Comparison of developmental trajectories for place and cued navigation in the Morris water task

Previous studies investigating the development of place and cued learning using the Morris water task are in disagreement regarding the day in development that each type of learning emerges. Here, place and cued navigation in the water task were examined in differently aged groups of young male andfemale rats (P] 7, P18, P19, P20, and P24) during a single day of training. When only distal cues were present, P20 and P24 but not younger rats learned the location of the hidden platform. In contrast, when a proximal cue marked the platform location, rats as young as PI 7 showed evidence of cue-controlled navigation, although only PI 8 and older rats exhibited cued learning. In line with most previous studies, these results indicate that cued learning emerges earlier in development than place learning and support a dissociation of developmental trajectories for the neural systems underlying the two types of navigation. (c) 2007 Wiley Periodicals, Inc.