Short-term 2.1 GHz radiofrequency radiation treatment induces significant changes on the auditory evoked potentials in adult rats.

PURPOSE: There is a growing interest in the usage of radiofrequency radiation (RF) as a noninvasive brain stimulation method. Previously reported data demonstrated that RF exposure caused a change in brain oscillations. Therefore, we aimed to investigate effects of RF on brain oscillation by measuring the auditory response of different brain regions in rats. MATERIALS AND METHODS: Rats were randomly divided into three groups (n = 12 per each group): Cage control (C), sham rats (Sh), and rats exposed to 2.1 GHz RF for 2 h/day for 7 days. At the end of the exposure, auditory evoked potentials (AEPs) were recorded at different locations in rats. Latencies and amplitudes of AEPs, evoked power, inter-trial phase synchronization, and auditory evoked gamma responses were obtained in response to an auditory stimulus. Furthermore, TBARS levels and 4-HNE, GFAP, iNOS, and nNOS expressions were evaluated in all groups. RESULTS: Peak-to-peak amplitudes of AEPs were significantly higher in the RF group compared with the Sh group. There is no significant difference in peak latencies of AEPs between groups. Beside, evoked power, inter-trial phase synchronization, and auditory evoked gamma responses were significantly higher in the RF group compared with the Sh group. In addition, the RF group had significantly lower TBARS and 4-HNE levels than the Sh group. There were no significant differences between groups for GFAP, nNOS, and iNOS levels, and between the C and RF groups for all parameters. CONCLUSIONS: Our present findings suggest that short-term RF treatment under chosen experimental conditions have statistically significant effect on neuronal networks of rats by probably reducing oxidative damage. However, this effect must be further studied for possible noninvasive brain stimulation.

Effects of Intratympanic Dexamethasone on High-Dose Radiation Ototoxicity In Vivo.

BACKGROUND: Stereotactic radiosurgery for lateral skull base tumors can cause hearing loss when the cochleae are exposed to high doses of single-fraction radiation. Currently, there are no known nondosimetric preventative treatments for radiation-induced ototoxicity. HYPOTHESIS: Intratympanic (IT) dexamethasone (DXM), a synthetic steroid, protects against radiation-induced auditory hair cell (HC) and hearing losses in rats in vivo. METHODS: Seven rats received radiation (12 Gy) to both cochleae. In irradiated rats and six nonirradiated rats, IT DXM was randomized to one ear, while tympanic puncture without DXM was performed on the contralateral ear. Baseline and 4-week postradiation auditory-evoked potential tests were performed. The cochleae were processed for HC viability. RESULTS: Cochleae exposed to radiation demonstrated more outer HC (OHC) loss in all turns than nonirradiated ears (p <0.05). OHCs were more susceptible to radiation injury than inner HCs in the middle and basal turns (p <0.05). In irradiated cochleae, there was a nonsignificant trend for less OHC loss with IT DXM in the basal turn when compared with placebo. IT DXM did not improve radiation-induced hearing threshold shifts; however, a high rate of tympanic membrane perforations occurred with irradiated ears which may contribute to this finding. CONCLUSION: Radiation induced loss of OHCs in all turns of the cochlea. IT DXM reduced OHC loss in the basal turn of irradiated ears; however, this finding did not achieve statistical significance. Although IT DXM did not affect radiation-induced hearing threshold shifts in adult rats in vivo, this may be due to a high rate of tympanic membrane perforations.

Repetitive transcranial magnetic stimulation improve tinnitus in normal hearing patients: a double-blind controlled, clinical and neuroimaging outcome study.

BACKGROUND AND PURPOSE: Tinnitus is a frequent disorder which is very difficult to treat and there is compelling evidence that tinnitus is associated with functional alterations in the central nervous system. Targeted modulation of tinnitus-related cortical activity has been proposed as a promising new treatment approach. We aimed to investigate both immediate and long-term effects of low frequency (1 Hz) repetitive transcranial magnetic stimulation (rTMS) in patients with tinnitus and normal hearing. METHODS: Using a parallel design, 20 patients were randomized to receive either active or placebo stimulation over the left temporoparietal cortex for five consecutive days. Treatment results were assessed by using the Tinnitus Handicap Inventory. Ethyl cysteinate dimmer-single photon emission computed tomography (SPECT) imaging was performed before and 14 days after rTMS. RESULTS: After active rTMS there was significant improvement of the tinnitus score as compared to sham rTMS for up to 6 months after stimulation. SPECT measurements demonstrated a reduction of metabolic activity in the inferior left temporal lobe after active rTMS. CONCLUSION: These results support the potential of rTMS as a new therapeutic tool for the treatment of chronic tinnitus, by demonstrating a significant reduction of tinnitus complaints over a period of at least 6 months and significant reduction of neural activity in the inferior temporal cortex, despite the stimulation applied on the superior temporal cortex.

