Stimulus-dependent oscillations and evoked potentials in chinchilla auditory cortex

Besides the intensity and frequency of an auditory stimulus, the length of time that precedes the stimulation is an important factor that determines the magnitude of early evoked neural responses in the auditory cortex. Here we used chinchillas to demonstrate that the length of the silent period before the presentation of an auditory stimulus is a critical factor that modifies late oscillatory responses in the auditory cortex. We used tetrodes to record local-field potential (LFP) signals from the left auditory cortex of ten animals while they were stimulated with clicks, tones or noise bursts delivered at different rates and intensity levels. We found that the incidence of oscillatory activity in the auditory cortex of anesthetized chinchillas is dependent on the period of silence before stimulation and on the intensity of the auditory stimulus. In 62.5% of the recordings sites we found stimulus-related oscillations at around 8-20 Hz. Stimulus-induced oscillations were largest and consistent when stimuli were preceded by 5 s of silence and they were absent when preceded by less than 500 ms of silence. These results demonstrate that the period of silence preceding the stimulus presentation and the stimulus intensity are critical factors for the presence of these oscillations.     

Effect of a Sound Stimulus on Postural Reactions

The effect of a sound stimulus on postural responses was studied in five subjects (four females and one male). Sound stimuli were noise signals successively applied to loudspeakers placed along an arc, simulating movement of a sound source. A subject stood on a platform centered relative to the arc so that the sagittal plane of the subject coincided with the plane of the arc. Stabilograms of the body's general center of gravity (GCOG) were recorded for 15 s, including 6 s of silence, auditory stimulation (1.6, 3.2, or 4.8 s), and silence after the signal was cut off. A slight decrease in the amplitude of displacement of the GCOG was observed during auditory stimulation. For a signal duration of 4.8 s, a slight forward shift of the GCOG was observed in the sagittal plane, in which the auditory image moved.     

Observations on the effects of vibration and noise on plasma ACTH and zinc levels, pregnancy and respiration rate in the guineapig

The responses of female guineapigs to vibration and noise were examined with the use of an apparatus designed to simulate transport. Peak levels of plasma ACTH and zinc concentrations were attained after 4 min of exposure to vibration and 80-90 dB of noise. The respiration rate, normally around 90/min, was increased to 103/min when the animals were moved (while still in their cages) to the experimental area; it rose to 129/min when the apparatus was switched on to expose the animals to vibration and noise. Those left adjacent to the apparatus and exposed to noise alone elevated their respiration rates to 115/min. Respiration rates returned to normal within 2.5 h. There was no apparent effect on the maintenance of pregnancy, gestation length, litter size or post-partum growth of the young born to guineapigs exposed to this vibration and noise for a period of 1 h at mid-term.     

Traumatic Stress Disorder Observed in an Adult Wild Captive Wolf (Canis lupus)

Music or other background sounds are often played in barns as environmental enrichment for animals on farms or to mask sudden disruptive noises. However, previous studies looking at the effects of this practice on nonhuman animal well-being and productivity have found contradictory results. This study monitored the vocal responses of piglets, as indicators of well-being, to evaluate the effect of various sounds played during 2 simulations of stressful farm procedures: (a) the 5 min the animals were held as if for castration and (b) the first 20 hr after weaning. The sound treatments included pink noise, music, vocalizations made by other piglets during actual castrations or the first hours after weaning, and silence (control). The study presented pink noise and music both with and without a binaural beat in the delta-theta frequency range. In both the handling and weaning situations, none of the sound treatments reduced the piglets' call rate below that heard during the control. Piglets vocalized most during playback of pink noise and least during silence and playback of calls from other pigs. These results suggest that playing music or other sounds provides no improvement in conditions for piglets during handling and weaning.     

Can Ambient Sound Reduce Distress in Piglets During Weaning and Restraint?

Music or other background sounds are often played in barns as environmental enrichment for animals on farms or to mask sudden disruptive noises. However, previous studies looking at the effects of this practice on nonhuman animal well-being and productivity have found contradictory results. This study monitored the vocal responses of piglets, as indicators of well-being, to evaluate the effect of various sounds played during 2 simulations of stressful farm procedures: (a) the 5 min the animals were held as if for castration and (b) the first 20 hr after weaning. The sound treatments included pink noise, music, vocalizations made by other piglets during actual castrations or the first hours after weaning, and silence (control). The study presented pink noise and music both with and without a binaural beat in the delta-theta frequency range. In both the handling and weaning situations, none of the sound treatments reduced the piglets' call rate below that heard during the control. Piglets vocalized most during playback of pink noise and least during silence and playback of calls from other pigs. These results suggest that playing music or other sounds provides no improvement in conditions for piglets during handling and weaning.     

