Caffeine
Conditions
Brief summary
"Learning from the rewards" is underlying the formulation of knowledge and habits in daily life. Caffeine is the most commonly used "psychoactive" substance that could change one's mind state by affecting the brain and nervous system. By such effects, caffeine enhances reward signals - dopamine - in human brains. In this research study, we will find out whether taking caffeine acutely or daily can enhance reward learning processes.
Detailed description
Reward learning is associated with the formulation of habits, memories, and beliefs. Positive (receiving an unexpected reward) and negative reinforcement (eliminating an unwanted state) learning are primarily modulated by striatal dopamine D1 and D2 receptors. While caffeine, a psychostimulant regularly consumed by 80% worldwide population, is known to facilitate striatal dopamine signaling, the potential of caffeine on enhancing reward learning in humans remains unknown. In this double-blind, randomized, crossover study, 36 young healthy non-smoking habitual caffeine consumers (daily dose 100 - 450 mg) who are aged between 18 and 40 will be examined. Each of the 36 participants (18 F, 18 M) will undergo an acute caffeine condition, a daily caffeine condition, and a daily placebo condition. Each condition consists of 7 days - 6 ambulatory days followed by 1 laboratory visit. In the ambulatory part, participants will abstain from caffeine, nicotine, medications, and recreational drugs. Compliance to the interventions and abstinence of caffeine will be monitored by salivary caffeine concentration every day. Bedtime and sleep quality will be recorded in sleep diary. On the laboratory visit, participants will perform cognitive tasks on a 2.5h task battery, which includes a probabilistic selection task, a motor inhibition task, and a salience attribution test. We also measure their arousal and anxiety levels 1h after the second intake on the laboratory visit. We will use Bayes factor analyses to test our confirmatory hypotheses (on the primary outcomes): 1) Caffeine enhances the accuracy of reward learning; 2) Daily intake of caffeine facilitates the negative reinforcement compared to acute its intake. On the secondary outcomes, we examine the exploratory hypotheses that caffeine enhances motor inhibition and motivational salience. Arousal and anxiety levels will be examined as a covariate which potentially contribute to the caffeine-induced changes in reward learning performance.
Interventions
DIETARY_SUPPLEMENTcaffeine
two doses per day: 200 mg caffeine in the morning; 100 mg caffeine in the afternoon
DIETARY_SUPPLEMENTmannitol
two doses per day: 200 mg in the morning \& 100 mg in the afternoon
Sponsors
Yu-Shiuan Lin
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
BASIC_SCIENCE
Masking
TRIPLE (Subject, Investigator, Outcomes Assessor)
Eligibility
Sex/Gender
ALL
Age
18 Years to 40 Years
Healthy volunteers
Yes
Inclusion criteria
* Age ≥ 18 and ≤ 40 * Clinically healthy * Non-smokers
Exclusion criteria
* Habitual caffeine intake \< 100 mg or \> 450 mg * Pregnant or lactating women * Women using hormonal contraceptives * BMI \< 18.5 or \> 29.9 * Sleep disturbance or extreme chronotypes * Nicotine or recreational drug users * Depression, anxiety, psychosis, or neurologic disorders * Severe heart or cardiovascular diseases * Diabetes or metabolic diseases * Under chronic medications * Incapable to operate the tasks or comprehend the study information in German or English * Users of the Bopomo alphates utilized as stimuli in the reward learning tasks * Current enrolment in other clinical trials
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| The accuracy (% of correct answers) in implicit learning through different probabilities of monetary reward feedback | 1-hour after the second intake on the 7th day | Through a probabilistic selection task, participant will go through a training phase to learn the rules which options may be more likely to return monetary feedback, and the knowledge learned will be tested in a second phase where the task difficulty is increased, and no feedback is provided. The overall accuracy in the testing phases will be examined, as well as the accuracies in choosing or avoiding the highest and lowest reward-probability stimuli. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| The errors in motor inhibition (rates of false alarm) in a motor inhibition task | 1.5-hour after the second intake on the 7th day | Through a reaction-inhibition task (Go/NoGo), participants will go through two phases of the task: 1) Only respond to a specific stimulus when it shows; 2) Respond to all stimuli except for the specific stimulus. The accuracy in motor inhibition will be indicated by the errors made in the no-go signals (i.e. false alarm). |
| Salience attribution behaviors | 1.5-hour after the second intake on the 7th day | subjective perception towards the probabilities (0 -100%) of reward feedback from each choice in the probabilistic selection task. |
Countries
Switzerland
Contacts
PRINCIPAL_INVESTIGATORYu-Shiuan Lin, PhD
Centre for Chronobiology, University Psychiatric Clinics Basel
Outcome results
None listed