Individual differences in dopamine function underlying the balance between model-based and model-free control

Abstract

Reinforcement learning involves a balance between model-free (MF) and model-based (MB) systems. Recent studies suggest that individuals with either pharmacologically enhanced levels of dopamine (DA) or higher baseline levels of DA exhibit more MB control. However, it remains unknown whether such pharmacological effects depend on baseline DA.Here, we investigated whether effects of L-DOPA on the balance of MB/MF control depend on ventral striatal baseline DA. Sixty participants had two functional magnetic resonance imaging (fMRI) scans while performing a two-stage sequential decision-making task under 150 mg L-DOPA or placebo (counterbalanced), followed by a 4-hour 18 F-DOPA positron emission tomography (PET) scan (on a separate occasion).We found an interaction between baseline DA levels and L-DOPA induced changes in MB control. Individuals with higher baseline DA levels showed a greater L-DOPA induced enhancement in MB control. Surprisingly, we found a corresponding drug-by-baseline DA interaction on MF, but not MB learning signals in the ventromedial prefrontal cortex. We did not find a significant interaction between baseline DA levels and L-DOPA effects on MF control or MB/MF balance.In sum, our findings point to a baseline dependency of L-DOPA effects on differential aspects of MB and MF control. Individual differences in DA washout may be an important moderator of L-DOPA effects. Overall, our findings complement the general notion where higher DA levels is related to a greater reliance on MB control. Although the relationship between phasic DA firing and MF learning is conventionally assumed in the animal literature, the relationship between DA and MF control is not as straightforward and requires further clarification.

L-DOPA administration shifts the stability-flexibility balance towards attentional capture by distractors during a visual search task

“…Our data indicated a training effect in that the RT distractor effect was slightly reduced the second time the participants performed the task (Theeuwes 1992 ). The PET data at hand had already shown the expected correlates with relevant parameters in other analyses, for example, with body mass index (Lee et al 2018 ) and with working memory capacity (Lee et al 2019 ). PET indices were within the range of different healthy adult samples at other sites (e.g., Deserno et al 2015 ).…”