Auditory analysis of the sound source approaching and withdrawing: psychoacoustic and neurophysiological correlates

The findings seemed to be based on direction and velocity of modelling the radial sound source shifting in free acoustic field. The threshold and the optimal parameters of the acoustic model imitating the approaching and withdrawing of the sound source shifting in silence and under conditions of noise, were established. A correlation between peak-to-peak amplitudes of the N1-P2 components of auditory EPs and the imitated direction of the sound shifting, was shown. The role of different left and right hemispheres' areas in perception of the radial sound source was analysed. The detector features of the central auditory neurones were shown as a possible mechanism of estimating the sound source approaching and withdrawal.     

R-weighting provides better estimation for rat hearing sensitivity

Since sounds may induce physiological and behavioural changes in animals, it is necessary to assess and define the acoustic environment in laboratory animal facilities. Sound studies usually express sound levels as unweighted linear sound pressure levels. However, because a linear scale does not take account of hearing sensitivity-which may differ widely both between and within species at various frequencies-the results may be spurious. In this study a novel sound pressure level weighting for rats, R-weighting, was calculated according to a rat's hearing sensitivity. The sound level of a white noise signal was assessed using R-weighting, with H-weighting tailored for humans, A-weighting and linear sound pressure level combined with the response curves of two different loudspeakers. The sound signal resulted in different sound levels depending on the weighting and the type of loudspeaker. With a tweeter speaker reproducing sounds at high frequencies audible to a rat, R- and A-weightings gave similar results, but the H-weighted sound levels were lower. With a middle-range loudspeaker, unable to reproduce high frequencies, R-weighted sound showed the lowest sound levels. In conclusion, without a correct weighting system and proper equipment, the final sound level of an exposure stimulus can differ by several decibels from that intended. To achieve reliable and comparable results, standardization of sound experiments and assessment of the environment in animal facilities is a necessity. Hence, the use of appropriate species-specific sound pressure level weighting is essential. R-weighting for rats in sound studies is recommended.     

耳鸣动物模型的建立及药物对大鼠耳鸣的影响

目的：建立耳鸣动物模型并测试药物对动物耳鸣的影响。方法：让动物形成耳内有声音存在是安全的、而耳内无声音感往往伴随着危险因素这样一个条件反射,当动物有耳鸣时把它也作为部分安全的信号,在行为中表现出来。用注射水杨酸钠的造成动物耳鸣,通过不同组别大鼠行为实验的结果判断动物耳鸣的存在与否及药物的作用。结果：大鼠注射水杨酸钠后有鸣产生,抗癫痫药Ｌａｍｏｔｒｉｇｉｎｅ不能有效地缓解耳鸣,补肾中药复方改善了水杨     

Prenatal Loud Music and Noise: Differential Impact on Physiological Arousal,Hippocampal Synaptogenesis and Spatial Behavior in One Day-Old Chicks

Prenatal auditory stimulation in chicks with species-specific sound and music at 65 dB facilitates spatial orientation and learning and is associated with significant morphological and biochemical changes in the hippocampus and brainstem auditory nuclei. Increased noradrenaline level due to physiological arousal is suggested as a possible mediator for the observed beneficial effects following patterned and rhythmic sound exposure. However, studies regarding the effects of prenatal high decibel sound (110 dB; music and noise) exposure on the plasma noradrenaline level, synaptic protein expression in the hippocampus and spatial behavior of neonatal chicks remained unexplored. Here, we report that high decibel music stimulation moderately increases plasma noradrenaline level and positively modulates spatial orientation, learning and memory of one day-old chicks. In contrast, noise at the same sound pressure level results in excessive increase of plasma noradrenaline level and impairs the spatial behavior. Further, to assess the changes at the molecular level, we have quantified the expression of functional synapse markers: synaptophysin and PSD-95 in the hippocampus. Compared to the controls, both proteins show significantly increased expressions in the music stimulated group but decrease in expressions in the noise group. We propose that the differential increase of plasma noradrenaline level and altered expression of synaptic proteins in the hippocampus are responsible for the observed behavioral consequences following prenatal 110 dB music and noise stimulation.     

