Several recent studies have found that women are more sensitive to pain during periods of low estrogen.

Now researchers are going one step further by studying whether the difference in pain sensitivity is reflected in brain activity as measured by functional magnetic resonance imaging (fMRI).

In an article published in the February 2006 issue of the Journal of Oral and Maxillofacial Surgery (JOMS), researchers document how they measured brain activation using fMRI, before and after painful heat stimuli.

The research team studied nine healthy, pain-free women 19-33 years of age, acquiring data during a period of high estrogen and a period of low estrogen. Researchers attached a small thermode to each subject’s lower cheek near the jaw, and then administered intermittent, high-temperature stimuli. Blood samples were taken after each scan to verify the appropriate level of estrogen.

They found that estrogens appeared to influence the activation pattern caused by painful stimulation. “The results of this study suggest that the affective component of pain may be enhanced during the low-estrogen phase of the menstrual cycle in healthy women,” concluded lead researcher Reny de Leeuw, DDS, PhD.

Estrogens appear to regulate several neurotransmitters systems in the brain, acting as vasodilators and increasing blood perfusion in the brain.

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