Monthly Archives: May 2010
Neural substrates underlying vestibular compensation: Contribution of peripheral versus central processing
The vestibulo-ocular reflex (VOR), which functions to stabilize gaze and ensure clear vision during everyday activities, shows impressive adaptation in response to environmental requirements. In particular, the VOR exhibits remarkable recovery following the loss of unilateral labyrinthine input as a result of injury or disease. The relative simplicity of the pathways that mediate the VOR, make it an excellent model system for understanding the changes (learning) that occur in the brain following peripheral vestibular loss to yield adaptive changes. This mini review considers the findings of behavioral, single unit recording and lesion studies of VOR compensation. Recent experiments have provided evidence that the brain makes use of multiple plasticity mechanisms (i.e., changes in peripheral as well as central processing) during the course of vestibular compensation to accomplish the sensory-motor transformations required to accurately guide behavior.
from the Journal of Vestibular Research
Better Hearing Institute Publishes Comprehensive Consumer Guide to Buying Hearing Aids
The Better Hearing Institute (BHI) announced today it has published a comprehensive consumer guide titled “Your Guide to Buying Hearing Aids” (www.betterhearing.org under “hearing loss treatment”). The publication is designed to help people who have made the decision to address their hearing loss and regain their quality of life with the use of hearing aids. The guidelines give confidence to first-time hearing aid buyers by providing a detailed, step-by-step breakdown of what to expect, ask, and look for when visiting a hearing care professional and purchasing a hearing aid. “This guide is designed to offer confidence and support by educating the consumer. We want to help ensure that anyone in need of a hearing aid receives the very best information and professional service available…”
from PRWeb.com
Sophono’s Alpha 1 Hearing Aids Get FDA Clearance
Sophono Inc. of Boulder, Colorado has received FDA approval to market the firm’s Alpha 1 line of bone conducting hearing aids, according to Boulder County Business Report. There are three configurations of the Alpha 1 based on the same audio processor that features four channels, 16 frequency bands, and four programs.
from MedGadget.com
Know that noise? Scientists probe formation of auditory memories
New research uses “noise,” sound waves formed from many thousands of completely unpredictable random numbers played as a sound, to probe how the human brain acquires auditory memories. The study, published by Cell Press in the May 27 issue of the journal Neuron, reveals that learning new sounds is quick, robust, and long-lasting, resembling a sudden insight.
from EurekAlert.org
Tonic and phasic contributions to the pathways mediating compensation and adaptation of the vestibulo-ocular reflex
Processes of vestibular compensation mediate recovery of many aspects of vestibular dysfunction following unilateral vestibular injury. The VOR in response to high-frequency, high-acceleration head movements, however, retains an enduring asymmetry. Head movements that are inhibitory with respect to semicircular canals on the intact side lead to a diminished VOR whereas head movements that are excitatory for semicircular canals on the intact side lead to a VOR that returns close to normal. We review our work directed toward understanding the processes of VOR compensation to high-frequency, high-acceleration head movements and the related topic of adaptation to changes in the visual requirements for a compensatory VOR. Our work has shown that the processes of both compensation and adaptation to these stimuli can be described by a mathematical model with inputs from tonic and phasic components. We have further shown that the dynamics of regular afferents have close resemblance to the tonic pathway whereas the dynamics of irregular afferents match those of the phasic pathway.
from the Journal of Vestibular Research
Vestibular compensation: New clinical and basic science perspectives
No abstract available.
from the Journal of Vestibular Research
Integration of nonlabyrinthine inputs by the vestibular system: Role in compensation following bilateral damage to the inner ear
Inputs from the skin and muscles of the limbs and trunk as well as the viscera are relayed to the medial, inferior, and lateral vestibular nuclei. Vestibular nucleus neurons very quickly regain spontaneous activity following a bilateral vestibular neurectomy, presumably due to the presence of such nonlabyrinthine inputs. The firing of a small fraction of vestibular nucleus neurons in animals lacking labyrinthine inputs can be modulated by whole-body tilts; these responses are eliminated by a spinal transection, showing that they are predominantly elicited by inputs from the trunk and limbs. The ability to adjust blood distribution in the body and maintain stable blood pressure during movement is diminished following a bilateral vestibular neurectomy, but compensation occurs within a week. However, bilateral lesions of the caudal portions of the vestibular nuclei produce severe and long-lasting cardiovascular disturbances during postural alterations, suggesting that the presence of nonlabyrinthine signals to the vestibular nuclei is essential for compensation of posturally-related autonomic responses to occur. Despite these observations, the functional significance of nonlabyrinthine inputs to the central vestibular system remains unclear, either in modulating the processing of vestibular inputs or compensating for their loss.