Neuromagnetic responses to chords are modified by preceding musical scale.

Previous psychological studies have shown that musical chords primed by Western musical scale in a tonal and modal schema are perceived in a hierarchy of stability. We investigated such priming effects on auditory magnetic responses to tonic-major and submediant-minor chords preceded by major scales and tonic-minor and submediant-major chords preceded by minor scales. Musically trained subjects participated in the experiment. During MEG recordings, subjects judged perceptual stability of the chords. The tonic chords were judged to be stable, whereas the submediant chords were judged to be unstable. Dipole moments of N1m response originating in the auditory cortex were larger in the left hemisphere for the submediant chords than for the tonic chords preceded by the major but not minor scales. No difference in the N1m or P2m moment was found for the chords presented without preceding scales. These results suggest priming effects of the tonal schema, interacting with contextual modality, on neural activity of the auditory cortex as well as perceptual stability of the chords. It is inferred that modulation of the auditory cortical activity is associated with attention induced by tonal instability and modality shift, which characterize the submediant chords.

Scalp localization of human auditory cortical activity modified by GSM electromagnetic fields.

PURPOSE: This study attempted to determine whether there is a localized effect of GSM (Global System for Mobile communications) microwaves by studying the Auditory Evoked Potentials (AEP) recorded at the scalp of nine healthy subjects and six epileptic patients. MATERIALS AND METHODS: We determined the influence of GSM RadioFrequency (RF) on parameters characterizing the AEP in time or/and frequency domains. A parameter selection method using SVM (Support Vector Machines)-based criteria allowed us to estimate those most altered by the radiofrequencies. The topography of the parameter modifications was computed to determine the localization of the radiofrequency influence. A statistical test was conducted for selected scalp areas, in order to determine whether there were significant localized alterations due to the RF. RESULTS: The epileptic patients showed a lengthening of the scalp component N100 (100 ms latency) in the frontal area contralateral to the radiation, which may be due to an afferent tract alteration. For the healthy subjects, an amplitude increase of the P200 wave (200 ms latency) was identified in the frontal area. CONCLUSIONS: The present study suggests that radiofrequency fields emitted by mobile phones modify the AEP. Nevertheless, no direct link between these findings and RF-induced damages in brain function was established.

Temporal resolution properties of human auditory cortex: reflections in the neuromagnetic auditory evoked M100 component.

UNLABELLED: Previous work has provided evidence for a brief, finite ( approximately 35 ms) temporal window of integration (TWI) in M100 formation, during which stimulus attributes are accumulated in processes leading to the M100 peak. Here, we investigate resolution within the TWI by recording responses to tones containing silent gaps (0-20 ms). Gaps were inserted in 1 kHz tones in 2 conditions: +10 ms post-onset (10 ms masker) wherein the masker and gap of longest duration (20 ms) were contained within the initial 35 ms of the stimulus and +40 ms (40 ms masker) wherein all gaps were inserted +40 ms post-onset. Tones were presented binaurally and responses sampled from both hemispheres in 12 adults using a twin 37-channel biomagnetometer (MAGNES-II, BTi, San Diego, CA). Results--10 ms masker: M100 latency was prolonged and amplitude decreased as a function of gap duration, even with the shortest duration (2 ms) gap, indicating that integrative processes underlying M100 formation are sensitive to fine-grained discontinuities within a brief, finite TWI. Results--40 ms masker: M100 latency and amplitude were unaffected by gaps inserted at +40 ms, providing further evidence for an M100 TWI of <40 ms. CONCLUSION: within a brief integrative window in M100 formation, population-level responses are sensitive to discontinuities in sounds on a scale corresponding to psychophysical detection thresholds and minimum detectable gap thresholds in single unit recordings. Cumulatively, results provide evidence that M100 resolution for brief fluctuations in sounds reflects temporal acuity properties that are both intrinsic to the auditory system and critical to the accurate perception of speech.

Effects of 900 MHz electromagnetic fields exposure on cochlear cells' functionality in rats: evaluation of distortion product otoacoustic emissions.

In recent years, the widespread use of mobile phones has been accompanied by public debate about possible adverse consequences on human health. The auditory system is a major target of exposure to electromagnetic fields (EMF) emitted by cellular telephones; the aim of this study was the evaluation of possible effects of cellular phone-like emissions on the functionality of rat's cochlea. Distortion Products OtoAcoustic Emission (DPOAE) amplitude was selected as cochlea's outer hair cells (OHC) status indicator. A number of protocols, including different frequencies (the lower ones in rat's cochlea sensitivity spectrum), intensities and periods of exposure, were used; tests were carried out before, during and after the period of treatment. No significant variation due to exposure to microwaves has been evidenced.

