Figure 6.

Morris water maze (MWM) performance in rats given massed or distributed trials. Sprague-Dawley CD IGS (Charles River strain 001) adult male rats were randomly divided into two groups of equal numbers and tested in a 244-cm diameter tank with either massed (back-to-back) or distributed trials (spaced 10 minutes apart) during hidden platform acquisition, reversal, and shift phases with the platform in the SW, NE, and NW quadrants, respectively, and platform sizes of 10, 7, and 5 cm, respectively. Both groups first received acclimation trials in a 244 × 10 cm straight swimming channel (4 trials given back-to-back) on a single day. After this, rats received 6 days of learning to a fixed hidden platform for four trials per day from randomized start positions, balanced such that they received one trial from each of four start positions each day. The platform was in the SW quadrant, and start positions were arranged such that two were from cardinal positions (N and E) and two were from distal ordinal positions (NW and SE) to eliminate very close start positions (W and S). Average latency to reach the platform is shown (mean ± SEM). Because both groups were untreated, latency, path length, and cumulative distance indices gave the same results. There were no significant differences on straight-channel training trials. There was a marginally significant main effect of trial spacing during hidden platform acquisition: analysis of variance showed a nearly significant effect of group (F(1,14) = 4.33; p < 0.06); there were no significant differences on reversal or shift trials. There were no significant group × day interactions. The trial spacing trend on acquisition suggested that the distributed group learned the task faster than the massed group, except on day 6 when the groups converged. Group sizes were eight per group.