PMS may have a flip side. Brain researchers have found that an important brain circuit changes its activity right along with women's fluctuating hormone levels. As this ScienCentral News video explains, it's the brain circuit that seeks and experiences pleasure.
Many women say their moods follow a monthly cycle. Now brain researchers have scientific evidence that women's hormonal changes affect the reward circuits -- areas of the brain that produce feelings of pleasure.
"No one had ever actually imaged the reward system of the brain during the menstrual cycle," says Karen Berman, who led the research at the National Institute of Mental Health.
"This is a very fundamental part of our brain that has great evolutionary significance because it helps us to find out what in the environment is important for us to pay attention to for survival," she explains. "We thought this would be a very important brain network to study because people who have mood disorders, women who have menstrually related mood problems likely aren't activating and processing with this system in a normal fashion."
WEB EXTRA: Karen Berman talks more about her research on brain circuit changes with women's fluctuating hormone levels.
Berman and her team used functional MRI to image women's brains at two key points in their cycle -- before ovulation when the hormone estrogen increases, and after ovulation when the hormone progesterone dominates. The volunteers played a slot-machine game to win money, activating the brain's reward systems.
"In human beings, monetary rewards seem to affect the same systems that drugs do, that pleasure does ... that giving to others does," she says.
As they reported in Proceedings of the National Academy of Sciences, the scans showed that on average, women's reward circuits were more active before ovulation than after.
MRI brain scans show that the same rewards lit up women's reward circuits more before ovulation than after. This image shows how much more by subtracting the average amount of activity after ovulation from the amount before ovulation. image: Karen Berman
"We found that women's brains before the menstrual cycle actually are more active in particular parts of the reward system than after they have ovulated," Berman says. "In other words the response to the potential of a reward was greater in very important parts of the brain."
Berman says these findings could help explain more than mood swings. "We do know that women are more vulnerable to drugs of abuse during the early part of their menstrual cycle and this may relate to the fact that the reward system is more aroused and more excitable during that period," she says.
The team also tested male volunteers and found that, on average, men's reward circuits are different from women's. "Men doing the same task, anticipating and getting the very same reward activated different parts of their brains and showed a very different picture of their reward circuitry," says Berman, adding that these findings shouldn't be interpreted as reinforcing stereotypes about women. "I think it's wonderful to know that we are different, although there is certainly variance in the male population and the female population in how these rewarding stimuli are processed in the brain."
Karen Berman, National Institute of Mental Health
"There's lots of evidence that women's brains are different than men's, but I also think there's considerable evidence that every person's brain is unique, and that variability is probably at least as great as the generalizations we can make about male and female brains," she adds. "I think it's part of what makes the world very exciting-- we may have different views on the world and how we may problem-solve and I think this is a very important biological demonstration of that fact."
She notes that women are also at different risk than men of disorders that involve the reward circuit.
"This might help us to begin to learn how to intervene and provide better treatments for neuropsychiatric illnesses such as schizophrenia and depression where women have different kinds of problems than men and also for problems that are menstrually related like very severe PMS," she says.
Karen Berman took MRI scans at two key points in their cycle -- before and after ovulation.
While women with severe PMS or other mood disorders were excluded from this first study, the team is now beginning to use the same methods to study women with mood disorders that may be affected by sex hormones.
"This is sort of a proof of concept," says Berman. "We wanted to show our methods were sensitive to these changes and that the changes were related to female hormones. If we began by studying women with mood disorders or PMS it would be very hard to determine which changes in the brain were affected by the hormones we were studying, and which were affected by the problems these women may be experiencing."
Berman's research was published in the Proceedings of the National Academy of Sciences early online edition, January 29, 2007 and funded by the National Institute of Mental Health intramural research program.