Delayed development of place navigation compared to directional responding in young rats.

Recent work from our laboratory demonstrates that both young and adult rats show a preference for directional responding over place navigation in the Morris water task. Based on these findings, previous studies on the postnatal development of spatial learning have most likely assessed the ontogeny of directional responding instead of true place navigation. Here, we examined the development of directional responding and place navigation among young male and female rats using two variants of the Morris water task that specifically require directional and place responses. In the place variant, the hidden platform remained in the same absolute spatial location regardless of pool position. In the direction variant, the platform remained in the same direction in the room regardless of pool position. We found that ability to solve the direction task emerged around 20 to 21 days of age, whereas ability to solve the place task did not emerge until 26 to 27 days of age. These findings indicate that directional responding and place navigation exhibit different developmental trajectories and suggest that the 2 forms of navigation have different neurobiological bases.