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

“Comparison of Cochlear Microphonics Magnitude with Broad and Narrow Band Stimuli in Healthy Adult Wistar Rats”

AbstractObjective: Cochlear microphonic (CM) is a cochlear AC electric field, recorded within, around, and remote from its sources. Nowadays it can contribute to the differential diagnosis of different auditory pathologies such as auditory neuropathy spectrum disorder (ANSD). The aim of this study was to compare CM waveforms (CMWs) and amplitudes with broad and narrow band stimuli in 25 healthy male young adult Wistar rats.Methods: Using an extratympanic technique in ECochG (Electrocochleography) recording, CMWs in response to click and tonal stimuli with different octave frequencies were recorded at a high intensity level in subjects. The CMW amplitudes were calculated by a graphical user interface (GUI) designed in MATLAB. The data was analyzed by One-way ANOVA test.Results: The CMW magnitude increased upon an increase in band width stimulation. Across tonal stimuli, the CMW amplitudes at lower frequency tones were larger than those at higher frequency tones. Those findings were statistically significant (P< 0.001).Conclusion: This study found that CMW most likely is a reflection of spatial summation of voltage drops generated by hair cell groups in response to acoustic stimulation. In order to production nature of CM potentials as well as their very small magnitudes especially with tonal stimuli, thus, we recommend using click stimulation for CM potential recording especially in patient with ANSD that CM plays an important role in its differential diagnosis and follow u

A Model to Determine the Level of Serum Aldosterone in the Workers Attributed to the Combined Effects of Sound Pressure Level, Exposure Time and Serum Potassium Level: A Field-Based Study

Background: Occupational exposure to excessive noise is one of the biggest work-related challenges in the world. This phenomenon causes the release of stress-related hormones, which in turn, negatively affects cardiovascular risk factors. Objectives: The current study study aimed to determine the level of workers’ serum aldosterone in light of the combined effect of sound pressure level, exposure time and serum potassium level. Methods: This cross-sectional, descriptive, analytical study was conducted on 45 workers of Gol-Gohar Mining and Industrial Company in the fall of 2014. The subjects were divided into three groups (one control and two case groups), each including 15 workers. Participants in the control group were selected from workers with administrative jobs (exposure to the background noise). On the other hand, participants in the case groups were selected from the concentrator and pelletizing factories exposed to excessive noise. Serum aldosterone and potassium levels of participants were assessed at three different time intervals: at the beginning of the shift and before exposure to noise (7:30 - 8:00 AM), during exposure to noise (10:00 - 10:30 AM), and during continuous exposure (1:30 - 2:00 PM). The obtained data were transferred into SPSS ver. 18. Repeated measures analysis of variance (ANOVA) was used to develop the statistical model of workers’ aldosterone level in light of the combined effect of sound pressure level, exposure time, and serum potassium level. Results: The results of the final statistical model to determine the level of serum aldosterone based on the combined effect of sound pressure level, exposure time and serum potassium level indicated that the sound pressure level had a significant influence on the human’s serum aldosterone level (P = 0.04). In addition, the effects of exposure time and serum potassium on aldosterone level were statistically significant with P-values of 0.008 and 0.001, respectively. Conclusions: The obtained model in the study revealed that the results of predictive models to determine aldosterone level were very similar to real values; therefore, the obtained values of this model were largely in line with the ones obtained from the field

Assessment of the Effects of Different Sound Pressure Levels on Distortion Product Otoacoustic Emissions (DPOAEs) in Rats

