Very brief exposure to visual distal cues is sufficient for young mice to navigate in the Morris water maze

This set of two experiments investigated the capacities of C57BL/6 mice to integrate visual distal information. In the first study, we submitted mice of two ages (22 and 65 day old) to the place learning version of the Morris water task. After the acquisition phase, the mice were put in one of three conditions: (1) a classical probe test (only the platform was removed); (2) a rotating probe test (the platform was removed and the distal visual cues were rotated from 90°); and (3) a suppressing probe test (both the platform and the cues were removed). The results indicated that whatever their ages mice used preferentially the visual cues to locate the platform. In the second experiment, groups of mice of either age were subjected to 1 of 4 procedures. Separate groups of mice were required to escape onto a platform located in a fixed position either hidden or visible. Following escape, animals were either given unrestricted visual access to the extramaze environment for the duration of the platform interval (60 s, place learning and cue+place learning groups), or denied this opportunity by switching off the room lights (place-lights learning and cue+place-lights learning groups). The results of this second experiment indicate that whatever their age and the procedure used, mice performed equally and exhibited a spatial bias during the probe test. All together, these results suggest that as early as 22 days of age, mice integrate visual distal information especially while on the way to the goal, and this even so this information was not necessary to solve the task.