In this study the investigators compare three stimulants to each other. The effects of these agents on cognitive performance (eg, attention and memory) and on the brain are being measured. The hypothesis is that stimulants will have a positive effect on cognitive performance.

Each study participant will receive once a placebo and once methylphenidate or modafinil or caffeine. Methylphenidate (also known as Ritalin ®) is a drug that is used in the treatment of attention deficit / hyperactivity disorder (ADHD) in children, adolescents and adults. Modafinil ( Vigil ®) is a drug used in the treatment of narcolepsy (sleeping sickness). In the study. These substances are given in the study only once and in the dosages in which is also used for the treatment of the above diseases. In the case of caffeine , the dosage corresponds to two cups of coffee.

Inclusion Criteria:

• Men
• 18 - 35 years
• Written consent (according to Arzneimittelgesetz (AMG) § 40 (1) 3b)
• Good knowledge of German
• Right-handedness

Exclusion Criteria:

• Known hypersensitivity to the study medication
• All contraindications to the study medication: arrhythmia, hyperthyroidism , glaucoma , pheochromocytoma , congestive heart failure , diabetes mellitus, known liver and kidney dysfunction, vascular disease , angina, haemodynamically significant congenital heart disease , cardiomyopathy , myocardial infarction, channelopathies, arterial hypertension , cerebrovascular diseases , such as cerebral aneurysm , vascular abnormalities , including vasculitis and stroke.
• Participation in other clinical trials during or within one month prior to this clinical trial
• Medical or psychological circumstances that may endanger the proper conduct of the trial
• Existing serious somatic diseases, even if they are not covered by the contraindications according to product information
• Existing psychiatric disorders and psychiatric disorders in prehistory
• Smoker or ex-smoker for less than 5 years
• Regular caffeine consumption > 4 cups per day
• Subjects with irregular day -night rhythm (eg shift workers )
• Unwillingness to the storage and disclosure of pseudonymous data as part of the clinical trial
• Accommodation in an institution by court or administrative order (according to AMG § 40 (1) 4 )
• MRI contraindications ( eg pacemakers , metallic or electronic implants , metallic splinters , tinnitus, surgical clips )