Continuous Noise Exposure Research Articles

A Late Critical Period for Frequency Modulated Sweeps in the Mouse Auditory System.

Neuronal circuits are shaped by experience during time windows of increased plasticity in postnatal development. In the auditory system, the critical period for the simplest sounds—pure frequency tones—is well defined. Critical periods for more complex sounds remain to be elucidated. We used in vivo electrophysiological recordings in the mouse auditory cortex to demonstrate that passive exposure to frequency modulated sweeps (FMS) from postnatal day 31 to 38 leads to long-term changes in the temporal representation of sweep directions. Immunohistochemical analysis revealed a decreased percentage of layer 4 parvalbumin-positive (PV+) cells during this critical period, paralleled with a transient increase in responses to FMS, but not to pure tones. Preventing the PV+ cell decrease with continuous white noise exposure delayed the critical period onset, suggesting a reduction in inhibition as a mechanism for this plasticity. Our findings shed new light on the dependence of plastic windows on stimulus complexity that persistently sculpt the functional organization of the auditory cortex.

Research and Discussion on the Relationships between Noise-Induced Hearing Loss and ATP2B2 Gene Polymorphism

Long-term and continuous noise exposure can result in noise-induced hearing loss (NIHL), which is a worldwide problem resulting from the interaction of environmental and genetic factors. The ATP2B2 gene polymorphism can destroy cochlear hair cells and increase the risk of NIHL. A case-control study of 760 Chinese textile workers was conducted to investigate the relationship between ATP2B2 polymorphisms and NIHL susceptibility. Venous blood was collected and questionnaires were conducted by professional physicians. A case group and a control group which were typed by individuals' pure-tone audiometry test results were set. Three polymorphism sites of ATP2B2 were genotyped by using the PCR technique. Analysis results revealed that the C allele of rs3209637 (95%CI = 1.08–2.58, odds ratio (OR) = 1.67, P = 0.027) was a dangerous factor and could add to risks of NIHL in the Chinese employees. The data of stratified analysis revealed that individuals who are exposed to noise > 95 dB with the rs3209637 C genotype have a higher susceptibility to NIHL (OR = 1.34, 95%CI = 1.07–1.68). Multifactor dimensionality reduction analysis revealed that the interaction between rs14154 and rs3209637 is linked to increased NIHL risk, and for the interaction among rs14154, smoking and drinking had the same function (OR = 1.54 and 1.77, 95%CI = 1.15–2.07, 1.33–2.37, and P = 0.0037 and P < 0.0001, respectively). Our results suggest that genetic polymorphism rs3209637 C within ATP2B2 is a risk factor for NIHL among Chinese employees and rs3209637 C could be a potential biomarker for NIHL patients.

Investigation continuous noise exposure and occupational performance of the workers in the pharmaceutical industry: A Case Study in an Ampoule and Vial Production Industry

Introduction: Exposure to noise is considered as one of the most important health problems in various industries, especially pharmaceutical industry, which can ultimately lead to significant negative effects on labor force and occupational performance. The aim of this study was to investigate the relationship between continuous noise exposure and occupational performance of the workers in the pharmaceutical industry and ampoule production line in Iran. Method: This cross-sectional study was conducted through a descriptive-analytical method in 2015. The subjects were 100 workers exposed to noise in an ampoule and vial manufacturing factory in Iran. The sound measurement was carried out in accordance with ISO 9612: 2009. The Hersey and Goldsmith questionnaire (ACHIEVE model) was used to investigate the workers’ occupational performance, and the seven dimensions of the questionnaire as well as the final score of occupational performance was determined for each individual. Results: The results showed that there was a low inverse relationship between noise exposure and occupational performance of the total workers in all the halls which was statistically significant (P-value = 0/01, r2 = 0/256). It was also found that there was an inverse relationship between exposure to noise and the seven dimensions, but the relationship was statistically significant only for the dimensions of ability, clarity, and evaluation (P-value &lt;0.05). Conclusion: The present study showed that the workers in the pharmaceutical industry and ampoule production line were often exposed to higher-than-permitted sound level, and such exposures had negative effects on their occupational performance.

