Risk and Uncertainty: The Science of Decision-Making
Gambling With Serotonin
Julian Macoveanu and colleagues at the Danish Research Centre for Magnetic Resonance assessed the role the neurotransmitter serotonin has in making risky decisions. Serotonin has long been recognized as a key player in mood and stress. The study focused on serotonin's role in risk and reward-processing. Twenty healthy volunteers performed a gambling task while undergoing functional magnetic resonance imaging (fMRI). Participants had to choose between a low-payout option with six-to-one odds, and a high-payout choice with a one-in-seven chance of success.
Participants were asked to perform the same gambling task after receiving an injection of ketanserin, a drug that specifically blocks the 2A-type receptors for serotonin (5-HT2A). After receiving the drug, people were less likely to take a gambling risk. This change in behavior was also associated with activity changes in the prefrontal cortex, but only in the unexpected-loss condition when subjects chose to play it safe but lost anyway. The authors speculated that signaling through 5-HT2A receptors might soften the blow of the unfair loss. The findings may have implications for the treatment of mood disorders such as depression, which also feature disturbed serotonin signaling and changes in risk-taking behavior.
Exploit or Explore?
Robert Wilson of Princeton University presented work at Neuroscience 2011 investigating choices between a known option, such as a familiar standby item from a menu, or an unknown alternative, such as a new daily special. Wilson described choosing the familiar option as the "exploit" condition, whereas the "explore" choice would favor the unknown.
Most studies investigating ambiguous decision-making give subjects only one chance to choose between two options. Wilson and his colleagues gave volunteers the choice between known and unknown options in an electronic slot machine game. When the researchers asked participants to choose only once, they overwhelmingly chose the known option. This confirmed the results of other studies and the conventional wisdom that people make safe choices, given such an option.
However, the results changed when participants knew they would have multiple opportunities to choose: they began to sample from the unknown choices in an "explore" mode, Wilson said. In this sampling condition, people increased their value-rating of unknown items by about 15 percent. Importantly, the findings suggest humans don't eschew ambiguity altogether, but rather adjust attitudes about the choices at hand according to the demands of the task. With more chances to choose, people's decision-making process appeared to shift from a calculated loss-reward system to become more random. Wilson plans to investigate the neural underpinnings of these distinct behavioral processes. He suspects that noradrenergic activity in the locus coeruleus — a tiny brainstem nucleus with wide projections — might contribute to more exploratory behavior.
Camillo Padoa-Schioppa of Washington University in St. Louis investigated the adaptability of neurons when making choices in very different contexts. All day, he said, we make decisions based on value judgments that we assign to various options. Choices might range in value from a dollar spent buying a yogurt, to hundreds of thousands of dollars spent house-shopping. To make the decision, the brain compares input from, in this case, "dollar neurons" and "yogurt neurons," to determine if one should buy the yogurt. Padoa-Schioppa's work demonstrates that the same neurons that contribute to inexpensive decisions contribute to expensive decisions. These decision-making neurons use "range adaptation" to adjust their response properties according to the circumstances, much the same way retinal neurons adapt to varying light levels.
The researchers took recordings from the two key brain areas of monkey neurons: the orbitofrontal cortex, where lesions lead to impaired decision-making, and the anterior cingulate cortex, thought to participate in assigning value to choices. In both areas, they found neurons underwent range adaptation when monkeys faced choices.
Other presentations at Neuroscience 2011 illuminated complementary findings, including a Presidential Special Lecture from Ann Graybiel of the Massachusetts Institute of Technology providing evidence of flexible and inflexible activity in cortico-basal ganglia circuits involved in decision-making. Combined, this evidence provides an increasingly clear picture of the ways the brain chooses between options. At the cognitive, chemical, and cellular levels, these studies are yielding new information on a fundamental process that affects daily life.