Effects of enriched environments with different durations and starting times on learning capacity during aging in rats assessed by a refined procedure of the Hebb-Williams maze task.

Cognitive function as measured by the Hebb-Williams maze task was examined in Fischer 344 male rats that had been exposed to an enriched environment for periods of variable duration and at different starting ages. In one experiment, rats were exposed to environmental enrichment from weaning until the age of 2.5, 15, or 25 months. The results of 12 problems of the Hebb-Williams maze task showed that the enriched rearing condition improved the learning ability in all the age groups; however, factor analysis and ANOVA demonstrated that four of the 12 maze problems were not suitable for detecting the effect of age under different environmental conditions. Reanalysis of the results obtained with the other eight maze problems more clearly revealed both the effects of rearing condition and aging. The latter analysis demonstrated that the learning rate of rats reared under enriched conditions was faster than that of rats reared under standard social conditions. Short-term (3-month) exposure also had positive effects on cognitive function in both adult (11-month-old) and aged (22-month-old) animals. The effect of long-term exposure to an enriched environment starting at weaning was much greater than that of short-term exposure in aged rats, whereas the effects of both long-term and short-term exposure were almost the same in adult rats. These results show that aged animals still have appreciable plasticity in cognitive function, and suggest that environmental stimulation could benefit aging humans as well. Copyright 2002 Wiley-Liss, Inc.