Thesis (Ph. D. zoology)--Washington State University, December 2007. / Includes bibliographical references.

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Thesis (Ph. D.)--University of Oregon, 2000. / Title from title screen. Extent of document: xiv, 152 p. : ill. Includes vita and abstract. Includes bibliographical references (p. 146-152).

Advisers: Terry Takahashi and Richard Marrocco. xiv, 152 p. / Neurons in the barn owl's inferior colliculus (IC) derive their spatial receptive fields (RF) from two auditory cues: interaural time difference (ITD) and interaural level difference (ILD). ITD serves to restrict a RF in azimuth but the precise role of ILD was, up to this point, unclear. Filtering by the ears and head insures that each spatial location is associated with a unique combination of frequency-specific ILD values (i.e., an ILD spectrum). We isolated the effect of ILD spectra using virtual sound sources in which ITD was held fixed for all spatial locations while ILD spectra were allowed to vary normally. A cell's response to these stimuli reflects the contribution of ILD to spatial tuning, referred to as an “ILD-alone RF”. In a sample of 34 cells, individual ILD-alone RFs were distributed and amorphous, but consistently showed that the ILD spectrum is facilatory at the cell's best location and inhibitory above and/or below. Prior results have suggested that an IC cell's spatial specificity is generated by summing inputs which are narrowly tuned to frequency and selective for both ILD and ITD. Based on this premise, we present a developmental model which, when trained solely on a cell's true spatial RF, reproduces both the cell's true RF and its ILD-alone RF. According to the model, the connectivity between a space-tuned IC cell and its frequency-specific inputs develops subject to two constraints: the cell must be excited by ILD spectra from the cell's best location and inhibited by spectra from locations above and below but along the vertical strip defined by the best ITD. To assess how frequency-specific inputs are integrated to form restricted spatial RFs, we measured the responses of 47 space-tuned IC cells to pure tones at varying ILDs and frequencies. ILD tuning varied with frequency. Further, pure-tone responses, summed according to the head-related filters, accounted for 56 percent of the variance in broadband ILD-alone RFs. Modelling suggests that, with broadband sounds, cells behave as though they are linearly summing their inputs, but when testing with pure tones, non-linearities arise. This dissertation includes unpublished co-authored materials.

xiv, 152 p. Adviser: Terry Takahashi (Biology Dept.). Chapter 2 of this dissertation has been previously published in the Journal of Neurophysiology. Citation: Whitchurch EA and Takahashi TT. Combined auditory and visual stimuli facilitate head saccades in the barn owl (Tyto alba). J Neurophysiol 96: 730-745, 2006. / A print copy of this title is available through the UO Libraries under the call number: SCIENCE QL696.S85 W54 2006 / Survival depends on our ability to detect and integrate sensory information from multiple modalities, allowing for the most efficient behavioral response. For example, barn owls must combine sights and sounds from the environment to localize potential prey. A vole scurrying through a drift of dried leaves is more likely to meet its doom if a nearby owl can both faintly see and hear it. How does the brain take two physically discreet inputs and combine them into a unified representation of the surrounding multisensory world? Moreover, how is this internal representation transformed into the most efficient behavioral response? This dissertation comprises original research addressing these questions in the barn owl with two distinct approaches: First, Chapters II and III describe orientation behavior in response to auditory, visual, and audiovisual stimuli. Chapter II probes the effect of stimulus strength on saccadic behavior and the nature of audiovisual integration, and was taken from a co-authored publication. Chapter III explores the behavioral consequence of an induced stimulus asynchrony in audiovisual integration and was taken from a co-authored manuscript being prepared for publication. The second experimental approach is described in Chapters IV and V. These chapters probe the physiological basis of saccadic behavior by measuring single-neuron responses to auditory, visual, and audiovisual stimuli. Chapter IV describes how auditory responses of neurons from the external nucleus of the inferior colliculus depend on sound pressure level. Chapter V describes activity of optic tectum neurons in response to auditory, visual, and audiovisual stimuli. The behavioral findings described herein suggest that barn owls often incorporate both the speed of the auditory system and the accuracy of the visual system when localizing a multisensory stimulus, even when the two modalities are presented asynchronously. The physiological studies outlined in this dissertation show that sensory representations in the midbrain can be used to predict general trends in saccadic behavior: Neuronal thresholds were within the range of observed behavioral thresholds. Responses to multisensory stimuli were enhanced relative to unisensory stimuli, possibly corresponding to enhanced multisensory behavior. These data support fundamental rules in multisensory integration that may apply across species.

