Social Media Usage in Adolescent Girls

For each participant, there is a screening session, a month-long EMA assessment and two experimental fMRI sessions are planned.

After making sure the participants fill the inclusion and exclusion criteria, the investigators will invite them to the laboratory for a screening session (T0). In this session, the participants will provide written informed consent and assent in case of those under 18 years old and written, informed consent for those who are 18 year old. Furthermore, the participants will participate in a standardized clinical interview to screen for mental disorders (Kinder-DIPS). Subsequently, they will be informed about the study details. Finally, they will fill out questionnaires about personality, depressive symptoms, anxiety symptoms, gender identity and norms, mood, loneliness, social media disorder, internet use, social support, and fear of missing out.

Naturally cycling adolescent girls will join the two fMRI measurements (T1 \& T2) during the follicular and luteal phase of the menstrual cycle. Adolescent girls using combined oral contraceptives will join the first fMRI measurement during the pill intake period, and the second measurement during the break period. The fMRI sessions will comprise of filling out questionnaires, fMRI measurements, and blood collection for hormonal assessment.

Questionnaires on depressive symptoms, state anxiety, mood, gender identity, self-esteem, loneliness, fear of missing out (FOMO), social media disorder, internet use, social support and social media use will be administered through RedCap platform. This will ensure the assessment of subjective, self-report data and its changes throughout the measurement time of one month.

The sequence of fMRI measurements incudes four main parts, namely anatomical scan, resting-state scan, Effort Allocation Task (EAT), and diffusion tensor imaging (DTI). This protocol ensures the acquisition of the structural and functional data of the brain in the participants. The detailed protocol components are as follows:

1. Anatomical scan: This first sequence of the protocol ensures assessment and insight into the anatomy of the brain, thus providing structural data of the participants' brain. This will last approximately 8 minutes.
2. Resting-state scan: The next sequence involves participants watching a movie that was designed to improve imaging at rest for approximately 10 minutes. This sequence ensures insight into brain activity when no task is being performed and when the participant is at rest.
3. Effort Allocation Task (EAT): This next sequence aims to assess reward processing and reward behavior in the participants. During this task, participants have to exert physical effort on a grip force device when faced with monetary points at stake. There are two types of reward a participant can face; low and high reward. Additionally, there are two difficulty levels during the task, one being easier and the other more difficult. The payoff for the invested effort will be proportional to its duration. The task will last approximately 17 minutes.
4. Diffusion Tensor Imaging (DTI): During the final sequence, participants will undergo DTI assessment to ensure insight into white matter microstructure and connectivity. This will last approximately 7-8 minutes.

To thoroughly investigate the participants' experiences in their natural environments, Ecological Momentary Assessment (EMA) will be conducted. This will be done through an app called m-Path where participants will fill out daily questionnaires about social media use, self-esteem, premenstrual symptoms, and mood throughout one month. A daily questionnaire lasts approximately 10 minutes. This assessment will ensure data about subjective experiences with high ecological validity.