Recent rodent studies add to our understanding of how estrogen affects learning and memory. A study found that adult female rats took significantly longer to learn a new association when they were in periods of their estrus cycle with high levels of estrogen, compared to their ability to learn when their estrogen level was low. The effect was not found among pre-pubertal rats. The study follows on from an earlier study using rats with their ovaries removed, whose learning was similarly affected when given high levels of estradiol.
Human females have high estrogen levels while they are ovulating. These high levels have also been shown to interfere with women's ability to pay attention.
On the other hand, it needs to be remembered that estrogen therapy has been found to help menopausal and post-menopausal women. It has also been found to be detrimental. Recent research has suggested that timing is important, and it’s been proposed that a critical period exists during which hormone therapy must be administered if it is to improve cognitive function.
This finds some support in another recent rodent study, which found that estrogen replacement increased long-term potentiation (a neural event that underlies memory formation) in young adult rats with their ovaries removed, through its effects on NMDA receptors and dendritic spine density — but only if given within 15 months of the ovariectomy. By 19 months, the same therapy couldn’t induce the changes.
 . Latent inhibition is affected by phase of estrous cycle in female rats. Brain and Cognition [Internet]. Submitted ;In Press, Corrected Proof. Available from: http://www.sciencedirect.com/science/article/B6WBY-50XTT71-1/2/dd194fa5c932fb9f9c35e17e960a839a
 . Duration of estrogen deprivation, not chronological age, prevents estrogen's ability to enhance hippocampal synaptic physiology. Proceedings of the National Academy of Sciences [Internet]. 2010 ;107(45):19543 - 19548. Available from: http://www.pnas.org/content/107/45/19543.abstract