Consequences of Caffeine Intake in Sleep Restricted Teenagers

The goal of this clinical trial is to systematically investigate two prominent factors in teenagers' daily life: Caffeine and sleep restriction (SR) and their combined influence on sleep, cognition, and behavior in healthy adolescents. The main questions it aims to answer are:

The effects of caffeine under conditions of SR and SE:

* on sleep pressure and sleep continuity.
* on BOLD activity differences in reward related areas during a reward task (monetary incentive delay task) and on reaction times (behavioral aspect) in the same task.
* on BOLD activity differences during a risk taking task (wheel of fortune task) and on risky decision-making (behavioral aspect) in the same task.

Participants will be either in the SR or SE condition (between-subject). The protocol consists of 2x of approximately one week in which a participant will receive caffeine or placebo (within-subject) at the last two evenings.

The experiment consists of an ambulatory and a laboratory phase:

* The ambulatory phase consists of 5 nights, including 3 stabilization nights (8h sleep opportunity) prior to 2 nights consisting of either SR with 6h sleep opportunity or SE with 9.5h sleep opportunity. Participants will wear an actiwatch and fill out sleep diaries during this period.
* The laboratory phase will be the 6th evening, night and morning of the protocol and will be spent in our lab. Participants will do the following:
* treatment (caffeine vs. placebo) intake
* saliva sampling
* drug screening
* cognitive tests, including risk-taking and reward task
* filling in questionnaires (sleep diary, sleep quality, sleepiness, mood, expectancy)
* waking and sleep with EEG

The next day, participants will undergo an fMRI scan, including the following:

* resting-state scan
* structural scan
* arterial spin labeling scan
* reward task scan
* risk-taking task scan

Around the scan, participants will fill out/undergo:

* saliva sampling
* questionnaires (reward task, mood, sleepiness, expectancy)


Eligibility Criteria:
Inclusion Criteria:

* Age ≥ 14 and ≤ 17
* Clinically healthy
* Signed consent form of participant and legal guardian

Exclusion Criteria:

* Inability to operate tasks or understand the study information
* Participation in other clinical trials \<3 months prior to any possible study start date
* BMI P3 \< BMI-PC \< P97
* Any general health concerns or disorders (previous diagnosis of heart/cardiovascular/nephrological/endocrinological/diabetic/metabolic/chronobiologic/ psychiatric/neurological \[particularly epilepsy and parasomnia\] conditions) which may make participants vulnerable to potential negative effects of SR or caffeine or which may affect outcome measures
* Unavailability to complete the two study protocol weeks within a three-month period
* Trans meridian travel (\>2 time zones) \<1 month before any possible study start date
* Shift work \<3 months prior to any possible study start date
* Extreme chronotype MSFSC \< 3:00 / MSFSC \> 6:00 according to MCTQ
* Subjective sleep duration on school days \<7h or \>9h according to MCTQ
* Metallic prosthesis, metallic implants, or non-removable objects in the body (e.g., splinters, piercings) which affect MRI safety
* Tattoos with larger diameter than 10cm or above shoulder area, affecting MRI safety
* Claustrophobia
* Difficulties or problems in physical well-being and mental health based on the Swiss norm (T\< 35) for all genders aged 12-18 according to KIDSCREEN-27
* Daily nicotine use
* Use of medications or drugs that have contraindications and/or effects on outcome measures or use of specific drugs indicated in drug test
* Use of alcohol to an extent that it is likely to have contraindications and/or effects on outcome measures
* Any indication of previous withdrawal or oversensitivity to caffeine
* Sleep quality \>5 according to PSQI
* Problems of EEG compatibility
* Sleep efficiency \<70%
* Identification of sleep disorders
* Pregnancy
* Deviation from the stabilisation sleep-wake schedule by +-60 mins
* Deviation from protocol sleep-wake schedule by +-30 mins