unclear. We herein examined population-level frequency tuning in the auditory cortex of unilateral tinnitus patients with similar hearing levels in both ears using magnetoencephalography. We compared auditory-evoked neural activities elicited by a stimulation to the tinnitus and nontinnitus ears. Objective magnetoencephalographic data suggested that population-level frequency tuning corresponding to the tinnitus ear was significantly broader than that corresponding to the nontinnitus ear in the human auditory cortex. The results obtained support the hypothesis that pathological alterations in inhibitory neural networks play an important role in the perception of subjective tinnitus.NEW & NOTEWORTHY Although subjective tinnitus is one of the most common public health concerns that impair the quality of life of many individuals, no standard treatment or objective diagnostic method currently exists. We herein revealed that population-level frequency tuning was significantly broader in the tinnitus ear than in the nontinnitus ear. The results of the present study provide an insight into the development of an objective diagnostic method for subjective tinnitus.

Hemispheric asymmetry of auditory mismatch negativity elicited by spectral and temporal deviants: a magnetoencephalographic study.

One of the major challenges in human brain science is the functional hemispheric asymmetry of auditory processing. Behavioral and neurophysiological studies have demonstrated that speech processing is dominantly handled in the left hemisphere, whereas music processing dominantly occurs in the right. Using magnetoencephalography, we measured the auditory mismatch negativity elicited by band-pass filtered click-trains, which deviated from frequently presented standard sound signals in a spectral or temporal domain. The results showed that spectral and temporal deviants were dominantly processed in the right and left hemispheres, respectively. Hemispheric asymmetry was not limited to high-level cognitive processes, but also originated from the pre-attentive neural processing stage represented by mismatch negativity.

Hierarchical neural encoding of temporal regularity in the human auditory cortex.

Temporal regularity provides an important cue for the identification of natural sounds. Here, we measured auditory evoked cortical magnetic fields to investigate the neural processing of temporal regularity that cannot be tonotopically represented in the auditory periphery. Auditory steady state responses (ASSR) and sustained fields (SF) elicited by 40 Hz amplitude modulated periodic and non-periodic noises were analyzed. Periodic noises of 40-, 20-, and 5-Hz were prepared in the form of repeating frozen noises where the same noise segment appears at either each period (40 Hz), every second period (20 Hz), or every eighth period (5 Hz) of amplitude modulation. Compared to non-periodic white noises, periodic noises with repetition rates of 5-, 20-, and 40-Hz caused significantly increased SF amplitudes in both hemispheres. ASSR amplitudes were significantly enhanced for 20- and 40-Hz periodic noises in the right hemisphere while no enhancement was observed for periodic noises in the left hemisphere. The observed variation of the regularity effect between evoked response components and hemispheres may reflect the differences in the temporal integration window lengths adopted between ASSR and SF generators and also between the right and left auditory pathways.

History of silence affects auditory evoked fields regardless of intervening sounds: a magnetoencephalographic study.

The amplitudes of auditory evoked N1 m responses are known to depend on the length of the pre-stimulus silent interval. However, it remains unknown whether pre-penultimate silent intervals affect the auditory evoked responses elicited by test stimuli. In the present study, we investigated the N1 m responses elicited by a train of four successive tones with a silent interval of 1 s subsequent to that with a 0.25-, 0.5-, 2- or 4-s silent interval using magnetoencephalography. The results obtained demonstrated that the N1 m source strength decreased as the pre-penultimate silent interval became shorter. A history of silences had a significant impact on the N1 m source strength. Human brain activity that is modulated by silence history may play an important role in encoding a series of sound streams that include silences, such as speech and music.

Effect of background noise and memory load on listening effort of young adults with and without hearing loss.

