Click here for a higher res version...
ASA 2011:
Comparative Approaches to Peripheral Auditory Function
Date: Tuesday, May 24
Time: 8 AM - 12 PM
Location: Grand Ballroom C, Sheraton Seattle Hotel
Organizer
Christopher Bergevin
Dept. of Otolaryngology/Head & Neck Surgery, Columbia University
Questions? &rArr cb2811 [at] columbia.edu
&rArr Galley proof of session abstracts can be downloaded here (and are listed below on this page)
&rArr Flyer for the session can be downloaded upon the jump to here
Overview
This session will focus around the core idea of what comparative approaches have taught us about auditory function. Not simply that we use various animal models within the context of a particular scientific question, but what specifically we have learned about the process of auditory transduction (i.e., converting acoustic signals into neural representations) by directly comparing function (e.g., physiology, morphology, performance) across different types of ears. The comparative approach has been a big force in auditory science for many years (e.g., look at the variety of species Bekesy studied in Experiments in Hearing). However, given new measurement technologies (e.g., new methods for intra-cochlear measurements) and techniques (such as knockouts animal models via molecular biological techniques), many new insights have been gained in the last few years alone. Thus, the goal of this session will be to pool together recent highlights from a comparative point of view. The invited talks will be designed to be somewhat plenary in nature, hopefully inspiring younger investigators towards fruitful research directions/questions. The likely groups covered across the session ideally will encompass: mammals, birds, amphibians, reptiles, non-vertebrates (e.g., insects), and underwater species (e.g., fish, dolphins/ whales). A panel discussion will take place at the end that will aim to tie together the talks into a comprehensive point of view and synthesize new ideas (i.e., hopefully the whole is more than the sum of the parts!). Furthermore, the session should be of interest to those focused on bioacoustics, given the diverse range of different types of hearing explored.
Speakers
(abstracts are provided further below)
- Geoffrey Manley (Cochlear and Auditory Brainstem Physiology, Carl von Ossietzky University Oldenburg, Germany)
- Catherine Carr (Dept. of Biology, University of Maryland, MD USA)
- Sebastiaan Meenderink (Dept. of Physics and Astronomy, University of California, Los Angeles, CA
USA; Dept. of Neuroscience, Erasmus MC, Rotterdam, the Netherlands)
- Edward Walsh (Developmental Auditory Physiology Laboratory, Boys Town National Research Hospital, Omaha, NE USA)
- Glenis Long (Program in Speech and Hearing Sciences, CUNY Graduate Center, NY USA)
- Andrea Simmons (Dept. of Psychology, Brown University, Providence, RI, USA)
- Christopher Bergevin (Dept. of Otolaryngology/Head & Neck Surgery, Columbia University, NY USA)
Panel Discussion (in addition to the speakers indicated above)
- Moderator: Richard Fay (Parmly Hearing Institute and Dept. of Psychology, Loyola University, Chicago, IL USA)
- Philip X. Joris (Laboratory of Auditory Neurophysiology, University of Leuven, Belgium )
- NOTE: Audience participation will also be strongly encouraged
Schedule
(abstracts are provided further below)
- 8:00 Introduction
- 8:05 - Manley 'Lizard ears and simple solutions to auditory coding'
- 8:30 - Meenderink 'The teachings of anurans: mechanisms of auditory processing in the frog'
- 8:55 - Long 'Why bother looking at a range of species?'
- 9:20 - Bergevin 'Otoacoustic emission delays as a probe to measure cochlear tuning: Comparative validations'
- 9:45 - Break
- 10:00 - Walsh 'Comparative Cat Studies: Is the tiger an auditory specialist?'
- 10:25 - Carr 'ITD processing in birds and alligators: evolution of binaural circuits'
- 10:50 - Simmons 'Response properties and local connectivity of the cochlear nucleus of the big brown bat'
- 11:05 - Panel Discussion Moderated by R. Fay
- 12:00 - End
Abstracts
(extended versions; a pdf containing all the abstracts can be downloaded here)
- Lizard ears and simple solutions to auditory coding
- Presenter: Geoffrey Manley
- Abstract: The huge variety in the anatomy of lizard auditory organs, the basilar papillae, provides an optimal substrate for examining the relationship between structure and function. This talk examines different structural types of lizard ear and asks the questions: What does an auditory organ need to perform the basic tasks in the coding of acoustic stimuli such as sensitivity, tonotopicity and selectivity? How little does it take to build a useful hearing organ?
