Establishment of a cochlear injury model using bone-conducted ultrasound irradiation in guinea pigs and investigation on peripheral coding and recognition of ultrasonic signals.

The cochlea of guinea pigs was irradiated with different frequencies of bone-conducted ultrasound (BCU) at a specific dose to induce cochlear hair cell-specific injuries, in order to establish frequency-related cochlear hair cell-specific injury models. Cochlear near-field potentials were then evoked using BCU of different frequencies and intensities to explore the peripheral coding and recognition of BCU by the cochlea. The inner ears of guinea pigs were irradiated by 30 kHz at 100 db and 80 kHz at100 db BCU for 6h to create frequency-related, ultrasound-specific cochlear injury models. Then, 30 kHz and 80 kHz BCU of different intensities were used to evoke auditory brainstem response (ABR) thresholds, compound action potential (CAP) thresholds, and action potential (AP) intensity-amplitude input-output curves in the normal control group and the ultrasonic cochlear injury group. This allowed us to explore the coding and recognition of BCU frequencies and intensities by cochlear hair cells. Immunofluorescence assay of outer hair cell (OHC) Prestin and inner hair cell (IHC) Otofelin was performed to verify the injury models. Irradiation of guinea pig inner ears by 30 kHz and 80 kHz BCU at a specific dose induced hair cell injuries at different sites. Irradiation with low frequency BCU mainly induced OHC injury, whereas irradiation with high frequency BCU induced IHC injury; moreover, IHC injury was more serious than OHC injury. The 30 kHz-evoked ABR threshold was significantly higher in the 30 kHz ultrasonic cochlear injury group compared to the normal control group. The 30 kHz-evoked ABR threshold was significantly higher in the 30 kHz ultrasonic cochlear injury group compared to the 80 kHz ultrasonic cochlear injury group. The difference in the 80 kHz-evoked ABR thresholds were not significant between the 30 kHz and 80 kHz ultrasonic cochlear injury groups. The click- and 30 kHz-evoked AP intensity-amplitude curves for the 30 kHz ultrasonic cochlear injury group indicate that the AP amplitude evoked at the same intensity was higher in the 30 kHz-evoked group than the click-evoked group. The spatial positions of cochlear hair cells in guinea pigs had a coding function for the frequencies of low-frequency ultrasound. OHCs have an amplification effect on the coding of low-frequency ultrasonic intensities. The peripheral perception of high frequency BCU may not require the participation of cochlear hair cells.

Short-wavelength infrared laser activates the auditory neurons: comparing the effect of 980 vs. 810 nm wavelength.

Research on auditory neural triggering by optical stimulus has been developed as an emerging technique to elicit the auditory neural response, which may provide an alternative method to the cochlear implants. However, most previous studies have been focused on using longer-wavelength near-infrared (>1800 nm) laser. The effect comparison of different laser wavelengths in short-wavelength infrared (SWIR) range on the auditory neural stimulation has not been previously explored. In this study, the pulsed 980- and 810-nm SWIR lasers were applied as optical stimuli to irradiate the auditory neurons in the cochlea of five deafened guinea pigs and the neural response under the two laser wavelengths was compared by recording the evoked optical auditory brainstem responses (OABRs). In addition, the effect of radiant exposure, laser pulse width, and threshold with the two laser wavelengths was further investigated and compared. The one-way analysis of variance (ANOVA) was used to analyze those data. Results showed that the OABR amplitude with the 980-nm laser is higher than the amplitude with the 810-nm laser under the same radiant exposure from 10 to 102 mJ/cm2. And the laser stimulation of 980 nm wavelength has lower threshold radiant exposure than the 810 nm wavelength at varied pulse duration in 20-500 µs range. Moreover, the 810-nm laser has a wider optimized pulse duration range than the 980-nm laser for the auditory neural stimulation.

Effect of shorter pulse duration in cochlear neural activation with an 810-nm near-infrared laser.

