Clinical trial NCT05208294: The Role of Dopamine, Reward Learning and Prefrontal Activity in Expectation-induced Mood Enhancement
Official title: The Role of Dopamine, Reward Learning and Prefrontal Activity in Expectation-induced Mood Enhancement
Study type: INTERVENTIONAL
Overall status: COMPLETED
Phase: NA
Conditions: Placebo Effect on Mood Improvement
Keywords: placebo effect
treatment expectations
depression
reinforcement learning
mesolimbic dopamine
EEG
Lead sponsor: Philipps University Marburg
Sponsor class: OTHER
First posted: 2022-01-26
Enrollment: 297
Sex: ALL
Minimum age (years): 18
Maximum age (years): 60
Standard ages: ADULT
Accepts healthy volunteers: yes
Allocation: RANDOMIZED
Intervention model: PARALLEL
Intervention model description: A fully crossed 2x2 placebo design will be employed by giving participants either a placebo or a sulpiride capsule in combination with a low vs. high expectation manipulation.
Primary purpose: BASIC_SCIENCE

Brief summary: Although placebo effects on depressive symptoms are well documented, the underlying mechanisms and moderating factors of expectation effects on mood and depression are poorly understood. Various studies show reduced reward processing in clinical and subclinical depression, presumably due to abnormalities in the dopamine (DA) system. Here, the investigators will test whether expectation-induced mood enhancement is mediated by endogenous DA activity and reward learning, and moderated by individual differences in depression-related personality traits. Healthy participants (N=296) will be tested for potentially relevant personality traits and given an inactive substance (placebo) or a DA D2-receptor antagonist sulpiride (400 mg) in combination with a low vs. high expectation manipulation (fully crossed 2x2 placebo design) before performing a probabilistic reinforcement learning task, an effort expenditure task, and undergo a depressed mood induction procedure. Further, EEG indices will be assessed throughout the tasks.

The investigators expect that positive expectation improves participants' reinforcement learning, increases participants' willingness to make effort in order to obtain reward, and leads to less depressive symptoms as indicated by mood ratings upon depressive mood induction. If the overall effect of positive expectations is mediated by DA, high-dose sulpiride should block expectation-induced effects, i.e., the anticipated enhanced reinforcement learning and effort expenditure as well as mood improvement in the high vs. low expectation group.

Detailed description: The placebo effect, i.e., raising expectations towards a successful treatment by applying an inactive substance, reportedly improves therapeutic outcomes in clinical trials. Although there is supporting evidence for the neurotransmitter dopamine (DA) and reinforcement learning, i.e. learning from reward and punishment, to mediate this effect, to the knowledge of the authors, no study has tested these underpinnings yet. The objective of the present project is to investigate whether expectation-induced mood enhancement is mediated by DA activity and reward learning, and moderated by individual differences in depression-related personality traits. To this end, participants will be told to either receive a placebo (low expectation) or a medicine which is labeled as antidepressant (high expectation) that improves mood. Orthogonal to this expectation manipulation, participants actually receive either 400 mg of sulpiride (sulpiride group) or a placebo (inactive substance group). Sulpiride is a selective D2-recptor antagonist which presumably elevates DA levels in low doses and has been used as an antidepressant. However, as a part of the high expectation group's expectation manipulation, while participants are told to receive an antidepressant, the sulpiride group actually receives a dose that is presumably too high to increase DA levels and produce antidepressant effects. Rather, 400mg of sulpirid presumably leads to a blockade of dopamine receptors and may thereby block expectation placebo effects. Participants then undergo three tasks, in which behavioral and computational markers of reinforcement learning and willingness to make effort in order to obtain reward are investigated. Further, mood ratings upon depressive mood induction will be assessed. In addition to participants behavioral responses, EEG indices will be recorded throughout the tasks. Prior to testing, participants will be asked to fill out questionnaires with regard to personality traits as well as reward response. In order to assess dopamine-related plasma prolactin, the study physician will draw one blood sample (ca. 8 ml) at the beginning of the testing session (at approximately 9 a.m.) and one hour after substance intake (at approximately 10 a.m.), which presumably corresponds with the latency of the peak of the prolactin response to sulpiride. Saliva and gene samples will be collected for hypotheses that are tested in the context of the overarching collaborative research center 289 and preregistered elsewhere.

It is expected that positive expectation improves participants' reinforcement learning, increases participants' willingness to make effort in order to obtain reward, and leads to less depressive symptoms as indicated by mood ratings upon depressive mood induction. If the overall effect of positive expectations is mediated by DA, high-dose sulpiride should block expectation-induced effects, i.e., the anticipated enhanced reinforcement learning and effort expenditure as well as mood improvement in the high vs. low expectation group.

