@phdthesis{Brembs2000,
  author    = {Brembs, Bj{\"o}rn},
  title     = {An Analysis of Associative Learning in Drosophila at the Flight Simulator},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-1039},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2000},
  abstract  = {Most natural learning situations are of a complex nature and consist of a tight conjunction of the animal's behavior (B) with the perceived stimuli. According to the behavior of the animal in response to these stimuli, they are classified as being either biologically neutral (conditioned stimuli, CS) or important (unconditioned stimuli, US or reinforcer). A typical learning situation is thus identified by a three term contingency of B, CS and US. A functional characterization of the single associations during conditioning in such a three term contingency has so far hardly been possible. Therefore, the operational distinction between classical conditioning as a behavior-independent learning process (CS-US associations) and operant conditioning as essentially behavior-dependent learning (B-US associations) has proven very valuable. However, most learning experiments described so far have not been successful in fully separating operant from classical conditioning into single-association tasks. The Drosophila flight simulator in which the relevant behavior is a single motor variable (yaw torque), allows for the first time to completely separate the operant (B-US, B-CS) and the classical (CS-US) components of a complex learning situation and to examine their interactions. In this thesis the contributions of the single associations (CS-US, B-US and B-CS) to memory formation are studied. Moreover, for the first time a particularly prominent single association (CS-US) is characterized extensively in a three term contingency. A yoked control shows that classical (CS-US) pattern learning requires more training than operant pattern learning. Additionally, it can be demonstrated that an operantly trained stimulus can be successfully transferred from the behavior used during training to a new behavior in a subsequent test phase. This result shows unambiguously that during operant conditioning classical (CS-US) associations can be formed. In an extension to this insight, it emerges that such a classical association blocks the formation of an operant association, which would have been formed without the operant control of the learned stimuli. Instead the operant component seems to develop less markedly and is probably merged into a complex three-way association. This three-way association could either be implemented as a sequential B-CS-US or as a hierarchical (B-CS)-US association. The comparison of a simple classical (CS-US) with a composite operant (B, CS and US) learning situation and of a simple operant (B-US) with another composite operant (B, CS and US) learning situation, suggests a hierarchy of predictors of reinforcement. Operant behavior occurring during composite operant conditioning is hardly conditioned at all. The associability of classical stimuli that bear no relation to the behavior of the animal is of an intermediate value, as is operant behavior alone. Stimuli that are controlled by operant behavior accrue associative strength most easily. If several stimuli are available as potential predictors, again the question arises which CS-US associations are formed? A number of different studies in vertebrates yielded amazingly congruent results. These results inspired to examine and compare the properties of the CS-US association in a complex learning situation at the flight simulator with these vertebrate results. It is shown for the first time that Drosophila can learn compound stimuli and recall the individual components independently and in similar proportions. The attempt to obtain second-order conditioning with these stimuli, yielded a relatively small effect. In comparison with vertebrate data, blocking and sensory preconditioning experiments produced conforming as well as dissenting results. While no blocking could be found, a sound sensory preconditioning effect was obtained. Possible reasons for the failure to find blocking are discussed and further experiments are suggested. The sensory preconditioning effect found in this study is revealed using simultaneous stimulus presentation and depends on the amount of preconditioning. It is argued that this effect is a case of 'incidental learning', where two stimuli are associated without the need of reinforcement. Finally, the implications of the results obtained in this study for the general understanding of memory formation in complex learning situations are discussed.},
  subject      = {Taufliege},
