Summary: In one of the largest studies of its kind, researchers found that increasing dopamine levels with L-DOPA made people slightly more willing to wait for larger, delayed rewards—reducing impulsive decisions by about 20%. The study challenges earlier research suggesting that dopamine increases impulsivity, showing instead that it promotes patience and long-term thinking.
Using advanced cognitive modeling, the team found no changes in decision speed or evidence processing, implying dopamine influences how we value future rewards rather than how we make choices. The findings refine our understanding of dopamine’s role in self-control and decision-making, with implications for addiction and behavioral health.
Key Facts
- Reduced Impulsivity: L-DOPA increased participants’ willingness to wait for delayed rewards by roughly 20%.
- Stable Decision Processes: Dopamine did not affect decision speed or caution, only how future rewards were valued.
- Addiction Insight: Findings may explain how altered dopamine signaling contributes to impulsive behavior in substance use disorders.
Source: University of Cologne
A research team from the University of Cologne conducted one of the most comprehensive studies on dopamine and decision-making in humans so far, providing evidence for effects of the former on the latter.
Dopamine is a neurotransmitter involved in several functions, including motivation and reward.
The team at the Psychology Department led by Dr Elke Smith and Professor Jan Peters found that L-DOPA, a precursor of dopamine that increases dopamine levels in the brain, slightly increased the study participants’ willingness to wait for larger delayed rewards, decreasing impulsivity by about a 20 percent compared to placebo.
This modest effect challenges some earlier influential findings from much smaller studies, which had found that L-DOPA increased impulsive choices.
The study “Dopamine and temporal discounting: revisiting pharmacology and individual differences” has appeared in the Journal of Neuroscience.
When making decisions, people often prefer smaller immediate rewards over larger delayed ones, a tendency known as temporal discounting. Strong discounting is linked to more impulsive choices and is common when the brain’s dopamine system is altered, such as in substance use disorders and behavioural addictions.
While it is well known that dopamine influences decision-making, previous studies have produced inconsistent effects, sometimes making people more impulsive, and other times more willing to wait. Many of these studies had small sample sizes, making it difficult to draw firm conclusions.
To clarify these mixed findings, the research team conducted a comparatively large study, including additional covariates that may underlie individual differences in dopamine function and that may influence how people respond to dopamine-enhancing drugs.
In a double-blind randomised placebo-controlled within-subject study, 76 healthy male and female participants received either a placebo or L-DOPA, and chose between smaller immediate and larger delayed rewards.
Using cognitive modelling, a method that uses computer-based mathematical and statistical models to understand mental processes, they further examined how dopamine influenced more nuanced aspects of decision-making, including the rate of evidence accumulation, response caution and processing speed.
Participants showed the well-known “magnitude effect”, such that larger rewards lost their value less over time than smaller ones. L-DOPA made participants slightly more willing to wait for rewards overall, but it did not credibly change the magnitude effect.
Also, it did not credibly influence how quickly participants gathered information, how cautiously they made decisions, or how long they took to respond. This suggests that dopamine’s effect on waiting for rewards may not stem from changes in basic decision processes, but rather from how future rewards are valued over time.
The scientists also analysed measures that have long been assumed to reflect baseline dopamine levels, like working memory capacity, spontaneous eye-blink rate, and impulsivity, that would be expected to influence how individuals respond to L-DOPA.
These measures have been linked to dopamine activity in different brain circuits, including prefrontal areas involved in cognitive control and subcortical regions that support reward processing.
However, the team found no such interaction, suggesting that these measures may not be reliable direct indicators of baseline dopamine.
“Our findings show that L-DOPA increases humans’ willingness to wait for rewards, providing new evidence that challenges some earlier influential studies conducted in relatively small samples,” says Dr Elke Smith.
“Interestingly, we did not find that commonly used proxies for baseline dopamine, such as working memory capacity or, spontaneous eye-blink rate, or impulsivity, influenced this effect.
“In my view, while these measures may capture meaningful individual differences, they likely do not directly reflect baseline dopamine levels, and using them as such may not be valid.”
These insights contribute to a better understanding of the dopaminergic brain mechanisms guiding choices and help explain impulsive choices in conditions where dopamine signalling is altered, such as in addictions.
Future studies may address how dopamine influences decision-making in patient populations to help inform future interventions targeting dopaminergic function.
“Looking forward, future studies should examine how dopamine affects decision-making in patient populations and investigate potential interactions with hormonal fluctuations”, says Elke Smith.
Key Questions Answered:
A: They found that increasing dopamine made people less impulsive and more willing to wait for larger future rewards.
A: Earlier, smaller studies suggested dopamine might increase impulsivity, but this larger study shows the opposite effect.
A: It clarifies how dopamine affects patience and reward evaluation, helping to explain impulsivity in addiction and other dopamine-related conditions.
About this dopamine and neuroscience research news
Author: Eva Schissler
Source: University of Cologne
Contact: Eva Schissler – University of Cologne
Image: The image is credited to Neuroscience News
Original Research: Closed access.
“Dopamine and temporal discounting: revisiting pharmacology and individual differences” by Elke Smith et al. Journal of Neuroscience
Abstract
Dopamine and temporal discounting: revisiting pharmacology and individual differences
Disorders characterised by changes in dopamine (DA) neurotransmission are often linked to changes in the temporal discounting of future rewards.
Likewise, pharmacological manipulations of DA neurotransmission in healthy individuals modulate temporal discounting, but there is considerable variability in the directionality of reported pharmacological effects, as enhancements and reductions of DA signalling have been linked to both increases and reductions of temporal discounting.
This may be due to meaningful individual differences in drug effects and/or false positive findings in small samples.
To resolve these inconsistencies, we 1) revisited pharmacological effects of the DA precursor L-DOPA on temporal discounting in a large sample of N = 76 healthy participants (n = 44 male) and 2) examined several putative proxy measures for DA to revisit the role of individual differences in a randomised, double-blind placebo-controlled pre-registered study (https://osf.io/a4k9j/).
Replicating previous findings, higher rewards were discounted less (magnitude effect).
Computational modelling using hierarchical Bayesian parameter estimation confirmed that the data in both drug conditions were best accounted for by a non-linear temporal discounting drift diffusion model.
In line with recent animal and human work, L-DOPA reliably reduced the discount rate with a small effect size, challenging earlier findings in substantially smaller samples.
We found no credible evidence for effects of putative DA proxy measures on model parameters, calling into question the role of these measures in accounting for individual differences in DA drug effects.
