Stimulus perseveration in a water maze following exposure to controllable and uncontrollable shock.

When placed in a water-filled maze, mice display a pronounced preference for the illuminated over the nonilluminated arm of the maze. Exposure to inescapable shock increased the time spent in the illuminated arm of the maze, and decreased the frequency of entries into the nonilluminated arm. When animals that had received shock entered the nonilluminated arm they exhibited more activity per second than nonstressed animals. Controllability over the stressor enhanced the preference for the illuminated arm; however, the contribution of this variable was dependent on the number of shock trials mice received. Following 180 escapable or inescapable shock presentations the preference for the illuminated arm was enhanced. The propensity to approach the illuminated arm declined following a greater number (360) of escapable shock trials, while the preference for the illuminated arm did not decline in mice that received inescapable shock. Both escapable and inescapable shock were also found to produce a transient disruption of discrimination performance in a task where animals were required to emit a contraprepared response (swim to dark), whereas these treatments were without effect on performance of the highly prepared response of approaching the illuminated arm. It is provisionally suggested that enhancement of the perseveration represents an innate response to stressful stimuli, but as animals learn mastery over the response contingencies, the persistence in adopting such a response strategy wanes. Moreover, despite the differential effects of escapable and inescapable shock on the perseverative tendency, discrimination accuracy may not be differentially affected by these treatments in a task where acquisition progresses quickly and where explicit cues are associated with the correct and incorrect arms of the maze.