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Verarbeitung von Polarisationsmustern und visueller Eigenbewegung im Zentralkomplex der Heuschrecke zur räumlichen Orientierung
No full textDespite their relatively small brains with comparatively low neuron counts, insects show complex navigation behavior such as seasonal long-range migration, path integration, and precise straight-line movement. Spatial navigation requires a sense of current heading, which must be tethered to prominent external cues and updated by internal cues that result from movement.
Global external cues such as the position of the sun may provide a reference frame for orientation. Sunlight is polarized by scattering in the atmosphere, which results in a sky-spanning polarization pattern that directly depends on the current solar position and makes polarization information, like the sun itself, useful as an external reference cue. Internally, moving through the environment generates optic flow---the motion of the viewed scenery on the retina---, which may inform about turning maneuvers, movement speed, and covered distance. Many insects use these external and internal cues for orientation, and the neuronal center for spatial navigation likely is the central complex, a higher-order brain structure where sensory information is integrated to form an internal compass representation of the current heading.
This thesis addresses the question how celestial compass cues, specifically the polarization pattern, and optic flow are processed in the central complex of the desert locust, a long-range migratory insect. All chapters except the last one are electrophysiological studies in which single central-complex neurons were intracellularly recorded while presenting visual stimuli. The neurons' anatomy was histologically determined by dye injection in order to infer their role in the neural network.
The studies in Chapters 1 and 2 show that the central complex contains a neuronal compass that robustly signals the sun direction based on direct sunlight and the integration of the whole solar polarization pattern. This shows that the locust brain uses all available skylight cues in order to form a unified compass signal, enabling robust navigation under different environmental conditions.
The study in Chapter 3 further examines how neurons at the input stage of the central complex process skylight cues. Already at this stage, single neurons integrate visual information from large areas of the sky and have receptive fields suitable to build the skylight compass.
Chapter 4 sheds light on the detection sensitivity for the angle of polarization, finding that central-complex neurons are highly sensitive in this regard, adapted to analyze the skylight polarization pattern almost in its entirety and under unfavorable environmental conditions.
In Chapter 5 the locust central complex was scanned for neurons that receive optic flow information. Neurons at virtually all network stages are sensitive to optic flow, mainly uncoupled from skylight-cue sensitivity. This highlights that sensory information is flexibly processed in the central complex, presumably depending on the animal's current behavioral demands. Further, the study hypothesizes how horizontal turning motion is processed in order to update the internal heading representation, backed up by a computational model that adheres to brain anatomy and physiological data.
Altogether, these studies advance the understanding of how external and internal cues are processed in the central-complex network in order to establish a sense of orientation in the insect brain.
Finally, I contributed with data sets and programming code to the development of the InsectBrainDatabase (www.insectbraindb.org), a free online database tool designed to manage, share and publish anatomical and functional research data (Chapter 6).Trotz ihrer relativ kleinen Gehirne und vergleichsweise geringen Anzahl an Nervenzellen zeigen Insekten komplexes Navigationsverhalten.Navigation erfordert einen Sinn für die aktuelle Bewegungsrichtung im Raum. Diese Richtung ist relativ, sie muss deshalb an markante externe Punkte gebunden sein und kontinuierlich durch interne, aus der Eigenbewegung entstehende Signale korrigiert werden.
Der Sonnenstand kann als globaler externer Ankerpunkt für Navigation dienen. Sonnenlicht wird durch Streuung in der Atmosphäre polarisiert, wodurch ein systematisches Muster an Polarisationswinkeln im Himmel entsteht, das wie die Sonne selbst als externe Referenz dienen kann. Intern erzeugt Fortbewegung optischen Fluss -- die Bewegung des Umgebungsbildes auf der Retina. Daraus können Drehbewegungen, Geschwindigkeit und die zurückgelegte Strecke abgeleitet werden. Viele Insekten nutzen diese externen und internen Signale zur Orientierung; im Gehirn bildet vermutlich der Zentralkomplex (ZK) das Navigationszentrum. In diesem Gehirnareal führt die Verarbeitung sensorischer Informationen zur Entstehung eines internen Kompass-Signals, das fortlaufend die Körperausrichtung widerspiegelt.
