Published today in Current Biology, the study confirms an important role for dopamine in how human expectations are formed and how people make complex decisions. It also contributes to an understanding of how pleasure expectation can go awry, for example in drug addiction.
The study builds on earlier research which used brain imaging as participants imagined holiday destinations. An area of the brain called the straitum tracked expectations and the
scientists found that they could take that signal and predict what the participants would choose. The authors believed this was dopamine at work and set-up this study to further explore its role.
The research team examined estimated pleasure of future events before and after the administration of a drug called L-DOPA which is known to enhance dopamine function in the brain and is commonly used to treat patients with Parkinson's disease.
The 61 study participants were asked to rate their expectations of happiness if they were to holiday at each of 80 destinations, from Thailand to Greece. They were then given L-DOPA or a placebo and asked to imagine holidaying in those destinations.
The following day participants had to pick between a series of paired destinations that they had initially assigned with equal ratings, one member of the pair was imagined under L-DOPA the day before and the other under placebo. Finally, they rated the full set of 80 destinations again.
Ratings for particular destinations increased after they were imagined under L-DOPA's influence. That increase also affected the participants' selections the following day. Dr Sharot added: "We had reason to believe that dopamine would enhance expectations of pleasure in humans, but were surprised at the strength of this effect. The enhancement lasted at least 24 hours and was evident in almost 80 per cent of the subjects."
Citation: Tali Sharot, Tamara Shiner,Annemarie C. Brown, Judy Fan,Raymond J. Dolan, 'Dopamine Enhances Expectation of Pleasure in Humans', Current Biology Online 2009, doi:10.1016/j.cub.2009.10.025
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