  language  = {en}
}
@phdthesis{Putz2002,
  author    = {Putz, Gabriele},
  title     = {Characterization of memories and ignorant (S6KII) mutants in operant conditioning in the heat-box},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-4195},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2002},
  abstract  = {Learning and memory processes of operant conditioning in the heat-box were analysed. Age, sex, and larval desity were not critical parameters influencing memory, while low or high activity levels of flies were negatively correlated with their performance. In a search for conditioning parameters leading to high retention scores, intermittent training was shown to give better results than continuous training. As the memory test is the immediate continuation of the conditioning phase just omitting reinforcement, we obtain a memory which consists of two components: a spatial preference for one side of the chamber and a stay-where-you-are effect in which the side preference is contaminated by the persistence of heat avoidance. Intermittent training strengthens the latter. In the next part, memory retention was investigated. Flies were trained in one chamber and tested in a second one after a brief reminder training. With this direct transfer, memory scores reflect an associative learning process in the first chamber. To investigate memory retention after extended time periods, indirect transfer experiments were performed. The fly was transferred to a different environment between training and test phases. With this procedure an after-effect of the training was still observed two hours later. Surprisingly, exposure to the chamber without conditioning also lead to a memory effect in the indirect transfer experiment. This exposure effect revealed a dispositional change that facilitates operant learning during the reminder training. The various memory effects are independent of the mushroom bodies. The transfer experiments and yoked controls proved that the heat-box records an associative memory. Even two hours after the operant conditioning procedure, the fly remembers that its position in the chamber controls temperature. The cAMP signaling cascade is involved in heat-box learning. Thus, amnesiac, rutabaga, and dunce mutants have an impaired learning / memory. Searching for, yet unknown, genes and signaling cascades involved in operant conditioning, a Drosophila melanogaster mutant screen with 1221 viable X-chromosome P-element lines was performed. 29 lines with consistently reduced heat avoidance/ learning or memory scores were isolated. Among those, three lines have the p[lacW] located in the amnesiac ORF, confirming that with the chosen candidate criteria the heat-box is a useful tool to screen for learning and /or memory mutants. The mutant line ignP1 (8522), which is defective in the gene encoding p90 ribosomal S6 kinase (S6KII), was investigated. The P-insertion of line ignP1 is the first Drosophila mutation in the ignorant (S6KII) gene. It has the transposon inserted in the first exon. Mutant males are characterized by low training performance, while females perform well in the standard experiment. Several deletion mutants of the ignorant gene have been generated. In precise jumpouts the phenotype was reverted. Imprecise jumpouts with a partial loss of the coding region were defective in operant conditioning. Surprisingly, null mutants showed wild-type behavior. This might indicate an indirect effect of the mutated ignorant gene on learning processes. In classical odor avoidance conditioning, ignorant null mutants showed a defect in the 3-min, 30-min, and 3-hr memory, while the precise jumpout of the transposon resulted in a reversion of the behavioral phenotype. Deviating results from operant and classical conditioning indicate different roles for S6KII in the two types of learning.},
  subject      = {Taufliege},
  language  = {en}
}
@phdthesis{Schliemann2004,
  author    = {Schliemann, Andreas Ulrich},
  title     = {Untersuchung von miniaturisierten GaAs/AlGaAs Feldeffekttransistoren und GaAs/InGaAs/AlGaAs Flash-Speichern},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-20503},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2004},
