Use of Some Relevant Parameters for Primary Prediction of Brain Activity in Idiopathic Tinnitus Based on a Machine Learning Application.

INTRODUCTION: Tinnitus is one of the most common complaints, distressing about 15-24% of the adult population. Because of its pathophysiology heterogeneity, no curable treatment has been attained yet. Even though a neuromodulation management technique based on the tinnitus network model is currently being developed, it has not yet worked because the most involved brain areas still remain unpredictable from the patient's individual clinical and functional profile. A remarkable correlation between tinnitus network activity and the subjective measures of tinnitus like perceived loudness and annoyance and functional handicap is well established. Therefore, this study aimed to develop software for predicting the involved brain areas in the tinnitus network based on the subjective characteristics and clinical profile of patients using a supervised machine-learning method. METHODS: The involved brain areas of 30 tinnitus patients ranging from 6 to 80 months in duration were recognized by using QEEG and sLORETA software. There was a correlation between subjective information and those areas of activities in all rhythms by which we wrote our software. RESULTS: For verification and validation of the software, we compared and analyzed the results with SPSS data and the receiver operating characteristic (ROC) curves. CONCLUSIONS: The findings of this study confirmed the effectiveness of the software in predicting the brain activity in tinnitus subjects; however, some other important parameters can be added to the model to strengthen its reliability and feasibility in clinical use.

Evaluation of the effects of various sound pressure levels on the level of serum aldosterone concentration in rats.

INTRODUCTION: Noise exposure may have anatomical, nonauditory, and auditory influences. Considering nonauditory impacts, noise exposure can cause alterations in the automatic nervous system, including increased pulse rates, heightened blood pressure, and abnormal secretion of hormones. The present study aimed at examining the effect of various sound pressure levels (SPLs) on the serum aldosterone level among rats. MATERIALS AND METHODS: A total of 45 adult male rats with an age range of 3 to 4 months and a weight of 200 ± 50 g were randomly divided into 15 groups of three. Three groups were considered as the control groups and the rest (i.e., 12 groups) as the case groups. Rats of the case groups were exposed to SPLs of 85, 95, and 105 dBA. White noise was used as the noise to which the rats were exposed. To measure the level of rats' serum aldosterone, 3 mL of each rat's sample blood was directly taken from the heart of anesthetized animals by using syringes. The taken blood samples were put in labeled test tubes that contained anticoagulant Ethylenediaminetetraacetic acid. In the laboratory, the level of aldosterone was assessed through Enzyme-linked immunosorbent assay protocol. The collected data were analyzed by the use of Statistical Package for Social Sciences (SPSS) version 18. RESULTS: The results revealed that there was no significant change in the level of rats' serum aldosterone as a result of exposure to SPLs of 65, 85, and 95 dBA. However, the level of serum aldosterone experienced a remarkable increase after exposure to the SPL of 105 dBA (P < 0.001). Thus, the SPL had a significant impact on the serum aldosterone level (P < 0.001). In contrast, the exposure time and the level of potassium in the used water did not have any measurable influence on the level of serum aldosterone (P = 0.25 and 0.39). CONCLUSION: The findings of this study demonstrated that serum aldosterone can be used as a biomarker in the face of sound exposure.

The effects of abnormality of cVEMP and oVEMP on rehabilitation outcomes in patients with idiopathic benign paroxysmal positional vertigo.

