People constantly make complex decisions, from the more mundane--which restaurant to go to for dinner or which movie to go see--to the more profound--whether to have kids or not. Now, a new study published online on November 12th in Current Biology, a Cell Press publication, confirms an important role for the brain chemical dopamine in how people make such life choices, by influencing our expectations of the pleasure associated with their outcomes.
"Humans make much more complex decisions than other animals--such as which job to take, where to vacation, whether to start a family--and we wanted to understand the role of dopamine in making these types of decisions," said Tali Sharot of University College London. "Our results indicate that when we consider alternative options when making real-life decisions, dopamine has a role in signaling the expected pleasure from those possible future events. We then use that signal to make our choices."
Dopamine's role in reward learning and reward-seeking behavior has been established in animals, Sharot explained. In humans, however, much less was known. Her team recently found that when we imagine future events, activity in a dopamine-laden part of the brain tracks people's estimates of the expected pleasure to be derived from those events. Based on these findings, the researchers suspected that they could alter people's expectations, and with them their choices, by manipulating dopamine levels in the subjects' brains.
To find out in the new study, the researchers first asked people to rate their expectation of happiness if they were to vacation at each of 80 destinations, from Thailand to Greece. They then gave the participants either L-DOPA (a drug that increases dopamine concentrations) or a placebo and asked them to imagine vacationing in those destinations. The next day, participants had to pick between a series of paired destinations that they had initially assigned with equal ratings. However, one member of the pair was imagined under L-DOPA the day before, and the other under the placebo. Finally, participants rated the full set of 80 again.
The researchers found that the ratings for particular vacation places increased after they were imagined under L-DOPA's influence. That increase also affected people's selections between two alternatives the following day.
"We had reason to believe that dopamine will enhance expectations of pleasure in humans," Sharot said. "However, we were surprised at the strength of this effect. The enhancement lasted at least 24 hours and was evident in almost 80 percent of the subjects." She says it is possible that the effect will last for weeks or even months, but that's something the researchers haven't been able to test just yet.
The findings offer important new insights into how our expectations are formed, and ultimately why people do what they do, the researchers say. "Understanding how hedonic expectations are formed is critical both for understanding human action, which is largely driven by estimations of future pleasure and pain, and for understanding how pleasure expectation can go awry in a multitude of neuropsychiatric disorders that implicate dopamine, such as drug addiction," they write. "The current study highlights the neurobiological basis of this key aspect of human behavior, providing direct evidence of a critical role for dopamine in modulating the subjective pleasure expected to be derived from future life events."