OBJECTIVE: People with hearing loss often encounter difficulties in hearing under adverse conditions, such as listening in the presence of noise. Listening effort is an indicator used to assess listening difficulties in daily life. Although many studies on listening effort have been conducted in recent years, there is a notable gap in the exploration of how task load influences listening effort in young adults. This study compared the effects of background noise and memory load on task performance and subjective listening effort in young adults with and without hearing loss. METHODS: The study included a group of 8 adults with hearing loss (mean age: 24.1 ± 6.0 years) and a group of 16 individuals with normal hearing (mean age: 27.9 ± 4.9 years). A number memorizing task was conducted, involving two types of auditory digits (either three or seven digits) presented under multi-talker babble noise conditions of signal-to-noise ratio of -5 dB [SN -5 dB] or SN +5 dB. Participants determined whether the number presented in the encoding interval matched the one presented in the retrieval interval. Subsequently, they were asked to complete a questionnaire using a Visual Analog Scale (VAS) to assess their subjective listening effort. Percentage of correct responses, reaction times, and VAS ratings were compared between adults with and without hearing loss. RESULTS: Our results showed significant differences between the two groups in the percentage of correct responses and the reaction time under the SN -5 dB conditions, regardless of the memory load. Under the SN +5 dB conditions, a significant difference was found only in the percentage of correct responses for seven digits. In the normal hearing group, the percentage of correct responses and VAS ratings tended to decrease as the memory load increased, even under the same noise condition. Conversely, in the hearing loss group, a consistent trend could not be identified in the effects of noise and memory load on the percentage of correct responses and VAS ratings. CONCLUSION: These results suggest that in conditions of high noise load, young adults with hearing loss show a higher tendency for listening effort to be affected by other loads. We confirmed that for some participants with hearing loss, the task exceeded a certain level of difficulty in the SN -5 dB and seven digits condition, leading to a change in their motivation and strategy used. Future research should examine ways to control for participants' motivations.

Differential effects of temporal regularity on auditory-evoked response amplitude: a decrease in silence and increase in noise.

BACKGROUND: In daily life, we are continuously exposed to temporally regular and irregular sounds. Previous studies have demonstrated that the temporal regularity of sound sequences influences neural activity. However, it remains unresolved how temporal regularity affects neural activity in noisy environments, when attention of the listener is not focused on the sound input. METHODS: In the present study, using magnetoencephalography we investigated the effects of temporal regularity in sound signal sequencing (regular vs. irregular) in silent versus noisy environments during distracted listening. RESULTS: The results demonstrated that temporal regularity differentially affected the auditory-evoked N1m response depending on the background acoustic environment: the N1m amplitudes elicited by the temporally regular sounds were smaller in silence and larger in noise than those elicited by the temporally irregular sounds. CONCLUSIONS: Our results indicate that the human auditory system is able to involuntarily utilize temporal regularity in sound signals to modulate the neural activity in the auditory cortex in accordance with the surrounding acoustic environment.

Listening to tailor-made notched music reduces tinnitus loudness and tinnitus-related auditory cortex activity.

Maladaptive auditory cortex reorganization may contribute to the generation and maintenance of tinnitus. Because cortical organization can be modified by behavioral training, we attempted to reduce tinnitus loudness by exposing chronic tinnitus patients to self-chosen, enjoyable music, which was modified ("notched") to contain no energy in the frequency range surrounding the individual tinnitus frequency. After 12 months of regular listening, the target patient group (n = 8) showed significantly reduced subjective tinnitus loudness and concomitantly exhibited reduced evoked activity in auditory cortex areas corresponding to the tinnitus frequency compared to patients who had received an analogous placebo notched music treatment (n = 8). These findings indicate that tinnitus loudness can be significantly diminished by an enjoyable, low-cost, custom-tailored notched music treatment, potentially via reversing maladaptive auditory cortex reorganization.

Cognitive neural responses in the semantic comprehension of sound symbolic words and pseudowords.

