An Indiana University neuroscientist found that women's brains respond differently to male faces depending on the stage of the their menstrual cycle.
Around the time of ovulation, women showed more activity in brain regions associated with reward and less activity in brain regions associated with inhibition and cognitive control, according to research by Heather Rupp, research fellow at the Kinsey Institute for Research in Sex, Gender and Reproduction at IU Bloomington.
"These findings suggest that women's brain systems that process rewards may be more sensitive around the time that women are likely to conceive," Rupp said.
"The heightened sensitivity of this system around ovulation may generalize to other stimuli that activate the same system, such as drugs or alcohol. Therefore, these findings not only add to our basic understanding of the reward system and its role in female sexual behavior, but may also be clinically important; as women may be more likely to engage in risky sexual behavior or could be vulnerable to drug or alcohol abuse at this time."
Rupp used functional magnetic resonance imaging (fMRI) in her study, which found the following:
- Women exhibited greater brain activity in areas related to reward and face processing, including the medial orbitofrontal cortex, hippocampus, and occipital face areas, around the time of ovulation. Also during ovulation, less activity was observed at this time in brain regions associated with inhibition and risk, including the frontal cortex.
- When viewing the faces of men with a risky sexual history, the women exhibited less brain activity in brain regions associated with decision-making and reward, compared to when look at faces of low-risk men. This discrimination was strongest later in the cycle.
- In response to more masculine male faces, women showed more brain activity in areas associated with risk and emotion, such as the anterior cingulate and insula.
The study involved 12 heterosexual women ages 23 to 28 who were not using hormonal contraceptives or in committed relationships. Their brain activity was measured using an fMRI scanner around ovulation and later in the menstrual cycle. While in the scanner, each woman was shown 256 photos of male faces that varied in facial masculinity and sexual risk.
A computer morphing program altered the male face photos to appear more or less masculine. Sexual risk information included the man's number of previous sexual partners and typical condom use. The women were asked to indicate on a response paddle how likely they would be to have sex with the man depicted.
This research was presented at the annual meeting of the Society for Neuroscience, November 3 -7, 2007 in San Diego.
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