Oxytocin boosts reward-related brain activity for crying infants but not smiling ones
Researchers at Indiana University report that the hormone oxytocin increases activity in a brain region linked to reward when women view images of crying infants, but not when they view smiling infants. The finding suggests oxytocin may amplify the motivation to respond to an upset baby, an essential behavior in early caregiving.
In a study led by investigators from the IU Bloomington College of Arts and Sciences’ Department of Psychological and Brain Sciences and The Kinsey Institute, women in the first six months postpartum and women who had never been pregnant received either intranasal oxytocin or a placebo. While inside an fMRI scanner, participants viewed images of crying infants, smiling infants, sexual scenes, and neutral photographs such as landscapes.
Functional MRI results showed that oxytocin administration produced a pronounced increase in activation of the ventral tegmental area (VTA) when participants viewed crying infant images and sexual images. The VTA is a central structure in the brain’s reward circuitry. This increase occurred regardless of whether a woman was postpartum or nulliparous, indicating a common neural response to certain socially and reproductively relevant cues when oxytocin is present, according to Julia Heiman, professor in the Department of Psychological and Brain Sciences and senior research fellow at The Kinsey Institute, who served as senior author on the paper.
Oxytocin is a social neuropeptide that rises in association with breastfeeding, touch, bonding, and orgasm. The researchers designed the study to better understand how postpartum depressive symptoms and other postpartum changes might alter how new mothers process external cues during the demanding first months after birth. They were particularly interested in how shifts in sexual motivation and heightened responsiveness to infant signals are balanced during this period when infant care and parental bonding are critical.
Why did oxytocin affect the response to crying but not to smiling infants? Heiman and colleagues suggest that smiling infants generally elicit a broadly similar positive response across most adults, which may leave less room to detect oxytocin-driven differences in reward activation. By contrast, crying signals urgent need; oxytocin’s ties to reproductive and caregiving events may specifically enhance the salience and motivational pull of infant distress, helping prioritize caregiving actions when they are most crucial.
“There are tradeoffs in sexual responsiveness and attention to a new infant,” Heiman said. “What changes during the postpartum period, how those changes benefit both mother and infant, and how nurturing responses interact with sexual motivation depend on multiple influences. We still have much to learn about how parents adapt during this early phase.”
Although decreases in sexual desire are commonly reported in the postpartum period, this study found meaningful variability. Using The Kinsey Institute’s Sexual Inhibition/Sexual Excitation scales and a brief measure of sexual function for women, postpartum participants generally reported lower sexual desire, higher sexual inhibition, and reduced sexual excitation compared with nulliparous women. However, across both groups, women with higher sexual excitation scores showed greater VTA activation to visual sexual stimuli after oxytocin administration. In postpartum women specifically, self-reported sexual desire correlated positively with VTA responses to sexual images and with sexual excitation scores.
From an evolutionary perspective, Heiman noted, early parenthood is a time of focused nurturing and bonding, during which attention to the infant’s needs promotes survival. That does not mean sexual responsiveness disappears—rather, it may be less prominent or shifted while caregiving demands are high.
The published article, titled “Oxytocin increases VTA activation to infant and sexual stimuli in nulliparous and postpartum women,” lists Rebecca Gregory, Hu Cheng, Heather A. Rupp, Dale R. Sengelaub, and Julia R. Heiman as authors. The work appears in the journal Hormones and Behavior and examines VTA and nucleus accumbens (NAc) responses to infant and sexual images in 29 postpartum and 30 nulliparous women who received either intranasal oxytocin or placebo.
Key findings summarized by the authors include:
– Intranasal oxytocin increased VTA activation to crying infant images and to sexual images in both postpartum and nulliparous women.
– Oxytocin did not increase VTA activation to smiling infant images.
– Oxytocin produced changes in VTA but not in the nucleus accumbens.
– Postpartum women reported lower sexual excitation, higher sexual inhibition, and reduced sexual desire compared with nulliparous women.
– Sexual excitation scores across participants correlated with VTA activation and with subjective arousal to sexual images, and in postpartum women sexual desire correlated with VTA activation to sexual images.
These results suggest that postpartum decreases in sexual desire may be linked in part to reward-circuit activity in the VTA, while oxytocin can selectively boost VTA responses to salient infant and sexual cues. In practical terms, oxytocin may help shift reproductive priorities by enhancing the motivational salience of infant distress during early parenting.
Source: Jennifer Bass, Indiana University Bloomington
Image credit: TaniaVdB (public domain)
Abstract
Oxytocin increases VTA activation to infant and sexual stimuli in nulliparous and postpartum women
Postpartum changes often include reduced sexual desire and heightened responsiveness to infant cues—tradeoffs that may reflect altered activity in reward-related brain areas. This study examined how oxytocin and parity influence activation in the ventral tegmental area (VTA) and nucleus accumbens (NAc) in response to infant, sexual, and neutral images. Using fMRI, the authors measured responses in 29 postpartum and 30 nulliparous women who completed sexual inhibition/excitation scales and a brief sexual function index, then received intranasal oxytocin or placebo before viewing crying and smiling infant images, sexual images, and neutral photos. Intranasal oxytocin increased VTA activation to crying infant and sexual images in both groups but did not affect responses to smiling infants. Postpartum women showed lower sexual excitation, higher sexual inhibition, and reduced sexual desire compared with nulliparous women. Across parity groups, sexual excitation correlated with VTA activation and subjective arousal to sexual stimuli; in postpartum women, sexual desire correlated positively with VTA activation to sexual images. The findings indicate that postpartum decreases in sexual desire may be partially mediated by VTA activity, while oxytocin increases VTA—but not NAc—activation to salient infant and sexual cues, potentially contributing to altered reproductive priorities during the postpartum period.