Introduction: Sound symbolism is the phenomenon of sounds having non-arbitrary meaning, and it has been demonstrated that pseudowords with sound symbolic elements have similar meaning to lexical words. It is unclear how the impression given by the sound symbolic elements is semantically processed, in contrast to lexical words with definite meanings. In event-related potential (ERP) studies, phonological mapping negativity (PMN) and N400 are often used as measures of phonological and semantic processing, respectively. Therefore, in this study, we analyze PMN and N400 to clarify the differences between existing sound symbolic words (onomatopoeia or ideophones) and pseudowords in terms of semantic and phonological processing. Methods: An existing sound symbolic word and pseudowords were presented as an auditory stimulus in combination with a picture of an event, and PMN and N400 were measured while the subjects determined whether the sound stimuli and pictures match or mismatch. Results: In both the existing word and pseudoword tasks, the amplitude of PMN and N400 increased when the picture of an event and the speech sound did not match. Additionally, compared to the existing words, the pseudowords elicited a greater amplitude for PMN and N400. In addition, PMN latency was delayed in the mismatch condition relative to the match condition for both existing sound symbolic words and pseudowords. Discussion: We concluded that established sound symbolic words and sound symbolic pseudowords undergo similar semantic processing. This finding suggests that sound symbolism pseudowords are not judged on a simple impression level (e.g., spiky/round) or activated by other words with similar spellings (phonological structures) in the lexicon, but are judged on a similar contextual basis as actual words.

80 Hz auditory steady state responses (ASSR) elicited by silent gaps embedded within a broadband noise.

Introduction: Although auditory temporal processing plays an important role in speech comprehension, it cannot be measured by pure tone audiometry. Auditory temporal resolution is often assessed by behavioral gaps-in-noise test. To evaluate whether auditory temporal resolution could be objectively assessed, we measured the auditory steady state response (ASSR) elicited by silent gaps embedded within broadband noises at 80 Hz. Methods: We prepared six sound types as test stimuli. One was a continuous broadband noise without a silent interval as a control stimulus and the others were broadband noises with 80 Hz silent intervals of 0.4, 0.8, 1.6, 3.1, and 6.3 ms. Results: Significant ASSRs were recorded only when the gap length was longer than the behavioral thresholds and the ASSR amplitude increased as the gap length increased. Conclusion: Eighty Hertz gap-evoked ASSR appears to reflect the neural activity related to the auditory gap processing and may be used as an objective measure of auditory temporal resolution in humans.

Auditory sustained field responses to periodic noise.

BACKGROUND: Auditory sustained responses have been recently suggested to reflect neural processing of speech sounds in the auditory cortex. As periodic fluctuations below the pitch range are important for speech perception, it is necessary to investigate how low frequency periodic sounds are processed in the human auditory cortex. Auditory sustained responses have been shown to be sensitive to temporal regularity but the relationship between the amplitudes of auditory evoked sustained responses and the repetitive rates of auditory inputs remains elusive. As the temporal and spectral features of sounds enhance different components of sustained responses, previous studies with click trains and vowel stimuli presented diverging results. In order to investigate the effect of repetition rate on cortical responses, we analyzed the auditory sustained fields evoked by periodic and aperiodic noises using magnetoencephalography. RESULTS: Sustained fields were elicited by white noise and repeating frozen noise stimuli with repetition rates of 5-, 10-, 50-, 200- and 500 Hz. The sustained field amplitudes were significantly larger for all the periodic stimuli than for white noise. Although the sustained field amplitudes showed a rising and falling pattern within the repetition rate range, the response amplitudes to 5 Hz repetition rate were significantly larger than to 500 Hz. CONCLUSIONS: The enhanced sustained field responses to periodic noises show that cortical sensitivity to periodic sounds is maintained for a wide range of repetition rates. Persistence of periodicity sensitivity below the pitch range suggests that in addition to processing the fundamental frequency of voice, sustained field generators can also resolve low frequency temporal modulations in speech envelope.

Assessment of inner ear morphology and function in response to local positive pressure for Ménière's disease: a nonrandomized controlled trial.

