Reward motivation in humans and its relationship to dopamine D <sub>2/3</sub> receptor availability: A pilot study with dual [ <sup>11</sup> C]-raclopride and [ <sup>11</sup> C]-(+)-PHNO imaging
Bibliographic record
Abstract
Rodent studies suggest that dopamine signaling at D 2/3 receptors in the ventral striatum is critical for reward motivation. Whether this is also true in humans is unclear. Positron emission tomography studies in healthy humans have generally not observed a relationship between D 2/3 receptor availability in the ventral striatum and motivation. We developed the “mounting-effort for reward task” to assess high motivational demand for (a) gaining money (CS+), (b) losing money or avoiding electric shock (CS−), and (c) non-reward (Neutral). Receipt was contingent on participants making sufficient button responses relative to a “reward-threshold” determined by prior motor performance. This reward-threshold was dynamically increased if surpassed, making the task increasingly more difficult on every trial. The mounting-effort for reward task was preliminarily validated in 29 healthy volunteers (mean age: 25.83±3.58; 15 female). In this sample, %CS+ and %CS− significantly correlated with different dimensions of self-reported apathy. In a sub-sample of eight healthy volunteers (mean age: 25.75±1.91; four female), the mounting-effort for reward task demonstrated good test-retest reliability (%variance: 0.20–2.61%). Seven healthy male volunteers (mean age: 31.14±5.43) completed the mounting-effort for reward task and provided both [ 11 C]-raclopride and [ 11 C]-(+)-PHNO PET scans to assess D 2/3 receptor availability. %CS+ and %CS− were positively correlated with [ 11 C]-raclopride binding in the dorsal striatum. %CS+, %Cs−, and %Neutral were positively correlated with [ 11 C]-(+)-PHNO binding in the globus pallidus. Thus, increased expression of D 2 receptors in the dorsal striatum, and D 3 receptors in the globus pallidus, may be related to motivation for rewards. Larger positron emission tomography studies are required to formally validate the mounting-effort for reward task and replicate our pilot findings.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".