Dopamine Neurotransmission in Major Depression
The overall aim of this study is to utilize an integrative research model in order to dynamically assess reward-related dopamine (DA) transmission in major depressive disorder (MDD) and test the role of dysfunctional DA release in depression and anhedonia.
The first arm of this line of research (PET scan) aims to investigate phasic DA release in MDD during incentive motivation. The investigators will utilize an established molecular imaging technique to measure striatal DA release dynamically during performance of testing and control versions of a monetary incentive delay task, which involves anticipation and receipt of monetary rewards. In doing so, this experiment will link together independent lines of research that have associated depression with decreased hedonic responsiveness, impaired reinforcement learning and dysfunctional DA transmission. We hypothesize that, relative to matched controls, unmedicated MDD subjects will show reduced reward-related ligand (11C-raclopride) displacement. Reduced ligand displacement will be interpreted as indicating reduced task-induced release of endogenous striatal DA in response to reward-predicting cues and unpredictable reward in MDD subjects.
In the second arm of this research (EEG recording), the investigators aim to probe the spatio-temporal dynamics of brain mechanisms underlying positive and negative reinforcement learning in MDD and their relations to phasic DA. Participants will perform the probabilistic stimulus selection task (PSST) while event-related potentials (ERPs) are collected. The investigators expect that, relative to matched controls, unmedicated MDD subjects will show reduced positive reinforcement learning, potentiated negative reinforcement learning, and larger (i.e., more negative) feedback-related negativity (FRN) in response to positive reinforcement (indicative of reduced DA transmission). Moreover, the investigators hypothesize that a more negative FRN in response to positive reinforcement will be associated with decreased striatal raclopride displacement (i.e., lower release of endogenous DA) as measured by PET in the first part of the study. This experiment will investigate the effects of blunted DA transmission on behavioral and ERP markers of both positive and negative reinforcement learning.
|Major Depressive Disorder Anhedonia|
|Study Design:||Observational Model: Case Control|
|Official Title:||Dopamine Neurotransmission in Major Depression|
- Event-Related Potentials (ERPs) during PSST task [ Time Frame: At session 3, during the EEG recording ]
ERPs will be generated during performance of the probabilistic stimulus selection task (PSST). Feedback-locked ERPs will be computed within epochs starting 100 ms before the feedback and lasting 924 ms. ERPs will be baseline-corrected to the first 100 ms of the extracted epoch. The feedback-related negativity (FRN) will be defined as the most negative peak 200-400 ms at frontocentral electrodes (Fz, FCz, Cz) after positive or negative feedback.
Group (MDD vs. controls) x Trial Type (accuracy on Choose A vs. Avoid B) mixed ANOVA will be performed to test the hypothesis that relative to controls, MDD subjects will show reduced positive reinforcement learning but potentiated negative reinforcement learning. Group x Feedback Type (positive vs. negative) mixed ANOVA will be performed to test the hypothesis that MDD subjects will show larger FRN in response to positive reinforcement.
- [11C]raclopride binding potential [ Time Frame: At session 2, during the PET scan ]
[11C]Raclopride binding potential will be recording during participant's performance of the monetary incentive delay (MID) task and is taken as an indication of release of endogenous dopamine. A reduction in raclopride binding potential is taken as an indication of increased extra-cellular dopamine concentration.
A reference tissue method will be used to calculate voxelwise binding potential and generate statistical parametric images of changes in binding potential. The cerebellum will be used as reference tissue. In addition to voxelwise analyses, a regions-of-interest approach will be used to extract binding potential from caudate nucleus, putamen and ventral striatum using the procedure described by Laruelle's group. A multivariate analysis of variance (MANOVA) considering various striatal regions and using Group (MDD vs. Controls) as between-subject factor and Condition (reward vs. control task) as repeated measure will be performed.
- Behavioral Performance in Monetary Incentive Delay task [ Time Frame: During session 2 ]
Data recorded include response time and accuracy.
The task was modeled after prior work in non-human primates in order to maximize our ability to detect changes in [11C]raclopride binding potential, which will be taken as an indication of release of endogenous dopamine. At the outset of each trial, a visual cue signaling either potentially rewarding outcomes or no monetary incentive will be presented. After a fixed interval, participants will press a button in response to a red square target. A second interval will follow the target, after which visual feedback will notify participants whether they have won or not won money.
In the reward version of the task, 150 trials will be presented over 25 min. Among these trials, 112 will be reward and 38 will be no-incentive trials. For successful trials, based on participant's response time, participants earn between $1.00 and $1.80.
- Behavioral Performance in Probabilistic Stimulus Selection Task (PSST) [ Time Frame: During session 3 ]
Data recorded include response time and accuracy.
The PSST task examines whether participants exhibit a bias for choosing frequently reinforced stimuli or avoiding frequently punished stimuli, and thus to assess positive and negative reinforcement learning. MDD subjects and individuals at increased risk for depression are expected to be better at learning from punishment than reward in the PSST.
The task has two phases: a learning and a testing phase. In the learning phase, subjects are randomly presented with three different stimuli pairs (AB, CD, EF), and are instructed to choose one of the two stimuli by pressing a key. After the response, feedback is given to indicate whether the choice was correct or incorrect. Feedback is probabilistic and one stimulus in each pair is correct more often than the other.
- Questionnaire Data [ Time Frame: Sessions 1-3 ]Throughout the study, participants will complete self-report questionnaires assessing mood, stress levels, hedonic state, caffeine intake, nicotine intake and craving, and alcohol intake.
|Study Start Date:||March 2011|
|Study Completion Date:||December 2012|
|Primary Completion Date:||December 2012 (Final data collection date for primary outcome measure)|
|Individuals with Major Depressive Disorder|
|Healthy Control Individuals|
Please refer to this study by its ClinicalTrials.gov identifier: NCT01659814
|United States, Massachusetts|
|Belmont, Massachusetts, United States, 02478|
|Massachusetts General Hospital|
|Boston, Massachusetts, United States, 02114|
|Principal Investigator:||Diego Pizzagalli, PhD||Mclean Hospital|