TUESDAY, Oct. 26 (HealthDay News) -- Hormone levels at certain phases of the menstrual cycle affect women's emotional responses, finds a new study.

Researchers used MRI to study the brains of women who viewed a series of pictures and rated them as pleasant, unpleasant or neutral. This test was repeated at different stages of the women's menstrual cycles.

In the early follicular stage of the menstrual cycle, no areas of the women's brains showed significantly increased activation while viewing the pictures. But during the midpoint of their menstrual cycle, when hormone levels were higher, the women had increased activity in the lateral prefrontal cortex and other areas of the brain involved in processing emotional information, the researchers found.

The study was to be presented Oct. 25 at the annual meeting of the American Society for Reproductive Medicine in Denver, Colo.

"This research sheds light on what may prove to be an important role for hormones when it comes to processing emotions," president-elect Dr. Rogerio Lobo said in a society news release.

Previous studies have found that the rate of affective disorders (mood disorders) is two times higher in women than in men. Many experts believe this difference is due to sex hormones.

More information

WomensHealth.gov has more about menstruation, menopause and mental health.