How our brain evaluates options for decision making
In most decision-making situations we need to plan well ahead as values of choice options often change over time. How does our brain manage to make good predictions in such situations and select the best option for the future? Alexander Nitsch and Christian Doeller from the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) investigated this together with Nicolas Schuck from the Max Planck Institute for Human Development in their recent study published in Nature Communications.
Optimal decisions rely on our ability to plan well ahead. For example, if we invest in stocks, we estimate which stock will be most profitable for us in the future. In doing so, we consider how the value of a given stock might change over time and whether we might be better off investing in a different one to achieve a higher profit in the long term. In such decision-making situations the brain has to memorize the possible options and their values. Previous studies have shown that the brain represents knowledge in mental maps, such as in the case of spatial navigation. Such maps contain information about directions and distances between places and thereby support the prediction of future locations on certain paths. But does the brain also represent very abstract dimensions such as the values of different options during decision making in a mental map to make good predictions for the future?
Alexander Nitsch and Christian Doeller from MPI CBS together with Nicolas Schuck from MPI for Human Development addressed this question in the current study. Using functional magnetic resonance imaging (fMRI), they recorded the brain activity of study participants while they made decisions in a task. The participants first observed how the points or values of two options changed over several time points. Finally, they were asked to choose the option that yielded more points and therefore a higher profit at the next time point. This is exactly what participants did - they calculated the points for the future time point and thus noticed very well when one option suddenly became better than the other and when they should switch accordingly.
"It is exciting to see that while participants were solving the task, the entorhinal cortex in the brain represented a two-dimensional map of the values of the two options, an abstract mental map. In fact, the value changes over the time reflected paths with specific directions through this two-dimensional map," explains Alexander Nitsch, first author of the study. Christian Doeller, last author of the study, adds: "When we normally move in a room, so-called grid cells in the entorhinal cortex fire regularly at certain locations and thereby support navigation. With the help of magnetic resonance imaging, we have now been able to observe an fMRI signal associated with such grid cells, while the study participants moved in an abstract 'value space'." When asked at the end of the experiment, no one stated that they had explicitly imagined such a map. Interestingly, the researchers also saw another link between the decision-making task and spatial navigation: Participants who extrapolated the values more in the task also rated their spatial navigation skills better in a questionnaire.
The findings of the current study therefore show that the brain can process very abstract information such as the changing and future values of different choice options in a mental map and thus reveal a fundamental mechanism of the brain that may underlie prospective decision making.