Some women seem to get turned on by almost anything man-on-women action, man-on-man, woman-on-woman, animal-on-animal, and so on. This is what sex researchers find when studying sexual arousal. When female volunteers are asked to watch erotic movies while outfitted with a plethysmograph, an instrument for measuring blood flow to the vagina, they often get very hot and bothered “down there.” Problem is, when many of those same women are asked to report how aroused they actually feel “up there” they often say they’re not turned on at all. Sometimes they even say they’re repulsed.

So what’s going on? Do women even know what turns them on?

Such is the puzzle that has plagued sex researchers for decades. And it’s a topic clinical psychologist Meredith Chivers and her colleagues address in a recent study, a meta-analysis of 132 papers on the genital measures of sexual arousal.

Why don’t women’s genital and subjective responses always agree? Here are a few theories the researchers present:

Women’s genital responses are hidden from view and produce less prominent somatosensory cues. While men may get turned on by feeling themselves get erect, women do not. However, [studies have found that] even when women received feedback about their level of vaginal engorgement, correlations (between genital and subjective arousal) were low and statistically nonsignificant. [Being told we’re getting turned on doesn’t necessarily turn us on.]

Women may edit their self-report of feeling sexually aroused because of socially desirable responding. Positive affect directs attention to erotic stimuli, thereby increasing sexual response, whereas negative affect interferes in the processing of sexual cues, resulting in lower sexual response. Lower concordance among women may reflect their experience of negative affect while watching the

conventional, commercially available erotica that is primarily produced for men.

Interestingly, the authors suggest that genital response to sexual stimuli may be an evolved self-protection mechanism:

Female genital response is an automatic reflex that is elicited by sexual stimuli and produces vaginal lubrication, even if the woman does not subjectively feel sexually aroused… Female genital response entails increased genital vasocongestion, necessary for the production of vaginal lubrication, and can, in turn, reduce discomfort and the possibility of injury during vaginal penetration. Ancestral women who did not show an automatic vaginal response to sexual cues may have been more likely to experience injuries that resulted in illness, infertility, or even death subsequent to unexpected or unwanted vaginal penetration, and thus would be less likely to have passed on this trait to their offspring….Reports of women’s genital response and orgasm during sexual assaults suggests that genital responses do occur in women under conditions of sexual threat. That women can experience genital response during unwanted sex or when viewing depictions of sexual assault suggests that women’s vasocongestion response is automatically initiated by exposure to sexual stimuli, whether or not these stimuli are preferred, and without subjective appraisal of these stimuli as sexually arousing or desired.

During processing of sexual stimuli, brain areas associated with emotional inhibition are activated among women… Genital responses are not affected by involuntary inhibition involving the anterior cingulate cortex, but subjective responses are. [Incidentally, women’s anterior cingulate cortex is most active when we’re ovulating and attracted to macho, high-testosterone men. The ACC is activated when you’re in conflict about something. Is this also a self-protection mechanism warning us to proceed with caution?]

Bottom line: Physical arousal is no proof a woman is really turned on. To really get a woman hot and bothered, you have to start from the top.