Thesis (Ph. D.)--University of Oregon, 2006. / Typescript. Includes vita and abstract. "These investigations were supported in part by the National Institute on Deafness and Communication Disorders ... and the National Institute of General Medical Sciences"--P. viii. Includes bibliographical references (leaves 142-152). Also available for download via the World Wide Web; free to University of Oregon users.

Im Gehirn gemessene Extrazelluläre Feldpotentiale (EFPs) sind ein wichtiges Maß für neuronale Aktivität. In vielen Fällen ist der genaue physiologische Ursprung dieser Potentiale unbekannt oder umstritten. Der auditorische Hirnstamm der Schleiereule bietet eine ausgezeichnete Möglichkeit, die EFPs und ihren Ursprung zu untersuchen. Der Hirnstamm der Eule ist ideal, weil das Feldpotential in ihm sehr stark ist, weil die zugrundeliegende Anatomie wohl-untersucht ist, und weil das Potential sehr einfach durch auditorische Stimulation gesteuert werden kann. In dieser Arbeit präsentiere ich zwei Beispiele, in welchen ich mir die einzigartigen Eigenschaften der Schleiereule zunutze mache, um das EFP zu erforschen. Das erste Beispiel behandelt Axone, und ich zeige, dass neuronale Aktivität in Axonbündeln, welche eine charakteristische Endzone besitzen, ein starkes Dipolmoment erzeugen kann. Im zweiten Beispiel behandele ich Synapsen. Aus den EFPs der Synapsen konnte ich die Merkmale der synaptischen Kurzzeitplastizität extrahieren. Die Methoden und Erkenntnisse die ich entwickelt habe sind auf andere Organismen übertragbar und erweitern das Verständnis vom Einfluss unterschiedlicher anatomischer Strukturen auf das EFP. / Extracellular field potentials (EFPs) recorded in the brain are an important indicator of neural activity for neuroscientists. In many cases, their physiological basis is unknown or debated. The barn owl auditory brainstem provides an excellent opportunity to study these EFPs and their origins. The barn owl auditory brainstem is ideal because the field potentials are very large and very easily controlled by the auditory stimulus, and the underlying anatomy is well known. Here I present two examples of exploiting the unique properties of the EFP in the barn owl auditory brainstem. The first is concerned with axons, where I show that activity in axon bundles with characteristic termination zones generates strong dipole moments. The second example is concerned with synaptic currents, from which I was able to extract a signature of short-term plasticity. The methods and insights I developed are applicable to other organisms as well, and contribute to the general understanding of the roles different anatomical structures can play in the generation of EFPs.

Schleiereulen sind gute Nachtjäger und finden ihre Beute vor allem durch den Hörsinn. Die auditorische Lokalisierung in der horizontalen Ebene basiert dabei auf interauralen Zeitdifferenzen. Diese werden im Hirnstamm durch das Netzwerk von nucleus magnocellularis (NM) und nucleus laminaris (NL) in Orte umkodiert. Im NL kann ein extrazelluläres Potential (EP), das Neurophonpotential (NP) gemessen werden. Dieses hat eine erstaunliche zeitliche Präzision von unter 10 Mikrosekunden, und spiegelt den für die Stimulation benutzten Ton bis zu Frequenzen von 9 kHz wider. Wie kann eine solche Präzision erzeugt werden, und was kann man über den Ursprung des Potentials in dieser neuronalen Struktur lernen? Um diese Fragen zu klären, studiere ich in vivo gemessene NPs. Dadurch kann in Zukunft die Verbindung von neuronaler Aktivität und EP besser verstanden werden. Hunderte neuronale Stromquellen, die alle kohärent mit einer hohen Feuerrate aktiv sind, sind nötig, um ein solches NP zu erzeugen. Dabei sind Anzahl und Stromstärke der Neuronen im NL nicht ausreichend, um das NP zu erzeugen. Der Hauptanteil der Quellen besteht aus den Signalen, die den Input des NL formen: die Ströme der Ranvierschen Schnürringe entlang der Axone aus dem NM, sowie die synaptischen Ströme zu den Dendriten von NL Neuronen. Weiterhin können NPs, die als Antwort auf monaurale Stimulierung aufgenommen wurden, linear addiert werden, um die Antwort auf binaurale Stimulation zuverlässig vorherzusagen. Leichte Abweichungen von der Vorhersage könnten damit erklärt werden, dass einzelne, sehr nah an der Elektrode befindliche Neurone nichtlinear zum NP beitragen. Im Gegensatz zu anderen bisher untersuchten neuronalen Strukturen - auch homologer Hirnregionen - spiegelt das NP der Schleiereule Eingangs- statt Ausgangssignale wider. Dieser strukturelle Unterschied könnte erklären, wieso das Schleiereulengehirn höhere Genauigkeit erreicht, als das anderer Tiere. / The barn owl is a good night hunter and mainly localizes the prey with its auditory system. The auditory localization in the horizontal plane, based on interaural time differences, depends on the auditory brainstem circuit consisting of nucleus magnocellularis (NM) and nucleus laminaris (NL). An extracellular field potential (EFP), named neurophonic, can be recorded in the NL. It has a very high temporal precision of below 10 microseconds and replays the stimulating sound up to 9 kHz. In this thesis I study how an EFP with such a precision can be generated. Furthermore, what can we learn about the system and about the origin of the neurophonic in NL from these recordings? The answers will help connecting the neural activity to the EFP also in general. Firstly, hundreds of sources, all firing with a high rate and in a highly phase-locked manner, are needed to generate the neurophonic in NL. The number of the neurons in NL and the magnitude of their output currents are not high enough to alone give rise to the neurophonic. The majority of the neural sources conveys the input from NM to NL, i.e., the currents from the nodes of Ranvier in the afferent axons from NM, and the synaptic currents to the dendrites of the NL neurons. Furthermore, the neurophonics in response to monaural stimulation sum up linearly and predict accurately the neurophonics in response to binaural stimulation. This implies that the non-linear response of the NL neurons usually cannot be detected in the neurophonic, but that there might be a minor contribution from a single NL neuron when in the immediate vicinity of the electrode. All in all, the neurophonic in the barn owl''s NL seems to reflect the inputs to the nucleus, whereas usually the output is well represented in the EFP. Even in the homologue nuclei in chick and mammals the neurophonic is thought to reflect the output instead of the input. Thus, the exceptionality of the barn owl might be needed for the high precision in its NL.

