Dopaminergic Modulation of Motor Timing in Healthy Volunteers Differs as a Function of Baseline DA Precursor Availability
Bibliographic record
Abstract
Although numerous experiments in patients and animals implicate the dopamine (DA) system in timing, there are relatively few studies examining this effect in healthy volunteers. Moreover, the majority of these studies employed tasks of perceptual timing. We therefore investigated the DA modulation of motor timing in healthy volunteers using Acute Phenylalanine/Tyrosine Depletion (APTD), an amino-acid drink that reduces concentrations of the DA precursors tyrosine and phenylalanine. We also examined how APTD’s effects on timing might differ as a function of underlying DA function, as indexed by baseline levels of DA precursors. 18 healthy volunteers performed a Mixed Temporal Reproduction task, in which reproduction of five different sample durations (500 ms–1500 ms) were tested within a single testing block. Reproduction times conformed to Vierordt’s Law, such that the shortest durations were overestimated and the longest ones underestimated. Yet contrary to reported effects in Parkinson’s disease, we found no DA modulation of this ‘migration’ effect in our healthy volunteers. Instead, APTD produced systematic shifts in reproduction time across all durations. However, the direction of the shift differed according to individual differences in baseline levels of DA precursor availability. Specifically, APTD slowed reproduction times in participants with low baseline DA precursor levels whereas it speeded them in participants with high baseline levels. These apparently paradoxical effects can be reconciled in terms of the inverted U-shaped relationship between DA function and cognition. Finally, APTD had no effect on a test of temporal production in which participants were asked to provide spontaneous estimates of a one-second time interval. The differential effect of APTD on the reproduction versus production tasks suggests DA modulates the magnitude of the duration initially encoded into working memory, rather than clock-speed.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".