Auditory imagery mismatch negativity elicited in musicians.

A mismatch between auditory sensation and expectant imagery of syllables elicited a possible equivalent of mismatch negativity in a previous study. The purpose of this study was to verify whether auditory imagery from musical notation could also mediate such imagery-based mismatch negativity. Neuromagnetic recording was obtained from eight musicians, who were instructed to identify unpredictably occurring pitch mismatches between a random tone sequence and a visually presented musical score. The difference between incongruent and congruent responses showed a magnetic distribution consistent with two frontal-negative current dipoles bilaterally located in the vicinity of Heschl's gyrus, peaking at approximately 150 ms in latency. This imagery-based mismatch negativity may represent an early neural process of deviance detection between the sensory input and expectant imagery.

The intensity dependence of auditory evoked ERP components predicts responsiveness to reboxetine treatment in major depression.

INTRODUCTION: The intensity (loudness)-dependent amplitude change (IDAP) of auditory evoked event-related potential (ERP) components has been suggested as an indicator of central serotonergic neurotransmission. In patients with major depression, associations of high IDAP with favorable SSRI treatment outcome have been reported. This is the first study to assess the predictive value of the IDAP in SNRI treatment. METHODS: We evaluated the pre-treatment intensity-dependent change of auditory evoked P1, N1, P2, and P1/N1 and N1/P2 peak-to-peak amplitudes in 14 inpatients with major depressive episode (DSM IV) in the course of 24 days of treatment with the SNRI reboxetine (6-12 mg/d). RESULTS: Our data revealed a highly significant correlation between lower intensity-dependent N1 amplitude slopes prior to reboxetine treatment and stronger decrease of HDRS total score at Fz ( r = 0.86, P < 0.001), Fcz ( r = 0.91, P < 0.001), and Cz ( r = 0.93, P < 0.001). CONCLUSION: This result corroborates the hypothesis of the IDAP as a differential indicator of serotonergic versus noradrenergic antidepressant psychopharmacotherapy.

The intensity dependence of the auditory evoked N1 component as a predictor of response to Citalopram treatment in patients with major depression.

The intensity dependence of the auditory evoked N1 ERP component (IDAP) has been suggested as an indicator of central serotonergic neurotransmission with relevance to pharmacological treatment. We report the results of a study evaluating the IDAP in 16 in-patients fulfilling DSM-IV criteria for major depressive episode in the course of treatment with the SSRI Citalopram. Our data revealed a significant correlation between the intensity slopes of the N1 amplitude prior to Citalopram treatment and treatment response: patients with higher intensity slopes of N1 amplitude showed a significantly stronger decrease of HDRS-Score after Citalopram treatment than patients within the lower intensity slope ranges. Our results indicate an association of N1 amplitude intensity dependence with response to antidepressant treatment with Citalopram.

Effect of irradiation on vestibular evoked myogenic potentials in nasopharyngeal carcinoma survivors.

BACKGROUND: This study aims to investigate the effect of irradiation on vestibular evoked myogenic potentials (VEMPs) in nasopharyngeal carcinoma (NPC) survivors, because radiotherapy to NPC covers a column from the basal skull to the clavicle level. METHODS: Twenty-two irradiated NPC survivors and five fresh NPC patients were subjected to VEMP testing, which is evoked by short-tone burst (95 dBHL, 500 Hz) stimulation. Interactions among VEMPs and radiation effects, such as radiation dosage, postirradiation interval, radiation-induced otitis media, sensorineural hearing loss, or canal paresis, were then explored. RESULTS: The mean latencies of p13 and n23 in irradiated ears were significantly delayed compared with either pr-irradiated ears or normal control ears. Delayed VEMPs represented 50% in ears with a mean radiation dosage of 71 Gy, whereas it represented 100% in those with a mean radiation dosage of 123 Gy. Ears with radiation otitis media revealed higher occurrence (65%) of delayed VEMPs than those without radiation otitis media (29%, p <.05), possibly because of radiation sequela affecting the brainstem and neck. However, delayed VEMPs were unrelated to sensorineural hearing loss or canal paresis caused by irradiation. CONCLUSIONS: Delayed VEMPs in NPC survivors are possibly due to radiation-induced otitis media, a brainstem lesion, or neck fibrosis. Hence, VEMP testing may expand the test battery for clinicians to explore balance problems in NPC survivors after irradiation.

P300 as indicator of effects of prophylactic cranial radiation.

