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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.
Ziel der Studie war die Exploration von Funktionen des Kurzzeitgedächtnisses bei lese-rechtschreibschwachen Kindern (LRS) im Vergleich zu einer schriftsprachlich normal entwickelten Kontrollgruppe (KG). Gedächtnisfunktionen sollten im Hinblick auf Entwicklungsveränderungen über eine Altersspanne von acht bis dreizehn Jahren untersucht werden. Bei einem möglichen Gedächtnisdefizit sollte überprüft werden, ob dieses sich nur bei schriftsprachähnlichem Material äußerte 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 Gedächtnisspanne, zur Benennungsgeschwindigkeit und zur Suchrate unterzogen. In den Aufgaben zur Gedächtnisspanne 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 für ein schriftsprachorientiertes Defizit im Falle der Rechtschreibschwachen ließen sich den Aufgaben zur Gedächtnisspanne und zur Suchrate entnehmen. Zusammenfassend bestätigen die vorliegenden Ergebnisse Defizite in Funktionen des Kurzzeitgedächtnisses bei LRS. Über die untersuchte Altersspanne hinweg kam es nicht zu einer Annäherung der Leistungen der Rechtschreibschwachen an die der Kontrollgruppe, was für ein bleibendes Defizit im Fall der LRS spricht. Um zu eindeutigen Ergebnissen hinsichtlich der Schriftsprachabhängigkeit der Gedächtnisdefizite bei LRS kommen zu können, müssen weitere Studien abgewartet werden.
Characterization of memories and ignorant (S6KII) mutants in operant conditioning in the heat-box
(2002)
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.
No abstract available.
Errors in Prospective Memory
(2019)
Prospective memory is the ability to implement intentions at a later point in time in response to a specified cue. Such prospective memory tasks often occur in daily living and workplace situations. However, in contrast to retrospective memory there has been relatively little research on prospective memory. The studies by Harris (1984) and Einstein and MacDaniel (1990) served as a starting point for a now steadily growing area of research. Based on this emerging field of study this dissertation presents and connects and five journal articles, which further explore prospective memory by focusing on its potential errors.
The first article addresses the question if additional cognitive resources are needed after a prospective memory cue occurs to keep the intention active until it is implemented. The theory by Einstein, McDaniel, Williford, Pagan and Dismukes (2003), which suggested this active maintenance, could not be replicated. The second article demonstrated that interruptions between cue and the window of opportunity to implement the intention reduce prospective memory performance, especially if the interruption is tied with a change of context. Article three to five were focused on the erroneous implementation of a no longer active prospective memory task, so called commission errors. The suggested mechanism for their occurrence, the dual-mechanism account (Bugg, Scullin, & Rauvola, 2016), was not suited to explain the present results. A modification for the dual-mechanism account was formulated, which can account for prior work, as well as for the present data.
The results of all five articles also indicate that the moment of cue retrieval is even more relevant for prospective memory and its errors than previously accounted for.
Die vorliegende Arbeit ging zwei Hauptfragestellungen nach: (I) Inwiefern unterscheiden sich Experten in der Domäne Schach von Aussteigern aus der Expertisekarriere? (2) Wie verändern sich schachspezifische und generelle Gedächtnisparameter über einen Zeitraum von mehreren Jahren? Es wurden 27 Experten und Novizen mit einem durchschnittlichen Alter von knapp 12 Jahren zum ersten Meßzeitpunkt und von 16 Jahren zum zweiten Meßzeitpunkt untersucht. Die Aussteiger aus der Expertisekarriere zeigten bereits bei der Erstmessung schlechtere schachspezifische Gedächtnisleistungen als die übrigen Experten; die Annahme selektiver Aussteiger, die die Aussagekraft querschnittlicher Experten-Novizen-Vergleiche in Frage stellt, wird damit bestätigt. Sowohl für die Experten als auch für die Novizen zeigte sich ein Anstieg der schachspezifischen Gedächtnisleistung von der Erst- zur Zweitmessung. Während dafür bei Experten domänenspezifische Faktoren verantwortlich sein dürften, scheint dies bei Novizen auf die Entwicklung allgemeiner Gedächtnisparameter zurückzugehen.
Behavioral adaptation to environmental changes is crucial for animals’ survival. The prediction of the outcome of one owns action, like finding reward or avoiding punishment, requires recollection of past experiences and comparison with current situation, and adjustment of behavioral responses. The process of memory acquisition is called learning, and the Drosophila larva came up to be an excellent model organism for studying the neural mechanisms of memory formation. In Drosophila, associative memories are formed, stored and expressed in the mushroom bodies. In the last years, great progress has been made in uncovering the anatomical architecture of these brain structures, however there is still a lack of knowledge about the functional connectivity.
Dopamine plays essential roles in learning processes, as dopaminergic neurons mediate information about the presence of rewarding and punishing stimuli to the mushroom bodies. In the following work, the function of a newly identified anatomical connection from the mushroom bodies to rewarding dopaminergic neurons was dissected. A recurrent feedback signaling within the neuronal network was analyzed by simultaneous genetic manipulation of the mushroom body Kenyon cells and dopaminergic neurons from the primary protocerebral anterior (pPAM) cluster, and learning assays were performed in order to unravel the impact of the Kenyon cells-to-pPAM neurons feedback loop on larval memory formation.
In a substitution learning assay, simultaneous odor exposure paired with optogenetic activation of Kenyon cells in fruit fly larvae in absence of a rewarding stimulus resulted in formation of an appetitive memory, whereas no learning behavior was observed when pPAM neurons were ablated in addition to the KC activation. I argue that the activation of Kenyon cells may induce an internal signal that mimics reward exposure by feedback activation of the rewarding dopaminergic neurons. My data further suggests that the Kenyon cells-to-pPAM communication relies on peptidergic signaling via short neuropeptide F and underlies memory stabilization.
No abstract available.
No abstract available.
No abstract available.