In the time leading up to when they’re fertile:
From an evolutionary point of view, female sexual desire contributes greatly to the success of reproduction by coordinating sexual behavior. It is known that female sexual desire fluctuates with the menstrual cycle. However, little is known about the role of basic emotions during menstrual cycle.
We designed a facial EMG study to investigate facial expressions of joy during the menstrual cycle. 35 healthy women underwent 2 EMG sessions (T1 and T2). T1 took place in the follicular phase, T2 in the luteal phase. IAPS pictures of nude men (erotic stimuli) or of animals (control stimuli) were presented at both sessions. The activity of musculus zygomaticus major (responsible for expressing joy) was measured. We tested the hypothesis that zygomaticus activity is more pronounced in the follicular phase than in the luteal phase.
The main result was that during the follicular phase, significantly more zygomaticus reactions were observed than during the luteal phase. This effect was restricted only to erotic stimuli. We concluded that an increased positive emotional responsiveness to erotic stimuli during the follicular phase is an important precondition for the probability of sexual activity during the conceptive days and thus for the success of reproduction.
Source: “Why we haven’t died out yet: Changes in women’s mimic reactions to visual erotic stimuli during their menstrual cycles” from Hormones and Behavior, Volume 55, Issue 2, February 2009, Pages 267-271
Yeah, that bolded paragraph can cause headaches. In English: Women showed more positive reactions to pictures of naked men in the days before ovulation. Interesting to note was they didn’t ask the women how they felt. They tested the reactions of a facial muscle (zygomaticus major) that moves when you’re happy but that you can’t deliberately control (at least not without significant training.) Pretty smart.
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