Endogenous testosterone and exogenous oxytocin influence the response to baby schema in the female brain

Nurturing behavior may be critically influenced by the interplay of different hormones. The neuropeptide oxytocin is known to promote maternal behavior and its reduction has been associated with postpartum depression risk and child neglect. Contrariwise, the observed decrease in testosterone level during early parenthood may benefit caretaking behavior, whereas increased testosterone may reduce attention to infants. Here we used functional magnetic resonance imaging to investigate the interactive influence of testosterone and oxytocin on selective attention to and neural processing of the baby schema (BS). 57 nulliparous women performed a target detection task with human faces with varying degree of BS following double-blinded placebo-controlled oxytocin administration in a between-subjects design. Our results support the idea that oxytocin enhances attention to the BS. Oxytocin had a positive effect on activation of the inferior frontal junction during identification of infant targets with a high degree of BS that were presented among adult distractors. Further, activation of the putamen was positively correlated with selective attention to the BS, but only in women with high endogenous testosterone who received oxytocin. These findings provide initial evidence for the neural mechanism by which oxytocin may counteract the negative effects of testosterone in the modulation of nurturing behavior.


Supplementary Tables
shown between trials. Its duration was jittered for 500-2,500 ms and randomized between trials. The first paradigm was 16.4 minutes long.
The same odd-one-out procedure was repeated in the baseline task. In this task geometric figures were used as stimuli (triangles, squares, or circles). Each condition was shown 30 times (i.e., triangle target, square target, circle target with three distractors of the other shapes), so that the paradigm was 90 trials long. The baseline task was intended to control for the influence of the OT treatment on participants' RT in general. The baseline task was 6.4 minutes long.
Subjects were asked to identify the target (the one picture that didn't fit the other three pictures) as fast and as accurate as possible via button press. The button positions matched the picture positions. The time of trial appearance was not influenced by button press and hits or false responses were not displayed for the participant (see Figure 4 for schematic illustration of the target detection paradigm).
The fMRI measurement was followed by another saliva sample of the participant. 7

Hormone Samples
The salivary T concentrations of the participants were analyzed in our in-house laboratory. Eppendorf tubes (2 ml) and an instruction for saliva sampling were handed over in advance at the first meeting with the MR-physician. The participants were asked to collect three saliva samples over the course of 1 hour at home. They started directly after waking up on the day of testing. During the collection of morning saliva the participants were instructed to refrain from eating and consuming cigarettes or any products that could influence the hormone measurement (for example milk, chewing gum or lip balm). They could drink water between sampling intervals and were allowed to brush teeth directly after the first saliva sample, leaving a gap of at least 15 minutes between tooth brushing and the second saliva sample to avoid a potential blood contamination. One additional saliva sample was collected right before administration of OT or placebo and a final one was obtained after the fMRI measurement.
The samples were frozen at -20°C until analysis. For preparing an aliquot out of the three morning samples and to separate these and the other two samples from mucus, all samples were unfrozen and centrifuged at RCF 604 x g for 5 minutes (i.e., 3,000 rpm) in a common Eppendorf Minispin centrifuge.
After further refreeze and defrost of the samples, they were analyzed with a T luminescence immunoassay from IBL International (TECAN group global; Hamburg, Germany). Each sample, seven standards and two controls were pipetted twice on the assay plate. The analysis was performed according to the IBL manual. Formal sensitivity of the assay kit lies between 1.8 pg/ml and 500 pg/ml T in saliva. The intra-and inter-assay coefficient variances were declared to range between 1.47 -3.01 % and 4.04 -6.96 %.
To control for a potential pregnancy and to prevent cyclic changes in T level, we exclusively examined participants that used hormonal contraceptives. But it's important to note that previous research showed that the intake of oral contraceptives increased performance in affective responsiveness and that affective responsiveness was positively influenced by exogenous hormones through intake of oral contraceptives (pill-intake phase versus pill-free week 5 ). Further, the intake of combined oral contraceptives may decrease T concentrations in women 6 . Therefore, it will be of great interest to examine the influence of the intake of oral contraceptives as opposed to a natural menstrual cycle in a future study.

Behavioral data analysis
Two participants had to be excluded because they missed more than 30% of the trials. Another participant felt unwell during the fMRI measurement and did not finish the task.
One participant of the placebo group failed to bring the morning saliva samples and another participant missed a fingertip on the ring finger of the right hand, so we could not measure her 2D:4D ratio. These participants were nevertheless included.
We performed one-way ANOVAs to evaluate the differences between OT treated participants versus placebo treated participants in the RMET score, digit ratio, age and T measurements. A potential T modulation through OT administration was also analyzed with a one-way ANOVA. Mean T values (Tmorning, T concentration before fMRI measurement, T concentration after fMRI measurement and digit ratio), age and reading the mind in the eye test score (RMET -after 2 ) did not differ between the OT and the placebo group (see Table S4). The RMET score was not influenced by the Based on these analyses, the treatment and the placebo group were considered as comparable.
For analysis of the interaction between treatment and T concentration we calculated the median of the T concentration out of the sample before nasal spray administration. The median of the T concentration was 17.96 ± 16.6 pg/ml (n = 57).

fMRI data analysis
The whole brain measurement was set to thirty-nine axial slices with a voxel size of 3 Parameter estimates were extracted from spheres at the local maxima (IFJ: -33, 5, 49 with a radius of 3 mm and putamen: L: -21 14 -11; R: 30 -1 13; spheres with 6 mm radius).