The presence of utricular and saccular dysfunction impairs quality of life (QoL) in patients. The aims of the present study were to examine the effect of repositioning maneuvers on QoL of patients with idiopathic benign paroxysmal positional vertigo (BPPV) and to describe the effect of cervical vestibular-evoked myogenic potential (cVEMP) or ocular VEMP (oVEMP) abnormalities on patient recovery after rehabilitation. Thirty idiopathic BPPV patients with/without otolith dysfunctions (n = 15, each group) were included in this clinical trial study. Otolith dysfunction was determined using oVEMP and cVEMP abnormalities. EcochG and caloric tests were performed to rule out other causes of secondary BPPV. The QoL in groups of patients with idiopathic BPPV was assessed using a Persian version of the dizziness handicap inventory (DHI-P) before and after treatment with Epley's maneuver. Pre-treatment results showed significant handicaps in both groups. DHI-P scores were higher in BPPV patients with otolith dysfunction (total, functional, emotional, physical score: 34.13, 11.20, 7.06, 15.86, respectively) than those in patients without otolith dysfunction (total, functional, emotional, physical score: 25.46, 7.86, 6.13, 11.46, respectively, P < 0.05). After treatment, DHI-P scores decreased in both groups. However, in the otolith dysfunction group, DHI-P scores (total, functional, emotional, physical score: 9.20, 3.33, 1.33, 4.53, respectively) were higher than those in patients without otolith dysfunction (total, functional, emotional, physical score: 4.13, 0.93, 1.06, 2.00, respectively). In BPPV patients with cVEMP or oVEMP abnormalities, QoL is more compromised in comparison with that in BPPV patients without these dysfunctions. Otolith dysfunction enhances the negative effects of BPPV on QoL.

Evaluation of the effects of occupational noise exposure on serum aldosterone and potassium among industrial workers.

The existing literature indicates that occupational exposure to noise may have adverse effects on workers' health. The aim of this study was to evaluate the possible effects of exposure to different sound pressure levels (SPLs) on serum aldosterone and potassium concentration among Iranian blue collar workers in Golgohar Mining and Industrial Company in Sirjan, Kerman Province, Iran. This case-control study was performed on 45 workers of Golgohar Mining and Industrial Company. The subjects consisted of 30 workers from manufacturing departments and 15 office employees of the mining company. The controls, mainly with administrative jobs were exposed to 72 dBA SPL. Cases, in two separate groups, were exposed to noise levels of 88 dBA and 103 dBA, respectively. Noise intensity was measured at the desired locations. Noise measurements were performed according to the International Organization for Standardization (ISO) 9612. To measure the serum aldosterone and potassium concentrations, a 5 mL blood sample was taken from each worker at the specified time intervals and aldosterone concentration was determined using enzyme-linked immunosorbent assay (ELISA) test in the laboratory. Repeated measurement and Spearman's correlation coefficient analysis were used with α = 0.05. Exposure to the different levels of sound pressure resulted in different aldosterone concentrations and meanwhile an increase in the SPL did not affect the concentration of potassium. From 10:00 AM to 10:30 AM, as SPL increased, aldosterone concentrations did not increase significantly but from 13:30 PM to 14:00 PM, raised SPL led to a significant increase in aldosterone concentration. However, there was no correlation between the concentration of potassium and different factors. This study indicated that increases in SPLs affect aldosterone concentration but at the same time do not have significant effects on serum potassium level.

Modeling signal-to-noise ratio of otoacoustic emissions in workers exposed to different industrial noise levels.

INTRODUCTION: Noise is considered as the most common cause of harmful physical effects in the workplace. A sound that is generated from within the inner ear is known as an otoacoustic emission (OAE). Distortion-product otoacoustic emissions (DPOAEs) assess evoked emission and hearing capacity. The aim of this study was to assess the signal-to-noise ratio in different frequencies and at different times of the shift work in workers exposed to various levels of noise. It was also aimed to provide a statistical model for signal-to-noise ratio (SNR) of OAEs in different frequencies based on the two variables of sound pressure level (SPL) and exposure time. MATERIALS AND METHODS: This case-control study was conducted on 45 workers during autumn 2014. The workers were divided into three groups based on the level of noise exposure. The SNR was measured in frequencies of 1000, 2000, 3000, 4000, and 6000 Hz in both ears, and in three different time intervals during the shift work. According to the inclusion criterion, SNR of 6 dB or greater was included in the study. The analysis was performed using repeated measurements of analysis of variance, spearman correlation coefficient, and paired samples t-test. RESULTS: The results showed that there was no statistically significant difference between the three exposed groups in terms of the mean values of SNR (P > 0.05). Only in signal pressure levels of 88 dBA with an interval time of 10:30-11:00 AM, there was a statistically significant difference between the right and left ears with the mean SNR values of 3000 frequency (P = 0.038). The SPL had a significant effect on the SNR in both the right and left ears (P = 0.023, P = 0.041). The effect of the duration of measurement on the SNR was statistically significant in both the right and left ears (P = 0.027, P < 0.001). CONCLUSION: The findings of this study demonstrated that after noise exposure during the shift, SNR of OAEs reduced from the beginning to the end of the shift.

