A new paper which I will be discussing in tomorrow’s (edit: time constraints will push it to next week) post reminded me of a related one from last year.
Dopamine has been demonstrated to modulate reward prediction, and this study tested whether enhancing it while imagining future events influenced subjective estimations of future pleasure. Imagination, as discussed by the authors, enables us to estimate emotional reactions to future events.
L-DOPA (dihydroxy-L-phenylalanine) is a drug (also sold as a supplement here in the U.S.) that enhances dopaminergic function. The dose used was 100mg.
61 subjects rated 80 different vacation destinations on their expectation of happiness when vacationing there. They then were administered a placebo and completed a subjective questionnaire on mood state. Then, all were re-shown half of the destinations and told to imagine themselves vacationing there next year. After this, 2 randomized groups consumed either a dose (100mg) of L-DOPA (29 subjects) or a placebo (32). They then completed another subjective state questionnaire. Then, the other half of the destinations were shown and imagined like before.
The next day each subject was shown 40 pairs of destinations that they rated equally at first, and chose which of them they would rather vacation at, and rated again.
In essence, it was rating 2 destinations against one another, one that had been imagined under a placebo, and one under L-DOPA.
They found that expected pleasure ratings increased for destinations imagined after taking L-DOPA, and subjects whose ratings of predicted pleasure were enhanced under L-DOPA more likely chose the destination imagined under L-DOPA.
Imagination of hedonic expectation in the vacation destinations were enhanced by L-DOPA and influenced selection the next day even when L-DOPA was eliminated from the body.
To quote the authors:
“Previous studies have implicated the dopamine-innervated striatum in signaling expectations of pleasure during imagination of future life events . The current ﬁndings provide the ﬁrst evidence indicating a regulatory role for dopamine in generating such subjective hedonic expectations in humans. Note that these results should not be taken to imply that dopamine enhances the hedonic impact of reward per se. Instead, the ﬁndings indicate that dopamine modulates processes related to predictions of likely future pleasure in a manner reminiscent of its role in reward learning.”
“However, it is possible that the effects of dopamine on valuation are not limited to future events and that enhanced dopaminergic function during imagination modulates the present value of a stimulus, an idea best tested with stimuli that can be directly experienced or consumed.”
Sharot T, Shiner T, Brown AC, Fan J, & Dolan RJ (2009). Dopamine enhances expectation of pleasure in humans. Current biology : CB, 19 (24), 2077-80 PMID: 19913423