The chinchilla animal model for hearing science and noise-induced hearing loss.

The chinchilla animal model for noise-induced hearing loss has an extensive history spanning more than 50 years. Many behavioral, anatomical, and physiological characteristics of the chinchilla make it a valuable animal model for hearing science. These include similarities with human hearing frequency and intensity sensitivity, the ability to be trained behaviorally with acoustic stimuli relevant to human hearing, a docile nature that allows many physiological measures to be made in an awake state, physiological robustness that allows for data to be collected from all levels of the auditory system, and the ability to model various types of conductive and sensorineural hearing losses that mimic pathologies observed in humans. Given these attributes, chinchillas have been used repeatedly to study anatomical, physiological, and behavioral effects of continuous and impulse noise exposures that produce either temporary or permanent threshold shifts. Based on the mechanistic insights from noise-exposure studies, chinchillas have also been used in pre-clinical drug studies for the prevention and rescue of noise-induced hearing loss. This review paper highlights the role of the chinchilla model in hearing science, its important contributions, and its advantages and limitations.

Continuous but not intermittent noise has a negative impact on mating success in a marine fish with paternal care

Anthropogenic underwater noise is a global pollutant of increasing concern but its impact on reproduction in fish is largely unknown. Hence, a better understanding of its consequences for this important link to fitness is crucial. Working in aquaria, we experimentally tested the impact of broadband noise exposure (added either continuously or intermittently), compared to a control, on the behaviour and reproductive success of the common goby (Pomatoschistus microps), a vocal fish with exclusive paternal care. Compared to the intermittent noise and control treatments, the continuous noise treatment increased latency to female nest inspection and spawning and decreased spawning probability. In contrast, many other female and male pre-spawning behaviours, and female ventilation rate (proxies for stress levels) did not differ among treatments. Therefore, it is likely that female spawning decisions were delayed by a reduced ability to assess male acoustic signals, rather than due to stress per se and that the silent periods in the intermittent noise treatment provided a respite where the females could assess the males. Taken together, we show that noise (of similar frequency range as anthropogenic boat noise) negatively affects reproductive success, particularly under a continuous noise exposure.

FAKTOR-FAKTOR YANG BERHUBUNGAN DENGAN GANGGUAN PENDENGARAN PADA TENAGA KERJA PT BNT BENGKULU TENGAH

Continuous and uncertainty noise exposure have possibility in disruption of hearing.These disorders can be both temporary and permanent, besides the noise also can lead to a senseof uncomfortable, anxiety, stress, the increased of heart rate, as well as other disorders of OccupationalAccidents (KAK), Occupational Diseases and Diseases of Employment increased in thelast three years since the year 2012 until 2014 amounted to 5%, 7% and 10%. This study aimedto know the factors associated with hearing loss in labor of PT BNT. This research used observationalwith cross sectional approach. The sample in this research amounted to 56 peoplewith purposive sampling technique. Data were analised using univariat, bivariat Chi Squareand simple multivariate regress logistic regression. There was a significant relationship amongthe use of PPE of employment, labor knowledge of employment, age of employment, the periodof employment, the level of noise with hearing loss of labor of PT BNT. The most dominant factoraffecting hearing loss occurs was work period with Exp (B) 23.889. The use of Personal ProtectionTool for workers, especially Ears Protection in every working chance in the process ofcontinuous employment, increase the habit of using whether with or without supervision, maintainPersonal Protection Tool individually and continuously and for PT BNT In the process ofpersonal protective equipment should be fully prepared, especially Ear Protection Tool Equipment,check the health workforce in the process periodically and regularly, especially the auditorysystem, Enforce reward for workers who use Personal Protection Tool continuously and punishmentfor workers who often do not use Personal Protection Tool.