Diese Dissertation beschäftigt sich mit der Verarbeitung von Himmelskompass-Signalen, im Speziellen dem Polarisationsmuster, und optischem Fluss im ZK der Wüstenheuschrecke, einem über weite Strecken migrierenden Insekt. Alle Kapitel mit Ausnahme von Kapitel 6 sind elektrophysiologische Arbeiten, bei denen einzelne Nervenzellen intrazellulär abgeleitet und gleichzeitig das Tier visuell stimuliert wurde. Durch Farbstoff-Injektion konnte die Zellanatomie nachvollzogen werden und auf die Rolle im Nervensystem geschlossen werden.
Kapitel 1 und 2 zeigen, dass im ZK ein neuronaler Kompass implementiert ist, der sowohl durch Verarbeitung direkten Sonnenlichts als auch des Polarisationsmusters die Sonnenposition anzeigt. Das zeigt, dass das Heuschreckengehirn verschiedene Himmelskompass-Signale so verarbeitet, dass ein einheitliches Kompass-Signal entsteht, das Navigation unter unterschiedlichen Umweltbedingungen ermöglicht.
Darauf aufbauend wird in Kapitel 3 beleuchtet, wie in der Eingangs-Station des ZK Himmelskompass-Signale verarbeitet werden. Einzelne Zellen integrieren schon auf dieser Ebene visuelle Eindrücke über große Bereiche des Himmels und verfügen über rezeptive Felder, mit denen das Himmelskompass-Signal gebildet werden kann.
In Kapitel 4 wird die Wahrnehmungs-Schwelle für den Polarisationswinkel untersucht und gezeigt, dass ZK-Zellen in dieser Hinsicht hochsensitiv sind und deshalb nahezu das gesamte Polarisationsmuster des Himmels analysieren können.
Kapitel 5 behandelt die Verarbeitung optischen Flusses. Auf fast allen Netzwerk-Ebenen des ZK reagieren Einzelzellen auf optische Flussreize, und zwar weitgehend unabhängig von der Empfindlichkeit für Himmelskompass-Signale. Das impliziert, dass die Verarbeitung sensorischer Eindrücke im ZK vom Verhaltenskontext abhängt. Ferner wird gezeigt, wie Drehbewegungen verarbeitet werden könnten, um das interne Kompass-Signal zu justieren, gestützt durch eine rechnerische Modellierung, die auf anatomischen und physiologischen Daten basiert.
Zusammengenommen tragen diese Arbeiten zum Verständnis dessen bei, wie im Insektengehirn die Verarbeitung externer und interner Sinneseindrücke dazu führt, den Orientierungssinn zu formen.
Schließlich trug ich mit Datensätzen und Programmcode zur Entwicklung der InsectBrainDatabase (www.insectbrainDB.org) bei, einer frei zugänglichen Onlineplattform für die Verwaltung, Verteilung und Publikation von Forschungsdaten (Kapitel 6)
Raw data: Recording files and microscope image stacks
No full textEach archive contains the data for one neuron. The data set ID is the four-digit number after the last underscore of the folder name. The smr file is the raw recording data (recorded with Spike2, which is needed for reading). The mat file contains the same data, converted to mat for import with MATLAB. The mat file is used for data analysis, as documented in the code. The lif file is the raw confocal image stack of the specimen. The png file is a maximum projection of the specimen and provides an overview of the neuron morphology. All maximum projections are processed so that they display the frontal view on the specimen, i. e., a structure on the left half of the image corresponds to the structure in the right half of the imaged specimen. The spreadsheet file "_data-table.xlsx" contains the meta-data table of all data sets, which may be used for batch importing (see code documentation). The spreadsheet file "clusterSummary_rSquare-75-stimPooldLR.xls" contains the final results of the cluster analysis for visual field estimation. The archive "bootstrap.zip" contains the results from the bootstrap analysis. The contents should be extracted into the same directory as the data set folders in order to be found by the analysis scripts
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Integration of optic flow into the sky compass network in the brain of the desert locust
No full textThis repository accompanies the 2023 Frontiers manuscript 'Integration of optic flow into the sky compass network in the brain of the desert locust'. It contains physiological and meta data, code for their analysis, and code underlying the computational model and simulation.Deutsche Forschungsgemeinschaf
Integration of optic flow into the sky compass network in the brain of the desert locust (Frontiers Version)
No full textThis repository accompanies the 2023 Frontiers manuscript 'Integration of optic flow into the sky compass network in the brain of the desert locust'. It contains physiological and meta data, code for their analysis, and code underlying the computational model and simulation.Deutsche Forschungsgemeinschaf
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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