Oxytocin and Reward Processing in Women

This pharmaco-neuroimaging study will investigate four groups of women: (1) naturally cycling (NC) women in the follicular phase of the menstrual cycle (n = 25), (2) NC women in the luteal phase of the menstrual cycle (n = 25), (3) women taking combined oral hormonal contraceptives (OC) (n = 25), (4) women taking progestogen-only OC (n = 25).

All participants will take part in an intake session (T0) and two experimental sessions (T1 and T2) scheduled approximately four weeks apart. In the intake session (T0) the eligibility of the participants i.e., MRI compatibility, will be verified. Additionally, the participants will be asked to fill out questionnaires i.e., regarding their personality, sleep and eating behavior and perform standardized cognitive tests.

To disentangle the influence of oxytocin on reward processing and metabolism across different hormonal status in females, intranasal oxytocin (24 IU) will be administered in one experimental session and placebo in another, in a randomized and double-blind study design. The investigators will obtain sex steroids (e.g., progesterone, estrogen, testosterone) i.e., to verify the menstrual cycle phase, synthetic steroids (e.g., ethinylestradiol, levonorgestrel) and metabolic hormones (e.g., glucose, insulin, c-peptide) from blood samples in the two experimental sessions. In the baseline phase of each experimental session (T1 and T2), the investigators will assess the participants body composition with bioimpedance analysis and resting energy expenditure with indirect calorimetry. After the intranasal administration of oxytocin or placebo, a 3 Tesla (3T) functional magnetic resonance imaging (fMRI) session will follow including the Effort Allocation Task (EAT), an effort-based decision-making task, a resting-state fMRI and diffusion tensor imaging (DTI) scan. The experimental sessions will furthermore assess the participants mood, thirst and hunger throughout the experimental period and include a snack test to assess eating related behavior. Additionally, participants will be asked to fill out questionnaires assessing i.e., sleep, emotion regulation, decision making, sexual function and wellbeing.

The investigators hypothesize that, (1) the acute effect of oxytocin on reward processing in naturally cycling women is most pronounced during the follicular phase and (2) the acute effect of oxytocin on reward processing in women is dampened by the intake of oral contraceptive pills (OCs), in particular progestogen-only pills.

Inclusion criteria

• Body-mass index (BMI): 18-28 kg/m2
• Sex: female (since birth)
• Normal or corrected vision
• Natural menstrual cycle (NC) or intake of hormonal oral contraceptives (OC)
• NC: No hormonal contraception for at least 6 months; regular menstrual cycle (between 25 and 31 days) prior to participation
• OC: No hormonal contraception for at least 4 months, regular intake of OC pill

Exclusion criteria

• No German language fluency (due to German language test content)
• Smoking
• Medication taken within the last 6 weeks (except for OCs in the respective group)
• Current neurological or psychiatric disease (anamnestic survey)
• Current medical problems such as hormonal, metabolic, or chronic diseases (e.g., severe hypertension, diabetes, dysfunctions of the thyroid, or congestive heart failure)
• Pregnancy, delivery and lactation (current and within the last year; anamnestic survey, current pregnancy test)
• Premenstrual dysphoric disorder (PMDD), endometriosis or polycystic ovary syndrome (PCOS)
• Shift work
• NC: Any kind of hormonal treatment or contraception
• OC: Any kind of hormonal treatment or contraception (except OCs)
• Contraindication for MRI:
• Non-removable metal objects on or in the body
• Tattoos (if MRI-incompatible according to expert guidelines)
• Pathological hearing or increased sensitivity to loud noise
• Claustrophobia
• Operation less than three months ago
• Neurological disease or injury
• Moderate or severe head injury
• Intake of antidepressants or neuroleptics
• Restricted vision