Optical neural stimulation in the cochlea has been presented as an alternative technique to the electrical stimulation due to its potential in spatially selectivity enhancement. So far, few studies have selected the near-infrared (NIR) laser in cochlear neural stimulation and limited optical parameter space has been examined. This paper focused on investigating the optical parameter effect on NIR stimulation of auditory neurons, especially under shorter pulse durations. The spiral ganglion neurons in the cochlea of deafened guinea pigs were stimulated with a pulsed 810-nm NIR laser in vivo. The laser radiation was delivered by an optical fiber and irradiated towards the modiolus. Optically evoked auditory brainstem responses (OABRs) with various optical parameters were recorded and investigated. The OABRs could be elicited with the cochlear deafened animals by using the 810-nm laser in a wide pulse duration ranged from 20 to 1000 µs. Results showed that the OABR intensity increased along with the increasing laser radiant exposure of limited range at each specific pulse duration. In addition, for the pulse durations from 20 to 300 µs, the OABR intensity increased monotonically along with the pulse duration broadening. While for pulse durations above 300 µs, the OABR intensity basically kept stable with the increasing pulse duration. The 810-nm NIR laser could be an effective stimulus in evoking the cochlear neuron response. Our experimental data provided evidence to optimize the pulse duration range, and the results suggested that the pulse durations from 20 to 300 µs could be the optimized range in cochlear neural activation with the 810-nm-wavelength laser.

Safety assessment of trans-tympanic photobiomodulation.

We evaluated functional and morphological changes after trans-tympanic laser application using several different powers of photobiomodulation (PBM). The left (L) ears of 17 rats were irradiated for 30 min daily over 14 days using a power density of 909.1 (group A, 5040 J), 1136.4 (group B, 6300 J), and 1363.6 (group C, 7560 J) mW/cm(2). The right (N) ears served as controls. The safety of PBM was determined by endoscopic findings, auditory brainstem response (ABR) thresholds, and histological images of hair cells using confocal microscopy, and light microscopic images of the external auditory canal (EAC) and tympanic membrane (TM). Endoscopic findings revealed severe inflammation in the TM of C group; no other group showed damage in the TM. No significant difference in ABR threshold was found in the PBM-treated groups (excluding the group with TM damage). Confocal microscopy showed no histological difference between the AL and AN, or BL and BN groups. However, light microscopy showed more prominent edema, inflammation, and vascular congestion in the TM of BL ears. This study found a dose-response relationship between laser power parameters and TM changes. These results will be useful for defining future allowance criteria for trans-tympanic laser therapies.

Effect Of Electromagnetic Waves Emitted From Mobile Phone On Brain Stem Auditory Evoked Potential In Adult Males.

Mobile phone (MP) is commonly used communication tool. Electromagnetic waves (EMWs) emitted from MP may have potential health hazards. So, it was planned to study the effect of electromagnetic waves (EMWs) emitted from the mobile phone on brainstem auditory evoked potential (BAEP) in male subjects in the age group of 20-40 years. BAEPs were recorded using standard method of 10-20 system of electrode placement and sound click stimuli of specified intensity, duration and frequency.Right ear was exposed to EMW emitted from MP for about 10 min. On comparison of before and after exposure to MP in right ear (found to be dominating ear), there was significant increase in latency of II, III (p < 0.05) and V (p < 0.001) wave, amplitude of I-Ia wave (p < 0.05) and decrease in IPL of III-V wave (P < 0.05) after exposure to MP. But no significant change was found in waves of BAEP in left ear before vs after MP. On comparison of right (having exposure routinely as found to be dominating ear) and left ears (not exposed to MP), before exposure to MP, IPL of IIl-V wave and amplitude of V-Va is more (< 0.001) in right ear compared to more latency of III and IV wave (< 0.001) in left ear. After exposure to MP, the amplitude of V-Va was (p < 0.05) more in right ear compared to left ear. In conclusion, EMWs emitted from MP affects the auditory potential.

Auditory brainstem response changes during exposure to GSM-900 radiation: an experimental study.

The objective of the present study was to investigate the possible electrophysiological time-related changes in auditory pathway during mobile phone electromagnetic field exposure. Thirty healthy rabbits were enrolled in an experimental study of exposure to GSM-900 radiation for 60 min and auditory brainstem responses (ABRs) were recorded at regular time-intervals during exposure. The study subjects were radiated via an adjustable power and frequency radio transmitter for GSM-900 mobile phone emission simulation, designed and manufactured according to the needs of the experiment. The mean absolute latency of waves III-V showed a statistically significant delay (p < 0.05) after 60, 45 and 15 min of exposure to electromagnetic radiation of 900 MHz, respectively. Interwave latency I-III was found to be prolonged after 60 min of radiation exposure in correspondence to wave III absolute latency delay. Interwave latencies I-V and III-V were found with a statistically significant delay (p < 0.05) after 30 min of radiation. No statistically significant delay was found for the same ABR parameters in recordings from the ear contralateral to the radiation source at 60 min radiation exposure compared with baseline ABR. The ABR measurements returned to baseline recordings 24 h after the exposure to electromagnetic radiation of 900 MHz. The prolongation of interval latencies I-V and III-V indicates that exposure to electromagnetic fields emitted by mobile phone can affect the normal electrophysiological activity of the auditory system, and these findings fit the pattern of general responses to a stressor.

