The high levels of hormones during pregnancy affects memory and could have a lasting affect on a woman’s brain. Research indicates that these hormones can alter the structure of key parts of the central nervous system. These findings could help settle the debate over whether hormone replacement therapy in menopausal women changes the risk of developing Alzheimer’s disease in later life.
The study looked at two oestrogen hormones commonly used as treatment for menopausal women. The experiments were carried out on laboratory rats. However, the results are applicable to humans, the scientists said, since the same hormones and brain cells are involved. Researchers found that these hormones could have a complex effect on women, depending on their age and whether or not they had previously given birth.
The researchers found that the surge in oestrogen hormones during pregnancy can alter “neuroplasticity” or the re-growth of nerve cells in a part of the brain called the hippocampus. The hippocampus is responsible for aspects of memory and spatial awareness.
Liisa Galea of the University of British Columbia in Vancouver, Canada, said, “Our most recent research show that previous motherhood alters cognition and neuroplasticity in response to hormone therapy, demonstrating that motherhood permanently alters the brain. Hormones have a profound impact on our mind. Pregnancy and motherhood are life-changing events resulting in marked alterations in the psychology and physiology of women.”
“Our results argue that these factors should be taken into account when treating brain disorders in women,” she told the Canadian Association for Neuroscience.
One type of oestrogen hormone, oestradiol, was found to increase the production of new nerve cells in the hippocampus. It also appeared to increase the chances of these nerve cells surviving in the longer term.
Chronic, long-term exposure to oestradiol was seen to boost the memory of young female rats tested on how to escape from a maze. But when the rats were given oestrone, a different oestrogen hormone, which is a component of the most common forms of hormone replacement therapy, this memory boost was not present.
When oestrone was given to middle-age female rats who had given birth before, it appeared to impair the ability to learn and memorise. When given to female rats of the same age that had never given birth, the hormone therapy based on oestrone improved learning and memory as well as boosting neuroplasticity in the hippocampus. These findings suggest that pregnancy had affected the brain permanently.
Galea said that the findings suggest a possible explanation for some of the observations seen in the human female population which have been linked with pregnancy and childbirth, as well as hormone replacement therapy for menopausal women. This could have impact how age-related neurodegenerative disorders in women are treated.
“If you have given birth before, you have a better memory but experience an increased risk of developing Alzheimer’s like conditions. But we don’t know much about why this is the case,” Galea told The Independent.
When they are pregnant, women often feel that their memory is poorer. However, a couple of years after birth their memories improve. Even so, the memory of women who have given birth tends to decline faster in middle-age when compared to women who have not given birth, Galea said.
“The more children you have given birth to, the greater risk you face of getting dementia in later life. More children are probably enriching, but they are also probably more stressful,” she concluded.