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
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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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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it