Association between Exposure to Noise and Sleep and Mental Health Outcomes in a Nationally-Representative Sample of U.S. Adolescents

Background: In 1974, the U.S. Environmental Protection Agency (U.S. EPA) identified an equivalent 24-hour continuous average noise exposure level (LAeq, 24h) of &amp;lt; 55 A-weighted decibels to protect public health with an adequate margin of safety. To date, however, limited U.S.-based research has evaluated the relationship between noise pollution and health. We help fill this gap using data from a nationally-representative sample of U.S. adolescents.Methods: We used a cross-sectional geospatial sound model to estimate noise exposure at the block group level. We dichotomized noise as high (LAeq, 24h &amp;#8805; 55 dB) versus low (LAeq, 24h &amp;lt;55 dB). The National Comorbidity Survey Adolescent Supplement, conducted between 2001-2004 and including several self-reported sleep outcomes and DSM-IV disorder diagnoses, provided our study population. We evaluated the association between noise and sleep and mental health using doubly-robust targeted minimum loss-based estimation and propensity score matching to account for potential confounders, including air pollution.Results: The study included 4,508 urban-dwelling adolescents aged 13-18. Controlling for numerous adolescent, household, and environmental covariates, living in a high- versus low-noise census block-group was associated with later bedtimes on both weeknights and weekend nights (risk difference [RD]: 0.41 hours, 95% CI: -0.01, 0.83, and RD: 0.61 hours, 95% CI: 0.38, 0.84, respectively). We found no association with total number of hours slept. Further, we found that living in a high- versus low-noise census block-group was associated with 69% increased odds of an anxiety or depressive disorder (odds ratio [OR]: 1.69, 95% CI: 1.13, 2.25) and 79% increased odds of substance use disorder (OR: 1.79, 95% CI: 0.91, 2.66); we found no similar associations with behavioral disorders.Conclusion: We found evidence that noise exceeding the U.S. EPA threshold may hold adverse sleep and mental health consequences for U.S. adolescents.

Environmental noise inequity in the city of Barcelona

Environmental noise is a growing concern for urban planners and public health experts. Continuous noise exposure has implications for people’s physical and mental health. Urban planning strategies are also involved in the need for regular noise assessments within urban areas. The objective of this study is to evaluate the exposure to noise of vulnerable population groups in the city of Barcelona, and to determine whether they are affected by an environmental inequity regarding this nuisance. Assessment of noise levels was performed by two methods of analysis—real measures and simulation—in order to build the noise database at block level for the 10 districts of the city. The results obtained by various statistical tests and spatial regression analysis show that children and low-income individuals are not affected by environmental inequity. On the other hand, we found a positive relationship between noise levels and the other groups considered: namely, the unemployed and people over age 65.

The effect of aircraft, road, and railway traffic noise on stroke - results of a case-control study based on secondary data.

Aim:To examine the stroke risks associated with aircraft, road traffic, and railway noise exposure in a large case–control study.Materials and Methods:All people aged ≥40 years living around the Frankfurt airport that were insured by one of three large statutory health insurance funds between 2005 and 2010 were included in the study (n = 1,026,670). Address-specific exposure to aircraft, road, and railway traffic noise was estimated for 2005. We used insurance claim data to identify 25,495 newly diagnosed cases of stroke between 2006 and 2010 and compared them with 827,601 control participants. Logistic regression analysis was used to calculate the odds ratios adjusted for age, sex, local proportion of people receiving unemployment benefits, and if available individual indicators of socioeconomic status (education, occupation).Results:For 24-h continuous aircraft noise exposure, neither increased risk estimates nor a positive linear exposure–risk relation was found. However, stroke risk was statistically significantly increased by 7% [95% confidence intervals (95%CI): 2–13%] for people who were exposed to <40 dB of 24-h continuous aircraft noise, but ≥6 events of maximum nightly sound pressure levels ≥50 dB. For road and railway traffic noise, there was a positive linear exposure–risk relation: Per 10 dB the stroke risk increased by 1.7% (95%CI: 0.3–3.2%) for road traffic noise and by 1.8% (95%CI: 0.1–3.3%) for railway traffic noise. The maximum risk increase of 7% (95%CI: 0–14%) for road traffic noise and 18% (95%CI: 2–38%) for railway traffic noise was found in the exposure category ≥65 to <70 dB.Conclusion:This large case–control study indicates that traffic noise exposure may lead to an increase in stroke risk. It furthermore suggests that maximum aircraft noise levels at night increase the stroke risk even when continuous noise exposure is low, and thus highlights the relevance of maximum noise levels for research and policies on noise protection.

