Differential effects of inescapable shock on escape performance and discrimination learning in a water escape task

Abstract

The effects of inescapable shock on subsequent T-maze water escape and position discrimination performance were evaluated in seven experiments. Escapable shock did not disrupt water escape performance; however, escape performance was retarded 24 hr after inescapable shock. These deficits were not apparent if escape was possible upon stress inception; however, pronounced deficits were noted if sustained active responding was necessitated by briefly (3-5 sec) preventing escape. When water escape testing was conducted in relatively warm water (20 degrees C), the disruptive effects of preshock were not apparent. In colder water (15 degrees C), which increases the motor difficulty of the task, the disruptive effects of preshock were noted. When the motor difficulty of the task was increased further, by testing mice in 10 degrees C water, or when the associative difficulty was increased by using a vigorous reversal learning task, the differences between the preshocked and nonpreshocked groups were obviated. Exposure to inescapable shock did not disrupt position discrimination performance regardless of the motor difficulties of the task. Similarly, deficits of discrimination performance were not apparant in mice exposed to inescapable shock even when the associative difficulty of the task was increased by removing intramaze cues or by testing animals in a position discrimination reversal task. It is concluded that inescapable shock results in deficits of response maintenance but probably has a minor, if any, influence on cognitive/associative processes.