How the Human Brain Solves Complex Problems Using Simple Strategies

In a groundbreaking study conducted by researchers at the Massachusetts Institute of Technology (MIT), scientists have uncovered how the human brain efficiently navigates complex decision-making processes. The research, published in the esteemed journal *Nature Human Behaviour* on June 14, 2025, reveals that the brain employs two primary strategies—hierarchical reasoning and counterfactual reasoning—to simplify intricate problems into manageable steps.

The study's lead author, Professor Mehrdad Jazayeri, a distinguished member of MIT’s McGovern Institute for Brain Research and an investigator at the Howard Hughes Medical Institute, explains, "What humans are capable of doing is to break down the maze into subsections, and then solve each step using relatively simple algorithms. Effectively, when we don’t have the means to solve a complex problem, we manage by using simpler heuristics that get the job done."

The research involved volunteers who watched a ball disappear into a four-arm maze and subsequently guessed its exit based solely on two timed sounds. The outcomes demonstrated that human decision-making rarely involves evaluating every possible scenario. Rather, individuals utilize shortcuts to arrive at conclusions more efficiently, often relying on past experiences and learned behaviors.

The two strategies identified—hierarchical reasoning and counterfactual reasoning—serve distinct functions in problem-solving scenarios. Hierarchical reasoning entails deconstructing a problem into layers, addressing each segment sequentially. In contrast, counterfactual reasoning involves contemplating alternative outcomes based on different choices made in the past. This duality allows for adaptability in decision-making, accommodating the brain's limitations in processing capacity.

The MIT team's experimental design meticulously recorded each participant's timing accuracy, leading to the development of computer models that tested three scenarios: pure hierarchical reasoning, pure counterfactual thinking, and a flexible combination of both. Notably, real-world performance aligned with the flexible model, indicating that the brain typically favors a single path while intermittently backtracking when necessary.

"This is really a big question in cognitive science: How do we problem-solve in a suboptimal way, by coming up with clever heuristics that we chain together in a way that ends up getting us closer and closer until we solve the problem?" Professor Jazayeri stated, emphasizing the importance of understanding these cognitive processes.

The study also highlighted the role of memory in decision-making, particularly when individuals consider switching paths in the maze. Successful backtracking relies on recalling previous auditory cues, which can be challenging given the brain's limited capacity to hold multiple variables simultaneously. Participants with a strong memory recall were more likely to reconsider their decisions, while those uncertain of their memory tended to stick with their initial choices.

In addition to examining human behavior, the research team trained a neural network using the same maze task, revealing that artificial intelligence can mimic human problem-solving behavior under certain constraints. Jazayeri noted, "What we found is that networks mimic human behavior when we impose on them those computational constraints that we found in human behavior. This is really saying that humans are acting rationally under the constraints that they have to function under."

The implications of this research extend beyond academic inquiry; understanding how the brain navigates complex decisions holds significant potential for applications in various fields, including artificial intelligence design, business strategy, and real-world planning. As researchers aim to trace the neural signals that trigger shifts between hierarchical and counterfactual reasoning, further insights into cognitive functioning may emerge.

In conclusion, the study underscores the brain's remarkable ability to simplify complex problems through strategic reasoning, paving the way for future explorations into cognitive science and its practical applications across multiple disciplines.