Excessive exposure to noise can lead to Noise-Induced Hearing Loss. Otoacoustic emissions affect the microscopic biomechanical activities of healthy outer hair cells. The present study aimed at assessing the influence of various sound pressure levels on Distortion Product Otoacoustic Emissions (DPOAEs) in rats. To this end, 27 adult male rats with an age range of 3 to 4 months and a weight of 200 ± 50 g were randomly divided into nine groups of three. Three groups were considered as the control groups and the rest (i.e. Six groups) as the case groups. Rats of the case groups were exposed to sound pressure levels of 85, 95, and 105 dBA. White noise was used as the noise to which the rats were exposed. The signal to noise ratio (SNR) of otoacoustic emissions of rats’ ears was measured at different frequencies in an acoustic room using a DPOAE machine (4000 I/O manufactured by Homoth of Germany). The collected data were analyzed by the use of Statistical Package for Social Sciences (SPSS) version 18. The results of SNR measurement indicated that over 90% of the data had SNR values of 6dB or more. Furthermore, sound pressure level had a significant negative correlation with SNR, i.e. as the sound pressure level increased, the SNR declined (p<0.001). There was also a significant negative correlation between exposure time and SNR, meaning that increase in the exposure time led to decline in the SNR (p=0.008). It is thus concluded that higher sound pressure levels result in decrease in DPOAE levels

Effect of N-Acetylcysteine in Protecting from Simultaneous Noise and Carbon Monoxide Induced Hair Cell Loss

Background and Aim: N-acetylcysteine, a glutathione precursor and reactive oxygen species scavenger, is reported to be effective in reducing noise-induced hearing loss. Many workers in industry are exposed simultaneously to noise and chemical pollutants such as carbon monoxide. We investigated effectiveness of N-acetylcysteine in protecting the cochlea from simultaneous noise and carbon monoxide damages.Methods: Twelve rabbits were exposed simeltaneously to 100 dB sound pressure level of broad band noise and carbon monoxide 8 hours a day for 5 days. One hour before exposure, experimental group received 325 mg/kg of N-acetylcysteine while normal saline was administered for the control group. The protective effect of N-acetylcysteine was evaluated 3 weeks after exposure by histological assessment of the hair cells.Results: Simultaneous exposure to noise and carbon monoxide resulted in a considerable damage to the outer hair cells; however, the inner hair cells and the pillar cells remained intact. Use of N-acetylcysteine in the experimental group significantly reduced the extent of outer hair cell loss.Conclusion: N-acetylcysteine attenuates simultaneous noise and carbon monoxide induced hair cell damage in rabbits

The Protective Effect of Conditioning on Noise-Induced Hearing Loss Is Frequency-Dependent

We compared the extent of temporary threshold shift (TTS) and hair cell loss following high level 4 kHz noise exposure with those preconditioned with moderate level 1 and 4 kHz octave band noise. Fifteen Male albino guinea pigs (300- 350 g in weight) were randomly allocated into three groups: those exposed to 4 kHz octave band noise at 102 dB SPL (group 1, n=5); those conditioned with 1 kHz octave band noise at 85 dB SPL, 6 hours per day for 5 days, then exposed to noise (group 2, n=5); those conditioned with 4 kHz octave band noise at 85 dB SPL, then exposed to noise (group 3, n=5). An hour and one week after noise exposure, threshold shifts were evaluated by auditory-evoked brainstem response (ABR) and then animals were euthanized for histological evaluation. We found that TTS and cochlear damage caused by noise exposure were significantly reduced by 1 kHz and 4 kHz conditioning (P<0.001). We also showed that 4 kHz protocol attenuates noise- induced TTS but no significant TTS reduction occurred by 1 kHz conditioning. Both protocol protected noise-induced cochlear damage. We concluded that lower tone conditioning could not protect against higher tone temporary noise-induced hearing loss, thus conditioning is a local acting and frequency-dependent phenomenon

Bilateral Carotid Artery Occlusion and Cochlear Oxidative Stress and Hearing Loss in Rats