In order to assess the late adverse effects of cranial radiation on the central nervous system, 33 children with acute lymphocytic leukemia were examined through event-related potential P300, brain response analysis. P300 latency was significantly prolonged in children who received both prophylactic cranial radiation and intrathecal methotrexate. Although a longitudinal study is necessary, we believe that P300 is useful in the assessment of the adverse effects of cranial radiation in children with acute lymphocytic leukemia.

Potenciales evocados auditivos del tallo cerebral / Evoked potentials auditory of cerebral stem

Presentamos el análisis de las curvas de intensidad-latencia de 20 sujetos normales en edades comprendidas entre 15-35 años. La estimulación acústica se efectúo con clicks, usando un equipo marca Amplaid, modelo MK-10, presentados monoauralmente a través de audífonos, pasando 2000 clicks a una tasa de 11/seg. Se considera de gran importancia establecer las curvas de intensidad/latencia en población normal para poder comparar con registros patológicos

[The characteristics of perceptive learning and memory in psychopathological states]. / Osobennosti pertseptivnogo obucheniia i pamiati pri psikhopatologicheskikh sostoianiiakh.

Dynamics is studied of visual images recognition in patients with schizophrenia under the influence of small doses of ionizing radiation used with therapeutic purpose. Functional state of the brain is evaluated by amplitude-temporal parameters of visual and auditory EPs. After conducted therapy no changes in responses to light flashes are found, and in auditory EPs in a part (the first group) of patients there is an increase of the component N1 amplitude in the frontal area. The same group is characterized by lower parameters of visual images recognition. Conclusion is made about the presence of non-specific changes of visual gnosis in patients with schizophrenia and about involvement of the associative frontal structures in pathologic process. Possible mechanisms of disturbance of the perceptive learning and memory processes in schizophrenia are discussed.

The effect of brain radiotherapy on the P3 component of ERP's.

Nine patients with lung cancer without brain metastasis were studied pre and post brain prophylactic radiotherapy (30 Gy) to verify the effect of radiation on the cognitive processes. The P3 component of event-related potentials was used in this study. The latencies pre and post-radiation were compared and a significant delay (p less than 0.01) was detected in patients after treatment. These results suggest that brain radiotherapy may produce a cognitive impairment, as reported by many Authors.

[Effect of low-energy laser irradiation on the functional state of the acoustic analyzer (experimental study)]. / Vliianie izlucheniia nizkoenergeticheskogo lazera na funktsional'noe sostoianie slukhovogo analizatora (eksperimental'noe issledovanie).

The acoustic function of guinea-pigs (in terms of ERA) before and after middle ear laser treatment (LHe-75, radiation intensity 15-17 mW, total dose 63 J/cm2, number of exposures 14) was investigated. The experiment was carried out using three groups of animals. Group 1 included healthy young animals. Group 2 consisted of adult animals with no signs of otitis media suppurativa. Group 3 involved adult guinea-pigs with chronic suppurative otitis media. After laser treatment all the animals showed increase of amplitudes of all ERA peaks, specifically of the first peak, an increase of the A1/A4 ratio, and an insignificant shortening of L1 at low sound intensities in group 1 and group 2 animals. This may suggest a greater excitation of the first component of the acoustic system. The group 3 animals exhibited a greater L1; this indicates that laser therapy of an untreated cavity during chronic otitis media may aggravate the pathological process. This pathology requires pretreatment of the middle ear cavity and laser therapy in combination with other therapeutic measures. None of the treated animals showed changes of the second time interval, whereas the third time interval (central time of conduction) became shorter, particularly on the side exposed to laser treatment. Our findings demonstrated differences in responses of adult and young animals to laser treatment (distinct shortening of the central time of conduction in those latter) which obviously needs further study.

Brainstem auditory evoked potentials after irradiation of nasopharyngeal carcinoma--report on two cases with myelopathy of the brainstem.

Brainstem auditory evoked potentials (BAEP) were recorded in two patients with nasopharyngeal carcinoma (NPC) irradiated 14 and three years ago respectively and compared with 15 healthy controls. The patients had features of post-irradiation myelopathy of the brainstem with reduced gag reflex, unilateral vocal cord paralysis and fasciculation of the tongue. The first patient had a blind left eye. The second patient had quadriparesis. All ears revealed post-irradiation otitis media changes and mixed deafness. BAEP was not recognizable in the left ear of the first patient and was normal in the left ear of the second patient. Simultaneous electrocochleogram and BAEP were recorded from the right ear of the first case. The wave I-V latency interval were prolonged in both right ears. In the absence of local recurrence and brain secondaries, these BAEP changes are attributed to the post-irradiation myelopathy of brainstem.