Experimental study of potential adverse effects on the auditory system of rabbits exposed to short-term GSM-1800 radiation.

PURPOSE: The effects of the electromagnetic (EM) radiation emitted by a mobile phone on the central auditory system of rabbits are investigated in this paper. Auditory brainstem response (ABR) measurements were performed before and after short-term exposure to EM radiation. MATERIALS AND METHODS: Excitation was provided by a GSM-1800 emitter placed in contact with the (randomly selected) ear of the anesthetized rabbit/subject. The latency of waves I, II, III, IV, V and the interpeak latencies I-III, I-V, III-V were recorded, for both ears, before (baseline recordings) and after 1, 15, 30, 45 and 60 minutes of exposure to the EM radiation. The repeated measures one-way analysis of variance (ANOVA) followed by the post hoc Tukey test for pairwise comparisons was performed in order to decide about the significance of the results. RESULTS: The statistical tests indicated that, as regards the ear ipsilateral to the radiating module, the mean latencies of waves I, II, III, IV, V, I-III, I-IV after 60 min exposure, the mean latencies of waves I, III, IV, V, I-III, I-IV after 45 min exposure and the mean latencies of waves I, III, IV, V, I-IV after 30 min exposure, were significantly prolonged compared to the corresponding baseline values. Statistically significant differences were also found for certain peak and interpeak latencies for 60 min exposure as compared with the corresponding results for 1 min and 15 min exposure. No statistically significant delay was observed for the latencies before and after the exposure, for the ear contralateral to the radiation source. CONCLUSIONS: Although we found that more than 30 min exposure to GSM-1800 radiation resulted in prolongation of certain ABR components of rabbits, further investigation may be needed into the potential adverse effects on the auditory pathways.

Effect of shock wave power spectrum on the inner ear pathophysiology in blast-induced hearing loss.

Blast exposure can induce various types of hearing impairment, including permanent hearing loss, tinnitus, and hyperacusis. Herein, we conducted a detailed investigation of the cochlear pathophysiology in blast-induced hearing loss in mice using two blasts with different characteristics: a low-frequency dominant blast generated by a shock tube and a high-frequency dominant shock wave generated by laser irradiation (laser-induced shock wave). The pattern of sensorineural hearing loss (SNHL) was low-frequency- and high-frequency-dominant in response to the low- and high-frequency blasts, respectively. Pathological examination revealed that cochlear synaptopathy was the most frequent cochlear pathology after blast exposure, which involved synapse loss in the inner hair cells without hair cell loss, depending on the power spectrum of the blast. This pathological change completely reflected the physiological analysis of wave I amplitude using auditory brainstem responses. Stereociliary bundle disruption in the outer hair cells was also dependent on the blast's power spectrum. Therefore, we demonstrated that the dominant frequency of the blast power spectrum was the principal factor determining the region of cochlear damage. We believe that the presenting models would be valuable both in blast research and the investigation of various types of hearing loss whose pathogenesis involves cochlear synaptopathy.

[Effects of electromagnetic field from cellular phones on selected central nervous system functions: a literature review]. / Wplyw pola elektromagnetycznego dorecznych telefonów komórkowych na wybrane funkcje osrodkowego ukladu nerwowego--przeglad literatury.

In the opinion of some experts, a growing emission of man-made electromagnetic fields (EMF), also known as electromagnetic is a source of continuously increasing health hazards to the general population. Due to their large number and very close proximity to the user's head, mobile phones deserve special attention. This work is intended to give a systematic review of objective studies, assessing the effects of mobile phone EMF on the functions of the central nervous system (CNS) structures. Our review shows that short exposures to mobile phone EMF, experienced by telephone users during receiving calls, do not affect the cochlear function. Effects of GSM mobile phone EMF on the conduction of neural impulses from the inner car neurons to the brainstem auditory centres have not been detected either. If Picton's principle, saying that P300 amplitude varies with the improbability of the targets and its latency varies with difficulty of discriminating the target stimulus from standard stimuli, is true, EMF changes the improbability of the targets without hindering their discrimination. Experiments with use of indirect methods do not enable unequivocal verification of EMF effects on the cognitive functions due to the CNS anatomical and functional complexity. Thus, it seems advisable to develop a model of EMF effects on the excitable brain structures at the cellular level.