  abstract  = {Im Rahmen dieser Arbeit wurden elektronische Bauelemente wie Feldeffekttransistoren, elektronische Speicherelemente sowie resonante Tunneldioden hinsichtlich neuartiger Transporteigenschaften untersucht, die ihren Ursprung in der Miniaturisierung mit Ausdehnungen kleiner als charakteristische Streul{\"a}ngen haben. Die Motivation der vorliegenden Arbeit lag darin, die Physik nanoelektronischer Bauelemente durch einen neuen Computercode: NANOTCAD nicht nur qualitativ sondern auch quantitativ beschreiben zu k{\"o}nnen. Der besondere Schwerpunkt der Transportuntersuchungen lag im nicht-linearen Transportbereich f{\"u}r Vorw{\"a}rtsspannungen, bei denen die Differenz der elektrochemischen Potentiale im aktiven Bereich der Bauelemente bei Weitem gr{\"o}ßer als die thermische Energie der Ladungstr{\"a}ger ist, da nur im nicht-linearen Transportbereich die f{\"u}r eine Anwendung elektronischer Bauelemente notwendige Gleichrichtung und Verst{\"a}rkung auftreten kann. Hierzu war es notwendig, eine detaillierte Charakterisierung der Bauelemente durchzuf{\"u}hren, damit m{\"o}glichst viele Parameter zur genauen Modellierung zur Verf{\"u}gung standen. Als Ausgangsmaterial wurden modulationsdotierte GaAs/AlGaAs Heterostrukturen gew{\"a}hlt, da sie in hervorragender struktureller G{\"u}te mit Hilfe der Molekularstrahllithographie am Lehrstuhl f{\"u}r Technische Physik mit angegliedertem Mikrostrukturlabor hergestellt werden k{\"o}nnen. Im Rahmen dieser Arbeit wurde zun{\"a}chst ein Verfahren zur Bestimmung der Oberfl{\"a}chenenergie entwickelt und durchgef{\"u}hrt, das darauf beruht, die Elektronendichte eines nahe der Oberfl{\"a}che befindlichen Elektronengases in Abh{\"a}ngigkeit unterschiedlicher Oberfl{\"a}chenschichtdicken zu bestimmen. Es zeigte sich, dass die so bestimmte Oberfl{\"a}chenenergie, einen {\"a}ußerst empfindlichen Parameter zur Beschreibung miniaturisierter Bauelemente darstellt. Um die miniaturisierte Bauelemente zu realisieren, kamen Herstellungsverfahren der Nanostrukturtechnik wie Elektronenstrahllithographie und diverse {\"A}tztechniken zum Einsatz. Durch Elektronmikroskopie wurde die Geometrie der nanostrukturierten Bauelemente genau charakterisiert. Transportmessungen wurden durchgef{\"u}hrt, um die Eingangs- und Ausgangskennlinien zu bestimmen, wobei die Temperatur zwischen 1K und Raumtemperatur variiert wurde. Die temperaturabh{\"a}ngigen Analysen erlaubten es, die Rolle inelastischer Streuereignisse im Bereich des quasi-ballistischen Transports zu analysieren. Die Ergebnisse dieser Arbeit wurden dazu verwendet, um die NANOTCAD Simulationswerkzeuge soweit zu optimieren, dass quantitative Beschreibungen von stark miniaturisierten, elektronischen Bauelementen durch einen iterativen L{\"o}sungsalgorithmus der Schr{\"o}dingergleichung und der Poissongleichung in drei Raumdimensionen m{\"o}glich sind. Zu Beginn der Arbeit wurden auf der Basis von modulationsdotierten GaAs/AlGaAs Heterostrukturen eine Vielzahl von Quantenpunktkontakten, die durch Verarmung eines zweidimensionalen Elektronengases durch spitz zulaufende Elektrodenstrukturen realisiert wurden, untersucht. Variationen der Splitgate-Geometrien wurden statistisch erfasst und mit NanoTCADSimulationen verglichen. Es konnte ein hervorragende {\"U}bereinstimmung in der Schwellwertcharakteristik von Quantenpunktkontakten und Quantenpunkten gefunden werden, die auf der genauen Beschreibung der Oberfl{\"a}chenzust{\"a}nde und der Erfassung der realen Geometrie beruhen. Ausgehend von diesen Grundcharakterisierungen nanoelektronischer Bauelemente wurden 3 Klassen von Bauelementen auf der Basis des GaAs/AlGaAs Halbleitersystems detailliert analysiert.},
  subject      = {Galliumarsenid},
  language  = {de}
}
@phdthesis{Bennetz2004,
  author    = {Bennetz, Maike},
  title     = {Auff{\"a}lligkeiten in Ged{\"a}chtnisfunktionen bei Kindern mit Lese-Rechtschreibschw{\"a}che},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-10941},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2004},
  abstract  = {Ziel der Studie war die Exploration von Funktionen des Kurzzeitged{\"a}chtnisses bei lese-rechtschreibschwachen Kindern (LRS) im Vergleich zu einer schriftsprachlich normal entwickelten Kontrollgruppe (KG). Ged{\"a}chtnisfunktionen sollten im Hinblick auf Entwicklungsver{\"a}nderungen {\"u}ber eine Altersspanne von acht bis dreizehn Jahren untersucht werden. Bei einem m{\"o}glichen Ged{\"a}chtnisdefizit sollte {\"u}berpr{\"u}ft werden, ob dieses sich nur bei schriftsprach{\"a}hnlichem Material {\"a}ußerte oder ob es sich um ein allgemeineres Defizit handelte. Insgesamt 65 lese-rechtschreibschwache und schriftsprachlich normal entwickelte Kinder der Altersgruppen 8-9 Jahre, 10-11 Jahre und 12-13 Jahre wurden Aufgaben zur Ged{\"a}chtnisspanne, zur Benennungsgeschwindigkeit und zur Suchrate unterzogen. In den Aufgaben zur Ged{\"a}chtnisspanne und zur Benennungsgeschwindigkeit zeigten die lese-rechtschreibschwachen Kinder deutlich schlechtere Leistungen als die Kontrollgruppe, und beide untersuchten Gruppen verbesserten sich in ihren Leistungen mit ansteigendem Alter. Hinweise f{\"u}r ein schriftsprachorientiertes Defizit im Falle der Rechtschreibschwachen ließen sich den Aufgaben zur Ged{\"a}chtnisspanne und zur Suchrate entnehmen. Zusammenfassend best{\"a}tigen die vorliegenden Ergebnisse Defizite in Funktionen des Kurzzeitged{\"a}chtnisses bei LRS. {\"U}ber die untersuchte Altersspanne hinweg kam es nicht zu einer Ann{\"a}herung der Leistungen der Rechtschreibschwachen an die der Kontrollgruppe, was f{\"u}r ein bleibendes Defizit im Fall der LRS spricht. Um zu eindeutigen Ergebnissen hinsichtlich der Schriftsprachabh{\"a}ngigkeit der Ged{\"a}chtnisdefizite bei LRS kommen zu k{\"o}nnen, m{\"u}ssen weitere Studien abgewartet werden.},
