Tuesday, November 18, 2014

Can Neuroscience Validate the Excuse “Not Tonight, Dear, I have a Headache?"

Men and women experience fluctuations in sexual motivation over a lifetime. Whether sexual desire is enhanced or diminished at any particular time can depend on a number of factors and circumstances, but researchers from McGill University recently set out to determine specifically how pain impacts sexual behavior.1 Results from this study, published in The Journal of Neuroscience earlier this year, were the topic of the most recent “Neuroethics and Neuroscience in the News” discussion facilitated by Emory Women’s Gender and Sexuality graduate student Natalie Turrin and Neuroscience graduate student Mallory Bowers.

To study how pain impacts sexual motivation, researchers used a partitioned Plexiglas chamber where the partition contained small, semi-circular openings only large enough for the female mice to pass through (this study required that male mice be greater than 45 g and female mice smaller than 25 g). In this set-up, the females were free to either cross the partition and engage in sexual activity with the male mice or “escape” to the side where the males were unable to follow. Sexual motivation in this study was measured by how many total mounts occurred, and since mounting involves male participation, time spent on the male side of the chamber was also a measure of female sexual motivation. When researchers injected female mice with inflammatory agents in the vulva, hind paw, tail, or cheek to induce pain, female mice consistently participated in less mounting behavior and spent less time on the male side of the cage compared to no injections. Males, on the other hand, when injected with the same inflammatory agents in either the penis, hind paw, tail, or cheek, experienced unimpeded sexual activity (total number of mounts did not decrease compared to controls) in an open field paradigm where the males had unrestricted access to the females. Although it has been observed that female mice can have a higher sensitivity to pain than male mice,2 researchers observed that male and female mice exhibited the same level of sensitivity towards inflammation to the hind leg according to the mouse grimace scale (MGS), a visual observation of a mouse’s facial features to determine pain levels.

The final experiments to study sexual activity involved rescuing the lack of sexual motivation from female mice using either an antinflammatory agent or two different prosexual drugs. The analgesic pregabalin reversed the reduction of total mounts that resulted from inducing pain in females, and according to the MGS, also reduced the level of pain. “Prosexual” drugs, apomorphine (APO) and melanotan-II (MT-II), had the same rescuing effect, but based on the MGS, did not have the ability to relieve pain from the inflammatory injections. It should be noted though that APO increases locomotion3 in mice, which may partially account for the females moving towards the male side of the cage more often.

From these experiments, researchers concluded that female mice have lower levels of sexual motivation when in pain, but even in penile pain, male mice maintain a desire to participate in sexual activity. However, the decrease in sexual motivation can be rescued in females by either pain reduction or aphrodisiacs, in this case a dopamine agonist (APO) or an α-melanocyte-stimulating hormone analog (MT-II). Perhaps these claims made regarding mice are reasonable, but it is even more problematic that the authors confidently extrapolate the results to humans. The final line of the abstract reads “These findings suggest that the well known context sensitivity of the human female libido can be explained by evolutionary rather than sociocultural factors, as female mice can be similarly affected.”

Of course, media outlets ran with this conclusion and multiple articles were published with definitive titles like “Women ARE more likely to go off sex when they are in pain” and “That headache excuse is real: For females, pain kills sexual desire.” The authors of this paper perpetrated the idea that a woman’s lack of sexual motivation at any given moment is either a biological or a sociocultural one. In the press release and the paper, the authors refer to the apparently common aphorism “Not tonight, dear, I have a headache,” and mention that this would be evidence that sometimes wives are in too much pain to have sex that has been initiated by their husbands. But sexual relations are so much more complicated than just a simple relationship such as a pain from a headache equals lack of sexual motivation. What if the woman (or man, for that matter) doesn’t really have a headache, but there is another underlying reason that a partner is too embarrassed to share? Or, what if pain from a headache makes you feel less sexy, and that feeling is the sexual deterrent, not the pain alone? Pain, either directly or indirectly, would most likely make a person feel less sexual, but why does is take a study with mice (who aren’t insecure about love handles or annoyed with a spouse due to an insensitive comment) to validate this thought? It is reminiscent of neuro-realism, the idea that attaching a brain scan to any study or correlation suddenly qualifies the findings as real or more true.4 While this study only involved mice, researchers did use fMRI to study the difference between the brains of women with and without acquired hypoactive sexual desire disorder (HSDD) in this paper.5 But no one - including females, their sexual partners, researchers, or doctors - really wins when it is being advertised that the female libido is something that can be can characterized as either biologically or socioculturally driven. 

