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Abstract
The present thesis investigated the role of stimulus properties in the function of the hippocampal formation in memory. In nine experiments, fornix-transected (FX) rats and sham-operated (SH) controls were trained on various spatial (radial arm maze) and nonspatial (radial arm maze and odor recognition) memory tasks. In the first series of experiments (Chapters II and III), two widely used radial maze tasks were modified in order to examine if, in addition to the spatial nature of stimulus information, choice behaviors and task parameters could account for the performance of FX-transected rats. In the place task, results demonstrated that the impairment of the FX group could be explained by the disruption of both spatial and working memory processes. In the standard cue task, unexpected results showed that the location of relevant stimuli and the stability of their topological relationships somewhat influenced FX-transected rats' performance. In a second series of experiments (Chapter IV), new cue tasks were utilized to examine the role of relational memory. The findings suggested that the information was processed on a relational basis rather than on an individual basis, even in cue tasks. They were also consistent with the hypothesis that a functional hippocampal memory system is required to disambiguate overlapping relations between stimuli presented simultaneously. In a final set of experiments (Chapters V and VI), the role of stimulus properties was examined in two nonspatial tasks requiring recognition of simple and complex olfactory stimuli. The results indicated that FX-transected rats were impaired on recognition of stimuli comprising either a single component-or multiple overlapping components. Overall, this thesis made three contributions to the investigation of the function of the hippocampal formation in memory: (1) it demonstrated that the parameters of a memory task and the stimulus properties may influence significantly the performance of FX-transected rats; (2) it confirmed that the function of the hippocampal formation is not dedicated exclusively to spatial information; and (3) it indicated that this function appears heterogeneous rather than specialized.