Figure 1.

Experimental paradigm. (A) In the novel object recognition (NOR) task, rats were first presented with two identical objects (sample phase, 5 min, left), and returned to their home cage for 2 min. During this period, one of the two objects was replaced with a novel object whose location (east or west) was varied randomly across subjects. During the test phase (right), the rats were allowed to explore the two objects for 5 min. The rats' starting positions in the sample and test phases were identical: facing the south wall. (B) In the egocentric (EOR) and allocentric (AOR) object-place recognition tasks, all aspects of the sample phase were identical: the rats were presented with two novel objects. As for the NOR task, they faced the south wall at the start of this sample phase. After a 5 min exploration period, the rats were returned to their home cage for 2 min. During this period, one object was replaced with an identical copy of the other. The position of this object duplicate was counterbalanced across trials. In the EOR task, the starting position of the rat was identical to that used in the sample phase (facing the south wall, blue arrow). In the AOR task, the rats' starting position varied across trials (facing the east or west wall, black arrow). Four such trials were conducted, on four consecutive days.