Hearing aid or tinnitus masker: which one is the best treatment for blast-induced tinnitus? The results of a long-term study on 974 patients.

The aim of this longitudinal study was to explore whether a hearing aid or noise generator would be an effective audiological treatment for blast-induced chronic tinnitus. The amount of satisfaction from different hearing devices (hearing aid, noise generator, or both) during different time periods (1, 6, 12 and 24 months after fitting) was assessed. The 974 subjects enrolled in this study were Iran-Iraq war veterans, suffering from tinnitus for at least 2 years. About 84% of the subjects preferred just a hearing aid. Only 2.7% chose the noise generator, and the others preferred to use both devices. There were no significant differences between the hearing thresholds of the 3 groups. The satisfaction score for the hearing aid and combined devices increased by time but decreased for the noise generator. There was no correlation between the satisfaction score and parameters such as hearing thresholds, audiogram configuration and tinnitus pitch. We concluded that, compared with a noise generator, the most long-lasting treatment for blast-induced tinnitus is a hearing aid. The possible cause for such a performance is probably the recovery of the auditory function and neuroplasticity through the hearing aid.

Effects of stimulus presentation mode and subcortical laterality in speech-evoked auditory brainstem responses.

OBJECTIVE: Speech-evoked auditory brainstem responses (ABR) are sensitive to the manipulation of stimulus parameters, including how the stimulus is presented, i.e. monaurally or binaurally. Therefore, this parametric study was designed to compare the effect of binaural and monaural stimuli presentation on speech-evoked ABR features in the parallel assessment of subcortical asymmetry of speech stimuli acoustic elements. DESIGN: Electrophysiological responses to the speech syllable /da/ were recorded within three stimulus presentation modes. STUDY SAMPLE: Forty-eight normal hearing monolingual Persian speakers were included in the current study as volunteer cases. RESULTS: Shorter right ear latency was observed for peaks A and E, but the overall response timing was comparable within different stimulus presentation modes. Binaural stimulation generally led to larger response than monaural stimulation and affected the encoding of speech spectral elements. Moreover, no significant interpeak interval difference was observed in the sustained portion of responses. Response to the right and left ear stimulation was highly correlated, and a symmetrical pattern was observed between the two ears. CONCLUSIONS: The timing of speech-evoked responses is not related to the stimulus presentation mode; however, binaural stimulation produces more robust responses. Lateral asymmetry in the representation of speech elements was not considerable at the brainstem level.

Validity and reliability of the Persian version of the dizziness handicap inventory.