Via The Telegraph

One reason for ascribing a biological reason to the lack of sexual motivation could involve drug development; if a biological target can be found that is responsible for diminishing sex drive, then perhaps there is a pill to fix that. The work in the paper was supported by a Pfizer Pain Research Award from Pfizer Canada, and Pfizer Canada did kindly provide the pregabalin that was used in the sexual recovery research. There have been a number of pharmaceutical companies that have sought FDA approval for low female sexual desire,6 even when the diagnosis of disorders such as HSDD and female sexual dysfunction (FSD) are controversial. One example though is Lybrido, a drug meant to treat HSDD. (Mallory actually gave a journal club talk last year about the implications of pharmaceutical companies targeting the female sex drive with a focus on Lybrido). Lybrido is interesting because it was ineffective in a cohort of women who “suffer from HSDD as a result of inhibitory mechanisms,” resulting from negative associations with sex and for that reason Lybridos was developed.7 Lybidos has an additional component that targets the prefrontal cortex areas of the brain and is meant to alleviate these inhibitory mechanisms.8 A discussion of drug development for women that have negative associations with sex is beyond the scope of this post, but the mentality that this could be relieved with only a pill is grossly overly simplifying the complexities of the female libido and how this affects relationships women have with their sexual partners. If researchers in academia though are willing to commit to the idea that female sexuality can be classified as solely biologically determined, then can we really expect that pharmaceutical companies, marketing campaigns, and sensationalized news articles won’t try to capitalize on that idea?

Via The Neurocritic

References 

(1)  Farmer, M. A.; Leja, A.; Foxen-Craft, E.; Chan, L.; MacIntyre, L. C.; Niaki, T.; Chen, M.; Mapplebeck, J. C. S.; Tabry, V.; Topham, L.; Sukosd, M.; Binik, Y. M.; Pfaus, J. G.; Mogil, J. S. Pain Reduces Sexual Motivation in Female But Not Male Mice. J. Neurosci. 2014, 34, 5747–5753.
(2)  Mogil, J. S. Sex Differences in Pain and Pain Inhibition: Multiple Explanations of a Controversial Phenomenon. Nat. Rev. Neurosci. 2012, 13, 859–866.
(3)  Horn, C. C.; Kimball, B. A.; Wang, H.; Kaus, J.; Dienel, S.; Nagy, A.; Gathright, G. R.; Yates, B. J.; Andrews, P. L. R. Why Can’t Rodents Vomit? A Comparative Behavioral, Anatomical, and Physiological Study. PLoS ONE 2013, 8, e60537.
(4)  Racine, E.; Bar-Ilan, O.; Illes, J. fMRI in the Public Eye. Nat. Rev. Neurosci. 2005, 6, 159–164.
(5)  Woodard, T. L.; Nowak, N. T.; Balon, R.; Tancer, M.; Diamond, M. P. Brain Activation Patterns in Women with Acquired Hypoactive Sexual Desire Disorder and Women with Normal Sexual Function: A Cross-Sectional Pilot Study. Fertil. Steril. 2013, 100, 1068–1076.e5.
(6)  Shames, D.; Monroe, S. E.; Davis, D.; Soule, L. Regulatory Perspective on Clinical Trials and End Points for Female Sexual Dysfunction, in Particular, Hypoactive Sexual Desire Disorder: Formulating Recommendations in an Environment of Evolving Clinical Science. Int. J. Impot. Res. 2006, 19, 30–36.
(7)  Lybrido http://www.emotionalbrain.nl/lybrido (accessed Oct 30, 2014).
(8)  Lybridos http://www.emotionalbrain.nl/lybridos (accessed Oct 30, 2014).


Want to cite this post?

Strong, K. (2014). Can Neuroscience Validate the Excuse “Not Tonight, Dear, I have a Headache?" The Neuroethics Blog. Retrieved on , from http://www.theneuroethicsblog.com/2014/11/can-neuroscience-validate-excuse-not.html

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