Hypotheses:

1. Expectation enhancement (high vs. low) within the placebo group is associated with lower negative mood ratings after the mood induction procedure.
2. Expectation enhancement (high vs. low) within the placebo group enhances computationally modeled reward learning parameters and EEG markers of reward processing during the reinforcement learning task.
3. Within the placebo group, the expectation effect on negative mood ratings mentioned in (1) is correlated with the expectation effect on reward learning parameters in the probabilistic reinforcement learning task mentioned in (2).
4. Across the two expectation groups and within the placebo group, reward learning parameters and electrophysiological markers of reward processing are positively correlated with questionnaire measures of agentic extraversion (and negatively with self-reported depressive symptoms).
5. In the sulpiride group, the effects described in (1), (2), and (3) are lower than in the placebo group.
6. The prolactin response to sulpiride is correlated with the magnitude of expectation effects on reinforcement learning, negative mood, and self-reported agentic extraversion as well as depressive symptoms.
7. High levels of the personality trait agentic extraversion (and low levels of depressive symptoms) are associated with higher expectancy effects on negative mood.

Eligibility criteria: Inclusion Criteria:

* Right-handed
* Aged 18-60 years
* German native speaker
* Informed consent
* Normal or corrected sight

Exclusion Criteria:

* Current pregnancy
* Current or history of general medical, neurological or psychological disorders, which preclude sulpiride intake
* Self-reported presence of mental disorders
* Liver, kidney, and bowel disorders
* Regular smoking
* Reported alcohol abuse
* Illegal drug intake
* Regular drug intake by prescription in the past three months
* Dreadlocks
* BMI \< 19 or \> 30
* Unremovable metal objects around the head
* Previous knowledge of Japanese characters
* Excessive caffeine intake (\> 8 cups per day)

Primary outcomes:
measure: The Positive and Negative Affect Schedule (PANAS)
timeFrame: Five time points: approximately 3 hours after treatment (i.e., substance intake), approximately 4 hours after treatment, approximately 4.5 hours after treatment, approximately 4.75 hours after treatment, and approximately 5 hours after treatment.
measure: The probabilistic reinforcement learning task
timeFrame: This will be the first task participants undergo approximately 3 hours after treatment (i.e., substance intake) followed by the two other tasks.
measure: The Effort Expenditure for Rewards Task (EEfRT)
timeFrame: This will be the second task participants undergo which follows the probabilistic reinforcement learning task (approximately 4 hours after treatment) followed by the mood induction procedure.
Secondary outcomes:
measure: Mood ratings
timeFrame: Simultaneously as PANAS (see primary outcome 1).
measure: EEG responses to mood induction
timeFrame: Approximately 4. 5 hours after treatment (i.e., during the mood induction procedure which follows the probabilistic reinforcement learning task and the EEfRT tasks).
measure: EEG responses to reward feedback
timeFrame: Approximately 3 hours after treatment (i.e., simultaneously during the probabilistic reinforcement learning task).
Other outcomes:
measure: State-Trait-Anxiety-Depression Inventory (STADI)
timeFrame: For trait aspects: one week to two days prior to the experiment; for state aspects: approximately 30 minutes before treatment.
measure: Behaviroal Approach System Sensitivity (BIS BAS)
timeFrame: One week to two days prior to the experiment session.
measure: Perceived Stress Scale (PSS-10)
timeFrame: One week to two days prior to the experiment session.
measure: Somatosensory Amplification Scale (SSAS)
timeFrame: One week to two days prior to the experiment session.
measure: Big Five Short Screener (BFI-10)
timeFrame: One week to two days prior to the experiment session.
measure: Beck Depression Inventory (BDI-II)
timeFrame: One week to two days prior to the experiment session.
measure: Generic Assessment of Side Effects (GASE)
timeFrame: Approximately 30 minutes prior to treatment.
measure: Generic Rating for Treatment Pre-Experiences, Treatment Expectations, and Treatment Effects (G-EEE)
timeFrame: Approximately 30 minutes prior to treatment.
measure: The Positive Valence System Scale (PVSS)
timeFrame: Approximately 30 minutes prior to treatment.
measure: The Snaith-Hamilton Pleasure Scale (SHPS)
timeFrame: Approximately 30 minutes prior to treatment.
measure: PANAS trait and state
timeFrame: For trait level, one week to two days prior to the experiment session; for state level, approximately 30 minutes prior to treatment.
measure: The Temporal Experience of Pleasure Scale (TEPS)
timeFrame: One week to two days prior to the experiment session.
measure: Mood and Anxiety Symptom Questionnaire (MASQ-30)
timeFrame: One week to two days prior to the experiment session.
measure: Revised Life-Orientation-Tests (LOT-R)
timeFrame: One week to two days prior to the experiment session.
measure: Reinforcement Sensitivity Theory Personality Questionnaire (RST-PQ)
timeFrame: One week to two days prior to the experiment session.
Locations:
city: Marburg
country: Germany
facility: Department of Psychology, Differential Psychology and Personality Research, Philipps-University of Marburg
state: Hessen
Study officials:
affiliation: Philipps University Marburg
name: Erik M Mueller, Prof. Dr.
role: PRINCIPAL_INVESTIGATOR
References: