The hormone didn’t have the same effect on women viewing images of smiling infants.
Indiana University researchers studying postpartum depression have found that the hormone oxytocin increased activation in a reward-sensitive area of the brain when women viewed images of crying infants, but not when they viewed images of smiling ones. The researchers say oxytocin might spark the motivation to help an upset baby.
The new work, published in the journal Hormones and Behavior by investigators from the IU Bloomington College of Arts and Sciences’ Department of Psychological and Brain Sciences and IU’s The Kinsey Institute, gave women in the first sixth months postpartum and women who had never had children either a nasal dose of oxytocin or a nasal placebo. The subjects then viewed images of crying infants, smiling infants, sexual activity and neutral items like nature photos.
Brain activity measured by functional magnetic resonance imaging while the women viewed the images showed that the oxytocin group, regardless of child status, showed a significant increase in activation in the ventral tegmental area, which is associated with the brain’s reward circuity, when the subjects viewed the crying infants and sexual images, according to Julia Heiman, a professor in the Department of Psychological and Brain Sciences and senior research fellow at Kinsey who was senior author on the paper.
Oxytocin is a social neuropeptide closely associated with nurturing behaviors like breastfeeding and bonding that also increases in humans with touch and during orgasm. The researchers want to understand how depression affects the processing of the external world during the first six months postpartum, a time when infant development and parental adaptations are rapid and demanding. They also want to know just how decreased motivation toward sexual interests gets balanced between infant demands and the need of most families to maintain and nurture their pair bonds.
Why only crying babies and not the smiling ones? Heiman thinks that most adults have similar reactions to a smiling infant so fewer differences in “reward” can be found. But oxytocin, especially given its connection to significant reproductive events for women, might facilitate the appeal and motivation to help an upset baby since responding to infant distress is so critical in the early months of life.
“We know there are tradeoffs in terms of sexual responsiveness and in terms of attention to a new infant, who requires care and affection,” she said. “What changes during the postpartum period, how these changes positively impact the mother and the infant, and to what extent this nurturing response overrides sexuality, we are learning, depends on a number of influences.”
Though the postpartum period is known as a time of less sexual desire for women, this latest study showed variability. Using a scale developed at The Kinsey Institute to measure sexual inhibition and sexual excitation, the postpartum women reported lower desire, more inhibition and less excitation in general. Yet those women who had a higher sexual excitation score also showed more activation in the ventral tegmental area of the brain with visual sexual stimuli when given oxytocin, regardless of whether they were new mothers or never mothers.
“From an evolutionary perspective, this a nurturing period, a time of focus and bonding with a new baby, whose life and future depend on attentive parenting, yet sexual sensitivity does not evaporate,” Heiman said. “It just may be less obvious in the first months following birth.
“People forget about the ‘other parent’ even though between 54 percent and 91 percent of babies in the U.S. are born into married or cohabitating couples,” Heiman said. “There remains a lot to uncover about this early phase of life and how the key players adapt. We want to understand what is lost and what is gained in the service of healthy outcomes.”
Co-authors with Heiman on the paper, “Oxytocin increases VTA activation to infant and sexual stimuli in nulliparous and postpartum women,” were former IU graduate student Rebecca Gregory, IU senior scientist Hu Cheng, Kinsey research fellow Heather A. Rupp and IU professor Dale R. Sengelaub.
Source: Jennifer Bass – Indiana University Bloomington
Image Credit: The image is credited to TaniaVdB and is in the public domain
Original Research: Abstract for “Oxytocin increases VTA activation to infant and sexual stimuli in nulliparous and postpartum women” by Rebecca Gregory, Hu Cheng, Heather A. Rupp, Dale R. Sengelaub, and Julia R. Heiman in Hormones and Behavior. Published online March 2015 doi:10.1016/j.yhbeh.2014.12.009
Oxytocin increases VTA activation to infant and sexual stimuli in nulliparous and postpartum women
After giving birth, women typically experience decreased sexual desire and increased responsiveness to infant stimuli. These postpartum changes may be viewed as a trade-off in reproductive interests, which could be due to alterations in brain activity including areas associated with reward. The goal of this study was to describe the roles of oxytocin and parity on reward area activation in response to reproductive stimuli, specifically infant and sexual images. Because they have been shown to be associated with reward, the ventral tegmental area (VTA) and nucleus accumbens (NAc) were targeted as areas of expected alterations in activity. Oxytocin was chosen as a potential mediator of reproductive trade-offs because of its relationship to both mother–infant interactions, including breastfeeding and bonding, and sexual responses. We predicted that postpartum women would show higher reward area activation to infant stimuli and nulliparous women would show higher activation to sexual stimuli and that oxytocin would increase activation to infant stimuli in nulliparous women. To test this, we measured VTA and NAc activation using fMRI in response to infant photos, sexual photos, and neutral photos in 29 postpartum and 30 nulliparous women. Participants completed the Sexual Inhibition (SIS) and Sexual Excitation (SES) Scales and the Brief Index of Sexual Function for Women (BISF-W), which includes a sexual desire dimension, and received either oxytocin or placebo nasal spray before viewing crying and smiling infant and sexual images in an fMRI scanner. For both groups of women, intranasal oxytocin administration increased VTA activation to both crying infant and sexual images but not to smiling infant images. We found that postpartum women showed lower SES, higher SIS, and lower sexual desire compared to nulliparous women. Across parity groups, SES scores were correlated with VTA activation and subjective arousal ratings to sexual images. In postpartum women, sexual desire was positively correlated with VTA activation to sexual images and with SES. Our findings show that postpartum decreases in sexual desire may in part be mediated by VTA activation, and oxytocin increased activation of the VTA but not NAc in response to sexual and infant stimuli. Oxytocin may contribute to the altered reproductive priorities in postpartum women by increasing VTA activation to salient infant stimuli.
“Oxytocin increases VTA activation to infant and sexual stimuli in nulliparous and postpartum women” by Rebecca Gregory, Hu Cheng, Heather A. Rupp, Dale R. Sengelaub, and Julia R. Heiman in Hormones and Behavior. Published online March 2015 doi:10.1016/j.yhbeh.2014.12.009