Central Auditory Responses Research Articles

Cochlear Synaptopathy Changes Sound-Evoked Activity Without Changing Spontaneous Discharge in the Mouse Inferior Colliculus.

Tinnitus and hyperacusis are life-disrupting perceptual abnormalities that are often preceded by acoustic overexposure. Animal models of overexposure have suggested a link between these phenomena and neural hyperactivity, i.e., elevated spontaneous rates (SRs) and sound-evoked responses. Prior work has focused on changes in central auditory responses, with less attention paid to the exact nature of the associated cochlear damage. The demonstration that acoustic overexposure can cause cochlear neuropathy without permanent threshold elevation suggests cochlear neuropathy per se may be a key elicitor of neural hyperactivity. We addressed this hypothesis by recording responses in the mouse inferior colliculus (IC) following a bilateral, neuropathic noise exposure. One to three weeks post-exposure, mean SRs were unchanged in mice recorded while awake, or under anesthesia. SRs were also unaffected by more intense, or unilateral exposures. These results suggest that neither neuropathy nor hair cell loss are sufficient to raise SRs in the IC, at least in 7-week-old mice, 1–3 weeks post exposure. However, it is not clear whether our mice had tinnitus. Tone-evoked rate-level functions at the CF were steeper following exposure, specifically in the region of maximal neuropathy. Furthermore, suppression driven by off-CF tones and by ipsilateral noise were reduced. Both changes were especially pronounced in neurons of awake mice. This neural hypersensitivity may manifest as behavioral hypersensitivity to sound – prior work reports that this same exposure causes elevated acoustic startle. Together, these results indicate that neuropathy may initiate a compensatory response in the central auditory system leading to the genesis of hyperacusis.

Timbre representation and property analysis of underwater noise based on a central auditory model

In order to establish quantitative timbre representation of underwater noise, this paper tries to build a relationship between essential timbre scores and central auditory responses to stimulus based on partial least squares regression, and use regression coefficients to interpret the physical meaning of each dimension. In order to verify the utility of this method, this paper extracts a large amount of timbre descriptors as independent variables for comparisons, and it is shown that the predictive ability of the central auditory model is better. Finally it is found from two types of timbre representations that the first three dimensions in the timbre space can be respectively interpreted as high-frequency energy ratio, spectral flatness and temporal continuity; however, dimension 4 cannot be related to any acoustical features.

Neural Representations of Courtship Song in theDrosophilaBrain

Acoustic communication in drosophilid flies is based on the production and perception of courtship songs, which facilitate mating. Despite decades of research on courtship songs and behavior in Drosophila, central auditory responses have remained uncharacterized. In this study, we report on intracellular recordings from central neurons that innervate the Drosophila antennal mechanosensory and motor center (AMMC), the first relay for auditory information in the fly brain. These neurons produce graded-potential (nonspiking) responses to sound; we compare recordings from AMMC neurons to extracellular recordings of the receptor neuron population [Johnston's organ neurons (JONs)]. We discover that, while steady-state response profiles for tonal and broadband stimuli are significantly transformed between the JON population in the antenna and AMMC neurons in the brain, transient responses to pulses present in natural stimuli (courtship song) are not. For pulse stimuli in particular, AMMC neurons simply low-pass filter the receptor population response, thus preserving low-frequency temporal features (such as the spacing of song pulses) for analysis by postsynaptic neurons. We also compare responses in two closely related Drosophila species, Drosophila melanogaster and Drosophila simulans, and find that pulse song responses are largely similar, despite differences in the spectral content of their songs. Our recordings inform how downstream circuits may read out behaviorally relevant information from central neurons in the AMMC.

An Evoked Potential Study of the Developmental Time Course of the Auditory Nerve and Brainstem in Children Using Cochlear Implants

Central auditory responses to electrical stimulation from a cochlear implant were studied in 75 pre-lingually deafened children and 11 adults. Electrically evoked auditory brainstem response (EABR) latencies significantly decreased with duration of cochlear implant use and were not significantly affected by the age at implant activation. Significant decreases in early latency waves and interwaves occurred within the first 1–2 months of implant use, whereas longer term changes (6–12 months) were found for eV and eIII-eV, which measure activity in the more rostral brainstem. Comparisons to acoustically evoked auditory brainstem response (ABR) in children with normal hearing suggested shorter interwave EABR latencies, reflecting either distinct neural generators or increased neural synchrony, but similar rates of change in the later latency eV and eIII-eV with time in sound. In sum, normal-like development of the rostral auditory brainstem is promoted by cochlear implant use in children of a wide range of ages.

Auditory neuropathy in siblings with Waardenburg's syndrome

We report two siblings with a family history of Waardenburg's syndrome (WS) for whom the audiological profile corresponds to auditory neuropathy (AN). They have; (1) bilateral severe to profound hearing loss, (2) robust oto-acoustic emissions (OAEs) in both ears, and (3) no auditory evoked responses at 95 dBnHL bilaterally. Electrocochleography (ECochG) and auditory middle and late latency potentials were performed in one of the children. Results showed cochlear and neural activities in both ears. Central auditory responses were not conclusive. These children did not have any history of neonatal illness and one child was diagnosed with AN at the age of 3 weeks and the other at the age of 11 months.

Responses of central auditory neurons modeled with finite impulse response (FIR) neural networks

To simulate central auditory responses to complex sounds, a computational model was implemented. It consists of a multi-scale classification process, and an artificial neural network composed of two modules of finite impulse response (FIR) neural networks connected to a maximum network. Electrical activities of single auditory neurons were recorded at the rat midbrain in response to a repetitive pseudo-random frequency modulated (FM) sound. The multi-scale classification process divides the training dataset into either strong or weak response using a multiple-scale Gaussian filter that based on response probability. Two modules of FIR neural network are then independently trained to model the two types of responses. This caters for the possible differences in neuronal circuitry and transmission delay. Their outputs are connected to a maximum network to generate the final output. After training, we use a different set of FM responses collected from the same neuron to test the performance of the model. Two criteria are adopted for assessment. One measures the matching of the modeled output to the actual output on a point-to-point basis. Another measures the matching of bulk responses between the two. Results show that the proposed model predicts the responses of central auditory neurons satisfactorily.