Stress and Auditory Responses of the Otophysan Fish,Cyprinella venusta,to Road Traffic Noise

Noise pollution from anthropogenic sources is an increasingly problematic challenge faced by many taxa, including fishes. Recent studies demonstrate that road traffic noise propagates effectively from bridge crossings into surrounding freshwater ecosystems; yet, its effect on the stress response and auditory function of freshwater stream fishes is unexamined. The blacktail shiner (Cyprinella venusta) was used as a model to investigate the degree to which traffic noise impacts stress and hearing in exposed fishes. Fish were exposed to an underwater recording of traffic noise played at approximately 140 dB re 1 μPa. Waterborne cortisol samples were collected and quantified using enzyme immunoassay (EIA). Auditory thresholds were assessed in control and traffic exposed groups by measuring auditory evoked potentials (AEPs). After acute exposure to traffic noise, fish exhibited a significant elevation in cortisol levels. Individuals exposed to 2 hours of traffic noise playback had elevated hearing thresholds at 300 and 400 Hz, corresponding to the most sensitive bandwidth for this species.     

人为噪声对动物的非听觉影响

噪声在环境中广泛存在,城市化的迅速发展也使野生动物接触到人为噪声的机会增大。越来越多的证据表明,人为噪声在许多方面影响着人类的健康以及野生动物的生存。对这些研究进行总结发现,噪声会改变动物的生理状态,使其处在较高的应激水平,进而影响动物的抗氧化能力和免疫能力,甚至使雏鸟的端粒缩短。人为噪声的存在还会影响动物的学习和认知能力,干扰动物觅食、交流等行为。这些因素累积就可能会降低动物后代的存活率,改变物种丰度,对动物的生存造成威胁。对人为噪声带来的非听觉影响的研究,有助于更全面地了解噪声的潜在危害,采取更为积极的缓解应对措施。     

降低外淋巴钙浓度对耳蜗电位的影响

本实验在人工灌流条件下降低鼓阶外淋巴钙的浓度,观察其对听神经动作电位（ＣＡＰ）、耳蜗微音器电位（ＣＭ）以及蜗内直流电位（ＥＰ）的影响,以分析钙离子的作用机制。无钙液鼓阶灌流使ＣＡＰ、ＣＭ幅度可逆地下降,但不明显地改变ＣＡＰＩ／Ｏ曲线的非线性特征。无钙外淋巴灌流并不改变ＥＰ以及用缺氧法得到的负相ＥＰ（Ｎ－ＥＰ）,但使ＥＰ对强声给－撤时的快速变化趋于消失。本文讨论了这些耳蜗生物电改变所提示的钙离子作用的可能机制。     

Contrasting mechanisms for hidden hearing loss: Synaptopathy vs myelin defects

Hidden hearing loss (HHL) is an auditory neuropathy characterized by normal hearing thresholds but reduced amplitudes of the sound-evoked auditory nerve compound action potential (CAP). In animal models, HHL can be caused by moderate noise exposure or aging, which induces loss of inner hair cell (IHC) synapses. In contrast, recent evidence has shown that transient loss of cochlear Schwann cells also causes permanent auditory deficits in mice with similarities to HHL. Histological analysis of the cochlea after auditory nerve remyelination showed a permanent disruption of the myelination patterns at the heminode of type I spiral ganglion neuron (SGN) peripheral terminals, suggesting that this defect could be contributing to HHL. To shed light on the mechanisms of different HHL scenarios observed in animals and to test their impact on type I SGN activity, we constructed a reduced biophysical model for a population of SGN peripheral axons whose activity is driven by a well-accepted model of cochlear sound processing. We found that the amplitudes of simulated sound-evoked SGN CAPs are lower and have greater latencies when heminodes are disorganized, i.e. they occur at different distances from the hair cell rather than at the same distance as in the normal cochlea. These results confirm that disruption of heminode positions causes desynchronization of SGN spikes leading to a loss of temporal resolution and reduction of the sound-evoked SGN CAP. Another mechanism resulting in HHL is loss of IHC synapses, i.e., synaptopathy. For comparison, we simulated synaptopathy by removing high threshold IHC-SGN synapses and found that the amplitude of simulated sound-evoked SGN CAPs decreases while latencies remain unchanged, as has been observed in noise exposed animals. Thus, model results illuminate diverse disruptions caused by synaptopathy and demyelination on neural activity in auditory processing that contribute to HHL as observed in animal models and that can contribute to perceptual deficits induced by nerve damage in humans.     

