Spring bursts forth with vibrant color, intoxicatingly sweet floral scents and sex. That’s right, relations. While monogamy in the rest of the animal kingdom is more of a myth, human pair-bonding gives the reward system a long-term buzz of activity and contributes to both physical and mental health. Oxytocin, the hormone produced when engaging in hugging, kissing and intercourse reduces jealousy and increases partner attractiveness. How unfortunate would it be if a product existed that could disturb this natural rhythm: altering the level of attraction and diminishing sexual functioning. There is - and almost 10 million women in the US are using it: hormonal contraception.
The hypothalamic peptide oxytocin has distinct sexually dimorphic effects. In women, it has been shown to reduce anxiety, increase intensity of orgasm and reduce imagination of sexual infidelity. This little molecule biases men towards perceiving their female partners as more alluring and even distances them from other attractive women. Clearly, the evidence implies oxytocin has powerful effects on cognitive and emotional processing which facilitates pair-bonding.
So what happens when steroid-based hormonal contraception (HC) is thrown into the mix? Nothing good. Studies show use of HC decreases attractiveness ratings of masculine faces, reduces response to erotic stimuli and increases jealousy. One study even showed wives who discontinue HC tended to be less satisfied with marriage if they perceived their husband’s face to be unattractive.
Studies show hormonal contraception drastically alter the way a partner’s attractiveness is perceived.
Given the strong link between the rewarding feeling of seeing a partner’s face and oxytocin, a group at the University of Bonn, Germany proposed birth control use significantly dampens this mechanism. 40 females in romantic heterosexual relationships (half on HC and half freely cycling at same point in their cycle) were randomly assigned to either intranasal administration of oxytocin or placebo before the start of an fMRI scan. The group cleverly took into account 1. time since they saw their partner and 2. whether they had an argument with them within the past week. The task was simple – lay in the scanner and attend to pictures of a partner, a close (same sex) friend, and a stranger. After the scan, the participants rated all photos on a scale of 0- most unattractive to 100-most attractive.
In freely cycling women, administering oxytocin enhanced attractiveness of their partner’s photo which paralleled with increased nucleus accumbens and ventral tegmental area responses. The two brain areas shown below are part of the primary reward circuit which release dopamine in response to reward-related stimuli. No surprise there: the partner’s face elicits pleasant feelings and arouses freely cycling women.
However, in women using HC this mechanism was markedly disturbed. Attractiveness ratings of women who received oxytocin were not different from those who just received the placebo.
Oxytocin does not affect attractiveness rating or arousal in women taking hormonal contraception.
Although the reward pathways were stimulated in women on HC, they were not stimulated enough to rate the photo higher. This implies women on HC need more oxytocin to override the interaction of hormones, especially if their endogenous oxytocin levels are low. One potential mechanism is the direct binding of progesterone to the oxytocin receptor instead, inhibiting oxytocin function.
Interestingly, the oxytocin effect on the reward pathway to the familiar person was only evident in women on HC. Women on birth control mimic the hormonal profile of pregnancy, thus they are likely to see a bond with a female as more rewarding for social support.
The benefit of human pair bonding extends beyond cuddling. The profound connection between two people that lasts well into old age is a fragile and sometimes inexplicable thing. Considering a pill could easily temper with this most remarkable event, its value should not be taken lightly.
*Note: Women taking contraception in this investigation used a variety of methods and doses. The study did not test between the different types and coupled with the interaction between endogenous oxytocin and sex hormones at different phases of the cycle, follow-up studies should tease apart differences in their analysis.