BACKGROUND: Dizziness as a common symptom affecting many aspects of the patient's life and it is hard to be fully evaluated. The dizziness handicap inventory (DHI) is a reliable self-perceived questionnaire in the evaluation of dizziness impacts. The purposes of this study are translation of the DHI to Persian language and measuring its psychometric properties, including face, content, discriminate and construct validity, internal consistency and reliability. MATERIALS AND METHODS: The English version of the DHI is translated to Persian language based on international quality of life assessment protocol. 97 participants, including 57 patients with mean age of 44.5-year-old and 40 healthy people (mean age of 34.1) participated in this study during the period of November 2012 to June 2013 in audiology clinics of Tehran University of medical sciences. RESULTS: The Persian version of DHI showed good face and content validity. The internal consistency of DHI-P was good, the Cronbach's alpha was 0.79, 0.82, 0.83, and 0.90 for total and emotional, physical and functional subscales; respectively, in reliability, There was a high correlation between test re-test scores (r = 0.90, P = 0.000). Intraclass correlation coefficient (ICC) was 0.96 for total score and 0.92, 0.92, and 0.96 for emotional, physical and functional subscales; respectively. CONCLUSION: Considering good psychometric properties, we suggest that DHI-P can use for evaluating the dizziness effects on quality of life in Persian population.

The Effect of Computer-Based Auditory Training on Speech-in-Noise Perception in Adults: a Systematic Review and Meta-Analysis.

To investigate the effectiveness of computer-based auditory training on speech-in-noise perception in adults. With no language restriction, 11 databases were searched from 1990 to 2020. We included any clinical trial studies with concurrent comparison groups that examined the effectiveness of computer-based auditory training programs in adults. The primary outcome was a speech in noise perception that was estimated using the "difference pretest-posttest-control" index (dppc2). The risk of bias was assessed using the Cochrane collaboration tool for assessing the risk of bias in randomized trials. The certainty of the evidence was investigated using the GRADE in two primary outcomes. Twenty three studies were included in two subgroups based on primary outcome: 12 studies with speech perception threshold and 11 studies with speech-in-noise test scores. Computer-based auditory training resulted in a speech in noise perception improvement (dppc2: -0.69, 95%CI: -1.11 to -0.26; I2 = 69.6%, p = 0.00) and (dppc2: 0.71, 95%CI: 0.38-1.03, I2: 17.8%, p = 0.27) respectively in both subgroups. 19 studies were judged to have a high risk of bias and 3 studies had a low risk of bias and the strength of the evidence was low in both primary outcomes. This finding indicates that computer-based auditory training can be a moderately effective intervention for speech-in-noise perception in adults. However, due to the low quality of primary studies and the low certainty of the evidence, the results are not yet definite. Prospero registration number: CRD42021233193. Supplementary Information: The online version contains supplementary material available at 10.1007/s12070-023-03920-0.

Comodulation Masking Release in Tinnitus Frequency and One Lower Octave of Tinnitus Frequency.

Inhibitory function is the basis of many perceptual and non-perceptual abilities in the auditory system. In people with tinnitus, decreased inhibitory function in the central auditory system has been proven. This disorder is caused by an increase in neural activity caused by an imbalance between stimulation and inhibition. The aim of this study was to evaluate and compare inhibitory function in persons who had tinnitus, at and one octave lower than the tinnitus frequency. Studies show that inhibition has very important role in comodulation masking release. According to inhibitory dysfunction in people with tinnitus, in this study we assessed comodulation masking release in tinnitus frequency and one lower octave. Participants were divided into two groups. Group 1 consisted of 7 individuals with unilateral tonal tinnitus at 4 kHz and group 2 included 7 individuals with unilateral tonal tinnitus at 6 kHz. Paired test, in each group separately, showed that the comodulation masking release and Across Frequency comodulation masking release differed significantly between tinnitus frequency and one octave lower in each group (p < 0.05). In fact, the disinhibition in the area around the frequency of the tinnitus seems to be greater than the tinnitus frequency area. It seems that the results of CMRs can be used in planning and managing the treatment of people with tinnitus (such as sound therapy, etc.).

The Effect of Combined Auditory Training on Concurrent Sound Segregation in Young old: A Single-Blinded Randomized Clinical Trial.

