Hormone replacement therapy (HRT) may improve the memory of postmenopausal women, a new study in the US suggests.

Many women experience declines in their memory during and after menopause, a change thought to be due, in part, to the rapid hormonal changes they weather during that time.

Now, research from the University of Michigan Health System in the US suggests that hormone therapy might help women retain certain memory functions. In a study in the new issue of The Journal of Clinical Endocrinology & Metabolism, they report that a group of postmenopausal women showed more brain activity during a visual memory test than did women who were not taking the hormone therapy.

The 10 postmenopausal women in the study, ages 50-60, were given hormone therapy or a placebo for four weeks, followed by a month with no medication, and then four weeks of the other treatment. Their brain activation was measured as they were shown a complex grid of 81 squares, with 40 of them darkened to form a pattern.

Participants were asked to find the matching image from a choice of two, with the new set of images presented after varying time periods (one to four seconds). During the time that the two images were shown, participants were asked to choose the one that matched the initial grid by pressing one of two buttons on an MRI (magnetic resonance imaging)-compatible response pad.

Those who were taking combined estrogen-progestin hormone therapy showed significantly increased activity in the prefrontal cortex, a region of the brain that is critical in memory tasks, compared with those on placebo (a pill with no medicinal value). The researchers used images from functional MRI, or fMRI, to compare the participants' brain activity.

"Our findings suggest that even relatively short periods of hormone therapy have effects on the memory systems that may be of benefit to some women during the perimenopausal transition or early post-menopause," says lead author Yolanda R. Smith, associate professor in the Department of Obstetrics and Gynecology at the U-M Medical School.

"Other studies have indicated that long-term hormone therapy is not beneficial for the prevention of chronic illnesses," Smith says. "But our study indicates that the effects of short-term hormone therapy on brain circuitry and function warrant further study."

The role of oestrogen in maintaining brain function is of great significance as the population ages and the incidence of dementia increases, says senior author Jon-Kar Zubieta, associate professor of psychiatry and radiology at the U-M Medical School.

Zubieta notes that working memory - that is, a limited-capacity storage system that allows the brain to actively maintain and manipulate information that is critical for conducting many daily activities over short time periods - has been demonstrated to be less efficient in older adults. This decline has been linked with changes in the prefrontal cortex.

"Our finding of increased activation in the prefrontal cortex in older women using hormone therapy is important and suggestive of potential therapies that need to be explored further," he says. "Eventually, this could lead to new options for women as they enter a time when memory problems typically develop."