Ménière's disease (MD) is an inner ear disorder in which the main pathological feature is endolymphatic hydrops (EH). Positive pressure therapy (PPT) using a portable device is now a second-line therapy for intractable MD when initial medical treatment fails. However, it remains unknown whether PPT causes the morphological and functional changes of inner ear in patients with active MD in accordance with reduction of vertigo attacks. In this nonrandomized controlled trial of 52 patients with MD, the volume of EH significantly decreased with reduction of vertigo attacks during 8 months of PPT combined with medications while the volume of that significantly increased with medications alone. There was no difference between Control group (n = 26) and PPT group (n = 26) regarding the vertigo control, however, PPT group achieved a significant functional improvement of vertical semicircular canals. The effect of volume reduction by PPT has been firstly demonstrated and the functional changes of all semicircular canals during PPT have been firstly examined. Morphological and functional changes in the inner ear by administrating local positive pressure are quite different from those caused by medications alone.Clinical trial registration: UMIN-CTR UMIN000041164 (registered on July 20, 2020).

Antivertiginous Effect of Caloric Stimulation for Acute Peripheral Vertigo.

OBJECTIVE: To clarify therapeutic effect of caloric stimulation for acute peripheral vertigo. PATIENTS: Two patients with acute peripheral vertigo accompanied by spontaneous nystagmus. INTERVENTIONS: Therapeutic. MAIN OUTCOMES AND MEASURES: Changes in the maximum slow phase velocity of spontaneous nystagmus and subjective vertigo. RESULTS: Reduction in the maximum slow phase velocity of spontaneous nystagmus and mitigation of subjective vertigo was observed in both patients. CONCLUSION: Caloric stimulation could be one potential option as a suppressant for acute peripheral vertigo.

Development of receptive vocabulary and verbal intelligence in Japanese children with unilateral hearing loss.

OBJECTIVE: In the past, it was believed that unilateral hearing loss has a minimal impact on the speech and language development in children. However, several studies have suggested that some school-age children with unilateral hearing loss have learning impairments in language. In the present study, we first examined whether preschool-age children with unilateral severe-to-profound hearing loss (UHL) have delays in the development of receptive vocabulary and verbal intelligence. In the follow-up study, we tested the children again after school admission. The objective of the present study was to reveal the development of receptive vocabulary and verbal intelligence from preschool to school years in children with UHL. METHODS: Fifteen Japanese preschool-age children with UHL and a control group of 20 age-matched Japanese children with bilateral normal hearing (NH), who were examined because articulation disorder was suspected, were enrolled in this study. The development of receptive vocabulary and verbal intelligence was evaluated using the Picture Vocabulary Test-Revised (PVT-R) and the Wechsler Intelligence Scale, respectively. The present retrospective study was approved by the Committee for Medical Ethics of Tokushima University Hospital (#3801). RESULTS: The scaled score (SS) of the PVT-R and verbal intelligence quotient (VIQ)/verbal comprehension index (VCI), but not performance intelligence quotient/perceptual reasoning index in children with UHL were significantly lower than those in the control children with NH at preschool-age. The SS of the PVT-R and VIQ/VCI in children with UHL significantly improved after school admission. In the subgroup analysis, the SS of the PVT-R in the lower receptive vocabulary group of children with UHL at preschool-age was significantly increased after school admission, but the SS in the normal and higher receptive vocabulary group of children with UHL at preschool-age were still around the standardized mean of SS after school admission. CONCLUSION: These findings suggest that the development of receptive vocabulary and verbal intelligence was delayed in preschool-age children with UHL and that most of them caught up to exhibit normal language ability after school admission.

Sound processing hierarchy within human auditory cortex.