This study aimed to investigate the behavioral results of perceptual learning in young old using double-vowel discrimination tasks in combined auditory training programs. In a single-blind randomized clinical trial, 35 participants were randomly divided into three groups and received different auditory training programs for six sessions using the software. To compare the double-vowel discrimination score, CV in noise test, and reaction time to the first and second vowels pre- and post-intervention, an analysis of variance was conducted. The discrimination score in the double vowel task and CV in noise test improved after training with no significant difference between the groups. After auditory training, the lowest RT1 was observed in the first intervention group, whereas RT2 decreased only in the second intervention. The present study showed that combined auditory training programs are as effective as conventional auditory training programs in improving speech perception in the elderly. Modifications in the sensory cortex could be investigated using electrophysiological recordings, but this was not conducted because of the pandemic. Supplementary Information: The online version contains supplementary material available at 10.1007/s12070-023-03923-x.

Gap pre-pulse inhibition of the cortical auditory evoked potentials as a possible objective tinnitus assessment tool.

Objectives: The objective assessment tests overcome the variability of subjective methods. Cortical recordings with gap pre-pulse inhibition of the acoustic startle reflex stimulus have been used as objective tinnitus assessments in humans. This study aims to investigate this possible objective tinnitus test and compare gap-induced inhibition in different stimulus parameters and brain regions. Materials & Methods: Twenty People (18-50 years old) without hearing loss and tinnitus were included. The sound stimuli consisted of continuous background noise with a loud startle tone preceded by a silent gap (20 and 40 ms duration, 120 and 150 ms distance from the startle). The N1-P2 complex amplitude and topoplot maps were extracted in 27-channel cortical response recording after signal processing. Four brain regions of interest (ROI) of anterior-frontal, centro-frontal, right, and left temporal were investigated. Results: The results showed that the maximum inhibition occurred in a 40 ms gap duration and 150 ms distance in all 4 ROIs. In comparing ROIs, the centro-frontal and left temporal regions revealed the most inhibition (p<0.05). The decrease in the amplitude of the N1 and P2 in that region could also be traced in the 100 and 200 ms topoplots. Conclusion: Gap-induced inhibition was observed in all gap-embedded stimuli and all ROIs. However, the 40-150 mode and centro-frontal and left temporal regions had maximum inhibition in normal subjects. It provides a promising tool for objectively assessing tinnitus in humans with particular implications in children.

Regularity of background auditory scene and selective attention: A brain oscillatory study.

There are scarce data related to the facilitative effects of regularity encoding on auditory selective attention during every day listening conditions. Therefore, present study aimed to investigate how temporal and spectral regularities of background auditory stream affect auditory selective attention at both levels of brain neural oscillatory activities and involved cortical locations. EEG was recorded in healthy young adults listening to two concurrent auditory streams including background and foreground ones in three conditions differing for background auditory stream which was characterized by having spectral or temporal sound regularities and random structure. The neural sources of EEG bands during recognizing target sounds in the foreground stream were determined via standardized Low-Resolution brain Electromagnetic Tomography (sLORETA). Sound regularities of the background auditory stream had no significant effect on the EEG relative power during the task of selective attention. In all conditions, there was a significant increase in the relative power of EEG alpha and beta frequency bands. sLORETA localized significant increase of mentioned bands in the precuneus of parietal lobe; medial frontal gyrus of frontal lobe and insula of sub-lobar in temporal regularity, spectral regularity and random conditions respectively. These results revealed that although temporal and spectral acoustic regularities of competitor auditory stream had no facilitative effect on alpha-related brain processing during selective attention, different brain cortical locations were activated with the introduction of these regularities. This result might provide preliminary evidence for some degree of brain neural specialization in the processing of temporal and spectral regularities during auditory selective attention tasks.

Vestibular Assessment in Patients with Persistent Symptoms of Mild Traumatic Brain Injury.

