Mood cycles. Regions of brain activity (in orange) change--along with hormone levels, ovulation, and uterine lining--from postmenstrual (left) to premenstrual (right) phases.

It's Just That Part of the Brain

Bewildering mood swings and a hankering for chocolate: Those are the stereotypical signs of premenstrual syndrome. But what's really going on in women's heads during "that time of the month?" A new study shows that women's brains may be hard at work keeping their hormonally heightened emotions at bay--whether they're aware of it or not.

Long considered the seat of personality, a part of the frontal lobe of the brain called the orbitofrontal cortex (OFC) is associated with mood, decision-making, and motivation. Research suggests the region may inhibit certain behaviors and regulate emotions. Few studies, however, have looked directly at changes in brain function and processing across the menstrual cycle, says neurologist David Silbersweig of Weill Medical College at Cornell University in New York.

Silbersweig and his team used functional magnetic resonance imaging (fMRI) to study 12 subjects' neural response to 80 words. The team included negative words, such as rape, assault, and death; neutral words, such as bookcase and clarinet; and positive words, such as safe and gentle. To test how emotions altered behavior premenstrually compared to postmenstrually, the researchers also measured how quickly the women performed a simple motor task: When they saw a word in normal font, they pressed a button, but held off if it was italicized.

The researchers found that negative words hurt. When viewing negative words, premenstrual women showed increased activity in the medial OFC, which may inhibit behavioral and emotional responses, and lower activity in the lateral OFC, which may control sensory and evaluative functions. The premenstrual response to negative words was stronger than during the postmenstrual phase or to either neutral or positive words. Furthermore, during the premenstrual phase, the women performed the button-pressing task more slowly, suggesting the brain had to work a bit harder, the researchers report online this week in the Proceedings of the National Academy of Sciences.

Although the functions of the various OFC subregions aren't well understood, the region appears to be working harder in premenstrual women by simultaneously inhibiting negative behavior and suppressing negative sensory response, Silbersweig says.

"It's a great piece of work," says psychiatrist Scott Rauch of Massachusetts General Hospital in Boston. This study clearly establishes that the menstrual phase can have an impact on brain activity--and understanding that brain chemistry is a critical step to figuring out what might underlie observed differences in mood and anxiety disorders between the sexes, he adds.

Related sites
Functional Neuroimaging at Cornell (Silbersweig's site)
Biomedical Imaging at Massachusetts General Hospital