Further development of an episodic-like task in rats.

Abstract

This thesis aimed to study the impairment observed in rats with fornix damage when performing an episodic memory task that requires recall of the location of objects in a context. To test whether the impairment may have been due to a spatial memory dysfunction, the same group of animals was tested in a spatial control task which is the same in all aspects to the episodic memory task except that there is no role of context. Animals without damage on the fornix gave evidence that the task was not working. This poor performance may have been caused by the experience or the age of the animals or slightly different procedures compared to previous published work. To explore this aspect, a group of young and non-experienced animals was taken to study their performance on the task. Still poor results were obtained which led to study slightly modifications on the procedures which may improve those. There was some evidence that procedural differences may have contributed to different results compared to previously published work. With the aim of improving the task, some modifications were studied. In this sense, the absence of the habituation object did not improve the preference to explore the more novel one but a preference for the location whereby the habituation object used to be was found. The presence of a completely novel object showed good results in the sense of animals having a preference to explore this object. In addition, a novel version of the task showing a cue object to the rat associated to the location where the complete novel object would be, also showed good results. On this basis, the task was found to be a reliable task to study cued recall in the rat. The study of some conditions on this cued recall task showed that animals were able to remember after 20 minutes delay when the cue object was only explored for 1 minute. To investigate whether animals may have been used cues to solve the task, a test was performed which showed that the performance of the animals on the task may have been a result of odour detection rather than memory.