Introduction: This study aimed to evaluate the effects of bilateral carotid artery occlusion on cochlear oxidative stress and hearing status in rats. Methods: The rats were divided into two sets. The first set was used for electrophysiological recording (click and 4 kHz tone burst auditory brainstem responses and electrocochleography) on the day before surgery and then on the first, fourth, and seventh days after surgery. Animals of the second set were used for biochemical analysis. The cochlea of animals in the second set was collected on the first, fourth, and seventh days after carotids occlusion for biochemical analysis. For the control groups, no carotids occlusion was done. For ischemia induction, both common carotid arteries were occluded for 20 minutes. Results: Electrophysiological analysis showed that burst auditory brainstem thresholds significantly elevated after common carotid arteries occlusion on the first, fourth, and seventh days after surgery with abnormal electrocochleography results at 75%, 70%, and 85% on the first, fourth, and seventh days after surgery, respectively. The electrophysiological finding confirmed by biochemical results that showed malondialdehyde and nitric oxide levels increased and superoxide dismutase and catalase activities decreased after occlusion in cochlea tissue. Conclusion: This study showed that bilateral common carotid artery occlusion increases cochlear oxidative stress and induces hearing loss in rats

Correlation Analysis of the Tinnitus Handicap Inventory and Distress Network in Chronic Tinnitus: An EEG Study

Introduction: Tinnitus is a common disorder with a considerable amount of distress that affects the patient`s daily life. No objective tools were approved for measuring tinnitus distress. It can be estimated only by subjective scales and questionnaires, albeit, the Electroencephalography (EEG) studies have reported some alterations regarding tinnitus distress network. This study aimed to investigate the correlation between Tinnitus Handicap Inventory (THI) and the recorded EEG data.  Methods: A total of 33 chronic tinnitus cases (9 females) with the mean age of 42.67 years were recruited. Their THI scores were collected, and a 3-minute EEG recorded with eye closed at resting-state. The correlation analysis was performed on THI scores and the current density in the selected Region of Interests (ROIs) concerning the distress network for the eight frequency bands. The patients grouped depending on the THI cutoff point of 56 into low and high THI groups, and then the groups were compared for source analysis and functional connectivity between ROIs using standardized low-resolution brain electromagnetic tomography. Results: A significant positive correlation was seen between THI scores and the electrical activity in the Anterior Cingulate Cortex (ACC), the prefrontal cortex, and the parahippocampus for an alpha band (P<0.05) and in the ACC for beta (P<0.01). Source analysis showed significant differences with increased activity in the high THI group for alpha, beta and gamma bands. Functional connectivity was also elevated in the high THI group between the ROIs in alpha and beta bands. Conclusion: THI can be a useful tool for measuring tinnitus distress, and it has a high correlation with EEG data

Gap Pre-pulse Inhibition of the Cortical Auditory Evoked Potentials as a Possible Objective Pinnitus Assessment Tool

ObjectivesThe 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 &amp; MethodsTwenty 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 anterio-frontal, centro-frontal, right, and left temporal were investigated. ResultsThe 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&lt;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.ConclusionGap-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

Auditory Brainstem Responses in Children Treated with Cisplatin

Background and Aim: In view of improvement in therapeutic outcome of cancer treatment in children resulting in increased survival rates and the importance of hearing in speech and language development, this research project was intended to assess the effects of cisplatin group on hearing ability in children aged 6 months to 12 years.Methods: In this cross-sectional study, hearing of 10 children on cisplatin group medication for cancer who met the inclusion criteria was examined by recording auditory brainstem responses (ABR) using the three stimulants of click and 4 and 8 kHz tone bursts. All children were examined twice: before drug administration and within 72 hours after receiving the last dose. Then the results were compared with each other.Results: There was a significant difference between hearing thresholds before and after drug administration (p<0.05). Right and left ear threshold comparison revealed no significant difference.Conclusion: Ototoxic effects of cisplatin group were confirmed in this study. Insignificant difference observed in comparing right and left ear hearing thresholds could be due to small sample size. auditory brainstem responses test especially with frequency specificity proved to be a useful method in assessing cisplatin ototoxicity