The amplitude sensitivity of mouse inferior collicular neurons in the presence of weak noise

Natural auditory environment consists of multiple sound sources that are embedded in ambient strong and weak noise. For effective sound communication and signal analysis, animals must somehow extract biologically relevant signals from the inevitable interference of ambient noise. The present study examined how a weak noise may affect the amplitude sensitivity of neurons in the mouse central nucleus of the inferior colliculus (IC) which receives convergent excitatory and inhibitory inputs from both lower and higher auditory centers. Specifically, we studied the amplitude sensitivity of IC neurons using a probe (best frequency pulse) and a masker (weak noise) under simultaneous masking paradigm. For most IC neurons, weak noise masking increases the minimum threshold and decreases the number of impulses. Noise masking also increased the slope and decreased the dynamic range of the rate amplitude function of these IC neurons. The strength of this noise masking was greater at low than at high sound amplitudes. This variation in the amplitude sensitivity of IC neurons in the presence of the weak noise was mostly mediated through GABAergic inhibition. These data indicate that in the real world the ambient weak noise improves amplitude sensitivity of IC neurons through GABAergic inhibition while inevitably decreases the range of overall auditory sensitivity of IC neurons.     

Narwhals react to ship noise and airgun pulses embedded in background noise

Anthropogenic activities are increasing in the Arctic, posing a threat to niche-conservative species with high seasonal site fidelity, such as the narwhal Monodon monoceros. In this controlled sound exposure study, six narwhals were live-captured and instrumented with animal-borne tags providing movement and behavioural data, and exposed to concurrent ship noise and airgun pulses. All narwhals reacted to sound exposure with reduced buzzing rates, where the response was dependent on the magnitude of exposure defined as 1/distance to ship. Buzzing rate was halved at 12 km from the ship, and whales ceased foraging at 7–8 km. Effects of exposure could be detected at distances > 40 km from the ship.At only a few kilometres from the ship, the received high-frequency cetacean weighted sound exposure levels were below background noise indicating extreme sensitivity of narwhals towards sound disturbance and demonstrating their ability to detect signals embedded in background noise. The narwhal''s reactions to sustained disturbance may have a plethora of consequences both at individual and population levels. The observed reactions of the whales demonstrate their auditory sensitivity but also emphasize, that anthropogenic activities in pristine narwhal habitats needs to be managed carefully if healthy narwhal populations are to be maintained.     

Predisposition for and Prevention of Subjective Tinnitus Development

Dysfunction of the inner ear as caused by presbyacusis, injuries or noise traumata may result in subjective tinnitus, but not everyone suffering from one of these diseases develops a tinnitus percept and vice versa. The reasons for these individual differences are still unclear and may explain why different treatments of the disease are beneficial for some patients but not for others. Here we for the first time compare behavioral and neurophysiological data from hearing impaired Mongolian gerbils with (T) and without (NT) a tinnitus percept that may elucidate why some specimen do develop subjective tinnitus after noise trauma while others do not. Although noise trauma induced a similar permanent hearing loss in all animals, tinnitus did develop only in about three quarters of these animals. NT animals showed higher overall cortical and auditory brainstem activity before noise trauma compared to T animals; that is, animals with low overall neuronal activity in the auditory system seem to be prone to develop tinnitus after noise trauma. Furthermore, T animals showed increased activity of cortical neurons representing the tinnitus frequencies after acoustic trauma, whereas NT animals exhibited an activity decrease at moderate sound intensities by that time. Spontaneous activity was generally increased in T but decreased in NT animals. Plastic changes of tonotopic organization were transient, only seen in T animals and vanished by the time the tinnitus percept became chronic. We propose a model for tinnitus prevention that points to a global inhibitory mechanism in auditory cortex that may prevent tinnitus genesis in animals with high overall activity in the auditory system, whereas this mechanism seems not potent enough for tinnitus prevention in animals with low overall activity.     

Noise-invariant Neurons in the Avian Auditory Cortex: Hearing the Song in Noise

Given the extraordinary ability of humans and animals to recognize communication signals over a background of noise, describing noise invariant neural responses is critical not only to pinpoint the brain regions that are mediating our robust perceptions but also to understand the neural computations that are performing these tasks and the underlying circuitry. Although invariant neural responses, such as rotation-invariant face cells, are well described in the visual system, high-level auditory neurons that can represent the same behaviorally relevant signal in a range of listening conditions have yet to be discovered. Here we found neurons in a secondary area of the avian auditory cortex that exhibit noise-invariant responses in the sense that they responded with similar spike patterns to song stimuli presented in silence and over a background of naturalistic noise. By characterizing the neurons'' tuning in terms of their responses to modulations in the temporal and spectral envelope of the sound, we then show that noise invariance is partly achieved by selectively responding to long sounds with sharp spectral structure. Finally, to demonstrate that such computations could explain noise invariance, we designed a biologically inspired noise-filtering algorithm that can be used to separate song or speech from noise. This novel noise-filtering method performs as well as other state-of-the-art de-noising algorithms and could be used in clinical or consumer oriented applications. Our biologically inspired model also shows how high-level noise-invariant responses could be created from neural responses typically found in primary auditory cortex.     

