Making Mental Map Of Decision-making Process

In the well-known thought experiment known as the prisoner's dilemma, one individual has to decide whether to stay silent or talk to the police about their crime based on how they anticipate an accomplice will react. RIKEN researchers have gained insights into how the brain incorporates such predictions about choices made by others into the decision-making process¹.

Past studies have identified brain structures and circuits involved in predicting and interpreting the behavior of others. However, it was unclear how predictions of others' behavior influence our choices.

Hiroyuki Nakahara of the RIKEN Center for Brain Science and his team hope to uncover more about this process. "We're especially interested in understanding how human social capabilities are realized in the human brain," Nakahara says.

His team is exploring this question using a brain-imaging technique known as functional magnetic resonance imaging (fMRI), which maps changes in brain activity during different behaviors or in response to various stimuli.

The researchers performed fMRI on participants engaged in a simple computer-based task, where they had to choose between two options, each having a certain number of points assigned to them. However, the number of points was also influenced by the options that other individual had chosen in the same trial.

The researchers compared these patterns of brain activity relative to other fMRI experiments in which subjects either made choices in isolation or predicted the choices of others without acting on that information.

Multiple brain areas showed activity when determining how likely the other participant in a given experiment is to make a particular choice. But only the amygdala was significantly more activated compared with the control experiment. "The amygdala thus stands out when a subject adjusts their own choice based on their prediction of how others are likely to respond," says Nakahara.

"But other brain regions were involved in computing a person's own choices based on the predicted likely and unlikely choices of other individuals, specifically the posterior cingulate cortex and the right dorsolateral prefrontal cortex for the predicted likely and unlikely choices of others, respectively," explains Nakahara.

The computations performed by these various brain regions are then integrated and analyzed to determine which choice is likely to yield the greatest reward based on the other participant's predicted behavior.

This experiment was deliberately designed to explore only the most fundamental aspects of socially informed decision making, notes Nakahara. "We tried to investigate, after stripping away many and various factors that might occur in different social occasions, a core brain process for predicting others' choices and using those for one's own choices," he says.

His team plans to incorporate that missing complexity in future work.