Dorsal cochlear nucleus responses to somatosensory stimulation are enhanced after noise-induced hearing loss.

Multisensory neurons in the dorsal cochlear nucleus (DCN) achieve their bimodal response properties [Shore (2005) Eur. J. Neurosci., 21, 3334-3348] by integrating auditory input via VIIIth nerve fibers with somatosensory input via the axons of cochlear nucleus granule cells [Shore et al. (2000) J. Comp. Neurol., 419, 271-285; Zhou & Shore (2004)J. Neurosci. Res., 78, 901-907]. A unique feature of multisensory neurons is their propensity for receiving cross-modal compensation following sensory deprivation. Thus, we investigated the possibility that reduction of VIIIth nerve input to the cochlear nucleus results in trigeminal system compensation for the loss of auditory inputs. Responses of DCN neurons to trigeminal and bimodal (trigeminal plus acoustic) stimulation were compared in normal and noise-damaged guinea pigs. The guinea pigs with noise-induced hearing loss had significantly lower thresholds, shorter latencies and durations, and increased amplitudes of response to trigeminal stimulation than normal animals. Noise-damaged animals also showed a greater proportion of inhibitory and a smaller proportion of excitatory responses compared with normal. The number of cells exhibiting bimodal integration, as well as the degree of integration, was enhanced after noise damage. In accordance with the greater proportion of inhibitory responses, bimodal integration was entirely suppressive in the noise-damaged animals with no indication of the bimodal enhancement observed in a sub-set of normal DCN neurons. These results suggest that projections from the trigeminal system to the cochlear nucleus are increased and/or redistributed after hearing loss. Furthermore, the finding that only neurons activated by trigeminal stimulation showed increased spontaneous rates after cochlear damage suggests that somatosensory neurons may play a role in the pathogenesis of tinnitus.

Effects of a static magnetic field on audiogenic seizures in black Swiss mice.

Effects of a static magnetic field (SMF) with strong gradient components were studied in black Swiss mice. Exposure to SMF (100-220 mT, 15-40 T/m for 1h) did not affect the threshold for detecting auditory brainstem responses. Serial seizures elevated the hearing threshold at some frequencies, but there was no difference between SMF-exposed and unexposed control mice. EEG changes were recorded during audiogenic seizures. Pretreatment with SMF prolonged seizure latency in response to stimulation with white noise of increasing intensity from 74 to 102 dBA (1 min interval between 2 and 4 dBA increments) without significant effects on seizure severity. Gender-related differences were not statistically significant. Stimulation with 10 min sound steps revealed prolongation of latency and reduction of seizure severity in SMF-exposed, but not unexposed, mice. Pretreatment with phenytoin (5 mg/kg) in combination with SMF had significantly greater effects on seizure latency and severity than either pretreatment alone. These findings indicate that the SMF studied here under different conditions elevated seizure threshold and had anticonvulsant properties in Black Swiss mice and increased the efficacy of a conventional anticonvulsant drug.

A fully implantable stimulator for use in small laboratory animals.

This paper describes a low cost, fully implantable, single channel stimulator that can be manufactured in a research laboratory. The stimulator generates charge-balanced biphasic current pulses which are delivered to a bipolar electrode array for chronic stimulation of neural tissue in free-running laboratory animals such as rats and mice. The system is magnetically coupled and contains no batteries or external leadwires. The subject is placed in a chamber surrounded by three orthogonal coils of wire which are driven to generate a magnetic field. Currents are induced in wire coils in the implanted stimulator then regulated to produce biphasic current pulses with fixed amplitude of up to 500 microA. Phase duration is adjustable from 25 to 250 micros per phase. Charge balance is maintained by capacitive coupling and shorting of the electrodes between pulses. Stimulus rate can be continuously varied, and the temporal precision of the stimulus means that the stimulator can be used in behavioural experiments or for generating electrically evoked potentials. We describe the application of this stimulator for chronic electrical stimulation of the auditory nerve (i.e. a cochlear implant); however it will have application in other areas of neuroscience requiring controlled safe electrical stimulation of neural tissue over extended periods. Circuit diagrams and manufacturing details are provided as supplementary data.

Short GSM mobile phone exposure does not alter human auditory brainstem response.