Both attention and masking sounds can alter auditory neural processes and affect auditory signal perception. In the present study, we investigated the complex effects of auditory-focused attention and the signal-to-noise ratio of sound stimuli on three different auditory evoked field components (auditory steady-state response, N1m, and sustained field) by means of magnetoencephalography. The results indicate that the auditory steady-state response originating in primary auditory cortex reflects the signal-to-noise ratio of physical sound inputs (bottom-up process) rather than the listener's attentional state (top-down process), whereas the sustained field, originating in nonprimary auditory cortex, reflects the attentional state rather than the signal-to-noise ratio. The N1m was substantially influenced by both bottom-up and top-down neural processes. The differential sensitivity of the components to bottom-up and top-down neural processes, contingent on their level in the processing pathway, suggests a stream from bottom-up driven sensory neural processing to top-down driven auditory perception within human auditory cortex.

Neurophysiological Evaluation of Right-Ear Advantage During Dichotic Listening.

Right-ear advantage refers to the observation that when two different speech stimuli are simultaneously presented to both ears, listeners report stimuli more correctly from the right ear than the left. It is assumed to result from prominent projection along the auditory pathways to the contralateral hemisphere and the dominance of the left auditory cortex for the perception of speech elements. Our study aimed to investigate the role of attention in the right-ear advantage. We recorded magnetoencephalography data while participants listened to pairs of Japanese two-syllable words (namely, "/ta/ /ko/" or "/i/ /ka/"). The amplitudes of the stimuli were modulated at 35 Hz in one ear and 45 Hz in the other. Such frequency-tagging allowed the selective quantification of left and right auditory cortex responses to left and right ear stimuli. Behavioral tests confirmed the right-ear advantage, with higher accuracy for stimuli presented to the right ear than to the left. The amplitude of the auditory steady-state response was larger when attending to the stimuli compared to passive listening. We detected a correlation between the attention-related increase in the amplitude of the auditory steady-state response and the laterality index of behavioral accuracy. The right-ear advantage in the free-response dichotic listening was also found in neural activities in the left auditory cortex, suggesting that it was related to the allocation of attention to both ears.

Rupture-Like Shrinkage and Regrowth of Endolymphatic Hydrops in Ménière's Disease During Remission.

OBJECTIVE: To clarify pathophysiological characteristics of Ménière's disease during the remission phase. PATIENTS: Two Ménière's disease patients with different disease durations, whose endolymphatic hydrops was longitudinally observed using 3-T magnetic resonance imaging. INTERVENTIONS: Diagnostic. MAIN OUTCOMES AND MEASURES: Morphological changes of endolymphatic hydrops visualized using 3-T magnetic resonance imaging. RESULTS: Rupture-like shrinkage and regrowth of endolymphatic hydrops during the remission phase was observed in both patients. CONCLUSION: The remission phase with hearing improvement could be as important as vertigo attacks in Ménière's disease.

A new combined index of SUVmax of lymph node in PET / CT by a weighting coefficient plus its maximum minor axis in CECT to evaluate occult lymph node metastasis in clinical N0 patients with tongue cancer.

To predict occult nodal metastasis in clinical N0 patients with tongue cancer, we developed combined index (CI) : SUVmax of the largest lymph node in PET / CT by weighting coefficient plus its maximum minor axis (< 10 mm) in contrast-enhanced CT (CECT). In this retrospective study, 57 clinical N0 patients with tongue cancer, who underwent elective supraomohyoid neck dissection at cervical levels of I-III were enrolled. The cutoff value of SUVmax of 2.0 obtained using receiver operating characteristic (ROC) analysis predicted the postoperative positive cervical levels containing metastatic lymph nodes from clinical N0 cervical levels in tongue cancer patients with a sensitivity of 54.5% and a specificity of 78.2%. The cutoff value of CI with weighting coefficient of 1.5 obtained using ROC analysis was 9.8 at the maximum area under the curve of 0.750. The cutoff value of 9.8 predicted the postoperative positive cervical levels containing metastatic lymph nodes from clinical N0 cervical levels in tongue cancer patients with a sensitivity of 68.2% and a specificity of 81.5%. These findings suggest that CI of functional PET / CT and morphological CECT components might improve the diagnostic performance of occult nodal metastasis to select clinical N0 patients with tongue cancer preferable for elective neck dissection. J. Med. Invest. 68 : 154-158, February, 2021.