Can rats control previously acquired spatial information? Evidence of "directed forgetting" phenomenon in delay-interposed radial maze behavior.

"Directed forgetting" is a method and a phenomenon used to investigate whether organisms can control memory with instructions to forget, and to remember. We examined directed forgetting phenomenon in rats, using a modified radial maze task. In the delay-interposed radial maze task, a 120-min delay followed four correct choices, during which rats were placed in either a white or black box, that signaled whether a second-half performance will be required (remember (R)-trial), or not (forget (F)-trial) after the delay. R- and F-trials were repeated 5 times each, followed by a "probe test," in which the second-half performance was conducted, although the F-cue was presented during the delay period. Rats made more errors in the probe test than in the R-trial. These results demonstrate the "directed forgetting" phenomenon in a radial maze task in rats, and suggest that rats can indeed control previously acquired spatial information, even situations with a long retention interval interposed. Although the mechanism by which presentation of the "forget-cue" influences rats' information processing remains unclear, several brain regions, including the medial prefrontal cortex and the hippocampal CA3 area, were shown to be more activated in the "remember"-cued trial than in the "forget"-cued trial, suggesting that these areas are potentially related to the "directed forgetting" phenomenon of spatial information demonstrated in the study.