  language  = {de}
}
@phdthesis{Fischer2004,
  author    = {Fischer, Matthias},
  title     = {Lokalisierung eines Ged{\"a}chtnisses bei Drosophila melanogaster},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-8050},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2004},
  abstract  = {Es konnte in dieser Arbeit gezeigt werden, daß das olfaktorische Kurzzeitged{\"a}chtnis von Drosophila melanogaster in den Pilzk{\"o}rpern lokalisiert ist. Zu Beginn dieser Doktorarbeit war bekannt, daß die Pilzk{\"o}rper notwendig f{\"u}r das Geruchsged{\"a}chtnis sind. Drei unabh{\"a}ngige Methoden der Ablation bzw. Ver{\"a}nderung der biochemischen Eigenschaften der Pilzk{\"o}rper hatten zu dem selben Ergebnis gef{\"u}hrt, daß funktionierende Pilzk{\"o}rper unentbehrlich f{\"u}r den Aufbau eines Geruchsged{\"a}chtnisses sind. Noch informativer als ein Experiment, in dem durch Zerst{\"o}rung einer Struktur eine Leistung unm{\"o}glich gemacht wird ist der umgekehrte Weg, der durch einen gewebespezifischen „rescue" die Leistung wiederherstellt. Dazu wurde in dieser Arbeit das wildtypische Allel des Gens rutabaga in rut-mutanten Fliegen mit Hilfe des Gal4/UAS-Systems ausschließlich in den Pilzk{\"o}rpern, bzw., im Gegenexperiment, nur außerhalb der Pilzk{\"o}rper zur Expression gebracht. rut kodiert f{\"u}r die Adenylatcyclase I, die mit synaptischer Plastizit{\"a}t bei Drosophila, Aplysia und M{\"a}usen in Verbindung gebracht wird. Man geht davon aus, daß synaptische Plastizit{\"a}t die molekulare Grundlage f{\"u}r Lernen und Ged{\"a}chtnis ist. Die AC I stellt cAMP her, dessen Menge und pr{\"a}zise Regulation die {\"U}bertragungsst{\"a}rke an Neuronen beeinflußt. Eine St{\"o}rung dieses Signalweges z. B. durch die rut-Mutation f{\"u}hrt zu einer Beeintr{\"a}chtigung des Ged{\"a}chtnisses bei Drosophila. rut wurde mit Hilfe des in Drosophila etablierten Gal4/UAS-Systems exprimiert: Der gewebespezifisch aktive Hefe-Transkriptionsfaktor Gal4 f{\"u}hrt dazu, daß das hinter einen Gal4-spezifischen UAS-Promotor klonierte wildtypische rut-Gen in denjenigen Zellen transkribiert wird, in denen der Transkriptionsfaktor vorhanden ist. Dies wurde in einer rut-Mutante durchgef{\"u}hrt, so daß in allen anderen Zellen keine funktionierende AC I vorhanden war. Die rut-abh{\"a}ngige synaptische Plastizit{\"a}t wurde damit ausschließlich auf die gew{\"u}nschten Regionen beschr{\"a}nkt. Das Expressionsmuster der Gal4-Linien wurde durch Immuncytochemie (Anti-Tau) sichtbar gemacht. Diese Fliegen wurden in einem klassischen Konditionierungsexperiment auf ihr Geruchs-Ged{\"a}chtnis untersucht. Dazu wurden einer Gruppe von Fliegen nacheinander 2 Ger{\"u}che pr{\"a}sentiert, von denen einer mit Elektroschocks gepaart war. Nach ca. 2 min konnten diese Fliegen sich f{\"u}r einen der beiden Ger{\"u}che entscheiden, die nun gleichzeitig aus 2 unterschiedlichen Richtungen dargeboten wurden. Je nach Lernleistung entschieden sich mehr oder weniger Fliegen f{\"u}r den vorher unbestraften Geruch. Es ergab sich, daß der Ort im Gehirn, an dem die wildtypische AC I exprimiert wurde, {\"u}ber die H{\"o}he des Ged{\"a}chtniswertes entschied: Die AC I ausschließlich in den Pilzk{\"o}rpern gew{\"a}hrte ein v{\"o}llig normales Ged{\"a}chtnis, wogegen die AC I außerhalb der Pilzk{\"o}rper das Ged{\"a}chtnis nicht gegen{\"u}ber der rut-Mutante verbessern konnte. Die Analyse der Expressionsverteilung von insgesamt 9 getesteten Fliegenlinien mißt {\"u}berdies dem \&\#61543;-Lobus des Pilzk{\"o}rpers eine besondere Bedeutung bei und l{\"a}ßt den Schluß zu, daß das hier untersuchte Ged{\"a}chtnis ausschließlich in den \&\#61543;-Loben lokalisiert ist. Dieses erfolgreiche rut-„rescue" - Experiment zeigt, daß rut-abh{\"a}ngige synaptische Plastizit{\"a}t ausschließlich in den Pilzk{\"o}rpern ausreichend f{\"u}r ein wildtypisches Ged{\"a}chtnis ist. Dieses Ergebnis vervollst{\"a}ndigt die Erkenntnisse von den Pilzk{\"o}rper-Ablationsexperimenten insofern, als nun die Aussage zutrifft, daß die Pilzk{\"o}rper notwendig und hinreichend f{\"u}r das olfaktorische Kurzzeitged{\"a}chtnis sind.},
