When presented with making a difficult decision, the human brain subconsciously uses a simple method in order to filter out options, according to results from the study. In addition, the study underlines how this method can result in poor decision-making, and may be associated to depression - a condition characterized by impaired decision-making.
The team analyzed 46 volunteers with no known psychiatric disorders, in order to examine how individuals make chains of multiple decisions, where every step relies on the previous step.
Usually, the total number of potential options is significantly too large to consider each choice individually. One solution is to avoid considering any choices where the initial step is negative - regardless of what the overall outcome would be. This 'pruning' decision-making bias, which was shown for the first time in this study, can cause people to make poor choices and miss out on rewards.
Dr. Quentin Huys, from the UCL Gatsby Computational Neuroscience Unit and lead author of the study, said:
"Imagine planning a holiday - you could not possibly consider every destination in the world. To reduce the number of options, you might instinctively avoid considering going to any countries that are more than 5 hours away by plane because you don't enjoy flying.
This strategy simplifies the planning process and guarantees that you won't have to endure an uncomfortable long-haul flight. However, it also means that you might miss out on an amazing trip to an exotic destination."
The researchers asked the participants to make a chain of decisions, in which they moved around a maze - on each step the participants either lost or won money.
The team found that paths starting with large money losses were instinctively avoided by the participants, even if these paths would have gained them the most money overall. Although none of the participants were actually clinically depressed, the researchers found that the amount of pruning the participants demonstrated was associated to the amount they reported experiencing symptoms of depression.
Neir Eshel, formerly at the UCL Institute for Cognitive Neuroscience and currently at Harvard Medical School, and co-author of the study, explained:
"The reflex to prune the number of possible options is a double-edged sword. Although necessary to simplify complicated decisions, it could also lead to poor choices."
The team link the connection with depressive symptoms to serotonin, a chemical in the brain involved in depression and avoidance. However, additional research is required in order to confirm this role for serotonin in pruning.
Dr. Tali Sharot, from UCL but not involved in the research, explained:
"This is a fascinating study linking "pruning" to depressive symptoms. The novel finding may have important implications for understanding and treating depression."