Having children changes more than a woman's life, researchers have found; hormonal changes during pregnancy and childbirth actually change her brain.

Those changes could have an impact on whether or not hormone therapy, often prescribed later in life to treat some symptoms of menopause, is effective or not, a study suggests.

Hormone therapy to treat cognitive problems in postmenopausal women has met with varying degrees of success, and motherhood earlier in a woman's life may explain the differences in outcome, says Dr. Liisa Galea of the University of British Columbia.

In studies using rats, hormone treatment using estrone, the predominant form of estrogen in older women, impaired cognitive performance in middle-aged rats that had been mothers, while it enhanced learning in rats that had not given birth.

"Our most recent research shows that previous motherhood alters cognition and neuroplasticity in response to hormone therapy, demonstrating that motherhood permanently alters the brain," Galea says.

Neuroplasticity is a measure of how neural pathways in the brain change in response to various factors.

Galea looked at two forms of estrogen - estrone and estradiol, the predominant type found in younger women - and their effect on neuroplasticity.

Both forms of estrogens were found to increase production of new cells in a region of the hippocampus known as the dentate gyrus, but only estradiol, and not estrone, significantly improved the survival of the new neurons and elevated resulting expression of a protein involved in neuroplasticity, she says.

"Hormones have a profound impact on our mind," she says. "Pregnancy and motherhood are life-changing events resulting in marked alterations in the psychology and physiology of a woman."

The research raises questions about considerations of hormone therapy for women, since estrone is a common choice for such treatments but may not have the same effect, depending on whether the woman has had children or not.

"Our results argue that these factors should be taken into account when treating brain disorders in women," says Galea, who presented the results of her study May 25 at the 9th annual Canadian Neuroscience Meeting in Vancouver, British Columbia.

Galea runs the Laboratory of Behavioral Neuroendocrinology at UBC, and says she "is interested in how hormones affect brain and behavioor. As anyone who has gone through puberty, menopause or pregnancy can attest, hormones have a profound impact on our mind."

The effects of pregnancy and mothering on brain function and morphology is one the main areas of the lab's research, she says.