Protective Effects of N-Acetyl-L-Cysteine on the Density of Spiral Ganglion Cells and Histological Changes Induced by Continuous Noise Exposure in Rats.

BackgroundNoise exposure causes loss of cochlea hair cells, leading to permanent sensorineural hearing loss, and initiates pathological changes to the bipolar primary auditory neurons (ANs). This study focuses on the effects of N-acetyl-l-cysteine (NAC) in protecting the density of spiral ganglion cells and in histological changes induced by continuous noise exposure in rats.MethodsTwenty-four male Wistar rats were randomly allocated into four experimental groups to receive NAC, saline, noise, or both noise and NAC. Noise exposure continued for ten days. Saline and NAC were injected daily during the noise exposure, and 2 days before and after the noise exposure. Evaluation of cochlear histopathology and the density of spiral ganglion cells was performed 21 days after exposure.ResultsIn the animals exposed to noise, a reduction in the density of spiral ganglion cells was evident in both the basal and middle turns of the cochlea. This improved on receiving NAC treatment (P = 0.046). In the histopathology evaluation, some histological changes, such as disorganised architecture of the outer hair and supporting cells and a slightly thickened basilar membrane, were found in the basal turns in the noise group.ConclusionNAC offered partial protection against noise exposure by improving the density of spiral ganglion cells and reducing morphological changes.

A history of noise exposure standards

In the 1950s, the Committee on Hearing, Bioacoustics and Biomechanics (CHABA) investigated and developed recommendations for a variety of noise exposures. In 1956, the United States Air Force published AF Regulation 160-3, generally considered to be the first hearing conservation program in the US. The Walsh-Healy Act regulations [41 CFR 50-204.10] defined noise limits for occupational noise exposure for government supply contracts and the Federal Coal Mine Health and Safety Act of 1969 (Public Law 91-173) adopted these limits for underground and surface coal mine operations. The Occupational Safety and Health Act of 1970 (Public Law 91-596) created the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH). NIOSH published Criteria for a Recommended Standard: Occupational Exposure to Noise in 1972. OSHA promulgated a regulation for occupational noise exposure and updated that with the Hearing Conservation Amendment 29 CFR Part 1910.95. The Mine Safety Administration has regulations for noise exposure that were updated in 1999, 30 CFR part 62. The military developed the materiel acquisition standard MIL-STD 1474E for high-level impulse noise. Existing and future needs for noise exposure standards for continuous, intermittent, and impulsive noise exposures will be discussed in this paper.

Demonstrating compliance of noise exposure experienced by British military aircrew with noise legislation in the United Kingdom

In 2005, the Control of Noise at Work Regulations were introduced into UK law and imposed two Exposure Limits Values, one for continuous noise and one for impulse noise. The Ministry of Defence (MOD) has mandated that the legislation will apply in full throughout the military, and hence, there has been a requirement to understand the types of exposure military operators are exposed to. Military aircrew have historically been exposed to high levels of continuous noise and the more stringent legislation has necessitated enhanced noise mitigation, including the development of new hearing protection technologies. However, in more recent years, military aircrew have become increasingly exposed to weapon firing and the MOD are now addressing the implications of the combined effects of the two different exposures and their impact on compliance with the legislation. In-flight measurement of continuous and impulse noise exposure has been conducted in a range of aircraft and the two exposures assessed for compliance with the legislative criteria. To meet the protection requirements in all platforms, enhanced hearing protection technologies are being developed, including Adaptive Digital Active Noise Reduction and comms processing techniques.