Aim: The estimated worldwide incidence of TBI is 10 million cases per year. Dizziness and imbalance are two common symptoms in mild TBI (mTBI). In about 10-15% of TBI patients, these symptoms remain for a long time and may show no recovery. These persistent symptoms may relate to different factors including vestibular abnormalities. The aim of this study is a vestibular assessment of patients with persistent symptoms of mTBI by different tests including computerized dynamic posturography. Materials and Methods: 21 patients with mTBI evaluated in this study. Patients were civilians with persistent symptoms. TBI did cause by blunt force trauma (mainly from falling) in the past 6 months. They had normal neurologic and musculoskeletal assessments and no temporal bone fracture. Several auditory and vestibular evaluations were performed for each patient. They included: case history, otoscopy, pure tone and speech audiometry, tympanometry, vestibular bedside examination (spontaneous nystagmus, gaze, saccade, pursuit, Dix-Hallpike maneuver, side-lying maneuver, roll, and Romberg test), cervical Vestibular Myogenic Evoked Potential (c-VEMP), Computerized Dynamic Posturography (CDP) and Dizziness Handicap Inventory (DHI). Results: Patients showed hearing loss in 10 (47.6%) and tinnitus in 4 (19.0%) cases. In ocular motor tests, patients had the most abnormal results in the pursuit test. 6 patients also had Benign Paroxysmal Positional Vertigo (BPPV) in the posterior canal. c-VEMP showed abnormal saccular function in 14 patients. In CDP, the composite scores were decreased relative to normal populations. Conclusion: vestibular tests showed abnormal results in most patients. Vestibular abnormality could relate to persisting symptoms of mTBI patients.

Vestibular Hypersensitivity in Patients with Chronic Noise Exposure.

It has been demonstrated that high-intensity noise exposure adversely affects the human balance function. The Tullio phenomenon (TP) refers to sound-induced imbalance which is resulted from hypersensitivity of vestibular end organs to normal acoustic stimuli. Although different etiologies have been attributed to TP, evidence on the role of excessive noise exposure in the development of this symptom is limited. The present study aims to assess the vestibular functions in patients manifesting TP symptom who were exposed to long-term excessive noise levels. This was an analytic cross-sectional study conducted on 17 males diagnosed with TP with a history of chronic noise-induced hearing loss (TP group) and 17 healthy individuals. All subjects in both groups underwent complete otological, videonystagmography (VNG), and cervical vestibular myogenic potential (cVEMP) assessments. The most common complaint in TP subjects was vertigo and imbalance. During the VNG assessment, we found abnormal positional nystagmus and caloric irrigation (vestibular hyperfunction) results in 4 (23.53%) and 9 (52.94%) patients, respectively. Seven (41.17%) patients indicated cVEMP thresholds which were abnormally lower than the normal values ( ≤ 70 dB HL). However, when both VNG and cVEMP results were considered together, the abnormal rate reached 70.58% (12 of 17 cases). Our findings showed that both the semicircular canal as well as otolith stuctures could be affected in TP patients with a history of chronic noise exposure.

Metabotropic glutamate receptor: A new possible therapeutic target for cochlear synaptopathy.

Objectives: Cochlear synaptopathy is a common cause of auditory disorders in which glutamate over-activation occurs. Modulating glutamatergic pathways has been proposed to down-regulate post-synaptic excitation. Materials and Methods: 12-guinea pigs as sham and test groups were exposed to a 4-kHz noise at 104 dB SPL, for 2 hr. Pre-exposure intra-tympanic injection with LY354740 and normal saline 9% was applied in the test and sham groups. The amplitude growth of ABR-wave-I and wave-III latency shift with noise were considered in pre- and post-exposure times. The synapses were observed by transmission electron-microscopy. Results: ABR thresholds recovered 1-week post-exposure in both groups. The reduction of wave-I amplitude at 4, 6, and 8 kHz were statistically different between pre- and 1- day post-exposure and recovered mostly in the sham group. The amount of latency shift in masked ABR was different between pre- and all post-exposure, and the response could not be detected at higher than 50 dB SL noise. However, the response detectability increased to 60 dB SL noise, and the significance of differences between pre- and post-exposure persisted only at the high level of noise in the test group. In electron-microscopy of sham samples, the size of the ribbon was larger, spherical with an irregularity, and hollow. The post-synaptic density was thicker and missed its flat orientation. Conclusion: The higher slope of the ABR-wave I amplitude, the more tolerance of noise in masked ABR, concomitant with the histological finding that revealed less synaptic damage, confirmed the therapeutic effect of LY354740 in cochlear synaptopathy.