BACKGROUND: There are about 1.6 billion GSM cellular phones in use throughout the world today. Numerous papers have reported various biological effects in humans exposed to electromagnetic fields emitted by mobile phones. The aim of the present study was to advance our understanding of potential adverse effects of the GSM mobile phones on the human hearing system. METHODS: Auditory Brainstem Response (ABR) was recorded with three non-polarizing Ag-AgCl scalp electrodes in thirty young and healthy volunteers (age 18-26 years) with normal hearing. ABR data were collected before, and immediately after a 10 minute exposure to 900 MHz pulsed electromagnetic field (EMF) emitted by a commercial Nokia 6310 mobile phone. Fifteen subjects were exposed to genuine EMF and fifteen to sham EMF in a double blind and counterbalanced order. Possible effects of irradiation was analyzed by comparing the latency of ABR waves I, III and V before and after genuine/sham EMF exposure. RESULTS: Paired sample t-test was conducted for statistical analysis. Results revealed no significant differences in the latency of ABR waves I, III and V before and after 10 minutes of genuine/sham EMF exposure. CONCLUSION: The present results suggest that, in our experimental conditions, a single 10 minute exposure of 900 MHz EMF emitted by a commercial mobile phone does not produce measurable immediate effects in the latency of auditory brainstem waves I, III and V.

Modeling Intracochlear Magnetic Stimulation: A Finite-Element Analysis.

This study models induced electric fields, and their gradient, produced by pulsatile current stimulation of submillimeter inductors for cochlear implantation. Using finite-element analysis, the lower chamber of the cochlea, scala tympani, is modeled as a cylindrical structure filled with perilymph bounded by tissue, bone, and cochlear neural elements. Single inductors as well as an array of inductors are modeled. The coil strength (~100 nH) and excitation parameters (peak current of 1-5 A, voltages of 16-20 V) are based on a formative feasibility study conducted by our group. In that study, intracochlear micromagnetic stimulation achieved auditory activation as measured through the auditory brainstem response in a feline model. With respect to the finite element simulations, axial symmetry of the inductor geometry is exploited to improve computation time. It is verified that the inductor coil orientation greatly affects the strength of the induced electric field and thereby the ability to affect the transmembrane potential of nearby neural elements. Furthermore, upon comparing an array of micro-inductors with a typical multi-site electrode array, magnetically excited arrays retain greater focus in terms of the gradient of induced electric fields. Once combined with further in vivo analysis, this modeling study may enable further exploration of the mechanism of magnetically induced, and focused neural stimulation.

Effects of exposure to 2100MHz GSM-like radiofrequency electromagnetic field on auditory system of rats.

INTRODUCTION: The use of mobile phones has become widespread in recent years. Although beneficial from the communication viewpoint, the electromagnetic fields generated by mobile phones may cause unwanted biological changes in the human body. OBJECTIVE: In this study, we aimed to evaluate the effects of 2100MHz Global System for Mobile communication (GSM-like) electromagnetic field, generated by an electromagnetic fields generator, on the auditory system of rats by using electrophysiological, histopathologic and immunohistochemical methods. METHODS: Fourteen adult Wistar albino rats were included in the study. The rats were divided randomly into two groups of seven rats each. The study group was exposed continuously for 30days to a 2100MHz electromagnetic fields with a signal level (power) of 5.4dBm (3.47mW) to simulate the talk mode on a mobile phone. The control group was not exposed to the aforementioned electromagnetic fields. After 30days, the Auditory Brainstem Responses of both groups were recorded and the rats were sacrificed. The cochlear nuclei were evaluated by histopathologic and immunohistochemical methods. RESULTS: The Auditory Brainstem Responses records of the two groups did not differ significantly. The histopathologic analysis showed increased degeneration signs in the study group (p=0.007). In addition, immunohistochemical analysis revealed increased apoptotic index in the study group compared to that in the control group (p=0.002). CONCLUSION: The results support that long-term exposure to a GSM-like 2100MHz electromagnetic fields causes an increase in neuronal degeneration and apoptosis in the auditory system.

Low-frequency hearing loss in prenatally stressed rats.

