Darlene R. Ketten

Histopathology of Cochlear Implants in Humans

The insertion of an intrascalar electrode array during cochlear implantation causes immediate damage to the inner ear and may result in delayed onset of additional damage that may interfere with neuronal stimulation. To date, there have been reports on fewer than 50 temporal bone specimens from patients who had undergone implantation during life. The majority of these were single-channel implants, whereas the majority of implants inserted today are multichannel systems. This report presents the histopathologic findings in temporal bones from 8 individuals who in life had undergone multichannel cochlear implantation, with particular attention to the type and location of trauma and to long-term changes within the cochlea. The effect of these changes on spiral ganglion cell counts and the correlation between speech comprehension and spiral ganglion cell counts were calculated. In 4 of the 8 cases, the opposite, unimplanted ear was available for comparison. In 3 of the 4 cases, there was no significant difference between the spiral ganglion cell counts on the implanted and unimplanted sides. In addition, in this series of 8 cases, there was an apparent negative correlation between residual spiral ganglion cell count and hearing performance during life as measured by single-syllable word recognition. This finding suggests that abnormalities in the central auditory pathways are at least as important as spiral ganglion cell loss in limiting the performance of implant users.

The chemistry, biology and vertical flux of particulate matter from the upper 400 m of the Cape Basin in the southeast Atlantic Ocean

Abstract Particulate matter, divided into to 53- and >53- μ m size fractions, was obtained using the Large Volume in situ Filtration System (LVFS), Southlant Expedition, R.V. Chain 115, and was analysed for chemical (dry weight, Na, K, Mg, Ca, carbonate, opal, Sr, C and N), organismal (species assemblage and population densities), and morphological distributions. Profiles from LVFS Stas. 4 to 8 covering regions of low to high productivity and coastal upwelling in the southeast Atlantic are compared with that from LVFS Sta. 2, equatorial Atlantic. Maxima in organism abundances and particulate mass were generally coincident and occurred at the base of the mixed layer or near-surface when the mixed layer was poorly developed or absent. A consistent distributional pattern of organisms was observed. Features of the particulate matter distributions attributed to the feeding activities of zooplankton are: strong vertical concentration gradients of mass, organic matter, and organisms; 10-fold enrichment with depth of the > 53- μ m fraction with coccolith carbonate; decrease in organic content from 100% at the surface to 50 to 60% at 400 m; fragmentation of most test material below 100 m; and the production of fecal pellets and fecal matter. Coccolithophorids and diatoms were the dominant sources of particulate carbonate and opal. One- to 53-μm organic C/N ratios were 7.3±0.5 (σ) in productive waters; the μ m ratios were lower. Particulate organic carbon was distributed uniformly below 200 m with concentrations reflecting surface productivity. The calcium to carbonate ratios exceeded unity with values as high as 2.5 being typical of surface waters near Capetown where diatoms dominated; the cycling of excess calcium is 1 to 2 × 10 13 mol yr −1 or approximately 20% of the annual carbonate precipitation by organisms. Vertical mass fluxes through 400m of Foraminifera, fecal pellets, and fecal matter were calculated for three stations using settling models and particle size distributions. Corresponding chemical fluxes of organic carbon, carbonate, and opal are given. Comparisons are made with recalculated fluxes for LVFS Sta. 2. Over 90% of the organic matter produced in the euphotic zone is recycled in the upper 400 m. The recycling efficiency is nearly 99% in areas of low productivity; the organic to carbonate carbon and the silicate to carbonate ratios are highest at locations where the mass flux is greatest.

