The female brain has a clever way of mitigating the stress experienced during menstruation: it flip-flops.
The region of the brain used for coping with stress flips to the opposite side of the brain during a woman's period - from an area linked to negative emotion to one that usually deals with cheerier thoughts.
Such a change could help women cope with the hormonal maelstrom going on in their bodies without causing huge behavioural shifts. Oestrogen levels levels, in particular, plummet around menstruation.
Jen-Chuen Hsieh, a neuroscientist at National Yang-Ming University in Taipei, Taiwan, and colleagues studied 14 women using a magnetoencephalograph ¬ a machine that measures magnetic waves created by brain activity. All their subjects were right-handed, to ensure that the left-right orientation of their brains matched.
When the women were shown frightening images, they normally triggered activity in the right half of the women's brains. This side of the brain tends to process negative feelings, such as anxiety. During the women's menstrual periods, however, the images activated areas in the left half of their brains, which handles positive emotions.
The switch in brain dominance during menstruation could help women cope with stress linked to hormone changes. Throughout their periods, participants' average scores on a test of anxiety hardly changed.
"I was really pleased to read this," says Jill Goldstein, a neuroscientist at Harvard Medical School in Boston. The paper dovetails with her previous work showing that women damp down activity in brain regions linked to stress during menstruation even though they their outward behaviour changed little during their cycle.
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