La lutte contre les rongeurs est souvent un enjeu majeur dans les agroécosystèmes. Nous avons conduit une étude comparative dans des plantations de palmiers à huile dans les provinces de Riau et de Bangka en Indonésie. Dans les deux zones, des chouettes ont été introduites pour la lutte contre les rats ; toutefois, à Riau les rats sont maintenus à des niveaux de population acceptables sans recours au raticide, tandis qu’à Bangka les dégâts des rats sont très importants et l’usage de raticide intensif. Nous avons comparé ce deux systèmes en terme d’abondance et/ou de régime alimentaire de deux prédateurs, chouettes et petits carnivores. D’après nos résultats, les petits carnivores sont beaucoup plus abondants dans les plantations à Riau qu’à Bangka, et le chat léopard (Prionailurus bengalensis) est absent à Bangka tandis que cette espèce domine à Riau. Nos résultats suggèrent également que la prédation sur les rats par les chouettes et les petits carnivores serait moindre à Bangka qu’à Riau. D’une manière générale, cette étude confirme l’hypothèse selon laquelle les petits carnivores, notamment les chats léopard, joueraient un rôle important dans la lutte contre les rats en palmeraies. Par ailleurs, nous avons analysé la distribution spatiale des petits carnivores en plantation. Nos résultats suggèrent que, bien que l’habitat palmeraie soit largement utilisé la nuit par certains petits carnivores comme le chat leopard, qui y trouve une abondante ressource alimentaire, la plupart des espèces sont dépendantes de la forêt. Les gestionnaires des palmeraies devraient adapter leurs pratiques, afin de favoriser les petits carnivores dans une perspective de lutte contre les rats. / Rodent pest control is often a major issue in agroecosystems. We conducted a 3-year comparative study (2010-2012) in oil palm plantations in Riau and Bangka provinces, in Indonesia: in both areas barn owls have been introduced for rat control, and were at least as abundant in Bangka plantations than in Riau, but in Riau rat populations have been maintained at an acceptable level without the use of rodenticide, whereas in Bangka intensive rodenticide applications did not prevent high levels of rat damage. We compared these two contrasting systems in terms of predator community (barn owls and small carnivores) abundance and/or diet. We found that small carnivores were much more abundant in Riau plantations than in Bangka, and that the leopard cat (Prionailurus bengalensis) was the dominant species in Riau while absent from Bangka. Our results on diet suggested that rat prey intake from barn owls and from the small carnivore community would be less in Bangka plantations than in Riau. Broadly, our results suggest that small carnivores, notably the leopard cat, play an important role in rodent control. In addition, we investigated spatial distribution of small carnivores within the oil palm habitat. Our results support the hypothesis that, although the oil palm may be habitable for some small carnivore species such as the leopard cat, where they supposedly forage at night, most species still need forest for their survival in oil palm landscapes. Oil palm plantations managers should adapt agricultural practices and land-use to enhance small carnivores, with the view to improve rodent control.