title: The impact of fornix lesions in rats on spatial learning tasks sensitive to anterior thalamic and hippocampal damage.
abstract: The present study sought to understand how the hippocampus and anterior thalamic nuclei are conjointly required for spatial learning by examining the impact of cutting a major tract (the fornix) that interconnects these two sites. The initial experiments examined the consequences of fornix lesions in rats on spatial biconditional discrimination learning. The rationale arose from previous findings showing that fornix lesions spare the learning of spatial biconditional tasks, despite the same task being highly sensitive to both hippocampal and anterior thalamic nuclei lesions. In the present study, fornix lesions only delayed acquisition of the spatial biconditional task, pointing to additional contributions from non-fornical routes linking the hippocampus with the anterior thalamic nuclei. The same fornix lesions spared the learning of an analogous nonspatial biconditional task that used local contextual cues. Subsequent tests, including T-maze place alternation, place learning in a cross-maze, and a go/no-go place discrimination, highlighted the impact of fornix lesions when distal spatial information is used flexibly to guide behaviour. The final experiment examined the ability to learn incidentally the spatial features of a square water-maze that had differently patterned walls. Fornix lesions disrupted performance but did not stop the rats from distinguishing the various corners of the maze. Overall, the results indicate that interconnections between the hippocampus and anterior thalamus, via the fornix, help to resolve problems with flexible spatial and temporal cues, but the results also signal the importance of additional, non-fornical contributions to hippocampal-anterior thalamic spatial processing, particularly for problems with more stable spatial solutions.
authors.affiliation: School of Psychology, Cardiff University, 70 Park Place, Cardiff CF10 3AT, Wales, UK. Electronic address: Julie.Dumont@dartmouth.edu.
authors.forename: Julie R
authors.initials: JR
authors.lastname: Dumont
authors.affiliation: School of Psychology, Cardiff University, 70 Park Place, Cardiff CF10 3AT, Wales, UK.
authors.forename: Eman
authors.initials: E
authors.lastname: Amin
authors.affiliation: School of Psychology, Cardiff University, 70 Park Place, Cardiff CF10 3AT, Wales, UK.
authors.forename: Nicholas F
authors.initials: NF
authors.lastname: Wright
authors.affiliation: School of Psychology, Cardiff University, 70 Park Place, Cardiff CF10 3AT, Wales, UK.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Dillingham
authors.affiliation: School of Psychology, Cardiff University, 70 Park Place, Cardiff CF10 3AT, Wales, UK.
authors.forename: John P
authors.initials: JP
authors.lastname: Aggleton
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001930:Brain Injuries / Q000150:complications* / Q000473:pathology; D017115:Catheter Ablation / Q000009:adverse effects; D003463:Cues; D003657:Decision Making; D004193:Discrimination Learning / Q000502:physiology; D004195:Disease Models, Animal; D020712:Fornix, Brain / Q000293:injuries* / Q000473:pathology; D006624:Hippocampus / Q000503:physiopathology*; D007859:Learning Disabilities / Q000209:etiology*; D008297:Male; D018782:Maze Learning; D009434:Neural Pathways / Q000502:physiology; D051381:Rats; D065853:Spatial Learning / Q000502:physiology*; D013788:Thalamus / Q000503:physiopathology*; D013997:Time Factors; D014163:Transfer, Psychology
keywords: Biconditional learning; Cognitive map; Configural learning; Hippocampus; Incidental learning; Thalamus