The Association between Noise, Cortisol and Heart Rate in a Small-Scale Gold Mining Community-A Pilot Study.

We performed a cross-sectional pilot study on salivary cortisol, heart rate, and personal noise exposures in a small-scale gold mining village in northeastern Ghana in 2013. Cortisol level changes between morning and evening among participants showed a relatively low decline in cortisol through the day (−1.44 ± 4.27 nmol/L, n = 18), a pattern consistent with chronic stress. A multiple linear regression, adjusting for age, sex, smoking status, and time between samples indicated a significant increase of 0.25 nmol/L cortisol from afternoon to evening per 1 dBA increase in equivalent continuous noise exposure (Leq) over that period (95% CI: 0.08–0.42, Adj R2 = 0.502, n = 17). A mixed effect linear regression model adjusting for age and sex indicated a significant increase of 0.29 heart beats per minute (BPM) for every 1 dB increase in Leq. Using standard deviations (SDs) as measures of variation, and adjusting for age and sex over the sampling period, we found that a 1 dBA increase in noise variation over time (Leq SD) was associated with a 0.5 BPM increase in heart rate SD (95% CI: 0.04–−0.9, Adj. R2 = 0.229, n = 16). Noise levels were consistently high, with 24-hour average Leq exposures ranging from 56.9 to 92.0 dBA, with a mean daily Leq of 82.2 ± 7.3 dBA (mean monitoring duration 22.1 ± 1.9 hours, n = 22). Ninety-five percent of participants had 24-hour average Leq noise levels over the 70 dBA World health Organization (WHO) guideline level for prevention of hearing loss. These findings suggest that small-scale mining communities may face multiple, potentially additive health risks that are not yet well documented, including hearing loss and cardiovascular effects of stress and noise.

Evaluation of brainstem auditory evoked potential in noise-induced deafness

Noise-induced hearing loss is an increasingly prevalent but preventable hearing disorder. The hearing deficit is of sensorineural type and its prevalence is next only to age-related hearing loss.1 Occupational health hazards have not received significant attention yet. The rail engine drivers who operate trains in an environment with extreme noise and temperature, is an example. The present study was done to determine whether BAEP is valuable in the early detection of change in the hearing capability of the subjects due to continuous noise exposure. This present study is a cross-sectional study that compares the hearing status of rail engine drivers, exposed to heavy noise for a duration of 10 years or more, and subjects working in quiet environment, matched for age, sex and work routine. The technique used in this study is Brainstem Auditory Evoked Potentials (BAEPs) along with personal interview, tuning fork tests. Of the 60 subjects that we studied, 36 (60%) reported to be having sensorineural deafness. BAEP is a simple, non-invasive technique to detect the change in the hearing capability even in the absence of specific symptoms, when the person himself is not aware of it.

METHOD AND APPARATUS FOR CONTINUOUS NOISE EXPOSURE MONITORING

A method for continuously monitoring noise exposure level of a person via measuring sound level within an ear canal of the person using a sound measurement means linked to a sound level recording device external to the ear canal, wherein the sound measurement means may be shielded from the environment by a hearing protective device, and wherein the cable does not interfere with the ability of the hearing protective device to reduce noise exposure level in the ear canal. Also provided are a system comprising a sound measurement means mounted within an ear canal of the person, an external sound level recording means and a linking cable. Further provided is a system for providing continuous noise exposure monitoring level of a person, and for providing radio communication in a noisy environment, said system comprising the above sound monitoring system linked to a radio signal transmission means, and is switchable between said sound level recording means in a recording mode and said radio signal transmission means in a communication mode.

