This task24 is similar to the one that we have used, the DNMTS forced choice. Animals, in a preliminary training phase, have learned the win-shift rule that reentries into an arm are not rewarded; during the DNMTS task the animal visits a subset of the total arms (e.g., 4 of 8 arms), and then a delay is interposed (seconds to hours). Subsequently, the animal is permitted to continue selecting arms but is rewarded only for first entries into arms that were not selected in the pre-delay. The difference from the forced choice paradigm described above is that the animal is free to select the arms to visit during the pre-delay portion of the task; no barriers or doors are utilized to determine the arm selection for the animal. A problem with this task can occur if an individual animal consistently chooses either the same arms or the same pattern of arms during the pre-delay session. This consistent pattern of choices would suggest that the animal is not using spatial working memory, but rather by selecting the same arms during each pre-delay session, a reference memory task is evolving. Since rewarded and unrewarded arms are consistent on each trial, the task has become trial-independent, which defines reference memory. If the animal consistently selects the same pattern of arms across trials, the animal is employing an egocentric strategy, that is, the subject is guiding its responses based on its location in the RAM as opposed to utilizing the spatial, extra-maze cues to navigate to obtain reward, i.e., an allocentric strategy.
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