Early postnatal sound exposure induces lasting neuronal changes in the inferior colliculus of senescence accelerated mice (SAMP8): a morphometric study on GABAergic neurons and NMDA expression

Senescence-acceleration-prone mice (SAMP8) provide a model to study the influence of early postnatal sound exposure upon the aging auditory midbrain. SAMP8 were exposed to a 9-kHz monotone of either 53- or 65-dB sound pressure level during the first 30 postnatal days, the neurons in the auditory midbrain responding selectively to 9 kHz were localized by c-fos immunohistochemistry and the following parameters were compared to control SAMP8 not exposed to sound: mortality after sound exposure, dendritic spine density, and quantitative neurochemical alterations in this 9-kHz isofrequency lamina. For morphometric analysis, animals were examined at 1, 4, and 8 months of age. Serial sections of the inferior colliculus were Golgi impregnated or stained immunohistochemically for the expression of 1 subunit of NMDA receptor or GABA. Mortality after exposure to 53 dB was the same as in controls, but was markedly increased from 7 months of age onward after postnatal exposure to 65 dB. No gross morphological alterations were observed in the auditory midbrain after sound exposure. However, sound exposure to 53 or 65 dB significantly reduced dendritic spine density by 11% at 4 months or by 11–17% both at 1 and 4 months of age, respectively. The effect of sound exposure upon neurons expressing the NMDA1 subunit was dose-dependent. Increasing with age until 4 months in control mice and remaining essentially stable thereafter, the percentage of NMDA1-immunoreactive neurons was significantly elevated by 40–66% in 1- and 8-month-old SAMP8 exposed to 53 dB, whereas no significant effect of 65 dB was apparent. The proportion of GABAergic cells declined with age in controls. It was significantly decreased at 1 month after 53 and 65 dB sound exposure. In contrast, it was elevated at later stages, being significantly increased at 4 months after exposure to 53 dB and at 8 months after exposure to 65 dB. The total cell number in the 9-kHz isofrequency lamina of SAMP8 decreased with age, but was not affected by exposure to either 53 or 65 dB. The present results indicate that early postnatal exposure to a monotone of mild intensity has long-term effects upon the aging auditory brain stem. Some of the changes induced by sound exposure, e.g., decline in spine density, are interpreted as accelerations of the normal aging process, whereas other effects, e.g., increased NMDA1 expression after 53 dB and elevated GABA expression after both 53 and 65 dB, are not merely explicable by accelerated aging.     

Sound production, hearing and possible interception under ambient noise conditions in the topmouth minnow Pseudorasbora parva

Sounds were produced by the topmouth minnow Pseudorasbora parva , a common Eurasian cyprinid, during feeding but not during intraspecific interactions. Feeding sounds were short broadband pulses with main energies between 100 and 800 Hz. They varied in their characteristics (number of single sounds per feeding sequence, sound duration and period, and sound pressure level) depending on the food type (chironomid larvae, Tubifex worms and flake food). The loudest sounds were emitted when food was taken up at the water surface, most probably reflecting 'suctorial' feeding. Auditory sensitivities were determined between 100 and 4000 Hz utilizing the auditory evoked potentials recording technique. Under laboratory conditions and in the presence of natural ambient noise recorded in Lake Neusiedl in eastern Austria, best hearing sensitivities were between 300 and 800 Hz (57 dB re 1 μPa v . 72 dB in the presence of ambient noise). Threshold-to-noise ratios were positively correlated to the sound frequency. The correlation between sound spectra and auditory thresholds revealed that P. parva can detect conspecific sounds up to 40 cm distance under ambient noise conditions. Thus, feeding sounds could serve as an auditory cue for the presence of food during foraging.     

The influence of auditory and visual experience on the phonotactic behavior of the cricket,Gryllus bimaculatus

Female crickets lacking experience with phonotaxis to conspecific calling song respond to trains of continuously repeated sound pulses (trill), whereas experienced females do not. In the present study such inexperienced crickets were tested for their responsiveness to trills of pulse repetition periods from 30 to 70 ms on a Y- shaped maze. Stimulation with a repetition period of 30 ms led to unexpectedly low phonotactic and exploratory activity. Initial stimulation with trills of 30- ms repetition period drastically reduced the responsiveness of inexperienced animals to conspecific calling song and other attractive stimuli. Effects of visual stimulation on the phonotactic behavior of female crickets are demonstrated. Threatening visual stimuli changed the behavior of experienced animals to a state that resembles that of inexperienced animals. The relevance of these observations is discussed with respect to the development of the auditory pattern recognition mechanism in crickets.