  language  = {de}
}
@phdthesis{Masek2005,
  author    = {Masek, Pavel},
  title     = {Odor intensity learning in Drosophila},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-15546},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2005},
  abstract  = {It has been known for a long time that Drosophila can learn to discriminate not only between different odorants but also between different concentrations of the same odor. Olfactory associative learning has been described as a pairing between odorant and electric shock and since then, most of the experiments conducted in this respect have largely neglected the dual properties of odors: quality and intensity. For odorant-coupled short-term memory, a biochemical model has been proposed that mainly relies on the known cAMP signaling pathway. Mushroom bodies (MB) have been shown to be necessary and sufficient for this type of memory, and the MB-model of odor learning and short-term memory was established. Yet, theoretically, based on the MB-model, flies should not be able to learn concentrations if trained to the lower of the two concentrations in the test. In this thesis, I investigate the role of concentration-dependent learning, establishment of a concentration-dependent memory and their correlation to the standard two-odor learning as described by the MB-model. In order to highlight the difference between learning of quality and learning of intensity of the same odor I have tried to characterize the nature of the stimulus that is actually learned by the flies, leading to the conclusion that during the training flies learn all possible cues that are presented at the time. The type of the following test seems to govern the usage of the information available. This revealed a distinction between what flies learned and what is actually measured. Furthermore, I have shown that learning of concentration is associative and that it is symmetrical between high and low concentrations. I have also shown how the subjective quality perception of an odor changes with changing intensity, suggesting that one odor can have more than one scent. There is no proof that flies perceive a range of concentrations of one odorant as one (odor) quality. Flies display a certain level of concentration invariance that is limited and related to the particular concentration. Learning of concentration is relevant only to a limited range of concentrations within the boundaries of concentration invariance. Moreover, under certain conditions, two chemically distinct odorants could smell sufficiently similarly such, that they can be generalized between each other like if they would be of the same quality. Therefore, the abilities of the fly to identify the difference in quality or in intensity of the stimuli need to be distinguished. The way how the stimulus is analyzed and processed speaks in favor of a concept postulating the existence of two separated memories. To follow this concept, I have proposed a new form of memory called odor intensity memory (OIM), characterized it and compared it to other olfactory memories. OIM is independent of some members of the known cAMP signaling pathway and very likely forms the rutabaga-independent component of the standard two-odor memory. The rutabaga-dependent odor memory requires qualitatively different olfactory stimuli. OIM is revealed within the limits of concentration invariance where the memory test gives only sub-optimal performance for the concentration differences but discrimination of odor quality is not possible at all. Based on the available experimental tools, OIM seems to require the mushroom bodies the same as odor-quality memory but its properties are different. Flies can memorize the quality of several odorants at a given time but a newly formed memory of one odor interferes with the OIM stored before. In addition, the OIM lasts only 1 to 3 hours - much shorter than the odor-quality memory.},
  subject      = {Taufliege},
  language  = {en}
}
@phdthesis{Thum2006,
  author    = {Thum, Andreas Stephan},
  title     = {Sugar reward learning in Drosophila : neuronal circuits in Drosophila associative olfactory learning},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-17930},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2006},