The Marine Mammal Ear: Specializations for Aquatic Audition and Echolocation

“Marine mammal” is a broad categorization for over 150 species that have one feature in common: the ability to function effectively in an aquatic environment. They have no single common aquatic ancestor and are distributed among four orders (see Appendix 1). Each group arose during the Eocene in either the temperate northern Pacific Ocean or in the Tethys Sea, a paleolithic body of water from which the Mediterranean and middle eastern limnetic basins were formed. Otariids (sea lions), odobenids (walrus), and marine fissipeds (sea otters) developed primarily in the Pacific, while the earliest cetacean (whale), sirenian (manatee and dugong), and phocid (true seal) fossils come from regions bordering Tethys Sea remnants (Kellogg 1936; Domning 1982; Barnes, Domning, and Ray 1985). The level of adaptation to the marine environment varies in marine mammals; many are amphibious and only the Cetacea and Sirenia are fully aquatic, unable to move, reproduce, or feed on land.

Beaked Whale Strandings and Naval Exercises

Mass strandings of beaked whales (family Ziphiidae) have been reported in the scientific literature since 1874. Several recent mass strandings of beaked whales have been reported to coincide with naval active sonar exercises. To obtain the broadest assessment of surface ship naval active sonar operations coinciding with beaked whale mass strandings, a list of global naval training and antisubmarine warfare exercises was compiled from openly available sources and compared by location and time with historic stranding records. This list includes activities of navies of other nations but emphasizes recent U.S. activities because of what is available in publicly accessible sources. Of 136 beaked whale mass stranding events reported from 1874 to 2004, 126 occurred between 1950 and 2004, after the introduction and implementation of modern, high-power mid-frequency active sonar (MFAS). Of these 126 reports, only two reported details on the use, timing, and location of sonar in relation to mass strandings. Ten other mass strandings coincided in space and time with naval exercises that may have included MFAS. An additional 27 mass stranding events occurred near a naval base or ship but with no direct evidence of sonar use. The remaining 87 mass strandings have no evidence for a link with any naval activity. Six of these 87 cases have evidence for a cause unrelated to active sonar. The large number of global naval activities annually with potential MFAS usage in comparison to the relative rarity of mass stranding events suggests that most MFAS operations take place with no reported stranding events and that for an MFAS operation to cause a mass stranding of beaked whales, a confluence of several risk factors is probably required. Identification of these risk factors will help in the development of measures to reduce the risk of sonar-related strandings.

STRUCTURE AND FUNCTION IN WHALE EARS

ABSTRACT Ultrasonic echolocation abilities are well documented in several dolphin species, but hearing characteristics are unknown for most whales. Vocalization data suggest whale hearing spans infra- to ultrasonic ranges. This paper presents an overview of whale ear anatomy and analyzes 1) how whale ears are adapted for underwater hearing and 2) how inner ear differences relate to different hearing capacities among whales. Whales have adaptations for rapid, deep diving and long submersion; e.g., broad- bore Eustachian tubes, no pinnae, and no air-filled external canals, that impact sound reception. In odontocetes, two soft tissue channels conduct sound to the ear. In mysticetes, bone and soft tissue conduction are likely. The middle ear is air-filled but has an extensible mucosa. Cochlear structures are hypertrophied and vestibular components are reduced. Auditory ganglion cell densities are double land mammal averages (2000–4000/mm). Basilar membrane lengths range 20–70 mm; gradients are larger than in ...

The influence of cochlear shape on low-frequency hearing

The conventional theory about the snail shell shape of the mammalian cochlea is that it evolved essentially and perhaps solely to conserve space inside the skull. Recently, a theory proposed that the spirals graded curvature enhances the cochleas mechanical response to low frequencies. This article provides a multispecies analysis of cochlear shape to test this theory and demonstrates that the ratio of the radii of curvature from the outermost and innermost turns of the cochlear spiral is a significant cochlear feature that correlates strongly with low-frequency hearing limits. The ratio, which is a measure of curvature gradient, is a reflection of the ability of cochlear curvature to focus acoustic energy at the outer wall of the cochlear canal as the wave propagates toward the apex of the cochlea.