Firstly, in common with other non-mammals, lizards and their relatives achieved sensitivity partly through the development of a simple, single-ossicle tympanic middle ear - independently of similar middle ears. The middle ears are connected through the head, providing for directional hearing by means of a pressure-gradient receiver system. Partially through this, they achieved directional hearing without massive neural processing and an auditory sensitivity quite comparable to that of any other land vertebrates at equivalent frequencies and temperatures.
Secondly, during their early evolution, lizards evolved a new type of hair cell whose frequency responses were determined by the morphological details of their stereovillar bundles and tectorial material. This development led to embryological processes that resulted in the systematic spread of hair cells according to the height of their bundles and thus frequency response - a tonotopic arrangement. In modern lizards, this can be achieved with a very small number of hair-cell rows, showing clearly that tonotopicity does not demand an extensive epithelium. Interestingly, the earliest (and some modern) lizards have a papilla that contains two hair-cell areas that both respond to higher frequencies and both were equally tonotopically organized - but in opposite directions (mirror image) along the length of the organ. Most modern lizard families have abandoned either one of these two areas. The result is that the direction of tonotopicity can be apical-basal (as in mammals and birds) or basal-apical, a unique arrangement. This demonstrates that there is nothing distinctive about the direction of tonotopicity.
Finally, different lizard families have achieved dissimilar degrees of frequency selectivity through manipulations of anatomical features, especially of the tectorial membrane. These manipulations mirror the pay-off between the size of the auditory papilla and its ability to selectively code for different frequencies. In a long papilla, frequencies can be spread over many hundreds of hair cells and tectorial patterns arranged to allow very local coupling of hair-cell bundles. This results in both sensitive and very selective frequency tuning. In short papillae, any frequency band occupies many fewer hair cells (sometimes <100 in total!). A tectorial coupling had to be abandoned to allow for useful tuning selectivity. The result is, however, poorer sensitivity and poorer tuning selectivity than in longer papillae. Nonetheless, lizards demonstrate that sensitive and selective hearing organs can be built using only a few hundred hair cells organized along a straight axis.
- The teachings of anurans: mechanisms of auditory processing in the frog
- Presenter: Sebastiaan Meenderink
- Abstract: Amphibians are one of the four classes of tetrapod vertebrates. The majority of amphibian species are anurans, better known as frogs and toads. Frog hair cells have served as a model for studying fundamental cellular processes including electrical tuning, forward and reverse transduction, and "cochlear" amplification. In most frogs, these processes act at much lower frequencies compared to the mammalian cochlea, and extrapolation of results to higher- frequency epithelia must be made with caution.
The gross anatomy of the anuran inner ear is unique among vertebrates in that it possesses two distinct organs specialized in the detection of airborne sounds. Moreover, there is no analog of the basilar membrane in these organs; hair cells are situated directly over the stationary, cartilaginous labyrinth. These structural differences are reflected in how sounds propagate within the inner ear. Specifically, travelling waves seem absent in frog. Despite this, otoacoustic emissions in anurans and mammals share many characteristics, and their comparative study may help to elucidate universal mechanical properties of the inner ear.
These examples, combined with numerous other types of experiments, have made the frog a useful substrate for the examination of cellular mechanisms, transduction, and macro-mechanical inner-ear properties underlying normal vertebrate hearing.
- Why bother looking at a range of species?
- Presenter: Glenis Long
- Abstract: Most anatomical and physiological research is conducted on a small subset of mammals and there are many pressures on auditory researchers to limit their research to a limited number of species with the assumption that this will permit us to explain normal and impaired hearing in humans. Otoacoustic emissions (OAE) provide a particularly useful comparative tool because very similar measures can be efficiently obtained from a range of species. A full understanding of OAE in the ear canal can be enhanced when simultaneous measurements are obtained both in the ear canal and within the cochlea. This paper will provide evidence from psychoacoustic, evoked potential and otoacoustic emission research that comparative research is essential if we are to fully understand human auditory processing.
