Der Einfluss des dorsalen Hippocampus auf das instrumentelle Lernen und die Verhaltensflexibilität im Tiermodell der Ratte

Brain damage is generally associated with a consequent limitation of cognitive abilities. This assumption is substantiated by a large amount of empirical data that has been obtained with the help of experimental brain lesions. In contrast to functional deficits, the finding of an increase in function or performance after brain lesions is less frequent, but it is nevertheless a recurring phenomenon in neuroscientific research. Specifically, the hippocampus of the mammalian cerebrum seems to play an important role with regard to the observed performance improvements. Many studies report that damage to the hippocampus results in an increase in performance of the subjects or experimental animals, when tasks with specific behavioral requirements are used. The aim of this work is to investigate the influence of hippocampal lesions on procedural and / or instrumental learning in the rat model. For this purpose, a rat version of the serial reaction time task (SRTT) was used to operationalize instrumental learning. Findings from a previous study by Eckart et al. (2012) suggested that rats with lesions of the dorsal hippocampus show declarative memory deficits, but, at the same time, show significant improvements in instrumental learning in the SRTT paradigm. In the first study of this thesis, it was shown that improvements in instrumental learning of lesioned rats are present even when a constant amount of learning experience is used for each experimental trial during the training phase of the SRTT. In addition, a deficit in extinction learning was observed in the experimental group. In the second study, it was shown that performance enhancements in the lesioned rats are also present, when a pseudorandomized stimulus presentation instead of a sequential stimulus presentation is used. In addition, lesioned rats showed a deficit in extinction learning when the food reward was devalued. Furthermore, a significant reduction of non-task-related behaviors in the experimental group was observed over the course of the training phase. In the third study, a deficit in behavioral flexibility after lesion of the dorsal hippocampus was observed in the experimental group. For this purpose, the rats were tested in an R-O decoupled variant of the SRTT after completion of the SRTT training. The data obtained from this work suggest that the performance improvements found in the SRTT are only a side effect of complex behavioral changes as a consequence of the lesion of the dorsal hippocampus. A specific explanatory approach for the observed performance improvements is discussed at the end of this thesis within the framework of the "Multiple Parallel Memory Systems" theory.