University of Illinois researchers said they determined rats exposed to a steady dose of estradiol were impaired on tasks involving working memory and response inhibition.

In the new study, rats were trained to press one of two levers to obtain a food reward. Those that alternated between the levers -- which were withdrawn from the rat enclosure for a few seconds between trials -- received a reward. Those that hit the same lever twice in a row got no reward.

The researchers said they found rats exposed to estradiol performed worse than their counterparts on the task, earning significantly fewer rewards.

A second set of tests measured the rats' ability to wait before responding to a stimulus. The rats had to wait 15 seconds before pushing a lever to get a reward. The scientists again noted the rats exposed to estradiol performed worse on that task than those not exposed to the hormone.

The study led by Professor Susan Schantz and graduate student Victor Wang is detailed in the journal Behavioral Neurosciences.