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|Title:||SPATIAL LATENT INHIBITION IN THE CONDITIONED CUE PREFERENCE TASK|
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|Authors/Affiliations:||1 Maliha Naeem*; 1 Norman White; |
1 McGill University, Montreal, QC, Canada.
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|Content:||Objective: This study is part of a larger project examining how rats learn to discriminate among locations in a spatial environment. The specific object of the study is to examine how rats learn to discriminate between separated arms on an 8-arm radial maze.|
Methods: Food-deprived rats were allowed to explore an 8-arm radial maze for 10 min with no food available (pre-exposure, PX), and then given a series of daily training trials (TT) in which they ate while confined on one arm of the maze and spent equal time confined with no food on an arm on the other side of the maze. When placed on the maze with no food available, rats may spend more time on the food-paired than on the unpaired arm, a conditioned cue preference (CCP), indicating that they have learned to discriminate between the two arm locations. Previous research showed that a minimum of 4 TT is required to learn this arm discrimination. However, if the PX session is omitted rats acquire the discrimination with only 2 TT. To clarify the relationship between pre-exposure and training we gave rats 0 or 1 PX followed by 1 to 4 TT (see Figure). Results: With no PX normal rats expressed a CCP with 2 TT, but not with 1, 3, or 4 TT. With 1 PX a CCP was observed with 1, 3 and 4 TT. This pattern suggests a complex interaction between the learning that occurs during unreinforced PX and during the TT. In an attempt to identify these processes the effects of lesions of brain structures critical for different kinds of learning were examined. It has previously been shown that fimbria-fornix lesions facilitate and amygdala lesions impair the CCP with 1px and 2 TT. We replicated this finding and showed that amygdala lesions also impair the CCP with 0 PX and 2 TT. With 0 PX and 4 TT, dorsal hippocampus, fimbria-fornix or amygdala lesions had no effect on the lack of a CCP. However, analysis of the lesions suggested that this may be true for more anterior but not posterior amygdala lesions which may have allowed a preference to appear (further investigation is required to examine this hypothesis) .We also found that amygdala lesions eliminate the CCP with 1 PX and 1 TT and replicated the previous finding that amygdala lesions block the CCP with 1 PX and 4 TT. Conclusion: Our findings suggest that learning to discriminate between separated maze arms is influenced by amygdala-mediated conditioned responses, which may facilitate or inhibit expression of the discrimination between the two maze arm locations. Future lesion studies may elucidate the interactions among the memory processes underlying this complex learning task.
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