Sound detection by the longfin squid (Loligo pealeii) studied with auditory evoked potentials: sensitivity to low-frequency particle motion and not pressure

SUMMARY Although hearing has been described for many underwater species, there is much debate regarding if and how cephalopods detect sound. Here we quantify the acoustic sensitivity of the longfin squid (Loligo pealeii) using near-field acoustic and shaker-generated acceleration stimuli. Sound field pressure and particle motion components were measured from 30 to 10,000 Hz and acceleration stimuli were measured from 20 to 1000 Hz. Responses were determined using auditory evoked potentials (AEPs) with electrodes placed near the statocysts. Evoked potentials were generated by both stimuli and consisted of two wave types: (1) rapid stimulus-following waves, and (2) slower, high-amplitude waves, similar to some fish AEPs. Responses were obtained between 30 and 500 Hz with lowest thresholds between 100 and 200 Hz. At the best frequencies, AEP amplitudes were often >20 μV. Evoked potentials were extinguished at all frequencies if (1) water temperatures were less than 8°C, (2) statocysts were ablated, or (3) recording electrodes were placed in locations other than near the statocysts. Both the AEP response characteristics and the range of responses suggest that squid detect sound similarly to most fish, with the statocyst acting as an accelerometer through which squid detect the particle motion component of a sound field. The modality and frequency range indicate that squid probably detect acoustic particle motion stimuli from both predators and prey as well as low-frequency environmental sound signatures that may aid navigation.

Deadly diving? Physiological and behavioural management of decompression stress in diving mammals

Decompression sickness (DCS; ‘the bends’) is a disease associated with gas uptake at pressure. The basic pathology and cause are relatively well known to human divers. Breath-hold diving marine mammals were thought to be relatively immune to DCS owing to multiple anatomical, physiological and behavioural adaptations that reduce nitrogen gas (N2) loading during dives. However, recent observations have shown that gas bubbles may form and tissue injury may occur in marine mammals under certain circumstances. Gas kinetic models based on measured time-depth profiles further suggest the potential occurrence of high blood and tissue N2 tensions. We review evidence for gas-bubble incidence in marine mammal tissues and discuss the theory behind gas loading and bubble formation. We suggest that diving mammals vary their physiological responses according to multiple stressors, and that the perspective on marine mammal diving physiology should change from simply minimizing N2 loading to management of the N2 load. This suggests several avenues for further study, ranging from the effects of gas bubbles at molecular, cellular and organ function levels, to comparative studies relating the presence/absence of gas bubbles to diving behaviour. Technological advances in imaging and remote instrumentation are likely to advance this field in coming years.

Three-Dimensional Reconstructions of the Dolphin EAR

The umwelt or perceptual world of odontocetes is largely defined by acoustic cues imperceptible to humans. Like bats, they use ultrasonic frequencies to echolocate. To penetrate this acoustic world, we must use indirect anatomical and psychophysical techniques. While bat research has incorporated anatomy and physiology to describe neural processing of echolocation signals, cetacean research, hampered by practical and legal restrictions, depends largely upon spectral and temporal analyses of emitted sounds coupled with behavioral observations. From these investigations, we have gained considerable information about the psycho-acoustics of dolphin echolocation, but we still know little about the receptor anatomy.

CT scanning and computerized reconstructions of the inner ear of multituberculate mammals

ABSTRACT The inner-ear structure of four multituberculate petrosals from the Late Cretaceous and Early Paleocene of North America was examined with computerized tomography (CT). Transverse CT scan images of these petrosals were digitized to produce a three-dimensional reconstruction of the acousto-vestibular spaces of multituberculates. Our investigation shows that the acousto-vestibular spaces of multituberculates are characterized by a straight cochlear canal and an extraordinarily enlarged vestibular cavity. Comparison of multituberculate inner-ear structures with those in other major mammalian clades suggests that the cochlea of multituberculates, which is similar to that of Morganucodon, is more derived than the cochlea of non-mammalian therapsids but more primitive than the coiled cochlea of therian and monotreme mammals. The extraordinary inflation of the vestibule of multituberculates is a uniquely derived character of most Cretaceous and Tertiary multituberculates, and it may be the synapomorphy ...