from the Journal of Vestibular Research
Presynaptic and postsynaptic ion channel expression in vestibular nuclei neurons after unilateral vestibular deafferentation
Vestibular compensation refers to the recovery of function occurring after unilateral vestibular deafferentation, but some patients remain uncompensated. Similarly, more than half of the operated chickens compensate three days after unilateral vestibular ganglionectomy (UVG), but the rest remain uncompensated. This review focuses on the studies performed on the principal cells of the chick tangential nucleus after UVG. The tangential nucleus is a major avian vestibular nucleus whose principal cells are all second-order, vestibular reflex projection neurons participating in the vestibuloocular and vestibulocollic reflexes controlling posture, balance, and eye movements. Using whole-cell patch-clamp approach in brain slice preparations, spontaneous spike firing, ionic conductances, and spontaneous excitatory postsynaptic currents (sEPSCs) are recorded in principal cells from controls and operated chickens three days after UVG. In compensated chickens, the proportion of spontaneous spike firing principal cells and their spike discharge rate are symmetric on the lesion and intact sides, with the rates increased over controls. However, in the uncompensated chickens, the spike discharge rate increases on the lesion side, but not on the intact side, where only silent principal cells are recorded. In all the experimental groups, including controls, silent principal cells are distinguished from spontaneous spiking cells by smaller persistent sodium conductances and higher activation thresholds for the fast sodium channel. In addition, silent principal cells on the intact side of uncompensated chickens have larger dendrotoxin-sensitive potassium conductances, with a higher ratio of immunolabeling for surface/cytoplasmic expression of a dendrotoxin-sensitive, potassium channel subunit, Kv1.1. Finally, in compensated chickens, sEPSC frequency is symmetric bilaterally, but in uncompensated chickens sEPSC frequency increased only on the lesion side, where the expression of Kv1.2 decreased in synaptotagmin-labeled terminal profiles on the principal cell bodies. Altogether, the specific sodium and potassium channels important for the development of spike firing pattern and/or presynaptic glutamate release on vestibular reflex projection neurons may be critically involved in changing postsynaptic neuron excitability after vestibular deafferentation.
from the Journal of Vestibular Research
Understanding Sound Sensitivity in Individuals with Autism Spectrum Disorders
Literature on sound sensitivity in individuals with and without autism spectrum disorders (ASD) is reviewed in this article. Empirical evidence is examined, and physiologic and psychoemotional-behavioral perspectives are described.There is virtually no evidence of true physiological differences in auditory systems of individuals with ASD. It is evident, however, that many people with ASD (a) feel fearful and anxious about sound, and (b) may experience unpleasant physiological sensations because of autonomic and/or behavioral responses to nonpreferred sounds, but (c) can learn to react in less stigmatizing, more effectively self-regulating ways. Current assessment and intervention practices are discussed, and a case is presented. Heightened understanding of this issue among caregivers and interventionists may ultimately improve life participation for individuals with ASD.
Participant expectancies in double-blind randomized placebo-controlled trials: potential limitations to trial validity
Conclusions Participants’ expectancies can undermine the validity of double-blind placebo-controlled RCTs. Researchers conducting these trials should assess participants’ beliefs about their treatment allocation and actively investigate if and how these beliefs may have influenced the trial’s outcome. Clinical Trials 2010; 7: 246—255. http://ctj.sagepub.com
from Clinical Trials
Interaural attenuation for Sennheiser HDA 200 circumaural earphones
Interaural attenuation (IA) was evaluated for pure tones (frequency range 125 to 16000 Hz) using Sennheiser HDA 200 circumaural earphones and Telephonics TDH-39P earphones in nine unilaterally deaf subjects. Audiometry was conducted in 1-dB steps using the manual ascending technique in accordance with ISO 8253-1. For all subjects and for all tested frequencies, the lowest IA value for HDA 200 was 42 dB. The present IA values for TDH-39P earphones closely resemble previously reported data. The findings show that the HDA 200 earphones provide more IA than the TDH-39P, especially at lower frequencies (≤500 Hz). It is concluded that contralateral masking should be applied during pure-tone audiometry with the HDA 200 earphones when the level at the test ear is more than 40 dB above the threshold of the non-test ear.
from the International Journal of Audiology
Polish sentence matrix test for speech intelligibility measurement in noise
The purpose of this study was to develop the Polish sentence matrix test (PSMT) to measure intelligibility of speech presented against a background noise. The PSMT consists of five columns containing: 10 names, 10 verbs, 10 numerals, 10 adjectives, and 10 nouns. Since each word was available as a separate sound file, it was possible to generate different sentences by juxtaposing randomly selected words taken from respective columns. This approach allows 100 000 unique sentences of a fixed grammatical structure to be generated. The speech reception threshold (SRT), i.e. the signal-to-noise ratio (SNR) providing 50% speech intelligibility and S50, the slope of an intelligibility function at the SRT point, were shown to be −9.6 dB and 17.1 %/dB, respectively. Note that in this study dB is regarded as dB SNR, otherwise reference is given. PSMT was also evaluated using an adaptive 1-up/ 1-down staircase procedure in investigations with and without participation of an experimenter. No significant differences were shown for SRTs obtained in these investigations.
from the International Journal of Audiology
Patterns of language and discourse comprehension skills in school-aged children with autism spectrum disorders
The present study examined patterns of language and discourse comprehension skills in Swedish school-aged children with autism spectrum disorders (ASD) (n = 16) as compared to a slightly younger group of typically developing children (n = 16) matched for non-verbal cognitive ability. Results suggested significantly lower abilities in narrative discourse comprehension for the ASD group, but not in oral receptive vocabulary or reception of grammar. This difficulty with discourse-level comprehension appeared to be of a general nature, as no evidence was found for the hypothesis that participants with ASD would find comprehension of inferential discourse information disproportionally more difficult than stated information, or for the hypothesis that discourse processing in ASD would be characterized by an elevated processing of explicitly stated narrative details. The study has clinical and educational implications, as the findings suggest that children with ASD would benefit from being offered specific support for discourse-level comprehension.
Recreational Noise and Its Potential Risk to Hearing
A practical review of some of the most-common threats to people’s hearing
from The Hearing Review
