Studying the Role of Brain Molecules for Decision Making

To simultaneously assess and dissociate choice preference and randomness in stable environments, the investigators plan to use two tasks: (1) a variant of the RISKGARP task, a well-established risky decision-making task and (2) a modified Becker-DeGroot-Marshak task that measures choice preference and the width of preference representations with the range of willingness to pay procedure (range-WTP). Note that wider representations should result in more choice randomness. The investigators will assess choice randomness also by repeating the same decision questions several times within each task and by relating the preferences measured by the RISKGARP task to those measured by the range-BDM task by using the same options in both tasks. To assess the impact of changing environments and learning on choice preference and randomness, participants will perform two established exploration/exploitation tasks. One (3) is a foraging task that has been combined with different pharmacological manipulations and the other (4) is a variant of the four-armed bandit task, which allows distinguishing value- or information-based exploration from random choice. Blood and saliva samples may be taken. Blood samples may be used to determine levels of the administrated substances and to assess genetic variation. Saliva samples may be used to determine cortisol and testosterone levels.

Inclusion criteria

• Physically and psychiatrically healthy (as defined by exclusion criteria) men and women aged 18-35 years
• Ability and willingness to participate in the study
• Willingness to not eat or drink any food/beverage containing caffeine or alcohol 12 hours prior to the administration of study medication (asked in screening session)
• Willingness to not eat or drink grapefruit or grapefruit related citrus fruits (e.g., Seville oranges, pomelos) from 7 days prior to the administration of study medication (asked in screening session)
• Good command of English language (be able to understand the task instructions and in the unlikely case of adverse effects inform the examiner)
• Signed informed consent

Exclusion criteria

• Serious past brain disease or injury
• Frequent headaches (of any sort, > 1/week) or migraine (irrespective of frequency)
• History of epileptic seizures
• Any neurological disorder
• Surgery to head or heart (MRI safety, potential metal pieces)
• Pacemaker, hearing aid or neurostimulator (MRI safety, metal pieces)
• Known cardiac or cardiovascular disease or anomaly
• Family history of sudden death due to cardiac arrhythmia
• High or low blood pressure, history of heart attack, infrequent heartbeat
• Respiratory problems (including difficulty with breathing through the nose)
• Glaucoma (present or past)
• Insufficiency of kidney or liver, acute liver disease
• Any psychiatric disorder (especially depression, mania, schizophrenia, addiction panic and suicidality)
• Severe vocal or motor tics (methylphenidate, data quality)
• Severe psychosomatic disorder (somatic complaints without clear medical cause, has a mental component)
• Potential metal parts in body (MRI safety; metal splinters, gun wounds, shrapnel or surgical clips)
• Pregnancy, nursing, or currently planned pregnancy
• Allergy to drugs, particularly methylphenidate, reboxetine or nicotine
• Severe intolerance to lactose including strong diarrhea after only a few mg (weak lactose intolerance is no exclusion criterion as medication only contains a very small dose (around 4 mg) of lactose)
• Oversensitivity to hot pepper sauce (e.g., tabasco)
• Currently taking any medication or recently participated in other clinical trials that might interfere with Methylphenidate and Reboxetine, especially MAO-Inhibitors (e.g. Aurorix (Moclobemid) and Azilect (Rasagilin), antipsychotics, antibiotics, and medication for heart diseases
• Currently taking any further medication (besides birth control) or natural products (infrequent intake of natural products and/or food supplements need to be mentioned to the examiner)
• Drug abuse (exclude people with a positive test)
• Serious acute or chronic disease that could interfere with participation in the experiments
• Inability to lie still in the scanner (e.g. due to itching, sneezing, coughing, claustrophobia)
• Inability to understand the instructions
• Participants with BMI < 18
• Clinically relevant score in STAI T (anxiety), measured during screening on a separate day
• ECG demonstrating QTcF >450 msec or a QRS interval >120 msec at screening. If QTcF exceeds 450 msec, or QRS exceeds 120 msec, the ECG should be repeated two more times and the average of the three QTcF/QRS values should be used to determine participant eligibility, measured during screening on a separate day
• Participants who eat or drink grapefruit or grapefruit related citrus fruits (e.g., Seville oranges, pomelos) or drinks from 7 days prior to the administration of study medication.
• Participants who eat or drink any food/beverage containing caffeine or alcohol 12 hours before the study
• Current smokers/tobacco consumers (exclude people whose cotinine level is higher than 50ng/ml with a urine test)
• Phenylketonuria
• Dental or jaw condition prohibiting gum chewing
• Pheochromocytoma
• Thyroid disorders
• Diabetes
• Type of angina where chest pain occurs at rest
• Unpredictable severe constricting chest pain
• Prickling or tingling of fingers and toes
• Buerger's Disease
• Throat irritation
• Peptic ulcers
• Esophagitis