Columns represent the ratio, GS explorations per hole/NGS explorations per hole, in the different age groups, for GS consisting of either hole# 0 or holes −1,0,1. This ratio provides an index of the accuracy with which rats of the same age group remember a given GS. Notice that this ratio is independent from the target-seeking activity level of rats in a given age group. Statistical comparisons are made versus the young group of each set. *: P<0.05; **: P<0.01. Number of young, old and senescent rats for PT1 was 30, 19 and 21 and for PT2 was 29, 20 and 24, respectively. Other details are as in Fig. 2.