Now, a new study at the University of Illinois at Urbana-Champaign suggests that the stress of any given task at least partially determines if hormones will help the mind.

Reporting in the August issue of Behavioral Neuroscience, four researchers show the introduction of a single stressor -- water temperature -- into a water maze prompted opposite responses among female rats with either high or low levels of estrogen and progesterone.

"Water temperature totally reversed who did better," said Janice M. Juraska, a professor of psychology and of neuroscience. "Proestrous rats, which have high hormone levels, did better when the water was warm, presumably because they were less stressed. Estrous rats did better when the water was cold, presumably because they are not as prone to get stressed during this time."

Proestrous rats are fertile and ready to mate, while estrous rats have low hormone levels and won't mate. For the study -- funded by a grant to Juraska from the National Science Foundation -- 44 female rats were divided into four groups. The two groups of rats in proestrus and the two groups in estrus had to learn the route and swim to a submerged platform in either warm (91 degrees Fahrenheit; 33 Celsius) or cold water (66.2 degrees Fahrenheit; 19 Celsius).

Many scientists have tried to answer the hormones-cognition question, but the various findings, measuring different tasks, have been inconsistent and often contradictory.

"These discrepancies of sometimes opposite results have been very difficult to resolve," Juraska said. "Even for simple tests of spatial behavior, high hormones can either help or hinder, and nobody has understood why."

Juraska's lab previously had shown in studies using the water maze that rats with high levels of hormones, either naturally occurring in the estrous cycle or with high doses administered into rats whose ovaries had been removed, do less well finding the platform.

Psychology doctoral student Marisa J. Rubinow, a co-author of the new study, wondered if stress during a task might be a factor in the varied results showing up in the literature. Now, after the new results, Rubinow and Juraska suggest that the timing and duration of stress, as well as the memory systems involved in a task, all may be factors that determine the effects of ovarian hormones on performance.

"Will hormones help how your brain works -- how you think, your cognition?" Juraska said. "I wish I had a simple answer. It depends on many things about the task, and one of them is how stressful the task is. There is no simple translation to behavior."

Other co-authors on the paper were Linda M. Arseneau, formerly in the department of animal sciences and now with the U. of I. Division of Research Safety, and J. Lee Beverly, a professor of animal sciences and of neuroscience.