  abstract  = {Genetic intervention in the fly Drosophila melanogaster has provided strong evidence that the mushroom bodies of the insect brain act as the seat of memory traces for aversive and appetitive olfactory learning (reviewed in Heisenberg, 2003). In flies, electroshock is mainly used as negative reinforcer. Unfortunately this fact complicates a comparative consideration with other inscets as most studies use sugar as positive reinforcer. For example, several lines of evidence from honeybee and moth have suggested another site, the antennal lobe, to house neuronal plasticity underlying appetitive olfactory memory (reviewed in Menzel, 2001; Daly et al., 2004). Because of this I focused my work mainly on appetitive olfactory learning. In the first part of my thesis, I used a novel genetic tool, the TARGET system (McGuire et al., 2003), which allows the temporally controlled expression of a given effector gene in a defined set of cells. Comparing effector genes which either block neurotransmission or ablate cells showed important differences, revealing that selection of the appropriate effector gene is critical for evaluating the function of neural circuits. In the second part, a new engram of olfactory memory in the Drosophila projection neurons is described by restoring Rutabaga adenlylate cyclase (rut-AC) activity specifically in these cells. Expression of wild-type rutabaga in the projection neurons fully rescued the defect in sugar reward memory, but not in aversive electric shock memory. No difference was found in the stability of the appetitive memories rescued either in projection neurons or Kenyon cells. In the third part of the thesis I tried to understand how the reinforcing signals for sugar reward are internally represented. In the bee Hammer (1993) described a single octopaminergic neuron - called VUMmx1 - that mediates the sugar stimulus in associative olfactory reward learning. Analysis of single VUM neurons in the fly (Selcho, 2006) identified a neuron with a similar morphology as the VUMmx1 neuron. As there is a mutant in Drosophila lacking the last enzymatic step in octopamine synthesis (Monastirioti et al., 1996), Tyramine beta Hydroxylase, I was able to show that local Tyramine beta Hydroxylase expression successfully rescued sugar reward learning. This allows to conclude that about 250 cells including the VUM cluster are sufficient for mediating the sugar reinforcement signal in the fly. The description of a VUMmx1 similar neuron and the involvement of the VUM cluster in mediating the octopaminergic sugar stimulus are the first steps in establishing a neuronal map for US processing in Drosophila. Based on this work several experiments are contrivable to reach this ultimate goal in the fly. Taken together, the described similiarities between Drosophila and honeybee regarding the memory organisation in MBs and PNs and the proposed internal representation of the sugar reward suggest an evolutionarily conserved mechanism for appetitive olfactory learning in insects.},
  subject      = {Taufliege},
  language  = {en}
}
@phdthesis{Pappert2007,
  author    = {Pappert, Katrin},
  title     = {Anisotropies in (Ga,Mn)As - Measurement, Control and Application in Novel Devices},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-23370},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2007},
  abstract  = {Ferromagnetic semiconductors (FS) promise the integration of magnetic memory functionalities and semiconductor information processing into the same material system. The prototypical FS (Ga,Mn)As has become the focus of semiconductor spintronics research over the past years. The spin-orbit mediated coupling of magnetic and semiconductor properties in this material gives rise to many novel transport-related phenomena which can be harnessed for device applications. In this thesis we address challenges faced in the development of an all-semiconductor memory architecture. A starting point for information storage in FS is the knowledge of their detailed magnetic anisotropy. The first part of this thesis concentrates on the investigation of the magnetization behaviour in compressively strained (Ga,Mn)As by electrical means. The angle between current and magnetization is monitored in magnetoresistance(MR) measurements along many in-plane directions using the Anisotropic MR(AMR) or Planar Hall effect(PHE). It is shown, that a full angular set of such measurements displayed in a color coded resistance polar plot can be used to identify and quantitatively determine the symmetry components of the magnetic anisotropy of (Ga,Mn)As at 4 K. We compile such "anisotropy fingerprints" for many (Ga,Mn)As layers from Wuerzburg and other laboratories and find the presence of three symmetry terms in all layers. The biaxial anisotropy term with easy axes along the [100] and [010] crystal direction dominates the magnetic behaviour. An additional uniaxial term with an anisotropy constant of ~10\% of the biaxial one has its easy axis along either of the two <110> directions. A second contribution of uniaxial symmetry with easy