Subchronic Jp-8 Jet Fuel Exposure Enhances Vulnerability To Noise-Induced Hearing Loss In Rats

Both laboratory and epidemiological studies published over the past two decades have identified the risk of excess hearing loss when specific chemical contaminants are present along with noise. The objective of this study was to evaluate the potency of JP-8 jet fuel to enhance noise-induced hearing loss (NIHL) using inhalation exposure to fuel and simultaneous exposure to either continuous or intermittent noise exposure over a 4-wk exposure period using both male and female Fischer 344 rats. In the initial study, male (n = 5) and female (n = 5) rats received inhalation exposure to JP-8 fuel for 6 h/d, 5 d/wk for 4 wk at concentrations of 200, 750, or 1500 mg/m3. Parallel groups of rats also received nondamaging noise (constant octave band noise at 85 dBlin) in combination with the fuel, noise alone (75, 85, or 95 dB), or no exposure to fuel or noise. Significant concentration-related impairment of auditory function measured by distortion product otoacoustic emissions (DPOAE) and compound action potential (CAP) threshold was seen in rats exposed to combined JP-8 plus noise exposure when JP-8 levels of 1500 mg/m3 were presented with trends toward impairment seen with 750 mg/m3 JP-8 + noise. JP-8 alone exerted no significant effect on auditory function. In addition, noise was able to disrupt the DPOAE and increase auditory thresholds only when noise exposure was at 95 dB. In a subsequent study, male (n = 5 per group) and female (n = 5 per group) rats received 1000 mg/m3 JP-8 for 6 h/d, 5 d/wk for 4 wk with and without exposure to 102 dB octave band noise that was present for 15 min out of each hour (total noise duration 90 min). Comparisons were made to rats receiving only noise, and thosereceiving no experimental treatment. Significant impairment of auditory thresholds especially for high-frequency tones was identified in the male rats receiving combined treatment. This study provides a basis for estimating excessive hearing loss under conditions of subchronic JP-8 jet fuel exposure.

Hearing effects from intermittent and continuous noise exposure in a study of Korean factory workers and firefighters

BackgroundSouth Korea and surrounding countries in East Asia are believed to have the highest proportion in the world of high frequency hearing loss due to occupational noise exposure, yet there has been limited information published in international journals, and limited information for control of noise in local workplaces beyond strategies from western countries. We exploit medical surveillance information from two worker groups to enhance local knowledge about noise-induced hearing loss and explore the possible importance of shift work to risk.MethodsFour-years of hearing data were evaluated for 81 male farm machine factory workers and 371 male firefighters who had successfully completed a health examination and questionnaires for the duration of the study period. The averages of hearing thresholds at 2, 3, and 4 kHz were used as the primary end-point for comparison. Repeat measure analysis adjusted for age, exposure duration and smoking status was used to measure the difference in hearing threshold between the two groups.ResultsNoise levels were measured in the factory at a mean of 82 dBA, with a range of 66-97. No concurrent measurements were taken for the firefighters, but historic comparison values showed a wider range but a similar mean of 76-79 dBA. Although losses during follow-up were negligible, the factory workers had significantly (P < 0.0001) more hearing loss at the baseline of the study than the firefighters in both ears at 2, 3, and 4 kHz, adjusted for age, duration of employment and smoking status. Among those with 10 years of employment, mean losses at these frequencies among the factory workers fell into the impairment range (> 25 dB loss). Firefighters also showed increased losses associated with longer exposure duration, but these were significantly less marked. Losses at lower frequencies (< or = 1 kHz) were negligible in both groups.ConclusionsKorean work environments with continuous noise exposure in the measured range should consider implementation of a hearing conservation program. Further evaluation of hearing loss in workers exposed to irregular or intermittent high noise levels, such as firefighters, is also warranted.