- Otoacoustic emission delays as a probe to measure cochlear tuning: Comparative validations
- Presenter: Christopher Bergevin
- Abstract: The ear is not only sensitive to sound, but selective as well: Tonotopic tuning of the inner ear provides a means to resolve incoming spectral information. Measurements of frequency selectivity have traditionally relied upon either subjective psychophysical or objective (but invasive) physiological approaches. Sounds emitted from a healthy ear, known as otoacoustic emissions (OAEs), have been proposed to both objectively and non-invasively estimate peripheral auditory tuning. Despite diverse inner-ear morphological variation across animals, OAEs are a universal feature and correlate well to an animal's range of 'active' hearing. Recent studies focusing on emission delays in response to a single 'stimulus frequency' (SFOAEs), conducted systematically across species in a variety of classes (mammals, aves, reptiles, & amphibians), support predictions relating emissions and tuning. Longer SFOAE delays presumably reflect the sharper tuning associated with resonant build-up time of the underlying auditory filters. Differences in tuning estimated from OAEs appear generally congruous with known anatomical and functional considerations: Larger sensory organs (i.e., more 'filters') with smaller ranges of audition exhibit sharper tuning. Comparisons made both broadly (inter-class) and within phylogenetically-matched groups (intra-family) indicate that SFOAE delays in humans are longer than any other species so far examined, suggestive of exceptionally sharper tuning.
- Comparative Cat Studies: Is the tiger an auditory specialist?
- Presenter: Edward Walsh (w/ Douglas Armstrong & JoAnn McGee)
- Abstract: Although representatives of the 41 extant cat species inhabit nearly every biome on the planet and have faced a highly diverse set of selection pressures during evolution, relatively little effort has been made to compare commonly measured features of peripheral auditory function among species representing the family. It is nonetheless reasonable to suggest that inner ear adaptation may have led to functional specialization in a subset of species given their extensive geographic range. In that light, frequency-threshold curves and response latency-intensity and -frequency relationships will be compared in cats of widely varying body mass inhabiting a variety of habitats. The body mass of felids spans a range of more than two orders of magnitude, with small cats like the desert sandcat, Felis margarita, weighing as little as 2 kg and the Amur tiger, Panthera tigris altaica, weighing as much as 300 kg. While most cats studied thus far appear to satisfy the conditions necessary to be labeled auditory generalists, the tiger, and perhaps members of the Panthera genus generally, may be exceptions and we will consider the possibility that the big cats are auditory generalists with regard to acoustic sensitivity, but exhibit a peripheral specialization affecting low-frequency response latencies.
- ITD processing in birds and alligators: evolution of binaural circuits
- Presenter: Catherine Carr
- Abstract: The auditory systems of birds and mammals use timing information from each ear to detect interaural time differences (ITD). In birds, the circuits that encode ITD are composed of delay lines and coincidence detectors. To determine if these circuits are evolutionarily conserved, we have compared the physiological and anatomical organization of the auditory nuclei of birds and their sister group, the crocodilians. In both groups, precisely timed spikes in the first order nucleus magnocellularis (NM) encode the timing of sounds, and NM neurons project to neurons in the nucleus laminaris (NL) that detect interaural time differences. NL neurons act as coincidence detectors, and encode ITD in both birds and crocodilians. In the crocodilians, however, the range of best ITDs represented in NL was larger than in birds, possibly because of the network of canals that connect the middle ear spaces. These interaural canals are also found in birds, and, for low frequency sounds, may in both groups provide a larger range of ITDs than predicted by actual head size.
- Response properties and local connectivity of the cochlear nucleus of the big brown bat
- Presenter: Andrea Simmons (w/ Seth S. Horowitz, Jonathan R. Barchi, & James A. Simmons)
- Abstract: We characterized responses of the cochlear nucleus (CN) in big brown bats using local field potentials and extracellular unit responses to tone bursts, forward and reversed FM sweeps, and pulse-echo pairs. Neurobiotin- filled pipettes were lowered through the inferior colliculus of anesthetized bats to depths from 3.2 to 4.3 mm based on stereotaxic coordinates. Re- sponse properties were correlated with local anatomical connectivity as shown by transport of neurobiotin from the recording site and immunohis- tochemical localization of GABA and of connexin 35/36 in alternate brain sections. In dorsal AVCN, response properties were similar to those seen in the nuclei of the lateral lemniscus. Recording sites in ventral AVCN near the insertion point of the auditory nerve showed unique characteristics, includ- ing very short latencies (1.5Ð3 ms) and oscillatory responses extending past the duration of the sound. Most sites were sharply tuned to low frequencies corresponding to the first harmonic of the FM sweep, and responded equally well to forward and reverse FM sweeps. Data indicate that early stages of auditory processing in the big brown bat are critical to echolocation hyperacuity and may be dependent on anatomical specializations of the AVCN. [Work supported by the NIH, ONR, and RI Space Grant (NASA).]