Pamela Falzarano

Forward masking properties of neurons in the dorsal cochlear nucleus: Possible role in the process of echo suppression

The majority of single unit studies in the auditory system have been carried out using stimuli whose temporal and spectral contexts are held constant. Relatively little attention has been given to the influence of context on unit response properties. Indeed, auditory nerve fiber responses are known to be context-dependent due to the property of forward masking, a phenomenon by which the response to one sound results in a reduction in the response to a subsequent sound. Forward masking might be expected to be even more influential at central levels of the auditory pathway where the responses are reshaped by additional synaptic interactions. The purpose of the present study was to characterize the forward masking properties of neurons in the dorsal cochlear nucleus (DCN). A tool was developed for measuring the response to a probe tone as a function of delay following a previous tone-burst. The frequency of the probe was held constant at the units characteristic frequency while the frequency of the leading tone (masker) was varied. These measures provided a description of neural masking effects in different temporal and spectral contexts. The data yielded two patterns of suppression. In the first pattern (Type A), the suppression of the probe response became evident immediately following offset of the masker; the suppression bandwidth showed a gradual narrowing as the delay between masker and probe was increased. In the second class (Type B), the suppression of the probe response did not become evident until well after offset of the masker; this pattern appeared more circumscribed in that the suppression bandwidth gradually increased as a function of delay up to a maximum then decreased with further increases in delay. The results imply that mechanisms intrinsic to the DCN contribute to further modification and reshaping of the spectral and temporal context of masking effects beyond those seen in the auditory nerve. It is hypothesized that such properties may be specialized for suppressing the response to echoes thus facilitating communication and localization of sound in enclosed spaces.

Healthcare Provider Cultural Competency: Development and Initial Validation of a Patient Report Measure

OBJECTIVE Health researchers have proposed that provider cultural competency may contribute to health disparities. Yet, this belief continues to lack empirical support, and this is due in part to measurement issues that have plagued the cultural competency construct. In the present research, we report on the development of a theoretically grounded, generally applicable, and patient report measure of provider cultural competency. DESIGN Samples of predominantly African American patients (N=310) were recruited from three urban medical clinics to complete a survey about their relationship with their physician. MAIN OUTCOME MEASURES We examined the factor structure, validity and other psychometric characteristics of a newly proposed patient report measure of provider cultural competency. RESULTS Psychometric analyses supported a tripartite model of cultural competency that was comprised of patient judgments of their physicians cultural knowledge, awareness, and skill. In addition, this result was replicated across multiple clinical contexts, while also demonstrating convergent and incremental validity when correlated with measures of trust, satisfaction and discrimination. CONCLUSION This newly proposed measure addresses prior limitations in cultural competency measurement and may enhance future research by providing a standardized tool for use in multiple clinical and cultural contexts.

Changes in the tonotopic map of the dorsal cochlear nucleus in hamsters with hair cell loss and radial nerve bundle degeneration

Hamsters were exposed to an intense tone (10 kHz) at levels and durations sufficient to cause hair cell loss and radial nerve bundle degeneration. A previous study reported changes in the tonotopic map of the dorsal cochlear nucleus (DCN) in hamsters with tone-induced stereocilia loss. Such changes appear similar to those observed by others in the auditory nerve following acoustic trauma, and suggest that the map alterations have a peripheral origin. However, the potential for tonotopic map reorganization after more severe lesions involving cellular degeneration in the cochlea has not yet been determined. The purpose of the present study was to determine how the tonotopic map of the DCN appears in animals with severe cochlear injury involving hair cell loss and radial nerve bundle degeneration. Neural population thresholds and tonotopic organization were mapped over the surface of the DCN in normal unexposed animals and those showing tone-induced lesions. The results indicate that cochlear lesions characterized mainly by radial bundle degeneration in a restricted portion of the organ of Corti cause changes in a corresponding region of the tonotopic map which reflect primarily changes in the shape and thresholds of neural tuning curves. In many cases the center of the lesion was represented in the DCN as a distinct characteristic frequency (CF) gap in the tonotopic map in which responses were either extremely weak or absent. In almost all cases the map area representing the center of the lesion was bordered by an expanded region of near-constant CF, a feature superficially suggestive of map reorganization (i.e., plasticity). However, these expanded map areas had abnormal tip thresholds and showed other features suggesting that their CFs had been shifted downward by distortion and deterioration of their original tips. Such changes in neural tuning following tone-induced loss of anatomical input to the central auditory pathway are similar to those observed in our previous study and by others in the auditory nerve following less severe acoustic trauma, and thus would seem to have a peripheral origin. Thus, changes in the DCN tonotopic map can be explained by peripheral modifications and do not seem to involve plastic changes (i.e., reorganization).

The development of the reticular lamina in the hamster: An examination of transitory features and their functional roles

This study examines the development of the reticular lamina in the Syrian golden hamster postriatally from birth to adulthood at 2 day intervals using the scanning electron microscope. During this period, numerous transitory features emerged whose roles were concerned primarily with the development of the tectorial membrane (TM). The principal findings were as follows. (1) The surface of the developing organ of Corti produced all the fibrous material composing the minor tectorial membrane (mTM) including radial and longitudinal fiber bundles which formed the skeleton of the TM, and spongy, amorphous material which formed its intervening ground substance. (2) Throughout most of the cochlear spiral, radial fiber bundles were seen extending from the microvilli of supporting cells and projecting toward the major tectorial membrane (MTM). In most of the basal turn, but not in the apical turn, these radial bundles were interwoven with longitudinal fiber bundles which emerged from the surface of Hensens cells. These findings indicate that the architecture of the TM is more complex in the basal turn than in the apex. (3) Increases in the dimensions of the reticular lamina resulted from the emergence of pillar cell headplates and growth in the diameter of hair cells and supporting cells. The emergence of pillar cell headplates was the principal factor contributing to increases in the radial dimension of the reticular lamina. This emergence was most dramatic between 10 and 12 days after birth (DAB) after the mTM completed its growth. Since the mTM appears to be bound medially to the MTM and laterally to the marginal pillars by 10 DAB, it seems likely that the growth of the reticular lamina after 10 DAB causes some stretching of the mTM both radially and longitudinally. (4) Completion of outer hair cell stereocilia growth at 8 DAB was followed by loss of supporting cell attachments of the TM (trabeculae) by 10 DAB, and coincided with the formation of marginal pillars from the third row of supporting cells. It is suggested that the formation of marginal pillars may be required for coupling of the TM to the tips of outer hair cell stereocilia and for induction of radial tension of the mTM. (5) Removal of the marginal pillar attachments occurred following completion of hair cell growth. (6) All structures on the reticular lamina appeared to have adult‐like characteristics by 20 DAB.