axis along one of the biaxial easy axes has a strength of only ~1\% of the biaxial anisotropy and is therefore barely visible in standard SQUID measurements. An all-electrical writing scheme would be desirable for commercialization. We report on a current assisted magnetization manipulation experiment in a lateral (Ga,Mn)As nanodevice at 4 K (far below Tc). Reading out the large resistance signal from DW that are confined in nanoconstrictions, we demonstrate the current assisted magnetization switching of a small central island through a hole mediated spin transfer from the adjacent leads. One possible non-perturbative read-out scheme for FS memory devices could be the recently discovered Tunneling Anisotropic MagnetoResistance (TAMR) effect. Here we clarify the origin of the large amplification of the TAMR amplitude in a device with an epitaxial GaAs tunnel barrier at low temperatures. We prove with the help of density of states spectroscopy that a thin (Ga,Mn)As injector layer undergoes a metal insulator transition upon a change of the magnetization direction in the layer plane. The two states can be distinguished by their typical power law behaviour in the measured conductance vs voltage tunneling spectra. While all hereto demonstrated (Ga,Mn)As devices inherited their anisotropic magnetic properties from their parent FS layer, more sophisticated FS architectures will require locally defined FS elements of different magnetic anisotropy on the same wafer. We show that shape anisotropy is not applicable in FS because of their low volume magnetization. We present a method to lithographically engineer the magnetic anisotropy of (Ga,Mn)As by submicron patterning. Anisotropic strain relaxation in submicron bar structures (nanobars) and the related deformation of the crystal lattice introduce a new uniaxial anisotropy term in the energy equation. We demonstrate by both SQUID and transport investigations that this lithographically induced uniaxial anisotropy overwrites the intrinsic biaxial anisotropy at all temperatures up to Tc. The final section of the thesis combines all the above into a novel device scheme. We use anisotropy engineering to fabricate two orthogonal, magnetically uniaxial, nanobars which are electrically connected through a constriction. We find that the constriction resistance depends on the relative orientation of the nanobar magnetizations, which can be written by an in-plane magnetic field. This effect can be explained with the AMR effect in connection with the field line patterns in the respective states. The device offers a novel non-volatile information storage scheme and a corresponding non-perturbative read-out method. The read out signal is shown to increase drastically in samples with partly depleted constriction region. This could be shown to originate in a magnetization direction driven metal insulator transition of the material in the constriction region.},
  subject      = {Anisotropie},
  language  = {en}
}
@phdthesis{Niewalda2010,
  author    = {Niewalda, Thomas},
  title     = {Neurogenetic analyses of pain-relief learning in the fruit fly},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-65035},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {All animals learn in order to cope with challenges imposed on them by their environment. This is true also for both larval and adult fruit flies as exemplified in pavlovian conditioning. The focus of this Thesis is on various aspects of the fruit flies learning ability. My main project deals with two types of learning which we call punishment-learning and pain-relief learning. Punishment learning happens when fruit flies are exposed to an odour which is followed by electric shock. After such training, flies have learned that that odour signals pain and consequently will avoid it in the future. If the sequence of the two stimuli is reversed such that odour follows shock, flies learn the odour as a signal for relief and will later on approach it. I first report a series of experiments investigating qualitative and parametric features of relief-learning; I find that (i) relief learning does result from true associative conditioning, (ii) it requires a relatively high number of training trials, (iii) context-shock training is ineffective for subsequent shock-odour learning. A further question is whether punishment-learning and pain-relief learning share genetic determinants. In terms of genetics, I test a synapsin mutant strain, which lacks all Synapsin protein, in punishment and relief-learning. Punishment learning is significantly reduced, and relief-learning is abolished. Pan-neuronal RNAi-mediated knock-down of Synapsin results in mutant-like