We investigated the possibility that hearing thresholds are altered in prenatally stressed rats raised in a normal auditory environment. Pregnant dams were assigned randomly to prenatally stressed and control groups. Half of the dams were subjected to the mild stressors of handling, exposure to a novel cage and saline injection at random times during lights-on daily. The hearing thresholds of young adult male offspring were assessed by recording auditory-evoked brainstem responses to 0.5, 1, 2, 4, 8, 16, 32 and 64 kHz pure tones. The resultant audiograms showed that prenatally stressed offspring had significantly higher hearing thresholds than control animals at 1, 2 and 4 kHz (t-tests, P<0.05). The threshold shifts caused by prenatal stress averaged 7.7 dB across frequencies. We conclude that prenatal stress causes low-frequency hearing loss, possibly due to increased vulnerability to noise-induced hearing loss, accelerated cochlear degeneration and/or disrupted cochlear development.

Enriched acoustic environment after noise trauma abolishes neural signs of tinnitus.

Noise-induced hearing loss induces reorganization of the tonotopic map in cat auditory cortex and increases spontaneous firing rate and neural synchrony. We showed previously that keeping cats after noise trauma in an acoustic environment enriched in high frequencies prevents tonotopic map reorganization. Here, we show the effects of low-frequency and high-frequency enriched acoustic environments on spontaneous firing rate and neural synchrony. Exposed cats placed in the quiet environment and in the low-frequency enriched acoustic environment showed increased spontaneous firing rate and synchrony of firing. In contrast, exposed cats placed in the high-frequency enriched acoustic environment did not show significant differences in spontaneous firing rate or synchrony compared with normal hearing controls. This is interpreted as an absence of putative neural signs of tinnitus.

Consequences of combined maternal, fetal and persistent postnatal hypothyroidism on the development of auditory function in Tshrhyt mutant mice.

Tshrhyt/hyt mutant mice express a point mutation in the gene encoding the thyrotropin receptor, and affected animals are congenitally hypothyroid and profoundly deaf as a consequence when the condition is untreated. In this investigation, a previously unrecognized developmental stage was identified in the hypothyroid, mutant progeny of hypothyroid dams by tracking developmental changes in the auditory brainstem response (ABR). ABR thresholds develop rapidly in normal, euthyroid animals, decreasing as much as 80 dB between P12 (postnatal day 12) and P15, with mature sensitivity being gradually acquired by P18. In contrast, Tshrhyt/hyt mutant mice remained profoundly deaf on P24 and although thresholds improved by approximately 30 dB by P60, residual frequency-dependent deficits of 20-70 dB were observed in animals exhibiting end-stage disease. The rate of threshold improvement in mutant mice was approximately ten times slower than in normal mice. While ABR wave latencies and interpeak intervals decreased early in postnatal life, values decreased over a delayed and protracted time period, reaching adult values well after those of controls attained maturity. As with normal mice, slopes of wave I latency-intensity curves were significantly steeper in immature animals than those observed in adults and decreased during development, but failed to achieve normal adult values and remained significantly steeper than those for controls. Findings reported here suggest that passive aspects of electromechanical transduction achieve maturity in Tshrhyt/hyt progeny of Tshrhyt/hyt mice and that development, limited as it may be, occurs most prominently in the basal half of the cochlea.

Effects of laserneedle stimulation in the external auditory meatus on brainstem and very early auditory evoked potentials in humans.

OBJECTIVES: For the first time, brainstem auditory evoked potentials (BAEP) and very early auditory evoked potentials (EAEP) were investigated in 23 volunteers (mean age: 26.5 +/- 3.6 years) under resting conditions and during continuous and frequency modulated (2 Hz) laser stimulation in the external auditory meatus. METHODS: Using a new ear adapter, the outer region of the auditory canal was stimulated with laser light (685 nm, 4 x 30-40 mW, duration: 10 minutes). RESULTS: The EAEPs were significantly changed during continuous (p=0.019), as well as frequency modulated (p=0.014) laser stimulation compared with control measurements. DISCUSSION: Physiologic alterations of inner ear mechanism such as extra-cerebral changes in conductance or stimulation-dependent depolarization processes in extra-cerebral regions of the auditory system could be possible explanations for the significant difference in measurement parameters.

A study of the effects of cellular telephone microwave radiation on the auditory system in healthy men.

We conducted a study of the effects of mobile cellular telephone microwave radiation on the auditory system in 20 healthy men. After the subjects underwent baseline measurements of transient evoked otoacoustic emission (TEOAE) and auditory brainstem response (ABR), they participated in three sessions of exposure to an electromagnetic field of 900 to 1,800 MHz produced by a cellular phone. Sessions ranged from 15 to 30 minutes in length. TEOAE and ABR were again measured after or during each exposure. Throughout the study, no significant changes in either measurement were noted. We conclude that the use of cellular phones does not alter the auditory system in the short-term.