L-DOPA (dopamine) and subjective hedonic expectation

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 [7]. 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.”
Keep this in mind for tomorrow.
So enhancing dopaminergic function during a stimuli can strengthen an association between the stimuli and its estimated hedonic response, and increase the likelihood of selecting that stimuli later on.  Or perhaps, and maybe this is a hint at future experiments:
“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.”
So does this suggest a way in which foods that influence dopaminergic function moreso than others might reinforce certain eating behaviors?  It needs to be tested directly in humans, but animal studies do indeed find relationships between dopamine and food reward.  More tomorrow.
It should also be noted that dopamine is not a pleasure chemical per se as commonly believed.  Its role in food reward is much more complex as i’ll explore in future posts.

Reference

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

  • Jackpark

    What might be a link between those outcomes and behavioral signs, e.g. people with low levels of excitability in relation to anticipated rewards and, say, predictors of Parkinsons?

  • Jackpark

    What might be a link between those outcomes and behavioral signs, e.g. people with low levels of excitability in relation to anticipated rewards and, say, predictors of Parkinsons?

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