Revealing neural pathways involved in adaptive decision making in primates

In a constantly changing world, animals, including humans, must adapt quickly to their environment and learn to make decisions that lead to the best possible outcomes. In most cases, this type of learning occurs through direct experience: when faced with a choice between two particular items or events, animals draw on previous experiences involving the same options.

However, animals with more developed brains, such as monkeys and chimpanzees, can also infer the outcome of a decision based on knowledge of similar past situations, even if they have not directly experienced those specific options before. Thus, the decision-making process often involves a balance between experience-based and knowledge-based behavioral strategies.

In primates, it is the orbitofrontal cortex (OFC) region that is in charge of this balance. Not only does it directly participate in decision-making, but it also helps to “update” the internal values ​​that primates use to evaluate the relevance of an option.

Furthermore, the OFC appears to be necessary to correctly evaluate options with which an individual has no direct experience. Despite this knowledge, the precise roles of the OFC in decision making and whether distinct roles rely on distinct neural pathways remain unclear and quite difficult to study.

Fortunately, as reported in an article published in Nature Communications On August 28, 2024, a Japanese research team managed to shed light on this question.

Using a cutting-edge approach previously developed by the team, they selectively activated and deactivated different neural pathways originating in the OFC in monkeys during newly designed behavioral tasks, revealing their independent functions. The study was led by Kei Oyama and group leader Takafumi Minamimoto, both of the National Institutes for Quantum Science and Technology.

In the behavioral tasks used for the experiments, the macaques had to choose between two images that were presented to them, and they were given a predetermined amount of juice as a reward based on their selection. The monkeys quickly learned to associate the images with the amount of juice they would receive.

The researchers periodically changed the set of images presented to the animals and also reversed the reward values, making the worst options become the best and vice versa. Overall, these tasks tested the monkeys’ ability to learn from experience (through trial and error) and to approach situations that were familiar to them (through knowledge-based inference).

While the monkeys performed these tasks, the researchers used a genetically engineered chemical switch called a chemogenetic receptor that could effectively turn OFC neurons on and off when a specific drug was administered. Guided by computed tomography, positron emission tomography, and magnetic resonance imaging, the team was able to assess the effects of locally injecting a drug that temporarily inhibited distinct neural pathways originating in the OFC.

By observing the monkeys’ performance over time, the researchers were able to determine the functions of these pathways. They found that the OFC pathway connecting the caudate nucleus is necessary for experience-based adaptation, while the OFC pathway connecting the mediodorsal thalamus is important for knowledge-based adaptation.

Since the structure of the monkey brain is surprisingly similar to ours, important conclusions relevant to humans can be drawn from these findings.

“One of the main implications of our work is that it could help explain why individuals approach the same situation in different ways. Some people may rely more on trial and error, while others prefer a more systematic approach based on prior knowledge,” Minamimoto says.

“These differences in thinking styles, or ‘thinking patterns,’ could be related to how each person’s brain activates these specific circuits, and understanding these variations could help us develop personalized strategies to improve decision-making and problem-solving abilities for those who might struggle with a particular type of thinking.”

Moreover, understanding the precise roles of brain structures is extremely useful when studying neuropathologies and psychiatric disorders.

“Our findings could contribute to new treatments for mental and neurological disorders such as obsessive-compulsive disorder, where patients have difficulty adapting to changing situations. By targeting the specific brain circuits involved in these two strategies, we may be able to create more effective therapies that help restore balance in thinking,” Oyama says.

“Finally, our research has applications in AI and robotics, where this understanding of brain circuits could inspire more adaptable systems, capable of switching from one problem-solving method to another depending on the situation.”

While the brain is undoubtedly one of the greatest enigmas in the known universe, studies like this provide a stepping stone toward a clearer picture of how it works under the hood, both in our heads and in those of our animal companions.

Provided by the National Institutes for Quantum Science and Technology