When you make a decision, certain neurons in your brain emit short bursts of the neurotransmitter dopamine. A new Yale study shows that when other factors wholly unrelated to the decision at hand - such as an unexpected sound - trigger these dopamine bursts it can lead to riskier decision-making.
The findings demonstrate how sounds around us may affect our choices and could also help researchers better understand dopamine systems in the brain and how they contribute to conditions like schizophrenia and depression.
The study was published Sept. 13 in Nature Communications.
"Many of us might have the intuition that hearing an unexpected sound would be distracting, that it might lead to errors or a loss of focus," said Robb Rutledge, an assistant professor of psychology in Yale's Faculty of Arts and Sciences and senior author of the study. "But when we think about the neurobiology, we know that dopamine plays a role in decision-making and a surprising sound leads to a short burst of dopamine."
That's because the sound may indicate something important, said Rutledge, like something rewarding. When we make a decision, short dopamine bursts may be involved, in part, because the brain is weighing how rewarding the options are.
Rutledge and Gloria Feng, a Ph.D. student in Rutledge's lab and lead author of the study, wondered if a surprising sound unrelated to a decision might influence the decision nonetheless, because of this shared dopamine action.
In a series of seven different experiments, the researchers tested the idea by assigning 1,600 people a task wherein they had to choose between a safe and a risky option that offered varying amounts of points. Before they made their choice, participants heard a sequence of tones. In the initial experiments, participants heard six tones in a row before each decision. But sometimes, the sixth tone of the sequence was different; the researchers called these sequences "rare" as they happened only 25% of the time.
The researchers then looked at how these rare sequences affected the choices participants made.
"We found that surprising sensory events, these unexpected sequences of tones, increased people's risk-taking," said Feng.
Specifically, participants chose the risky option on average 4% more after hearing the rare sequence than after hearing the common one. They were also more likely to choose the option they hadn't chosen in the previous trial after hearing the rare sequence.
In additional experiments, the researchers played both sequences equally as often, which eliminated both effects. Researchers also swapped the sequences so that the one ending on a different tone was played most often. In those experiments, rare sequences did not increase risky decision-making but still increased the likelihood of switching choices from the previous trial.
"That shows that these two effects are separable, which means there could be something different about the underlying neurobiology that's driving them," said Feng.
While the increases in risk-taking were not huge, said Rutledge, they were very consistent.
"Think about say an urban environment where there are so many sounds that are mostly irrelevant to our daily decisions," he said. "Maybe those sounds are affecting decisions even when we don't notice."
Rutledge wonders if these effects are common in certain noisy environments like casinos.
"If a slot machine goes off at the right moment, maybe someone at a Blackjack table is 4% more likely to make a riskier choice," he said. "It can have a big effect in that moment and certainly cumulatively over time."
Beyond decision-making, these findings also hold promise for understanding dopamine's role in the brain and its effect on mental illness.
Dopamine is involved in a lot of conditions, said Rutledge, including psychosis in schizophrenia.
"Schizophrenia can be enormously damaging, and hallucinations can be very stressful for the people who have them," said Rutledge. "We have some drug treatments for schizophrenia that block dopamine, but we need to do better. Similarly, there are some drugs for depression that target dopamine, and it would be great to know if we could use this method to understand the differences between people that respond better to dopamine or to serotonin drugs."
While researchers have tools to more precisely study the dopamine system in animals, the tools for use in humans are largely limited to pharmaceuticals that can change dopamine levels over longer periods of time.
"Using sounds, we might be able to deliver small, temporary bursts of dopamine in humans," said Feng. "This tool could help researchers better understand the effects dopamine has on the decisions we make."
