erative responding must be minimized by giving forced-choice information runs and detaining subjects following incorrect test run choices. Also, to prevent the use of odor trails, which females are especially prone to use, it is necessary to randomize the correct choice among the subjects in each squad. Mice can acquire the task if they are given three or more test runs per trial.
The task is an excellent assay of spatial working memory and has many potential applications in behavioral neuroscience. Versions of the task have been used to examine changes in working memory occurring with age ( Means & Kennard, 1991), and changes due to both facilitative ( Means & Fernandez, 1992; Means et al., 1991) and disruptive treatments ( Bass et al., 1992).
If cues associated with the escape platform are available during the test run of a DMTS task, rodents will use them before using working memory. If rodents are prevented from using nonmemory strategies, they readily acquire spatial DMTS water escape. If external cues remain constant, memory for an escape location, once established, is enduring and highly resistant to interference from interpolated activities. Young rats show excellent retention over 2-hr retention intervals. Working memory for escape locations appears to involve a process that requires time for the integration of information provided by a combination of actually performing the escape response and by experiencing constant environmental cues. Animals perform better on spatial than nonspatial DMTS tasks because only on spatial tasks can they use a representation involving a synthesis of response-related and constant environmental cues. Representations based on a synthesis of response-associated and constant environmental cues probably account for the general observation that "spatial memory can withstand greater retention intervals, and is more resistant to specific sources of interference than nonspatial memory" ( Spear, Miller, & Jagielo, 1990, p. 190).
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