Figure 2.

Delay-dependent memory performance in a DMP radial water maze task. A, Effect of varying the retention interval (delay between sample and test trials). Means ± SEM represent five trial blocks at each delay. Control trials (CON) involved no sample trial with the goal moved to a new location (find the platform yourself). Horizontal gray band indicates range of 10 control trials. After a control trial, rats were returned to the maze within 2 min for a short-delay trial (2-MIN). Rats were tested on a series of long delays (4–48 h) at both 6 and 12 months of age. B, Effect of varying the intersession interval on mean ± SEM errors. Errors doubled when rats were tested on two sample-test sessions with different goal arms in the same day. Each ISI was tested four times. C, The distribution of first error by type for all long-delay trials is shown for each delay. The percentage of rats making no errors (first choice was correct goal) is presented at no error (dark gray). Note that, with increasing delays, more rats made an initial error and that the majority of first errors are to the arms adjacent to the goal (white). Thus, at 1 h delay ∼50% of rats made at least one error, with the majority being to the adjacent arm and a smaller percentage to the goal of the previous day or one of the three other arms. This distribution did not vary as a function of delay (compare 1HR–48HR and MIN-2). During control trials, the majority of errors are, as might be expected, to the previous goal arm (black). The distribution of previous, adjacent, and other errors during control trials was significantly different from all other distributions (*p < 0.001, χ² test). All of the other distributions (1HR–48HR and 2-MIN) were not different from each other. D, The distribution of first error by type for all ISI trials. The distribution of previous, adjacent, and other errors during 2 h ISI trials was significantly different from distribution during 24 and 72 h ISI trials (*p < 0.001, χ² test). Notably, the distribution of error types during 2 h ISI trials was similar to the distribution during control trials, with the majority of rats initially choosing the previous goal arm.