Task solving by procedural strategies in the Morris water maze

The aim of the present work was to assess the importance of the "general procedural" components, when for rats it was impossible to employ extramaze allothetic information to reach the goal in the Morris water maze (MWM). Groups of Long-Evans rats (males, 70 days old) were trained (10 trials per day, over five consecutive days) following seven paradigms. Four paradigms differed in context (extramaze cues available; extramaze cues not available) and in platform location (constantly at the center of one quadrant of the water maze; at random at the center of any one of the quadrants). In the fifth paradigm, there were no extramaze cues available, and the platform was located at random distances from the maze wall. In the sixth paradigm, rats underwent the standard MWM training (extramaze cues available, invisible platform constantly placed in the center of one quadrant) but they were administered with scopolamine before the daily trials. In a seventh paradigm, the platform was visible. In all paradigms, the starting point was randomized with respect to the goal. When platform distance from the wall was random, there was no significant better performance after the trials. In all the six paradigms in which platform location was at a constant distance from the wall the times spent before reaching the platform decreased progressively, to become constant on Days 4 and 5. The groups which could not employ the allothetic extramaze component (extramaze cues not available; changing of the quadrant of platform location; scopolamine administration) showed a progressively better performance even though their delays on the last 2 days were longer than those of the "standard MWM" and "visible platform" groups. The slightly less efficient performance is attributable to the rat's search strategy, a "subcircular" swimming pattern within the geometric limits of the central areas of the quadrants, where the platform was constantly placed. That no extramaze allothetic information was employed is shown by the finding that on Day 6 (probe test: 90 s in the tank without platform) no animals exhibited preference for any quadrant, while the "standard MWM" group did show such a preference. It can be concluded that rats under conditions of constant relationship of the goal to the contours of the pool employ search strategies based on general procedural components. (C) 2003 Elsevier Science Inc. All rights reserved.