phenotypes, confirming the attribution of the phenotype to lack of Synapsin. Also, a rescue of Synapsin in the mushroom body of syn97 mutants restores both punishment- and relief-learning fully, suggesting the sufficiency of Synapsin in the mushroom body for both these kinds of learning. I also elucidate the relationship between perception and physiology in adult fruit flies. I use odour-shock conditioning experiments to identify degrees of similarity between odours; I find that those similarity measures are consistent across generalization and discrimination tasks of diverse difficulty. Then, as collaborator of T. V{\"o}ller and A. Fiala, I investigate how such behavioural similarity/dissimilarity is reflected at the physiological level. I combine the behaviour data with calcium imaging data obtained by measuring the activity patterns of those odours in either the sensory neurons or the projection neurons at the antennal lobe. Our interpretation of the results is that the odours perceptual similarity is organized by antennal lobe interneurons. In another project I investigate the effect of gustatory stimuli on reflexive behaviour as well as their role as reinforcer in larval learning. Drosophila larvae greatly alter their behaviour in presence of sodium chloride. Increasing salt concentration modulates choice behaviour from weakly appetitive to strongly aversive. A similar concentration-behaviour function is also found for feeding: larval feeding is slightly enhanced in presence of low salt concentrations, and strongly decreased in the presence of high salt concentrations. Regarding learning, relatively weak salt concentrations function as appetitive reinforcer, whereas high salt concentrations function as aversive reinforcer. Interestingly, the behaviour-concentration curves are shifted towards higher concentrations from reflexive behaviour (choice behaviour, feeding) as compared to associative learning. This dissociation may reflect a different sensitivity in the respective sensory-motor circuitry.},
  subject      = {Taufliege},
  language  = {en}
}
@article{SchneiderTautzGruenewaldetal.2012,
  author    = {Schneider, Christof W. and Tautz, J{\"u}rgen and Gr{\"u}newald, Bernd and Fuchs, Stefan},
  title     = {RFID Tracking of Sublethal Effects of Two Neonicotinoid Insecticides on the Foraging Behavior of Apis mellifera},
  series = {PLoS One},
  volume    = {7},
  journal   = {PLoS One},
  number    = {1},
  doi       = {10.1371/journal.pone.0030023},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-131753},
  pages     = {e30023},
  year      = {2012},
  abstract  = {The development of insecticides requires valid risk assessment procedures to avoid causing harm to beneficial insects and especially to pollinators such as the honeybee Apis mellifera. In addition to testing according to current guidelines designed to detect bee mortality, tests are needed to determine possible sublethal effects interfering with the animal's vitality and behavioral performance. Several methods have been used to detect sublethal effects of different insecticides under laboratory conditions using olfactory conditioning. Furthermore, studies have been conducted on the influence insecticides have on foraging activity and homing ability which require time-consuming visual observation. We tested an experimental design using the radiofrequency identification (RFID) method to monitor the influence of sublethal doses of insecticides on individual honeybee foragers on an automated basis. With electronic readers positioned at the hive entrance and at an artificial food source, we obtained quantifiable data on honeybee foraging behavior. This enabled us to efficiently retrieve detailed information on flight parameters. We compared several groups of bees, fed simultaneously with different dosages of a tested substance. With this experimental approach we monitored the acute effects of sublethal doses of the neonicotinoids imidacloprid (0.15-6 ng/bee) and clothianidin (0.05-2 ng/bee) under field-like circumstances. At field-relevant doses for nectar and pollen no adverse effects were observed for either substance. Both substances led to a significant reduction of foraging activity and to longer foraging flights at doses of >= 0.5 ng/bee (clothianidin) and >= 1.5 ng/bee (imidacloprid) during the first three hours after treatment. This study demonstrates that the RFID-method is an effective way to record short-term alterations in foraging activity after insecticides have been administered once, orally, to individual bees. We contribute further information on the understanding of how honeybees are affected by sublethal doses of insecticides.},
  language  = {en}
}