Low‐Dose D‐Methionine and N‐Acetyl‐L‐Cysteine for Protection from Permanent Noise‐Induced Hearing Loss in Chinchillas

Despite efforts at public health awareness and stringent industrial standards for hearing protection, noise-induced hearing loss (NIHL) remains a formidable public health concern. Although many antioxidants have proven to be beneficial in the laboratory for prevention of permanent NIHL, low-dose combinations of compounds with different biochemical mechanisms of action may allow long-term administration with fewer side effects and equal efficacy. The mixture of D-methionine and N-acetyl-L-cysteine administered at levels less than 10% of standard dosing has not been previously reported. Twenty-six female adult Chinchilla laniger were placed in 4 study groups, consisting of (1) a group receiving combination 12.5 mg/kg each D-methionine and N-acetyl-L-cysteine (DMET/NAC group), (2) a group receiving 12.5 mg/kg D-methionine (DMET-only group), (3) a group receiving 12.5 mg/kg N-acetyl-L-cysteine (NAC-only group), and (4) saline controls. Laboratory. All groups received twice-daily intraperitoneal injections 2 days prior to noise exposure, 1 hour before and after exposure on day 3, and for 2 days subsequently, totaling 10 doses of 125 mg/kg for each antioxidant over 5 days. Although NAC-only animals paralleled saline control recovery during 3 weeks, the DMET-only group revealed gradual improvement with statistically significant recovery in the middle frequencies. The DMET/NAC group showed significant improvement at most frequencies compared with controls (P < .001 and P < .05). Significant recovery of hearing was observed following continuous noise exposure with either DMET only or a combination of low-dose DMET/NAC, demonstrating a considerably lower dose of antioxidants required than previously reported for hearing recovery following acoustic trauma.

Pharmacological and deprivation-induced reinstatement of juvenile-like long-term potentiation in the primary auditory cortex of adult rats

Sensory cortices show a decline in synaptic plasticity (e.g., long-term potentiation, LTP) during postnatal maturation. We demonstrate a partial reversal of this decline in rat primary auditory cortex (A1) by pharmacological manipulations or modifications of the acoustic environment. In adult, anesthetized rats, field postsynaptic potentials (fPSPs) in A1 elicited by medial geniculate nucleus (MGN) stimulation consisted of two sequential peaks. Simultaneous application in A1 of a GABA(A) receptor agonist (muscimol) and GABA(B) receptor antagonist (SCH 50911), thought to result in a preferential inhibition of intracortical activity while preserving thalamocortical inputs, suggested that these two fPSP components largely reflect thalamocortical and intracortical synapses, respectively. Rats (postnatal day [PD]60-70) showed moderate LTP of fPSPs following theta-burst stimulation (TBS) of the MGN. Interestingly, repeated episodes (PD10-20 & 50-60) of patterned sound deprivation by continuous white noise exposure resulted in substantial LTP, an effect not seen with single exposure (PD10-20 or 50-60), or two episodes during adulthood (PD50-60 & 100-110). Thus, early sensory deprivation acts as a "prime," allowing subsequent deprivation to reinstate juvenile-like levels of LTP. Older (>PD200) rats that no longer exhibit LTP in A1 showed LTP of the first fPSP peak when TBS occurred during cortical zinc application. We conclude that the age-related decline of plasticity in A1 can be partially reversed by pharmacological techniques or manipulations of the acoustic environment during specific periods of postnatal life.

Aplicação da audiometria troncoencefálica na detecção de perdas auditivas retrococleares em trabalhadores de manutenção hospitalar expostos a ruído

The main purpose of this cross-sectional study was to investigate the presence of retrocochlear disease in a group of maintenance workers from a general hospital, who presents a history of noise exposure. Thirty one workers of three engineering sections with age range from 25 to 60 years and continuous noise exposure from 2 and 45 years, were examined. The evaluation included an audiometric occupational selection and auditory brainstem responses (ABR). ABR abnormalities were detected in seven patients (22.6%) and it was found latency increase of waves III (14.3%) and V (28.6%), and interpeak prolongation I-III (71.4%), III-V (28.6%) and I-V (85.7%). Among 35 ears with normal audition - right, left or both -, four (11,4%) ears presented retrocochlear disease. The high retrocochlear disease prevalence in workers exposed to noise lead us to suppose that this disturbance is more frequent than usually found; therefore it is underestimated in workers diagnostic evaluation. The presence of this kind of disturbance, even with the absence of audiometric alterations, suggests that ABR is more sensitive than the tonal audiometry for noise induced hearing loss investigation.