Hearing research
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Neurons in the nuclei of the lateral lemniscus (NLL) of the big brown bat, Eptesicus fuscus, show several distinctive patterns of response to unmodulated tones. Previous work suggests that sustained responders are specialized to transmit information about sound level and duration while onset responders transmit precise timing information. The biosonar signals of E. fuscus consist of multiple, downward frequency modulated sweeps that change in slope and repetition rate as the bat approaches a target. ⋯ For the majority of neurons in VNLLm, INLL and DNLL, the precision of synchronization was approximately equal for the downward and upward components of the SFM signal; in contrast, 69% of VNLLc neurons responded selectively to the downward component of the SFM signal. All VNLLc neurons and a subset of those in VNLLm, INLL, and DNLL responded synchronously to SFM signals only if the frequency excursions included a border of the excitatory frequency bandwidth, suggesting that the synchronous discharge was due primarily to the repeated passage of the stimulus frequency into and out of the excitatory portion of the response area. In the case of VNLLc neurons, only the high frequency border was effective; Other neurons, especially those in DNLL, responded synchronously to SFM signals with frequency excursions that were confined entirely within the excitatory response area.
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Comparative Study
Hair cell morphology and innervation in the basilar papilla of the emu (Dromaius novaehollandiae).
The emu, being a member of the rather primitive bird group of the palaeognathid Ratitae, may reveal primitives features of the avian basilar papilla. There are, however, no qualitative differences with the papillae of other birds such as the chicken or the starling. There are only quantitative differences in the continuous morphological gradients (such as hair cell height, stereovillar height) from neural to abneural, and from the base to the apex of the papilla. ⋯ Am. 101 (1997) 1574 1584). The afferent nerve fibers contacting the hair cells within the basilar papilla are rather thick, and there are a large number of afferent fibers that contact more than one hair cell. The zone of hair cells without afferent innervation (short hair cells) along the abneural edge of the basilar papilla is rather narrow in the emu.
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Randomized Controlled Trial Comparative Study Clinical Trial
Effect of anesthesia on transient evoked otoacoustic emissions in humans: a comparison between propofol and isoflurane.
The influence of general anesthesia (GA) on auditory brainstem responses (ABRs) has been widely studied in humans whereas few studies have been devoted as yet to its effect on cochlear micromechanical properties. This study was aimed at evaluating: (1) the effect of GA on transient evoked otoacoustic emissions (TEOAEs) in humans (n=10), and (2) to compare the effects induced by two different anesthetic agents: propofol (n=5) and isoflurane (n=5). ⋯ Under propofol, TEOAE amplitude was correlated with blood pressure changes in a highly significant manner, whereas under isoflurane TEOAE levels were completely independent of such hemodynamic patterns. These results infer that (1) the GA induced a decrease in TEOAE amplitude, and that (2) TEOAE changes induced by propofol could depend on the concomitant hemodynamic changes whereas isoflurane could be responsible for TEOAE changes depending on both, hemodynamic changes and its own pharmacological properties.
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Hair cells in the basilar papilla of birds have the capacity to regenerate after injury. Methods commonly used to induce cochlear damage are systemic application of ototoxic substances such as aminoglycoside antibiotics or loud sound. Both methods have disadvantages. ⋯ At day 48 the hair cells appeared to have recovered fully, except for the orientation of the hair cell bundles. The advantage of the local application of the aminoglycoside drug over systemic application is that it damages almost all hair cells in the basilar papilla and it has no toxic side effects. The damage is more extensive than with systemic application.
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The effects of outer hair cell (OHC) loss on evoked potential (EVP) thresholds, amplitudes and forward masking (FWM) functions have been fairly well characterized. In contrast, the effects of inner hair cell (IHC) losses are largely unknown, primarily due to the difficulty of producing selective IHC lesions. Recent studies have shown that IHCs of the chinchilla are preferentially damaged by the anticancer drug, carboplatin. ⋯ IC-EVP amplitudes at suprathreshold levels were sometimes depressed, sometimes enhanced, and in some cases unchanged. IHC lesions increased susceptibility to FWM, particularly at intermediate (10-20 ms) masker-probe intervals, without significantly changing the overall time course of FWM. The results provide new perspectives on the contribution of IHCs to FWM, and on the ability of the central auditory system to adapt to a significant reduction of neural input from the cochlea.