Adapted Morris Water Maze protocol to prevent interference from confounding motor deficits on cognitive functioning

Purpose/aim of the study: Cognitive functioning in the Morris Water Maze (MWM) is assumed to be reflected by path length. In this study, the interference of motor deficits, as a confounding factor on cognitive functioning, was assessed by means of a lateralization study with hemicerebellectomized (HCX) mice. This model is characterized by motor deficits restricted to the lesion side, allowing comparison within the model itself (left vs. right), rather than the effect of the manipulation on this measure (experimental vs. control).Materials and methods: Spatial learning was assessed after left or right hemicerebellectomy in adult mice by means of two MWM designs in which the location of the starting positions was altered for one condition in the adapted (Adap) MWM experiment, hypothesizing that motor impairments ipsilateral to the lesion side result in a difference in path length.Results: When the starting positions were equal for both conditions in the traditional (Trad) MWM experiment, path length during the acquisition phase and spatial memory were more affected for the left HCX, while these effects disappeared after mirroring the starting positions in the Adap MWM, implying that motor phenotype and corresponding increase in task difficulty are responsible for the contradictory results in the Trad MWM experiment.Conclusion: The differences found in the latter experiment were circumvented in the adapted MWM protocol, and therefore, excluding the motor deficit as a confounding factor on cognitive MWM parameters.