Amygdala response to negative images in postpartum vs nulliparous women and intranasal oxytocin

Abstract

The neuroendocrine state of new mothers may alter their neural processing of stressors in the environment through modulatory actions of oxytocin on the limbic system. We predicted that amygdala sensitivity to negatively arousing stimuli would be suppressed in postpartum compared to nulliparous women and that this suppression would be modulated by administration of oxytocin nasal spray. We measured brain activation (fMRI) and subjective arousal in response to negatively arousing pictures in 29 postpartum and 30 nulliparous women who received either oxytocin nasal spray or placebo before scanning. Pre- and post-exposure urinary cortisol levels were also measured. Postpartum women (placebo) demonstrated lower right amygdala activation in response to negative images, lower cortisol and lower negative photo arousal ratings to nulliparous women. Nulliparous women receiving oxytocin had lower right amygdala activation compared to placebo. Cortisol levels in the placebo group, and ratings of arousal across all women, were positively associated with right amygdala activation. Together, these findings demonstrate reductions in both amygdala activation and subjective negative arousal in untreated postpartum vs nulliparous women, supporting the hypothesis of an attenuated neural response to arousing stimuli in postpartum women. A causal role of oxytocin and the timing of potential effects require future investigation.

Keywords: amygdale; arousal; cortisol; oxytocin; postpartum.

Fig. 1

Average cortisol levels before and after MRI scanning in nulliparous and postpartum women. Nulliparous women had higher levels than postpartum women overall and post-scan. Only postpartum women demonstrated a decrease over time.

Fig. 2

Average ratings of arousal for negative photos within nasal spray groups by cohort. Nulliparous women receiving the placebo spray rated the photos to be more arousing than postpartum women receiving the placebo.

Fig. 3

Coronal slice showing functionally defined amygdala ROIs (circled in yellow) determined from main effect of negative–neutral (15, −4, −11), i.e. collapsing across cohort and spray condition.

Fig. 4

BOLD signal change as a function of stimulus valence, cohort and nasal spray group. There was a significant effect of cohort in only the placebo group in which nulliparous women had a higher right amygdala response than postpartum did in response to negative stimuli. Nulliparous women in the oxytocin group had lower levels of activation to negative pictures than did nulliparous women in the placebo group. This pattern was not observed for neutral images.

Fig. 5

BOLD signal change by nasal spray group in relation to cortisol levels taken following the fMRI scan. There was a significant positive relationship between cortisol (post) and right amygdala activation in response to negative images within the placebo, but not oxytocin, group.