Central auditory onset responses, and temporal asymmetries in auditory perception

Historically, central auditory responses have been studied for their sensitivity to various parameters of tone and noise burst stimulation, with response rate plotted as a function of the stimulus variable. The responses themselves are often quite brief, and locked in time to stimulus onset. In the stimulus amplitude domain, it has recently become clear that these responses are actually driven by properties of the stimulus’ onset transient, and this has had important implications for how we interpret responses to manipulations of tone (or noise) burst plateau level. That finding was important in its own right, but a more general scrutiny of the available neurophysiological and psychophysical evidence reveals that there is a significant asymmetry in the neurophysiological and perceptual processing of stimulus onsets and offsets: sound onsets have a more elaborate neurophysiological representation, and receive a greater perceptual weighting. Hypotheses about origins of the asymmetries, derived independently from psychophysics and from neurophysiology, have in common a response threshold mechanism which adaptively tracks the ongoing level of stimulation.

Developmental changes in P1 and N1 central auditory responses elicited by consonant-vowel syllables

Normal maturation and functioning of the central auditory system affects the development of speech perception and oral language capabilities. This study examined maturation of central auditory pathways as reflected by age-related changes in the P1/N1 components of the auditory evoked potential (AEP). A synthesized consonant-vowel syllable (ba) was used to elicit cortical AEPs in 86 normal children ranging in age from 6 to 15 years and ten normal adults. Distinct age-related changes were observed in the morphology of the AEP waveform. The adult response consists of a prominent negativity (N1) at about 100 ms, preceded by a smaller P1 component at about 50 ms. In contrast, the child response is characterized by a large P1 response at about 100 ms. This wave decreases significantly in latency and amplitude up to about 20 years of age. In children, P1 is followed by a broad negativity at about 200 ms which we term N1b. Many subjects (especially older children) also show an earlier negativity (N1a). Both N1a and N1b latencies decrease significantly with age. Amplitudes of N1a and N1b do not show significant age-related changes. All children have the N1b; however, the frequency of occurrence of N1a increases with age. Data indicate that the child P1 develops systematically into the adult response; however, the relationship of N1a and N1b to the adult N1 is unclear. These results indicate that maturational changes in the central auditory system are complex and extend well into the second decade of life.

Central auditory function in a hearing-impaired white mouse

The dysfuction of the stria vascularis in the viable dominant spotting mutant mouse results in the reduction or the absence of the endocochlear potential. However, these mutants respond to an intense acoustic stimulus with a Preyer reflex (pinna twitch). This study used 14C autoradiography and electromyography to investigate central auditory responses in this mutant. There were three main findings: (1) autoradiography demonstrated an increase in the metabolic rate within each of the central auditory nuclei during noise exposure compared with silence; (2) electromyographic recordings indicated that there was no tensor tympani muscle reflex; (3) the mutants were found to be susceptible to audiogenic seizures. It was concluded that the central auditory pathway of the viable dominant spotting mutant could be activated despite the abnormal striai function. Absence of the tensor tympani muscle reflex, together with auditory deprivation, might contribute to the susceptibility to audiogenic seizures.

Development of BSER in kittens: Evidence for different central and peripheral maturation rates

Brainstem evoked responses (BSER) were recorded in 30 kittens from 7 litters. Animals were unanesthetized but restrained. Signals were condensation clicks presented in free field. Latencies and amplitudes of BSER waves I and V were measured at various times during the first 90 postnatal days. Plots of BSER component latencies as a function of postnatal age were computer‐fitted by decaying exponentials of the form Y = a + b* exp(−cX). In all kittens, wave I latency attained adult status earlier than wave V. At 90‐dB peak SPL, for example, 95% of the adult latency value was achieved at a mean age of 34.4 days for wave I and 38.1 days for wave V. The age‐versus‐latency plots are not simple offsets of each other, however. Wave I latency shows only a rapid decline to its asymptotic value, but wave V latency shows a rapid decline phase followed by an extended period of slow decline. The data support the notion that maturation of central auditory responses is not explained entirely by maturation of the cochlea and auditory nerve.

The development of some peripheral and central auditory responses in the neonatal cat

The development of cochlear nerve action potential thresholds at different frequencies (AP audiograms) and inferior colliculus (IC) single unit thresholds and tuning was examined in barbiturate-anaesthetized kittens. AP thresholds decreased over the whole frequency spectrum during the first 5 weeks of life. Threshold to high-frequency stimulation remained higher in 7-week-old animals than in adults. These results are in contrast to previous reports which have suggested that the AP response and gross cochlear anatomy are mature by the end of the second week. These differences may be due to the fact that the AP audiogram technique provides a measure of the activity of discrete regions along the cochlear partition. IC units in animals younger than 3.5 weeks had significantly elevated thresholds and broader tuning than those of the adult cat. Comparison of AP audiogram and IC unit thresholds in the adult revealed that these indices show similar frequency-dependent sensitivity. The slower maturation revealed by the AP audiogram may be due to the greater number and/or synchrony of cochlear nerve discharges needed to produce the gross AP. If this were the case, perception of suprathreshold sounds might not develop as quickly as thresholds for sound detection.

Influence of Central Depressants on the Central Auditory Responses in the Cat

Influence of Central Depressants on the Central Auditory Responses in the Cat