L-DOPA and decision-making: no overall effect on exploration in a trial involving 75 adults

Exploring a new option or sticking with one that works

The study focuses on a specific trade-off: trying a new, potentially better option or continuing to choose an option that has already been rewarded. In particular, the researchers distinguish random exploration from exploration directed toward uncertain options. These behaviors measured in a task are not the same as everyday curiosity.

Dopamine is involved in this trade-off, but pharmacological studies have produced mixed results. The researchers therefore tested the hypothesis that individual characteristics might modify the response to L-DOPA, a dopamine precursor.

A controlled trial with no overall effect detected

The preregistered trial included 75 healthy participants, including 32 women, in a randomized, double-blind, placebo-controlled design. Participants performed a reinforcement learning task. The abstract specifies neither the dose administered nor the duration of the protocol.

L-DOPA had no overall effect on model parameters representing random exploration, directed exploration or the tendency to repeat a choice. This finding does not demonstrate an absolute absence of effect, but it does not support the idea of a uniform change in these behaviors.

Individual differences to interpret with caution

Working memory capacity modulated the effect of L-DOPA on random exploration, with a more pronounced effect in participants with higher capacity. The other proxy measures considered for characterizing baseline dopamine showed no credible effects. These measures do not directly measure dopamine in the brain.

When pooling the male participants’ data with those from an earlier study, for a total of 74 participants, the researchers observed an increase in uncertainty-dependent value weighting and choice perseveration. No credible drug effect was observed in women. However, this difference is not enough to demonstrate that responses genuinely differ between the sexes.

A physiological response does not prove a benefit

L-DOPA increased tonic pupil dilation. Pupil changes were also associated with exploration and prediction errors, while visual exploration behaviors were not altered by the drug.

These observations document decision-making mechanisms, not an improvement in cognition or everyday choices. Nor do they allow the findings to be extrapolated to addiction or schizophrenia, since the participants were healthy.

What we can take away

This trial does not support a simple promise that more dopamine precursor would promote exploration. The individual differences observed are avenues for research, not criteria for choosing an intervention.