The role of striatal dopamine in reward- versus punishment-based learning: a PET-fMRI study
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2018-08-01
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en
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There is considerable interindividual variability in learning from rewards and punishments. Because dopamine is a key mediator in this type of learning, we hypothesized that these differences originate from variability in baseline levels of dopamine, with high baseline dopamine favoring reward learning and low baseline dopamine favoring punishment learning. Our second aim was to investigate the relationship between baseline dopamine, learning from rewards versus punishments and associated blood-oxygenation level dependent (BOLD) signal in the striatum. We hypothesized a positive correlation between baseline dopamine and both reward- and punishment-learning related striatal BOLD.
We analyzed data of 54 participants that performed a deterministic reversal learning task, in which reversals were signaled by unexpected rewards or unexpected punishments, while being scanned using functional magnetic resonance imaging. These data were collected as part of a larger double-blind pharmacological PET/fMRI study. On three occasions participants received a dopaminergic drug (sulpiride or methylphenidate) or a placebo before performing a battery of tasks. Participants also underwent a dynamic [18]FDOPA positron emission tomography scan to quantify their baseline dopamine synthesis capacity. Because we were still blind to the drug manipulation at the time of analysis, all data were averaged over the three sessions.
We did not find significant correlations between dopamine synthesis capacity and individual differences in learning from rewards versus punishments, or associated striatal BOLD signal. Exploratory not-significant results indicated a potential positive correlation between dopamine synthesis capacity and reward versus punishment related striatal BOLD signal, which seems to be driven by decreased punishment learning.
Because all data were averaged over three sessions, potential effects of baseline dopamine levels alone (i.e. placebo session) might be masked by the effects of the dopaminergic drugs. Analyses of the full dataset, which take into account the drugs administered, are needed to assess the reliability of these results.
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Faculteit der Sociale Wetenschappen