The Relationship between Psychoacoustic and Electrophysiological Assessments of Temporal Resolution.

BACKGROUND: Temporal resolution is essential to speech acoustic perception. However, it may alter in individuals with auditory disorders, impairing the development of spoken and written language. The envelope of speech signals contains amplitude modulation (AM) that has critical information. Any problem reducing the listener's sensitivity to these amplitude variations (auditory temporal acuity) is likely to cause speech comprehension problems. The modulation detection threshold (MDT) test is a measure for evaluating temporal resolution. However, this test cannot be used for patients with poor cooperation; therefore, objective evaluation of MDT is essential. PURPOSE: The main aim of this study is to find the association between the auditory steady-state response (ASSR) and psychoacoustic measurement of MDT at different intensity levels and to assess the amplitude and phase of ASSR as a function of modulation depth. DESIGN: This was a correlational research. STUDY SAMPLE: Eighteen individuals (nine males and nine females) with normal hearing sensitivity, aged between 18 and 23 years, participated in this study. DATA COLLECTION AND ANALYSIS: ASSR was recorded at fixed AM rates and variable AM depths for carrier frequencies of 1,000 and 2,000 Hz with varying intensities. The least AM depth, efficient to evoke an ASSR response, was interpreted as the physiological detection threshold of AM. The ASSR amplitude and phase, as a function of AM depth, were also evaluated at an intensity level of 60 dB hearing level (HL) with modulation rates of 40 and 100 Hz. Moreover, the Natus instrument (Biologic Systems) was used for the electrophysiological measurements. An AC40 clinical audiometer (Intra-acoustic, Denmark) was also used for the psychoacoustic measurement of MDT in a similar setting to ASSR, using the two-alternative forced choice method. Pearson's correlation test and linear regression model and paired t-test were used for statistical analyses. RESULTS: A significant positive correlation was found between psychoacoustic and electrophysiological measurements at a carrier frequency of 1000 Hz, with a modulation rate of 40 Hz at intensity levels of 60 dB HL (r = 0.63, p = 0.004), 50 dB HL (r = 0.52, p = 0.02). A significant positive correlation was also found at a carrier frequency of 2000 Hz, with a modulation rate of 47 Hz at 60 dB HL (r = 0.55, p = 0.01) and 50 dB HL (r = 0.67, p = 0.002) and a modulation rate of 97 Hz at 60 dB HL (r = 0.65, p = 0.003). Moreover, a significant association was found between the modulation depth and ASSR amplitude and phase increment at carrier frequencies of 1,000 and 2000 Hz, with modulation rates of 40 and 100 Hz. CONCLUSION: There was a significant correlation between ASSR and behavioral measurement of MDT, even at low intensities with low modulation rates of 40 and 47 Hz. The ASSR amplitude and phase increment was a function of modulation depth increase. The findings of this study can be used as a basis for evaluating the relationship between two approaches in the clinical population.

Thyroid-Stimulating Hormone and Free Thyroxine Alterations in Subjects with Occupational Hearing Loss.

