Environmental enrichment: the influences of restricted daily exposure and subsequent exposure to uncontrollable stress.

Environmental enrichment has been proposed to enhance an animal's subsequent ability to learn. While this proposal has received considerable support from experiments involving maze tasks, it has received equivocal support from experiments employing operant and pavlovian tasks. The purpose of the present study is two-fold. The first is to demonstrate that a regimen of restricted daily exposure to environmental enrichment is capable of producing effects similar to those using more standard exposure regimens when compared to the most appropriate control, a group given social exposure. The second is to examine the proposed learning enhancement of environmental enrichment on an operant task both before and following exposure to uncontrollable stress. Uncontrollable stress, as interpreted by learned-helplessness theory, results in the formation of an expectancy of response-reinforcer independence which proactively interferes with the subsequent acquisition of response-outcome associations. It may be possible, then, that environmental enrichment and uncontrollable stress may interact in such a way as to allow the potential learning effects of environmental enrichment to be assessed on an operant task. Rats were exposed to differential environments; one group exposed to an enriched environment and another exposed to a social environment 2 hours daily for 30 days. Each group was then tested on the object-exploration test. Following the acquisition of an appetitive-operant response, a subset of these two groups was exposed to either controllable, uncontrollable, or no stress using parameters known to induce learned helplessness. Animals were then tested on an appetitive-noncontingent test. It was found that, while the enrichment procedure was effective in producing effects on the object-exploration test, environmental enrichment did not modify the acquisition of the operant or the effect produced by uncontrollable stress on the appetitive-noncontingent test.