Figure 4. At 30 day retention interval strong spatial memory for platform location is observed in animals trained on the hidden platform.

Adult male Wistar rats were trained in water maze either on a hidden (n=4) or a visible (n=4) platform as in Figure 1. In this case, however, the probe test was carried out 30 days, rather than 7 days, after the completion of training. All animals were sacrificed immediately after the probe test. Control animals (n=4) were handled but not exposed to the water maze. (A) Average swim latencies in seconds for 5 training days showing the significantly lower latencies for the visible platform group compared with the hidden platform animals (*p<0.05, repeated measures ANOVA). (B) Occupancy plots for the probe trial showing the percent time that both groups spent swimming in each quadrant. Animals trained on a hidden platform spent most of the time in the target quadrant where an escape platform had previously been submerged during training trials; animals from the visible platform group did not show preference towards any quadrant. (C) Quantitative data showing the percent time spent in annulus. The hidden platform group spent significantly more time in the annulus even 30 days after training compared with the visible platform animals (**p<0.01, one-way ANOVA) indicating strong long-lasting retention of platform location.