CONTEXT AND AIM: Occupational hearing loss (OHL) is caused by exposure to industrial noise. Alterations in the thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels are related to hearing loss. The purpose of this study is to investigate the TSH and FT4 level alterations in OHL. METHODS AND MATERIAL: Among 428 subjects, 144 male workers with normal hearing (NH), noise-induced hearing loss (NIHL), and high tone loss (HTL) (N = 48 in each group) were included in this study. All the subjects had normal TSH and FT4 levels. RESULTS: The TSH level is higher in the HTL and NIHL groups in comparison to NH, but it is only significant in the HTL group. The FT4 level is significantly lower in the NIHL group; however, the lower FT4 level in the HTL group is not significant when compared to the NH group. DISCUSSION: The NIHL group may turn into the HTL group over time. This process could be monitored by alteration in their TSH and FT4 levels. CONCLUSIONS: Alterations in the TSH and FT4 levels could be considered as a pathophysiology for OHL. More research is required to investigate the electrophysiological, physiological, and histological correlations of TSH and FT4 and different types of hearing loss caused by noise exposure.

Shannon entropy measures for EEG signals in tinnitus.

BACKGROUND AND AIM: Tinnitus is known as a common clinical symptom, and it comprehensively is essential to understand the underlying mechanisms. Time-varying EEG is considered an appropriate technique to explore brain regions and related activities, and nonlinear methods may extract the irregularities in the EEG signal and gather more expanded information. Therefore, we studied Shannon Entropy in EEG raw data obtained from normal subjects and compared it to data from chronic tinnitus sufferers before and after an intervention. METHODS: From the qEEG database of Iran University of Medical Sciences, the School of Rehabilitation Sciences, we have selected 23 healthy and 24 chronic tinnitus subjects. Nineteen subjects of the tinnitus group had benefited from a complete course of sound therapy (binaural beat for a month). QEEGs were measured with a 27-channel EEG amplifier in the sitting and eye-closed position for 3 min. Shannon entropy was investigated for all electrodes separately and compared among groups using a one-way ANOVA statistical test. FINDINGS: Our results revealed a significant difference between healthy and tinnitus subjects (p < 0.05). Post-hoc comparisons using the Bonferroni test showed increased entropy in the tinnitus group for all electrodes (p < 0.05) at low frequencies and most electrodes at mid frequencies. In addition, after the intervention, paired t-test showed a reduction in entropy to somehow above normal control levels for all electrodes at low-frequencies. Such results were accompanying clinical improvement after the intervention. CONCLUSION: The increased entropy in tinnitus patients might reflect the chaotic behavior of the brain. Nonlinear methods in EEG studies (Entropy) could be of great importance in understanding tinnitus neurophysiology and might potentially be a suitable criterion for clinical practice.

Brainstem Representation of Auditory Overshoot in Guinea Pigs Using Auditory Brainstem Responses.

Objective: It is easier for a listener to detect a brief tonal signal presented in a longer masking noise by increasing the delay between the signal and the masker. This phenomenon (overshoot) is influenced by a reduction in cochlear amplification and to date, there is no objective tool to investigate it. Therefore, a different paradigm of the auditory brainstem response (ABR) was utilized to measure auditory overshoot. It was assumed that increasing the delay onset time (DOT) between a signal and a masker reduces the latencies of waves I and III. Materials & Methods: Sixteen normal young male guinea pigs were tested. A tone burst stimulus (signal: 16 kHz, 5ms in duration) and wide-band noise (masker: 0.1-8.0 kHz, 100ms in duration) at three DOTs were used. To diminish the effect of the noise on waves, waveforms were subtracted from those derived from the noise burst alone. The absolute latency of the waves I and III, inter-peak latency of the waves I-III, and amplitude ratio of the waves III/I were compared for the 0, 30, and 100ms DOTs and five signal-to-noise ratios. Results: The latencies of increased from the 0 to 30ms DOT and then decreased from the 30 to 100ms DOT (p < 0.001). No significant changes were observed in the latency waves at the 100ms DOT compared to the 0ms DOT (p > 0.005). Moreover, there were no significant differences between the three DOTs regarding the inter-peak latency and amplitude ratio of the waves (p <0.005). Conclusion: The study results showed an overshoot-like electrophysiological effect using ABR. Therefore, an objective test was used to investigate auditory cochlear gain.